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Rough running after freeway miles--checklist
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bradself
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PostPosted: Sun Nov 30, 2014 5:37 pm    Post subject: Rough running after freeway miles--checklist Reply with quote

Had the car out over the weekend, about 25 freeway miles both there and back. Things start out fine in town, but after the 60-65mph run it idles super rough, develops an exhaust leak, generally loses a little power. It was also backfiring down freeway hills, throttle closed. I leaned the idle mixture at the computer, helped some, but would still chuf.

In the distant past it has cut off completely on the freeway , won't start again until it's cooled all the way off.

Here's what's good: timing is spot on, dwell is 48^, dizzy is good, trigger points are good, I'm 99.9% sure I've tracked down all vacuum leaks on the top of the motor. Plugs are brand new, NGK bp6et, PCV replaced with 3mm fixed orifice. Fuel pressure is dead on 28.

Here's what I'll do and check:
Adjust Valves (did them <300 miles ago)
Adjust TPS so it's spot on at idle.
Fresh Cap and rotor (tho these should be fine)
Injector flow, before a freeway run
Check fuel pressure after a run
Check head sensor resistance after a run

What else??


I don't have the dash pot because the idle hunts (and I could never figure out how to adjust it anyway, might be shot.) I could plumb in a Porsche decel valve.

The car has AMC stepped heads, stock valves, and 93mm dished pistons, no cylinder spacers, builder claimed he got 8.5:1. Stock DJet grind Web cam. Hope I don't have a cracked head.
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raygreenwood
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PostPosted: Sun Nov 30, 2014 9:21 pm    Post subject: Reply with quote

You want to check CHT while its running and max hot after a highway run by slipping the + probe into the cht T-1 connector and grounding the negative to the nearest point of ground to the sensor.

Dont play with the idle mixture knob on the ECU. Its a fairly coarse adjustment and only works on the idle factor...not the eunning factor. Its got 23-24 clicks if memory serves. Set it on 12...in the middle and adjust it later only after a few more items are checked.

Without the dashpot on the TB....you will always have some slight, annoyances at idle when coming to a stop with throttle closed....but it should not affect running.

If you went to the 3mm pcv orifice then a fuel mixture adjustment at the MPS is usually required. In some cases depending upon what your baseline fuel mixture WAS the 3mm orifice can be adjusted by a slight tweak to fuel pressure.....usually less/lower.....so generally if almost everything was spot on when you installed the PCV orifice ......I dknt like to do it with fuel pressure.

Question: is the epoxy seal that covers the outer full load stop screw on your MPS still intact?

Normally when you install the 3mm orifice you will be slightly rich across the whole range...which is what its sounds like. The poping on decel is, from excessive fuel combusting in the exhaust.
You either need a better decel valve, or proper adjustment of the decel valve.....or to drop the fuel mixture a bit.

If by Porsche decel valve....you mean the manual/vacuum operated one....yes...it works much better and is more adjustable. Its the same one that the 411/412 used with 4 speed and on a few automatics.
it also requires a small rubber boot vacuum connector for the plenum that goes between the plenum and the AAR. It can be gotten around if you dont have it.

Tell me about the epoxy MPS seal and I will tell you about carefully removing it to preserve the adjustment of the large aluminum screw it covers.....which is one of the MPS adjustments. ...but not the one you are looking for....yet.
Ray
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PostPosted: Sun Nov 30, 2014 11:20 pm    Post subject: Reply with quote

Hey Ray, the plug on the MPS I'm running is intact, I have a rebuilt spare with the epoxy removed but the original adjustment of the big outer screw has been lost in the process.

Yes,decel I'd the mechanical, non-electric Porsche decel valve from a 914.
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PostPosted: Mon Dec 01, 2014 12:30 am    Post subject: Reply with quote

Add to my list: compression check, one warmed up after city driving, one after a freeway run. During the long embattled process of the engine rebuild, 6K miles in and very bad running conditions cylinder 1 was at 85psi, the other three seemed pretty low for only 6K miles, 100-100-110. It was supposedly solved but the relationship with the mechanic at that point was so bad I don't recall how (rings, new piston and jug, or how.)

There's a decent motor known to me and available, but pricey at $650. As much or more of a mystery as mine. I fear my rebuild was slipshod, & tho it was claimed I got new pistons and cylinders I have to wonder. Compression test will put my mind at some ease, whatever the results.
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PostPosted: Mon Dec 01, 2014 6:38 am    Post subject: Reply with quote

If the actual compression ratio is lower than it should be....say under 8.0:1....it can make D-jet finicky to tune. Not untunable....but finicky.

On the MPS with the epoxy out...thats not a bad thing...but it does mean that the main fuel mixture has been adjusted before....and usually the outer full load stop is set wrong because about 99.9% of owners do not realize that the fat aluminum plug/screw is an adjustment as well.

So....use a dremel, a heat gun...soldering iron or a combo to remove the epoxy.

Try not to screw up the threads. You want the plug to turn very easily. One thing that works very well...and this scares some but has no negative effect....is to plug the airvent in the back section near the epoxy and sand the boss down until the aluminum of the plug is exposed all except for a thin ring around the edge. Drip some acetone on the epoxy and the plug should screw right out and push the ring of epoxy with it.
you may need to deepen the slot in the plug with a file or hacksaw blade to clean it up.

If you remove the plug when the MPS is out of the car....you must put a scribe mark on the plug and the body of the MPS and exactly count the turns and partial turns that the plug comes out. Write it down.

If the plug has already been removed....its not usually a huge deal. You are going to adjust it anyway....but its nice to know what the factory reference point was.

Underneath the outer plug (which called the full load enrichment stop) is a small screw. This is your main fuel mixture adjustment. If you look closely that center screw is screwed into a boss or ring. Surrounding that center screw...and part of the boss....you will notice that there is a recession in the shape of an allen key. That is the inner full load stop.

So....the MPS has three adjustments:
1. The inner full load stop which is usually a factory setting that prevents the copper diaphragm from being pulled in far enough at idle (max vacuum) to affect fuel mixture enough to cause an over lean mixture and stall the car.

2. The small center screw which is your main fuel mixture

3. The fat outer aluminum plug that is the outer full load stop. This prevents the copper plate from flexing outward too far usually in initial take off from a stop...and causing an overly rich stumble condition.

What you want to do....is adjust the center screw....only...while the engine is running. Turning this screw inward clockwise makes it leaner....outwards makes it richer.

You only need to move the screw about 1/8th to 1/10th of a turn at a time. Always make a scribe or sharpie mark so you know where your starting point was. Makes sure you are fully warmed up...everything is set like it should be and you are idling stable before you start.

BUT.....you need to make sure that the inward/inverted hex adjustment surrounding the center fuel mixture screw DOES NOT TURN...while you are moving the inner fuel mixture screw.
The tool for this is a hollow allen key. If you have a decent drill press you can make one.....or you can take a piece of plastic hex from a hobby shop and drill that out....or thickwall aluminum tube and file flats in it, after you drill the center out.

In about 70% of all MPS I have found the surrounding hex is tight enough not to turn, while turning the center screw. I mark the surrounding ring with a, sharpy so I can tell.

The outer, full load stop......once you have the epoxy out...and before you remove the plug or turn it....mark it....then install the mps in the car....with car warmed up and idling......turn the screw INWARD in very small increments....and count the #of turns. Screw it inward until it just starts to affect idle. It will try to stall.

This means you have contacted the boss on the copper diaphragm and are pushing it inward. STOP HERE! Count the turns. It will usually be about 3/4 turn minimum to about 1.25 turns maximum. Write it down.

CAUTION: YOU CAN ONLY RE INSTALL THE PLUG WHILE YOU ARE ADJUSTING WHEN THE ENGINE IS WARMED UP AND RUNNING.

If you arr not yet adjusting.....just return the plug to its original position and screw itco7t counting the total, number of turns and partial turns.

Most engines that are far from original due to age or having been rebuilt (which means virtually all, engines these days) heavily benefit from an outer full load stop readjustment...AFTER a main fuel mixture adjustment.

So mark the position of the outer screw stop.....make a tweak to the main fuel mixture when running...screw the, outer plug back in to exactly where it was and secure it with scotch tape forcthe moment. ...and drive a set circuit. If you need to pull over and make another tweak.....you will screw the outer plug/stop back in each time to the exact, mark you have made and drive the circuit again. Each time you arjust fuel mixture, during this drive/tweak process....the outer plug must yo back in to its original mark.

When you arr happy with your fuel mixture, how the car runs and decelerates......and/but....if you have a slight, hesitation or, stumble of the line from a, stop sign....enlist some help to discover if the car when taking off from a stop and stumbling.... is leaving a rich smelling puff, of exhaust or not.
if yes....the outer plug is, screwed out too far.....allowing the, diaphragm to flex too far out and over enrich for a split second. You screw it back inward about,1/8th turn at a time until the problem smooths out. Do not turn it back inward less than 5/8 from bottoming on the copper diaphragm ring. If you need to turn it in that far....your main fuel mixture or ignition timing, is not yet right or engine, efficiency may be way down (engine worn or compressikn ration way down).

Yes....an air fuel mixture sniffer is the very best way.....but not any, easier beacuse it does not read as accurately as it should with the stock exhaust.

If everything else is rihht with the engine .....dilgent driving and tweaking like this can make perfect adjustment.
then drive the, car for about 30 minutes and make sure it runctions properly, is not overheating.

Then let it cool, completely off, start it...and make sure it starts, properly, idles properly and drives well again. Tweak a little more if necessary. Ray
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bradself
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PostPosted: Mon Dec 01, 2014 8:01 pm    Post subject: Reply with quote

About the reman'd MPS with the epoxy removed: the inner full stop is already hard up against the backing plate, so with or without vacuum applied the outer full stop screw just runs hard up against the out adjustment ring, trapping the diaphragm. All three adjustments would need to be made on this one. I'm game, if it's possible to do by feel/ear. The inner stop turns quite easily with the mixture adjustment screw so I would need to make a hollow Allen key.

Reman'd by Fuel Injection Corp. USA. They may be local, if so they might set it at factory setting on their rig, I'll see. But homebrew would be better. --Brad
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PostPosted: Mon Dec 01, 2014 11:10 pm    Post subject: Reply with quote

bradself wrote:
About the reman'd MPS with the epoxy removed: the inner full stop is already hard up against the backing plate, so with or without vacuum applied the outer full stop screw just runs hard up against the out adjustment ring, trapping the diaphragm. All three adjustments would need to be made on this one. I'm game, if it's possible to do by feel/ear. The inner stop turns quite easily with the mixture adjustment screw so I would need to make a hollow Allen key.

Reman'd by Fuel Injection Corp. USA. They may be local, if so they might set it at factory setting on their rig, I'll see. But homebrew would be better. --Brad


Every single D-jet part from that company that I have ever bought is f'd up. The rebuild they do is..ok......but they have no idea how it works so they just, assemble it with no adjustment. Their trigger points are just as bad.

If the remanned part has a part #.....or if you can send me a picture.....I need to see the end with the spring horn on it......I can measure the gap between the inner stop and the keyhole plate and you can get it pretty close.

Also.....between the copper plate and rear housing with the aluminum plug.....inside there is an order to the stack up. It goes....rear casting......gasket....shim...plate....front housing........on some MPS......and the shim swaps to the other side of the copper plate on ither models.
This is one of the ways that the factory made a quick wholesale adjustment to the position of the copper diaphragm.
Put the shim on one side and it moves the plate one direction .....put it on thd other side and it moves it away.

So.....if we can identify what the original was for your reman....I can check the inner full load stop gap from the "keyhole" stop plate....and tell you the shim and gasket order so yiu can, double check the reman.
I have been able to successfully reset the inner full load stop this, way.

The armatures and coils arecfairly precisely made. The inner stop plate gaps are pretty close. Ray
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PostPosted: Tue Dec 02, 2014 12:43 am    Post subject: Reply with quote

Part # is 280 100 049

Ray, don't know what the spring horn is. There is no shim, the stack I found was in the order: casting with the plug, gasket, diaphragm, back plate.

I'll post pics tomorrow. Observation: it certainly seems during adjusting the outer stop plug would turn the inner stop ring.

Okay, thanks!!
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PostPosted: Fri Dec 05, 2014 11:55 pm    Post subject: Reply with quote

Not too much DJet diagnosis, will post a full list by Sunday, but have found so far a questionable intake rocker arm on cylinder 1, leaky injector in cyl 1, wobbly fuel pressure at idle and warmed up, wavers by a half pound, surely partial cause for hunting idle. It is rich at idle, as you surmised Ray, likely across the entire throttle. Fresh plug wires and cap/rotor will bring tune to baseline as new.

Cold compression is great, 120 all four. Ran the valves at a tight .006, easy .005. No shims in that reman MPS, I'll see if FuelInjectionCorp will sell me one.

Exhaust leak was just a blown gasket, fixed now. While I was at all this I installed a 2.0 liter throttle body, modified the snorkel. Lost the air inlet doung so, but I run the AAR with a baby K&N.

What do you think about putting a T in the cylinder heàd fresh air hose for the intake side of the Porsche decel valve? I'll take vacuum signal from the dashpot hose as I'm not running with it presently. I would the T the PCV hose to plenum for the out side of the decel valve.

Once the decel's in I'll get it out on the express way, do hot compression and the CHT reading. Air temp sensor is good, starts out cold at 200 ohms, I'll get a hot read on that too.
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PostPosted: Sat Dec 06, 2014 8:30 am    Post subject: Reply with quote

The 049 part # pegs it as a former 914 MPS......which cross matches exactly to the "E" series that was used in the 411/412.

There is a thin shim missing from the stack. Actually not so thin its about .020". I forgot to look at the stack up of the 049 vs the E......but it makes no matter. The shim was placed in these units to make a difference between adjustment for one application or another.

In other words....instead of having to make a large mixture screw adjustment to make a factory MPS that was designed to run in the 1.7 411/412/914.......run in a 2.0 914.....they simply swapped a shim from one side copper plate to the other.....then made fine adjustments with the mixture screw.

There should be enough adjustment in the screws that you can do without the shim.

I will measure and undisturbed E series today to find the gap between the middle adjuster ring face and the inner stop plate. I measure with a set of cheap hook end wire type feeler gauges.

You, want to support the MPS casting with some kind of clamp because you will need three hands. Since your car runs.....you are not terribly far off....so you will want to hold the center mixture screw still while you turn the inner full load stop ring outward. Each time you measure the gap between stop and plate with the wire feeler gauge....make sure you are not touching the adjuster screws with screwdrivers or anything that may flex the plate and give a false reading.
Once you get the inner stop right.....reassemble the MPS and check for vacuum leaks. Then start it and see if it runs.

If it will not start...or if it starts and then stalls quick....and if keeping the throttle open causes it to run but roughly and it pops....then its too lean.

This signals that moving the full load stop outward has allowed idle vacuum to pull the copper diaphram inward enough to put enough tension on the aneroid chamber and armature stack to drive it further into the induction coil......causing an excessively lean signal.
so....before you readjust the inner stop again.....move the center fuel mixture screw outward. ...1/8 turn at a time and retry the starting/idling to see if idle stabilizes.

If it takes more than about 1.5-2.0 total turns of the center mixture screw to get it rich enough to idle.....this may not be a problem unless the center screw protrudes enough to ding against the outer aluminum cap. If this happens.....you can turn the inner full load stop ring inward. ....maybe a half turn at most...but 1/8 turn at a time.
as you do this.....move the center mixture screw inward by the same amount.
You are trying to limit how far inward the copper diaphragm is moved without losing all of the inward movement of the full load stop.

Once you get suitable idle...proceed to adjust the outer full load stop like in my last post.
Use a small drop of superglue on the thread line to hold the inner full load stop ring still while you drive and adjust.

Now.....this is important.......before you start on a long stint of driving and adjusting.......drive the car for a few miles...even if its running rich. Get it fully warmed up. Then get out and check the CHT/temp sensor 2 for resistance. Record that reading.
it should be in cold weather...like below 40F...probably between 125 and 200 ohms max.

The problem with driving and adjusting is that stopping and starting at odd fuel mixture ranges can drive the CHT resistance down below what it should be reading....and that will artificially tweak your fuel mixture baseline....and this can cause you to adjust the MPS falsley. If weather is cold and you are running too rich. ....it can keep CHT resistance readings falsely too high...like over 200 ohms fully warmed up which will give excessively rich fuel baseline.

In hot weather.....the common issue is that the CHT resistance commknly getw driven down to about 70 ohms....to low...and it causes excessively lean condition making for hot starts and porr lean idle. This is what in well tuned engines I typically dind that adding an inline ballast resistor can make for much better running. Usually about 100-150 ohms....rarely nore than 200 ohms.

The solution to the tuning issue is to first drive it around and check what the temp sensor 2 drops down to....lowest resistance. If the weather is cool...say 50-75F.....and you find the sensor ohms in the 100-150 range.....that is just fine.
Go to Radio shack or any electronics store and buy a few resistors in that range...say....a 10p, a 125 and a 150 ohm. Take the one in the middle and crimp or solder on a connector to each end.

What you will do.....is once the car is fully warmed up and you are ready to start your driving and tweaking runs.....stop the car for a, moment.....pull the TS2 wire off the sensor pigtail.....connect the resistor straight to a good ground on the engine andcthen plug in the TS2 wire from the harness.....so you are temporarily installing a fixed resistor inline in place of the TS2 so that resistance stays at "normal running" stability while you tweak the MPS.

Once you get it running its best....pull and clean the plugs to make one more lengthy combined city highway run......probably 60/40 highway to city. Pull over and check the plugs to make sure you are not running too lean or rich.

Then take it home.....plug the ts2 back in......let it fully cool off.....see if it starts normally. See if it, drives normally. If not...verify whether its running rich or lean...then do a fine tuning tweaking run. Ray
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PostPosted: Sun Dec 07, 2014 6:58 pm    Post subject: Reply with quote

Hey Ray, CHT subjects first here, to see if I understand when to read the ohms.

I read first ice cold with the car off, 200 ohms, then with car running, 0 ohms. Second reading fully hot, after freeway run, engine running, 6.5M ohms. I did not read it fully hot with the engine off.

I want to solve the fuel pressure problem first, will search here and Samba T3 and STF for feeder pump reco's, you had mentioned a pump that was a bit pricey. I will also draw up a plumbing diagram for what I understand from your written description of using a LJet pump, I can't be spending $$$ on questionable DJet pumps anymore.

The one thing I can't get my head around using an LJet pump is the lack of the check valve on the DJet return fitting. Doesn't this valve maintain the fuel pressure on the return end of the loop? A spotty valve in a DJet pump can destabilize the pressure, correct?

My weekend got hijack'd all I was able to do was read the CHT. The car has about 500 pounds of spares in it right now, full spare front end in the trunk, rear suspension and transmission in the back. Car ran great on the freeway, had spare throttle and spare power, poor mileage tho, 10-12 mpg.

Rough running pulling off the freeway in city stop and go has ceased, I want to check the timing again to make sure it's not advanced. Hot start woes have appeared how ever, very curious, so will check timing. Need to replace the leaky injector I identified also, then I'll get on to the MPS. The process continues! Thanks a lot--Brad.
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PostPosted: Sun Dec 07, 2014 8:28 pm    Post subject: Reply with quote

bradself wrote:
Hey Ray, CHT subjects first here, to see if I understand when to read the ohms.

I read first ice cold with the car off, 200 ohms, then with car running, 0 ohms. Second reading fully hot, after freeway run, engine running, 6.5M ohms. I did not read it fully hot with the engine off.

I want to solve the fuel pressure problem first, will search here and Samba T3 and STF for feeder pump reco's, you had mentioned a pump that was a bit pricey. I will also draw up a plumbing diagram for what I understand from your written description of using a LJet pump, I can't be spending $$$ on questionable DJet pumps anymore.

The one thing I can't get my head around using an LJet pump is the lack of the check valve on the DJet return fitting. Doesn't this valve maintain the fuel pressure on the return end of the loop? A spotty valve in a DJet pump can destabilize the pressure, correct?

My weekend got hijack'd all I was able to do was read the CHT. The car has about 500 pounds of spares in it right now, full spare front end in the trunk, rear suspension and transmission in the back. Car ran great on the freeway, had spare throttle and spare power, poor mileage tho, 10-12 mpg.

Rough running pulling off the freeway in city stop and go has ceased, I want to check the timing again to make sure it's not advanced. Hot start woes have appeared how ever, very curious, so will check timing. Need to replace the leaky injector I identified also, then I'll get on to the MPS. The process continues! Thanks a lot--Brad.


I did not get a chance to measure the MPS. I had to leave town early for my Monday trip. Snow and ice.

Unless your voltmeter is set wrong....your CHT is shot.
When its cold.....it should read about 2300 ohms. In really cold weather some part #'s can read up to 3200 ohms.

You are in California right? in 50-60 degree weather cold...it should read maybe 1800+ ohms. Warmed up...in the 70 ohms minimum and about 125-200 average.

Sometimes you may end up reading the harness. So when you stop to check....go ahead and turn engine off , pull the plug and just read the sensor.

The L-jet fuel pump can run without a feeder pump. The check valve is usually either built into the outlet or part of the roller cell chamber inside.

The Airtex pump that others recommend for the ford escort(?) will work fine by itself in general. It has fuel capacity for a larger engine.

If you really want a bulletproof pump though...the Bosch 044 which is a CIS pump...is awesome. It flows about the same VOLUME as a D and L jet pump...but is capable of about 2.5 times the pressure at that flow....so in reality it flows about 2.5X a D-jet pump. It needs a feeder pump. Ray
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PostPosted: Mon Dec 08, 2014 5:58 pm    Post subject: Reply with quote

Okay, the CHT that's plugged in is 1600 cold, 46 hot. Don't know the part number. I have a T3 screwed into the other head that's 2550 cold, 105 hot, also don't know the exact part number. The T3 has the hot start problem, so I haven't been using it.

I ordered a couple 0280 130 012, I can't find the 003 reasonably priced.

The order of battle re: fuel pressure is oriented by price: if I can find an inexpensive feeder pump for the wobbly DJet pump installed, and the couple spares I have I'll do that. I'll search for Airtex at STF and see if that thread is there.

I'll change out the injectors tonight or tomorrow, eliminate the leaky one, get baseline on those, send mine for cleaning/r&r and have good spares.

If it's a quick answer, let me ask--what was the recommendation for wire to rebuild the harness? I'm not worried about connectors right now, just wondering about wire type. I'll search the T3 forum here where I believe the most spirited harness discussions were. I have a spare to rebuild, want to do this toot sweet, settle the fuel pressure problem, swap sensors, find a good rocker arm set, before I fiddle with the MPS. Okay, onward!
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PostPosted: Mon Dec 08, 2014 8:00 pm    Post subject: Reply with quote

In fact, for now, I'll put a 100 ohm resistor in series with the sensor that reads 1660/46.
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PostPosted: Mon Dec 08, 2014 9:31 pm    Post subject: Reply with quote

bradself wrote:
Okay, the CHT that's plugged in is 1600 cold, 46 hot. Don't know the part number. I have a T3 screwed into the other head that's 2550 cold, 105 hot, also don't know the exact part number. The T3 has the hot start problem, so I haven't been using it.

I ordered a couple 0280 130 012, I can't find the 003 reasonably priced.

The order of battle re: fuel pressure is oriented by price: if I can find an inexpensive feeder pump for the wobbly DJet pump installed, and the couple spares I have I'll do that. I'll search for Airtex at STF and see if that thread is there.

I'll change out the injectors tonight or tomorrow, eliminate the leaky one, get baseline on those, send mine for cleaning/r&r and have good spares.

If it's a quick answer, let me ask--what was the recommendation for wire to rebuild the harness? I'm not worried about connectors right now, just wondering about wire type. I'll search the T3 forum here where I believe the most spirited harness discussions were. I have a spare to rebuild, want to do this toot sweet, settle the fuel pressure problem, swap sensors, find a good rocker arm set, before I fiddle with the MPS. Okay, onward!


The type 3 sensor is reading pretty close to normal. If you are having hot starts ....meaningcwont start when hot after soaking for a, while and you have no fuel leaks or other issues....check the resistance of that type 3 sensor next time it hot starts.

If your baseline fuel mixture as set by the MPS is too lean or rich......then the TS2 is not CAUSE of the hot start.....its simply adding to the problem.
If you are already too rich from the MPS......and using the type 3 sensor that is almost normal....which will be richer than the one you are using now......it will be overrich after heat soak and will have a hot start problem just like one that is too lean.

The wire that works very well you can get from McMaster carr. Its teflon coated, silver plated copper wire. Its awesome! .
Whats nice is that even if you never put jacketing/sleeving around this wire.....it will not matter. You can just bind it up nicely and it will last forever. Very low resistance. You just need one main wire size. Ray
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Lars S
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Joined: October 04, 2007
Posts: 780
Location: Sweden
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PostPosted: Mon Dec 08, 2014 11:49 pm    Post subject: Reply with quote

raygreenwood wrote:
You want to check CHT while its running and max hot after a highway run by slipping the + probe into the cht T-1 connector and grounding the negative to the nearest point of ground to the sensor....
Ray


Do you check the resistance with the sensor still connected? To me the reading would be hard to tell right or wrong since the ECU is in parallell and also if the ignition is on there is a voltage from the ECU that disturbs the Ohm-meter.

bradself wrote:
....

If it's a quick answer, let me ask--what was the recommendation for wire to rebuild the harness? I'm not worried about connectors right now, just wondering about wire type. I'll search the T3 forum here where I believe the most spirited harness discussions were....


This guy has a lot of nice harness stuff:
http://bowlsby.net/914/WiringHarnesses/

Complete 1968-74 VW Type III and IV (D-Jet and L-Jet) Fuel Injection Harness can be special ordered and also restoration of old harnesses.


/Lars S
_________________
Porsche 914 -72, Bahia Red daily driver Smile
VW411 2-d -70, White, sold Sad
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold Sad
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raygreenwood
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PostPosted: Tue Dec 09, 2014 6:59 am    Post subject: Reply with quote

Lars S wrote:
raygreenwood wrote:
You want to check CHT while its running and max hot after a highway run by slipping the + probe into the cht T-1 connector and grounding the negative to the nearest point of ground to the sensor....
Ray


Do you check the resistance with the sensor still connected? To me the reading would be hard to tell right or wrong since the ECU is in parallell and also if the ignition is on there is a voltage from the ECU that disturbs the Ohm-meter.

bradself wrote:
....

If it's a quick answer, let me ask--what was the recommendation for wire to rebuild the harness? I'm not worried about connectors right now, just wondering about wire type. I'll search the T3 forum here where I believe the most spirited harness discussions were....


This guy has a lot of nice harness stuff:
http://bowlsby.net/914/WiringHarnesses/

Complete 1968-74 VW Type III and IV (D-Jet and L-Jet) Fuel Injection Harness can be special ordered and also restoration of old harnesses.


/Lars S


I had to go back through my notebooks this morning to see if I ever had any issues with piggy back checking while CHT sensor was connected.

Yes....you are correct....when running you have current. Dont check it while running.

However from my old notes....and bear in mind this is using a new harness.....I found that the resistance readings are similar enough to unplugged to not be an issue.
if in doubt.....unplug the sensor to check it. Just make sure you have an excellent connection....meaning both connectors and crimps in good shape with good strain reliefs and clean.
if not.....and this is why I originally many years ago....made notes to not unplug the CHT unless you have to.....is because if your connections are not excellent quality....to much plugging and unplugging if an imperfect connector pair can alter your connectivity enough in the middle of tuning the MPS....causing you to make serious adjusting errors.

I spoke to Jeff when he was just getting started maybe 2001. He does excellent work.
I disagree with a couple of his philosophies.....but his product is superb. He has worked hard to exactly replicate the factory harness and materials inclueing all wire gauges and materials.

From my research using better spec wire than stock.....you can go to all one wire gauge with no system changes at all. I also get rid of the stock connector in as many places as I can and use modified L-jet or EV-1. The stock connector is inferior and carries the seeds of its own failure (as noted in documents by both the designer....Bosch and manufacturer AMP). For normal life span if the system and engine was new requiring little extensive tuning.....for the excellent price.....the bone stock harness would be fine enough. However....any type 4 with D-jet 45 years on is not going to fit that profile. There will be aclot of plugging and unplugging while you are testing components. That makes for poor connections with original D-jet female connectors.

There is another person here on the Samba who also makes factory level harnesses.

I dont believe in "restoring" harnesses at all. If its 40 years old its, crispy. Pull the plugs off to build a new harness for if you must and scrap the rest.

If you buy a decent crimper....several good brands on the crimper, frames....but only one, brand has the best dies...Paladin tools......I can show you how to do new crimps with the ECU connectors.

Hopefully in the spring I can get back to the project I have for molding a D-jet plug that fits an L-jet female connector.....I am very close. This will allow all of the plugs to be converted to the better connectors making it a much better system. Ray
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Lars S
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PostPosted: Tue Dec 09, 2014 8:23 am    Post subject: Reply with quote

raygreenwood wrote:

I had to go back through my notebooks this morning to see if I ever had any issues with piggy back checking while CHT sensor was connected.

Yes....you are correct....when running you have current. Dont check it while running.



On the TS2 there is 8-9V from the ECU as soon as the ignition is turned on, engine running or not, this voltage should disturb the Ohm-meter reading since it uses its own internal voltage to measure the resistance (every Ohm meter has an internal battery).
However if you use the same Ohm-meter every time you measure with the ignition on and the sensor wired to the ECU you will get a reference value to compare with previous measurements but not an absolute Ohm-value.

/Lars S
_________________
Porsche 914 -72, Bahia Red daily driver Smile
VW411 2-d -70, White, sold Sad
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold Sad
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold Sad
Husqvarna 118cc, -47, Black, Sold Sad
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bradself
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Joined: January 13, 2013
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Location: SF, CA
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PostPosted: Tue Dec 09, 2014 12:12 pm    Post subject: Reply with quote

Thank you Lars, I know about that harness builder but cannot afford his wares; I'll rebuild my spare harness myself. This isn't my hobby car, it's my only car, and living on SS I cannot replace it, tho I often enough wish I could. Fresh CHTs are on the way, and I'll experiment with adding a resistor to the ones I have.

The mystery to me here is the poor mileage. All things being equal, and for discussions sake, what else besides the fuel mixture/delivery could ding the fuel efficiency?

I've replaced the injectors on the 1/2 side (1 was leaking,) bypassed the cold start injector and will try to get ahold of some resistors today. I acquired a Pertronix but will wait until the current set of points fall off the dwell angle before replacing them. The dizzy and trigger points are behaving well. The next item on the agenda is correcting the wobbly fuel pressure, then to work on the harness.

To clarify, there are two MPSs, the one without the shim is on the bench. The one in the car has never been apart, the epoxy seal is still in place. As it nominally works I'm adverse to taking it apart until the spare is sorted. I can't risk disabling the car, I park on the street and move it 6 days out of 7 for street cleaning.

Thanks Gents! Onward!
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Lars S
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Joined: October 04, 2007
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PostPosted: Tue Dec 09, 2014 12:33 pm    Post subject: Reply with quote

bradself wrote:


The mystery to me here is the poor mileage. All things being equal, and for discussions sake, what else besides the fuel mixture/delivery could ding the fuel efficiency?


You say the cold compression is about 120psi, not to gpod to me...with a CR of 8.5:1 I would expect more like 140, but the battery and starter condition plays a lot at compression tests.
Have you checked compression when hot, all plugs out?

/Lars S
_________________
Porsche 914 -72, Bahia Red daily driver Smile
VW411 2-d -70, White, sold Sad
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold Sad
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold Sad
Husqvarna 118cc, -47, Black, Sold Sad
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