D-Jet PhD Sticky. Newbies Need Not Enter. Advanced FI Tuning

[raygreenwood]

[Keith Park]

well Im glad you mentioned the washer thickness difference between diaphragms, I had not taken that into account when setting up the 007 diaphragm for the 037, the washer on the inside was thicker on the 037.

So I made measurements, took into account for the thicker washer and readjusted the 037 to what it was originally, which was about another 1/2 turn OUT (less protrusion) took it out for a quick try, didn't seem different but it hadn't warmed up yet. Will know more tomorrow as far as any differences.

Was distracted this weekend pulling this engine, replacing shaft seals and putting it back in due to an oil leak somewhere in the bellhousing. need to see why It sounds like I have a loose valve when cold, that's this weeks duty aside from the tuning.

Keith

[raygreenwood]

[Keith Park]

I didn't know that difference, fortunately when I install the seals I only install them flush with the outer case. Seal surfaces looked good.

Drove the car today, it seemed better. the zone between no throttle and where the mixture leans out to where it should be seemed less, only running too rich with slight throttle openings now, and the RPM needed to see it get a bit leaner with fully closed throttle decelerations was less than before. it took a half turn out of the inner stop to get this though.

That inner stop makes me nervous, but Im tempted to try another quarter turn out and see where it goes, it seems to be headed in the right direction and im certainly not seeing any spikes lean under light throttle.

One conclusion Im coming to though is that the bucking is, if not created by over-richness at least made worse by a rich mixture in those spots in the RPM
range that it happens. This bucking happened to the bone stock T3 motor I had in this car before, but it was never that bad... and Im pretty sure that that D jet was running richer than it needed to be, as I was more concerned with longevity of the engine than super tuned D jet.

Keith

[raygreenwood]

[Keith Park]

I probably should have posted in the engine forum on that seal before I did it, but I RTV'd in the outer diameter so it shouldn't walk, I did not do this with the previous seal but I don't think that was what was leaking, back of flywheel was dry. Ill remember that depth info.

OK, another quarter turn out on the inner stop, no difference. Let me sum up what I have done again:
Distributor: stock 2L 914 009, rebuilt it again, tightened up axial play on the shaft, cleaned up the plate and lubed, same for the weights, increased spring tension on the primary spring a smidge by bending the spring tab a bit.
trigger points slotted, and advanced as far as they will go. Mark 10 capacitive ignition. Ive tried adv from the stock 28 up to 32, no major difference, have it at 30 now, hoses off.

Throttle body: swapped in the one with the Vac adv and retard, no noticeable difference, both adv and retard are working.

Dcell valve, added one, no difference, temporarily removed it.

TPS: this was new, opened It and made sure the contacts were all doing what they should, no excessive play, installed and adjusted it. Tried removing wire 17, no noticeable difference but I did notice the off throttle mixture no longer went leaner. re-attached wire 17.



MPS, adjusted mixture to keep it under 14 on the highway, but the low end of the curve, with throttle slightly open is way too rich. Adjusted outer stop for no stumble off the line. Adjusted inner stop back to measurements from the sensor before it was touched, no difference, adjusted it OUT another half turn, MAYBE slightly less rich range under slight throttle.

Still haven't found a way to get rid of the super rich spot under very light throttle, this has been plaguing me!

any ideas on this??

Keith

[raygreenwood]

You are probably overall too rich.

When you are too rich or too lean...either on the main MPS armature adjustment or fuel pressure......the fine adjustments have no effect.....because each of these....inner syop, outer stop etc....are either momentary adjustments or only affect fuel mixtude when they operate....by maybe 3-5%.

Also....do not automatically advance the trigger plate. This has a HUGE effect.

Remember.....with D-jet......what seems like a suntle adjustment......making a subtle effect on running or driving.....changes tne vacuum signature. That makes LARGE changes at the MPS and ECU.

And.....each time you make a subtle adjustment like inner or outer stop.....virtually all of the other fuel adjustments also have to be readjusted to realize the benefit. These are not seperate, discrete adjustments. You cant say.....Im running good on everything else so if ai make a tweak to this screw it,should clean up X effect.

They are a interactive. Each adjustment you make changes the others to some extent.

The proper way to adjust the trigger timing position.....is with a fuel pressure gauge.

Make sure the fuel pressure is set and stable. With the car warmed up and idling steady...loosen the trigger plate screws with an offset screwdriver just enough that you can move the plate with effort.
Watch the fuel pressure gauge. As you move the trigger plate.....the idle with become rough as you move it....and the fuel pressure gauge will rattle wildly.....like a range of +5psi to -5 psi.....that is the effect on the MPS and pulsewidth that the injection timing jas on tje vacuum signature.
Move the plate until you have the steadiest fuel pressure and smallest range of neexle swing and then lock it down......and.....tben you have yo go back and readjust/check all three adjustments on the MPS. Ray

[Keith Park]

with the Web 73 I thought scootch the trigger points advanced as much as possible, which still isn't much. I cant get at one of the screws without removing the dizzy, so that is a task for another night. My fuel pressure is set to 28, the needle is rock steady, but could that be where im measuring it? I measure it on the feed line off the pump, not in the back, I figured non-compressible liquid, doesn't matter, but does it?

anyway, im still working on main mixture curve now, trying to get it linear, I have adjusted the mixture to stay under 14 on the highway, moving the inner stop shouldn't affect main mixture should it? I realize that when I get fine tuning Ill have to go back and forth but for now I just want to get the Gross curve right. I don't think im too rich on the highway, 22mpg seems about right, what do you think? around town its more of a gas hog.

Anyway, I have the inner stop 1/4 turn out from where I THINK it should be from measuring the original 037 diaphragm and taking into effect the new ones washer. With it this way, it is better, the curve is more linear. when I put my foot into it it riches up a bit as it should, rather than going leaner. the zone of super rich is shorter but still there so Im not there yet. with the inner stop out more, I DID have to lean out the main mixture adjustment, again, so it stays under 14 on the highway, this lean spot seems to be at about 1/3 throttle now. I shouldn't have to move the outer stop as that wont affect the main curve, should I also try changing the timing now too? that didn't help before and Im at 30deg cent adv now. With this main mixture able to be set leaner now as it doesn't lean out the top end as much its a bit leaner under light throttle now too and the bucking was considerably less on my test drive.

Perhaps I need to learn more about what the mixture curve reality should look like. Can a small rich spot be OK? how steady should the mixture be over the range? how much should it enrichen when you floor it or get heavy on the pedal? could it be my rich spot is a red herring as things do funny stuff on this particular muffler under these conditions? The only difference between this build and the last on where I didn't have this rich spot is the Muffler, its an end exit Ernst now as per recommendation, and of course where you measure it is also important.

I will move the inner stop out another 1/4 turn and see if the linearity improves further, adjusting main mixture if needed. There isn't much protruding now though....

Once I have a reasonable mixture curve, Ill start the fine tuning with ALL the variables.

Thanks for the help, Im starting to get there!

Keith

[raygreenwood]

Yss...the inner stop affects both the main mixture screw and the outer full load stop.

Think about it for a second. If you move the inner stop outward....allowing the diaphragm to suck inward farther.....the main mixture screw is in the center of that diaphragm and it increases the range of motion of that screw.

And yes.....tapping fuel preasure at the pump is totally different than tapping it on the injector ring for stability of readings.

For example.....The farther the pressure regulator is from the injector ring...the larger the head preasure is "above" it in the system....and the smoother the pressure fluctuation is. This exact technique is employed on all VW/Audi vehicles above mk 4 at least. They put the primary regulator immediately after the pump.....with a 6 bar (87 psi) pressure head....back by the gas tank...and do fine adjustment at the rail to 42 psi with an electronic or vacuum riaing rate regulator. It makes the fuel pressure rock solid to 1/2 psi resolution or better which is required by modern injection.

You need to test fuel pressure at the injector ring to see what its actually doing. That is where the pressure drop IS and where it causes the fluctuation that affects injector spray stability.

Edit.......just so you understand WHY the "incompressable liquid" factor does not work here...........its not because the fuel is not cooperating with the theory. Its because the system components are not cooperating.

The fuel system is not a hydraulic system or even a hydrostatic system. In a hydraulic system you have constant pressure from piston or pump in a CLOSED system the fluid NEVER leaves the system.

In a hydrostat.....you are doing much the same.....but you have pressurized the water or liquid in the tank connected to the line.....with air or gas pressure. Liquid pressure stays stable as long as more gas is forced into the pressure head in the tank to take the place as liquid exits the line under pressure.

The EFI fuel system uses parts of both hydraulic and hydrostatic.

Its not a closed system like hydraulic because you are using the fuel. Its leaving the system.

There are three major "harmonics" at play that cause the fuel pressure to have variation.

And....first.....understand....that in ANY EFI system....fuel pressure is KEY....KEY. Fuel dosage is: pressure X time = specific volume. Its even more critical in D-jet....because it uses a FIXED fuel pressure.

And.....it has no downstream 02 sensors to correct the mixture if and when pressure fluctuates. The design of the ECU ASSUMES fuel pressure is stable and correct at all times as it makes its fueling calculations. If it is fluctuating more than a little.....your fuel mixture will be all over the place.

The harmonics at play:

1. The roller cell in the pump. This is a circuit. In order for the volume that fills the cells of the pump to be pulled in at 0 pressure and exit the pump at 28 psi or higher.....it must make a full 360° circuit in the pump.

Each time the pump makes 1 revolution.....it loads up, slow slightly as the motor is back loaded and is then relieved of load.....as it "pops" that load of fuel out of the roller cell port and through the check valve that both keeps the fuel from back pressurizing the roller cells.

It does this at 5000 rpm on average. Thats 83 times per second. Its also not perfect. Before the fuel can be isolated past the check valve on the upstream side relieving pressure across the roller cell and unblocking new incoming fuel....there is always some back pressure that affects the loading of the roller cell chamber. ....but it takes/numerous several revolutions to affect and partly stall pressure through the pump...and acts as turbulence in both the inlet and exit port. It causes a noisey rattle to both the roller cells and check valve.

So the "buzz" you hear from the pump is not the motor. Its a combination of the rollers and check valves rattling. You discern an individual "buzz" as it runs....that equal about 1/2 or 2/3 the actual pump motor speed.

This process...squeezing the fuel....popping it past the check valve into the line...causes a small, very fine, rapid pressure oscillation...of maybe 1/4 to 1/5th psi ...almost too rapid to see on a very good gauge. It "looks" stable....unless you video it and slow it down. But this IS a pressure oscillation nonetheless.

2. Far away from the pump.....as each injector or pair of injectors open.....the pressure on the line drops each time. this happens because it takes time (even though its milliseconds).... time to refill that lost fuel line volume to bring that pressure back up.

You have to replace the fuel that is injected to bring pressure back up.

That creates a much larger "dip" or oscillation of the fuel pressure than the pump losses.....but this pressure oscillation is slower than the pressure oscillation at the fuel pump.
The pump pressure oscillation may happen at 40-50 times times per second. The injector oscillation...especially at idle.....happens at maybe 4 times per second. Its an oscillation you can actually SEE on the gauge needle.

Every few half seconds or so....the pump oscillation and injection pressure drop oscillation happen at the same time. You can even graph this.

So combined....you can get an extra 1/2 to 1 psi spike either high or low. You can see this by watching carefully with a GOOD pressure gauge Like a class 1A or better...or by video and slowing it down to half speed.

3. The third harmonic is HUGE. It is the opening and closing of the regulator metering plate. People imagine that the regulator acts like a hydraulic regulator....which is an orifice. It does not.

It is a spring loaded plate covering the exit/return tube. As all should know...any spring has an operating pressure and a "cracking" or un-seating pressure. For example of the spring in the regulator is set to regulate at 28 psi when open by say .001" to .003"....it can take as much as 10% or more of extra pressure to get the spring to move once its fully closed again.

So....when the injectors inject.....fuel pressure drops. The regulator plate slams shut so pressure can build up and rise again. Then it takes higher pressure to crack the plate open...upwards to 31-32 psi.....and then the cycle starts over.

You can HEAR this harmonic closing rattle by putting a stethoscope on the regulator.

This harmonic moves at the same rate as the injectors....but since its down stream....its offset by a time factor of a few 10ths of a second or so...and this same oscillation can play hell when it interacts with the other 2 oscillations every split second or so.

This oscillation is also what wears the regulator out. It erodes the metering plate. You can see the pictures in my D-jet fuel pressure regulator thread.

https://www.thesamba.com/vw/forum/viewtopic.php?t=656298&highlight=pressure+regulator

So....you need to measure fuel pressure up by the injectors.
Ray

[Keith Park]

GOOD READ, Thanks Ray!
well it was warm tonight and I decided not to put off the trigger timing. I put a gauge on the left bank of injectors and it agree'd that I had 28psi with the front gauge, that was good, but in moving the contacts back and forth, and I can only move them about 1/8 inch or so I see no difference, the gauge is pretty steady, I see a little vibration with the throttle opened just a bit but that's only .2psi or so, moving them back and forth doesn't change it at all, nor does the idle change. Hmmmm....

Anyway, I have the inner stop out as far as I dare now, the Oring is starting to show! its a bit better and more linear but the really rich just off closed throttle spot is still there. So I got thinking, and I have a feeling im putting a small band aid on a larger wound, it masks part of the problem but IT is not the problem itself.

So, its TOO rich between 15-20inHg or so, that means that the higher vacuum is not able to move the armature into the coil enough to lean it out, but WHY? OR... there is something else that is richening things up in that narrow zone and overcoming the signal from the MPS. What could that be? I do want to unplug the TPS again and try that but previous doing that didn't help. I did re-adjust the main mixture as lean as I could (staying under 14) and the lean area is mid throttle now and haven't touched the outer stop (it runs pretty smooth, except for the bucking when its in the rich zone). Are there any of the "subtile" adjustments that im not thinking of or trying to get that narrow rich zone settled?

what if I bumped the fuel pressure to 30 and then leaned out the main mixture, the FP is an across the board thing BUT, does it have more effect under heavier throttle? Hmmmm... I haven't messed with the FP yet.

Thanks for the help.

Keith

[raygreenwood]

[raygreenwood]

Let me put a little finer point on that last comment......

Please bear in mind that D-jet has no logic and no software. Its a cleverly designed "difference engine".

Internally its very similar to a "Lotus 1,2,3" chart/framework. Its an electronic spreadsheet. It allows a resistance and timing based, question and answer decision tree.....with a range.....of "If this....then that".

The problem is that while the system seems crude....and it is.....and it has very few sensors with limited range.....the sensors it has.....are actually quite sensitive for their day....and even sensitive enough that they could have worked for systems all the way up through Digifant 2.

The MPS is an elaborate MAP sensor. And because of the size of its components.....the diaphragm and aneroid....it gives a lot of multiplication to very fine vacuum impulses. It is decievingly sensitive......
But......
At the same time....its ability to affect fuel mixture.....its effective range by percentage.....and this is partly due to the ECU....can be too limited.

If you are trying to use a modern wideband....its going to show you dips and spikes in fuel mixture that D-jet either does not have enough logic to paper over....or is not quick enough to affect. That last part is critical. Its what this is about.

D-Jet...because of its fixed logic....has some similarities to K-jet....which is CIS mechanical which has no logic but great planning.

With K-jet.....because the iniectors spray constantly......no on/off rhythm...and they spray even when valve is closed.....they also have the excellent trait of spraying the full time the valve is open (great atomization).....if the idle mixture was set up like D-jet.....the K-jet system would run hideously rich at idle and low rpm.

So....K-jet is set up excessively lean at idle.....where as long as it gets enough fuel to idle smoothly...it does not matter because K-jet in its many variants has several very sensitive vacuum impulse enrichment devices that insure that as the throttle opens and load and advance start....this overly lean condition is fixed before there are any problems.

D-jet on the other hand.....as set up from the factory....runs slightly rich at idle...partly because of its paired injectors. Two ports run wet and two dry. This does not mean heavily....noticably rich. It means moderately richer than would be considered ideal in a more modern system. This is done by a combination of the temp sensors.....between them they account for about 10-15% give or take of the fuel mixture baseline.....and by the main armature setting of the MPS. Thats the center screw. The inner and outer full load stops are simply "out of bounds" settings for the main load screw.

The system is set slightly rich because....for instance....when taking off with normal driving and not greatly mashing the pedal down..... Think light to light in the city .....cracking the throttle small amounts will give you plently of initial fuel....a little too much for economy actually....but that fuel state turns toward lean almost instantly because your throttle is not,aftually open very far and about 60% of your pre throttle opening vacuum gets re-established.

So the initial slightly rich idle settings...helps to span the gap at these part throttle settings so you do not go excessively lean durimg heavy load and high advance conditions.

This corrective behavior was augmented in the early models by the pressure switch and by the MPS diaphragm in later models....and while the throttle plate is moving toward open...by the TVS...which is an accelerator pump function.

The traits of this system ...when you read it on a modern wideband....is sharp, quick swings from lean to rich as various systems....MPS, TVS, advance and rpm/throttle opening ...kick in and out.

The important thing to remember is that....what you are reading..... that alarms you as "non-linear"..... are after the fact. They are downstream. That event your wideband is reading has already happened....and things have already changed. Millisecond spikes of rich and lean.....are showing the slowness of the system logic. As long as that condition does not hang around, and you are not pinging and you are running evenly....you are good.

You are looking for the best middle of the road condition that is slightly leaner at idle than factory .....but it will not look linear by modern standards.

And......your ignition must be spot on. Bear in mind that if you are using for instance.....a pertronix module.....your distributor position is already off. This means that injection timing is already off from factory position relative to cam timing.

If you also have a different cam...you can be a little farther off. This can be far enough off that 1/8" of trigger plate adjustment is not enough to show benefit.

My trigger plate screw slots for when I was running a web 73....were slotted all the through the outer edge of the plate shield. It allowed a hair over 1/4" adjustment in either direction.

Also.....average D-jet from factory ran about 11.5- 12%-ish at idle when read with a standard sniffer. If you can get that to about 13.5 at idle....14 absolute tops.....and it must idle smooth.....then leave it there....and disconnect the wideband. Then tune the inner full load stop for best idle.....and tune the outer full load stop for best off the line response.....BUT....DO NOT....use the wideband for tuning these two adjustments. Because they are off the line and throttle closed on decel adjustments.....they are momentary impulse adjustments....and what the wideband has to say about their affect....is absolutely irrelevant. It will confuse you and cause you to make unecessary adjustments.

Then.....you drive and adjust.....using only the center armature screw and idle screw. You adjust purely for best power, smoothest transition and driveability. And....you need to be using a fixed resistor in place of the CHT...so that minor heating as you stop and to to adjust does not affect baseline fuel mixture while you are tuning the MPS.

Only AFTER you get excellent driveability....do you attach the wideband...and make sure you are not excessively lean or rich. Ray

[Keith Park]

OK, interesting observation on Kjet, my Golf used to do great on gas sitting there stuck in traffic every night while the Squareback didn't... now I know why!
First off, my trigger points will only rock back and forth about 1/8" on my dizzy, even if the screws are out. I can temporarily lean the idle to "unmask" the fuel pressure flutter and try and set them that way, would that work?

Im idling at about 12 AFR now, if I adjust that leaner, then the mid throttle will be too lean way into the 14's. I also get intermittent missing when I get into the 13's on occasion so I suspect it really wants to see low 13's at most on my gauge at least under lower RPM's.

I understand about the non-linearity, I never expected this to track all that well and to be honest, the car runs pretty well and Id probably be happy even with that rich spot under very light throttle IF.... that darn bucking didn't happen when its in that super rich zone, and Im talking mid 10's.
If I get into the 11's or higher I get little if any bucking so perhaps Im obsessed with trying to tune out that rich zone but that is why. I also think that that rich zone may be pulling my around town gas mileage too low, its fine on the highway. I guess with my particular setup, when Djet looks up the answer for all the inputs its getting under light throttle conditions, the answer its gets is "go Rich".

This condition WILL hang around for as long as you keep the throttle open that amount, open it more and it leans back, close it completely and it leans back.

This got me to thinking though, the "linearity" or best approximation of that would likely be set, if it were set mechanically and not in the ECU, by the shape of the armature. As you pointed out, these are VERY sensitive and minor differences, perhaps not visible without careful measurements might taylor a particular pressure sensor to a particular type of engine, maybe that is why so many different part numbers, do you think this is possible? That would explain the difficulty in tuning that out in my non-stock vacuum profile.

I still have a couple things to try, and one of them is bump the FP up a couple PSI and then adjust the main mixture leaner to compensate and see if that smooths out the rich zone. Ive run out of ideas to try and stop bucking other than mixture though.

Drivability is good, except for the bucking zones... and if I can only get the rich zone into the mid 11's, not even lean, the bucking can be tolerated.

[raygreenwood]

That bucking at very slight throttle at high rpm.... an very well be TVS adjustment.....and do not just adjust by the book...adjust and then cycle and carefully observe switch and wiper contact position and readjust.

Also....as you note the buckimg happens at a very rich spot. Thats because its, causkmg such a rich issue that it affects combustion efficiency.....affects vacuum signature....which affects MPS further.

What you need to know....nissing in the 13s.....is what your advance is doing. If you are advanced too high at 13s....thats an issue. If you are at part throttle....and high revs....you get higj vacuum....and getting vacuum advance added in. This is also why many 1.7 and 2.0 914 and 411/412....had an adustable vacuum advance to limit the amount of advance.

13s up to about 13.5 should not be an issue.

Also the trigger plate ....is it only moveable a total or 1/8"....meaning 1/16tb inch to each side?.....if so you may need to clearance the plate inside of the outer shield on some distributors.
It should have 1/4" or better....total movement.

When you say "lean the idle"....do you mean with the knob on the ECU? If so....STOP THAT! . That is for idle only....with throttle valve closed...which signals the ECU to be at idle mixture. It has no effect on driving once the throttle is open.

Only adjust fuel mixture with the center screw of the MPS.

But that leaning out.....told you something. Its a little to rich on main fuel mixture. And....at this,stage....when warmed up.....what is your CHT reading. And....next time you check this.....disconnect the ambient air temp sensor in the intake for a second and check. Ray

[Keith Park]

Right now I have the TPS adjusted with the 2 degrees of room before it opens the idle circuit, should I narrow this down? Ive messed with this in the last build and wasn't able to make it happy, and of course even with the TPS unplugged and/or the idle cutoff wire (17) disconnected it still bucks as before.

The missing happened even before I had the vacuum advance connected, with the old TB, its most noticeable when accelerating normally up to speed.
I did move the trigger points back in the other direction to try that and it seemed to miss less today, and remembering WAY back to when the last Stock engine was new (27 years ago) and I had an intermittent miss I found that I had the plug into the trigger contacts in BACKWARDS... and that was causing the problem so perhaps trigger contact timing is causing this? Ill know more if it behaves the same next few drives. I can clearance the dizzy body if necessary.

No, I didn't mean lean the idle on the ECU, that has limited range, I have it set full lean now and it has been for a while, since Idle has been on the rich side throughout this whole process.

ill have to check the sensor resistances, maybe tomorrow if I have a chance, I had the CHT set to 125 ohms hot when the weather was warmer, the other one I haven't looked at in a while.

Right now, with the inner stop turned out so far the mixture curve goes from super rich under those very light throttle conditions to rather lean, then richer when you get into the throttle more, and ive adjusted the main mixture to stay under 14 under the lean portion, I think what I may do is put the inner stop back closer to where it was supposed to be, this seems to richen up the lean spot in the middle, lean up the rich area under heavy throttle and extend the super lean slight throttle just a smidge... this may be the best compromise, then fine tune things... see how it goes, the bucking
wasn't horrible today but its still annoying at times.

and the last around town gas mileage was 16.7, yea, I was trying a few different things but I think Im on the rich side of where I should be.

Thanks

Keith

[Keith Park]

tried a couple things, just for shitty giggles...
tried a 007 MPS on it, this is a T3 70-71 unit, long nose, and the only thing I touched was the main mixture... it ran rather well but same kind of mixture curve once I had adjusted the main mixture in, still that rich area just off closed throttle, so the long/short nose units appear to give me close or the same results.

Then I tried a 116, this is a 73 T3 MPS, with the aneroid only, no diaphragm.
Mixture curve was decent once main mixture was adjusted, the rich spot off closed throttle was VERY narrow, still there though and even without the full load enrichment connected it did OK going to full throttle, BUT... under higher RPM (I assimilated highway by putting it in 3rd at 50) it was very rich under light throttle over a larger range, so better at lower RPM but worse at higher... still, interesting seeing how it would react.

With the trigger contacts advanced (I though I had them advanced, but actually had them retarded) the intermittent missing in the AFR 13's is much better, perhaps if I clearance the dizzy and get them just a bit more advanced I can run the 13's smoothly at lower RPM!

So progress, but still the bucking nemesis is there.

Keith

[Keith Park]

Put the inner stop back to where the factory had it, or as close as I could get.
Clearanced the distributor, advanced the trigger timing and that made a HUGE improvement, no more missing under light throttle in the 13's, or very minor now. I noodled with the shunt on the head temp sensor so get rid of the lean spot on warmup so that's better now. Runs well, just that rich spot at light throttle as has been there all along and the bucking.

Now for the TPS, it bucks unplugged as well, BUT... if it closes and enacts the idle the AFR gets leaner, into the 12's IF the RPM is high enough, does it do that at lower RPM too and the "Smog" just doesn't clear out of the muffler around the sensor at lower RPM?

Anywho, should I adjust the TPS so it hits idle circuit SOONER and potentially leans out more at small throttle openings or will that mess up off the line too much? OR do I want the eliminate as much of the 2 degree's of slop that the factory setting has so its not in that transitional state until the throttle is nearly closed?

Keith

[raygreenwood]

[Keith Park]

OK, so I want a little under 2deg of slop?
This particular TPS was new when I got it and seems to be
pretty well made, I have seen the sloppy ones that you mentioned in your
writeup on these and this one looks better. I will try and reduce that slop just a bit and pay more attention to how its adjusted. This may wait till spring as Im running out of weather now but maybe Ill get one more shot at it before its wraps for this season. Its running better now though and once I get the oil leaks taken care of... but that's a post for another forum

Thanks Ray.

[Keith Park]

OK, warm day, fixed the leaky cooler lines and had some time for the TPS.
here is a pix of the one I have. I have a good idea of how it works but still have a couple questions...
There is some play in the shaft as it should have, but the back and forth between the 2 contacts is pretty tight, sleeving one of the contacts would probably make it too tight but there is additional slop where the main shaft rocks the whole thing back and forth... I could stick a shim in there and tighten that up but im still a bit uncertain as to what im adjusting...
the opening of the idle circuit contacts after the throttle is lifted from closed
or the closing of the enrichment contacts? I think Im looking at a little different designed TPS than the one you were when you wrote the instructions but maybe im having a brain Fart.

Also, this is a 5pin TPS, with the full load enrichment wire not in the harness or not connected, BUT, half of the toothed accelerator pump contacts IS that unconnected end contact. Might I have the wrong TPS for this system (73 914 2L)?

It does buck with the throttle fully closed so I don't think ALL of it is from the TPS, unless that slop in the TPS is still a factor with the throttle fully closed.


im getting 15-16MPG around town, so that rich off throttle spot seems to be
dragging this down as the highway mileage is 22.... just fine. Id go a bit leaner, but the part throttle lean spot is well into the 13's now and I do get some intermittent missing although its ALOT better with the trigger points advanced.

Keith