TheSamba.com :: View topic - One question on my 73 SB FI auto trans about harsh idle .

Fri Jul 29, 2016 5:49 pm

Yesterday I drove a 20 mile round trip . 10 miles in 90* heat maybe 95 .

It was all street traffic 40 MPH tops. Lots of stop and go . It just fine going there and after 25 minute I came out and started it and it fired up normal yet the idle was down at least it felt lower and the engine even though it didn't miss and this only happened at a stop in drive foot on brake , as soon as I let off the brake it seemed fine. I checked the tach for idle and it was where it always is and the oil pressure and temp read what they normally do.

I have a very similar feel all the time this sort of vibration same thing only this time I could feel the vib in the steering wheel as well yet always it's mainly felt on the right side door and window this time that was less and the entire car had this slight vib and this harsh tone seemed like the way the engine was running different .

This is the first time I drove this car that trip since I replaced the MPS with the proper Bosch #. Even though the oil temp sat at 180* and got lower if I hit a spot of a street lined with trees .

I'll see what it does sat since at least the engine is cold and I can see if it's back to normal or something changed .

It's just odd that it was fine until the 25 minute cool off and re start.

Sat Jul 30, 2016 5:45 am

This is completely normal for an FI car.

Jim Adney has described what's happening -- when you shut off the engine, the heads cool faster than the rest of the engine. When you restart the car after 20-30 minutes of sitting, the head temp sensor thinks the engine is cooler than it really is, and this causes the engine to run a little rich when you restart it, making the idle rough. This goes away after the first 2-3 minutes, once the heads heat up again.

This only occurs in that 20-30 minute window. Less than that, and the heads are still warm enough. More than that, and the whole engine has time to cool down.

My car does the same thing.

You can read about this phenomenon by scrolling to the bottom of this page:
http://members.rennlist.com/pbanders/djetfund.htm
Note that although they describe a 10-15 minute window, in high ambient temperatures (like 90-95 degrees) this will occur after 20-30 minutes. I experience this all summer where I live, where it's 90-100 all summer.

Sat Jul 30, 2016 8:39 am

Donnie strickland wrote: This is completely normal for an FI car.

Jim Adney has described what's happening -- when you shut off the engine, the heads cool faster than the rest of the engine. When you restart the car after 20-30 minutes of sitting, the head temp sensor thinks the engine is cooler than it really is, and this causes the engine to run a little rich when you restart it, making the idle rough. This goes away after the first 2-3 minutes, once the heads heat up again.

This only occurs in that 20-30 minute window. Less than that, and the heads are still warm enough. More than that, and the whole engine has time to cool down.

My car does the same thing.

You can read about this phenomenon by scrolling to the bottom of this page:
http://members.rennlist.com/pbanders/djetfund.htm
Note that although they describe a 10-15 minute window, in high ambient temperatures (like 90-95 degrees) this will occur after 20-30 minutes. I experience this all summer where I live, where it's 90-100 all summer.

Yes....its been a common issue. And....Brad Anders actually breaks down on his site...what resistance the ECU really needs to see....versus what it commonly sees and what it is able to use.

It backs up what I have been saying for about 20 years now. The CHT was made to drop too low for running (it can drop as low as 70 ohms). Its also why on wome 914 models....they included an in line resistor of about 200 ohms for CHT.

In reality....he found that many the D-jet ECU's....have no response below 300 ohms....meaning no change. The reason they allow the CHT to go lower than 300 ohms is because it actually responds fairly quickly......and moderate changes in driving condition when you are right at the fully warmed up point...300 ohms.....can kick it back upward to 400+ causing poor ruuning. So keeping it margibally below 300 ohms....about 150-200 ohms is smart. Minor temp changes dont cause intermittent poor running that way.

The problem is that when it drops too low...100 ohms or less...it can be too far below the bottom cut off point to rapidly respond to enrich.

My testing has found that generally the ECU seems only to make noticable/measureable .....measureable by driving conditions.....od fuel enrichment.....in jumps of resistance.

Meaning.... You do not see incremental enrichment change followiing 1:1 with individual single ohm changes as the CHT resistance drops during warm up. The resolution inside the ECU is just not there.

It starts out in fairly coarse increments of 300-400 ohms from stone cold of about 2300-2500 ohms....and you see noticable enrichment changes about every 300-400 ohms.....until you get to about 1200 to 1500 ohms. Then you see better reaolution.....changes about every 150 to 175 ohms or so.

This does not really mean that the ECU is not making any fuel changes in smaller resistance increments.....its just that the engine is not,warmed up to the point where it can efficiently react to them.
As the engine and oil continues to warm up.....it becomes more efficient..mand responds to smaller changes in fuel mixture.

I believe the 200 ohm eesistor inline was also a common dealer fix on type 3.

One thing I have been experimenting with and should have ready by late this year or early 2017 when I get my engine in.....is getting away from the head mounted temp sensor 2.

Its really the wrong place for it for anything other than full warmed up or stone cold.

I have actually been able to replace the TS2 with a both a rheostat and a seven step resistor plate....meaning like a manual choke.....years ago.....and it worka really well. But I deally dont want to run manually the more I think about it.

So.....I am builing a,small resistor (thermistor actually) plate that has about 7 small value, dropping thermistors run in series. The larger value ones will be faster dropping...the smaller ones will be slower dropping.
All in all......once warmed up.....the bottom end resistance will be about 250 ohms.

The small resistor board will be ceramic coated......and then placed inside the crankcase in the oil.....where it will see much more uniform temperatures and better insulation to stop the start issue.
Its easy to do on the type 4 engine as it will be mounted to the back of the inspection plate.

Sorry for the length.....just some thoughts on the issue. Ray

Sat Jul 30, 2016 11:41 am

I started it cold today and it still seems to have this harshness . It runs the same yet I feel the vib in the steering wheel and can see the right front seat vib as well . It's more of a feel thing .

I can't say I would describe it as running rough yet something has changed to increase this vibration to now be felt in the steering wheel . Also I have this bracket for an XM radio and I can see it vibrate where I did notice it was not before.

It could be me yet this is the first time I had this happen . I don't usually look for things or pay that much attention yet I don't recall the vib in the steering wheel . It may have been there all along and I didn't feel it on the drive up there , at least I didn't notice it. This time it just seemed to stand out and was there the entire drive back and still feels this way today after it sat since last thursday .

I didn't check the HTC cold or hot I was in a rush just to go to the store before EVERYONE was there.

If I recall the HTC in there drops to 70 ohms last I checked yet it was not doing this.

As I said all that was different was the new MPS and it was the first time I drove with this MPS in hot weather .

I wonder if there is a change and it's not my imagination , very possible .

I wonder if I should check the female terminal ends of the TPS and MPS and trigger points to see if any are loose and the heat made one or more loose .

In 2009 I checked everything from the ECU plug to each connector and all seemed fine yet it was not hot or of course running . I need to check the HTC cold and hot . I did clean and tighten the ECU terminals in 2009 and the injector terminals but never the MPS or TPS or trigger .

I did try a 250 ohm resister before for the HTC it never seemed to change anything. This was when I was dealing with the engine running smoother with the IAD temp sensor un plugged in an attempt to get it to run richer which an unplugged air temp sensor does. When I did that the RPM picked up and the erratic miss I hear and feel at the exhaust was gone yet at the same time the idle would at times be 1000 idle to 1500 idle , it was all over the place and drove me nuts .

It's been better with the new MPS and the idle holds within 50 rpm .

Sat Jul 30, 2016 1:42 pm

So you put in a new/different MPS?....did you do any tuning or adjusting of it?

That is most probably it.....especially as you note its the first time you have driven in hot weather. When an engine is no longer new.....its vacuum signature changes over time as compression drops with wear and age.
Just dropping in an MPS that is adjusted largely.....but probably not exactly.... like the one you had....may cause the car to run well ....and quite similar to how it was.....but not exact. You may be a little leaner or richer.

When the ambient temperature rises.....the CHT (TS2) and IAT (TS1) are going to change your mixture even further. It will change how it runs. Ray

Sat Jul 30, 2016 2:49 pm

raygreenwood wrote: So you put in a new/different MPS?....did you do any tuning or adjusting of it?

That is most probably it.....especially as you note its the first time you have driven in hot weather. When an engine is no longer new.....its vacuum signature changes over time as compression drops with wear and age.
Just dropping in an MPS that is adjusted largely.....but probably not exactly.... like the one you had....may cause the car to run well ....and quite similar to how it was.....but not exact. You may be a little leaner or richer.

When the ambient temperature rises.....the CHT (TS2) and IAT (TS1) are going to change your mixture even further. It will change how it runs. Ray

No I didn't adjust the new MPS. I ran a hell of a lot better than it did with the one I had in there. At least I could set the idle speed and keep the TS1 plugged in. The one I had in the car for many years was a Bosch # 0 280 100 101 VW # 311 906 051 D and it's an E system the old one was a Bosch 0 280 100 106 VW # 311 906 051E and that came with this car and it ran the same with either one . I didn't look both looked the same and didn't know about these numbers back in 85 didn't
have internet until 2000. I just stuck it in because it was new at the time and came off a 72 with the only diff was the 72 didn't have the EGR crap.

See the issue now is yes it ran fine going the 10 mile trip , I didn't notice any change at all then after I restarted it it ran a bit different and sounded different . Then I drove it today It started fine and was cold yet it now still has this vibration and harsh sound . I thought after I let it set for a few days it would be back to where it was before . I can't describe the sound it's not engine noise it's more like exhaust drone I hear this ahead of both sides if I listen just ahead of the rear wheels . It has this Empi header and the quiet pack deal and the heat exchangers and the tubes from the fan to the HE's . Before I could hear the valve's slight tick, this is drown out by this what I would call exhaust drone . The drone was there before but not quite like this . No it was not perfect before but I could live with it . It still has plenty of power and I doubt the valve lash just suddenly changed.

All I can do is tomarrow check the HTC cold and look at the muffler and then maybe check the valve lash . I really have no idea where to go from here . it's just weird that if was fine going there then changed after I started it and drove back . It was not that hot out 95 at the top and not hills or freeway driving just a lot of stop and go traffic 40 mph max I just kept the auto trans in second gear because of the slow speed and stop and go . The only other change was I filled up with 87 octane instead of 89 over a week ago 1/3 of the tank was 89 yet it ran fine on 87 before.

It's been near 90 hear a few times this month and last month yet these were 2 mile trips and it was fine and the oil temp got close to 180* it was fine. I know it was not over heating even on this 20 mile round trip .

It seems like the 25 minute cool down it had after the 10 mile trip caused what ever changed to change, or it was something that was going on that suddenly showed up and may have even if I didn't make that 20 mile round trip. I listen by both rear fender air intakes and just hear a quite fan .

I realize this is an odd problem for anyone to tell without hearing it before and after .

I could be my ears , I have scalp dermatitis that is in my ears so the wax does not always come out and some did a few days before then i'm in a hot car and it's humid then in A/C it that building then back out in the heat and humid air . I noticed the oil temp didn't raise to 180* for at least 5 miles when I started out and when it sat for 25 minutes it was down to 160* . I heard no pinging or had no power loss.

We had this damn garage fire sept30 2015 then in nov 2016 they replaced the garage doors with steel ones so now it's hotter than blazes out there because the sun hits that door from the west so it hits 105* in there by noon .

In the morning I can take a look at a few things just to see if anything stands out . I really don't have any way of checking how lean or rich it is so all I can do is check a few things out and see what gives. It had to be the cool down that caused this change even if it's my hearing I can feel it this vib everywhere I place my hand on the car . Maybe an engine mount ?

Sat Jul 30, 2016 3:35 pm

I'll bet point gap/ dwell changed. That would be first on my checklist.

Sat Jul 30, 2016 3:46 pm

Tram wrote: I'll bet point gap/ dwell changed. That would be first on my checklist.

I have a pertronix .

Sat Jul 30, 2016 3:52 pm

blues90 wrote: Tram wrote: I'll bet point gap/ dwell changed. That would be first on my checklist.

I have a pertronix .

Though the "gap" does not change due to carbon burning with Pertronix. ....I would check everything anyway with the ignition. The module does vary with position so if you have not checked it for a,while.....its worth it.

The original answer thougb frkm early on is still the most probable. The fact that TS2 on all D-jet drops too low in resistance.....and shows the issue in hotter weather and has an odd cool down cycle is a known characteristic. Ray

Sat Jul 30, 2016 5:24 pm

raygreenwood wrote: blues90 wrote: Tram wrote: I'll bet point gap/ dwell changed. That would be first on my checklist.

I have a pertronix .

Though the "gap" does not change due to carbon burning with Pertronix. ....I would check everything anyway with the ignition. The module does vary with position so if you have not checked it for a,while.....its worth it.

The original answer thougb frkm early on is still the most probable. The fact that TS2 on all D-jet drops too low in resistance.....and shows the issue in hotter weather and has an odd cool down cycle is a known characteristic. Ray

I just a few months ago checked the pertronix gap .

I'm not sure I understand about the TS2 to low in resistance, if this is normal or should be checked cold and hot. Or do I need a resistor?

Sat Jul 30, 2016 5:49 pm

blues90 wrote: raygreenwood wrote: blues90 wrote: Tram wrote: I'll bet point gap/ dwell changed. That would be first on my checklist.

I have a pertronix .

Though the "gap" does not change due to carbon burning with Pertronix. ....I would check everything anyway with the ignition. The module does vary with position so if you have not checked it for a,while.....its worth it.

The original answer thougb frkm early on is still the most probable. The fact that TS2 on all D-jet drops too low in resistance.....and shows the issue in hotter weather and has an odd cool down cycle is a known characteristic. Ray

I just a few months ago checked the pertronix gap .

I'm not sure I understand about the TS2 to low in resistance, if this is normal or should be checked cold and hot. Or do I need a resistor?

The TS2....does not just react to the head temperature. It reacts to the temperature of the cooling air flowing over it....what little there is.

For instance....2-3 months ago when it was cooler outside....at the warmed up temperature of the CHT/TS2.....the resistance may have been 125-175 ohms.

Now its hot outside....so the cooling air is a little hotter and the head temp runs slightly hotter.....so the TS2 will usually hit rock bottom resistance of 75-100 ohms. That makes the fuel mixture leaner.

Also....since its hotter outside......the engine...meaning oil, cylinders, piston and crank and crankcase.....all cool off slower. In that 20-30 minute short stop range the engine may only cool off about 30-40 degrees. However the beads........with all of those fins.....may cool off a hundred degrees or more.
This brings the TS2 resistance back up....maybe to 250 ohms. That is too rich for the largely still warmed up engine. So......it runs like crap for a few minutes until the TS2 warms up and drops resistance again.

If you replaced the MPS back when it was still cool outside and the TS2 was not dropping down all the way from warm weather......it may have run just fine back in cool weather....but can be too lean in the hot weather. Ray

Sat Jul 30, 2016 6:02 pm

raygreenwood wrote: blues90 wrote: raygreenwood wrote: blues90 wrote: Tram wrote: I'll bet point gap/ dwell changed. That would be first on my checklist.

I have a pertronix .

Though the "gap" does not change due to carbon burning with Pertronix. ....I would check everything anyway with the ignition. The module does vary with position so if you have not checked it for a,while.....its worth it.

The original answer thougb frkm early on is still the most probable. The fact that TS2 on all D-jet drops too low in resistance.....and shows the issue in hotter weather and has an odd cool down cycle is a known characteristic. Ray

I just a few months ago checked the pertronix gap .

I'm not sure I understand about the TS2 to low in resistance, if this is normal or should be checked cold and hot. Or do I need a resistor?

The TS2....does not just react to the head temperature. It reacts to the temperature of the cooling air flowing over it....what little there is.

For instance....2-3 months ago when it was cooler outside....at the warmed up temperature of the CHT/TS2.....the resistance may have been 125-175 ohms.

Now its hot outside....so the cooling air is a little hotter and the head temp runs slightly hotter.....so the TS2 will usually hit rock bottom resistance of 75-100 ohms. That makes the fuel mixture leaner.

Also....since its hotter outside......the engine...meaning oil, cylinders, piston and crank and crankcase.....all cool off slower. In that 20-30 minute short stop range the engine may only cool off about 30-40 degrees. However the beads........with all of those fins.....may cool off a hundred degrees or more.
This brings the TS2 resistance back up....maybe to 250 ohms. That is too rich for the largely still warmed up engine. So......it runs like crap for a few minutes until the TS2 warms up and drops resistance again.

If you replaced the MPS back when it was still cool outside and the TS2 was not dropping down all the way from warm weather......it may have run just fine back in cool weather....but can be too lean in the hot weather. Ray

Yes That I understand . What I miss is it was hot driving there 10 miles and it didn't act this way and even after everything sat for 2 days it now runs like it did on the way back even when the engines cold. Also even though I've driven it a few times since replacing the MPS in hot weather not as far or as long it didn't do this.

Sat Jul 30, 2016 8:23 pm

So you have only,driven it a few times since repacinf the,MPS.....and over a wide range of time and weather changea it sounds like.

So you really dont have much of a baseline for whether it was running steady and nodmql kr not. 10 miles is barely warmed up.

I woule check EFI connections, fuel and condition of plugs. Ray

Sun Jul 31, 2016 12:35 pm

raygreenwood wrote: So you have only,driven it a few times since repacinf the,MPS.....and over a wide range of time and weather changea it sounds like.

So you really dont have much of a baseline for whether it was running steady and nodmql kr not. 10 miles is barely warmed up.

I woule check EFI connections, fuel and condition of plugs. Ray

All I know is with the new MPS even when it was driven in hot weather on short trips and the oil temp did get to 160* it still ran fine or at least didn't have this odd vibration. Plus it ran fine going the 10 miles trip up there and sat 20 to 25 minutes then the vibration came in to play and even since it sat since then it still has the vibration . It always had a vibration in drive at a stop yet it has changed . This leads me to think it had something to do with the cooling off period for the 20 + minutes .

I need to check a few things like the HTS and see what it reads cold and that would be 85 * . It seems odd the HTS would suddenly go bad after cooling down yet anything is possible . I need to drive it monday and see if I can describe it better . I know the HTS can't be open or it would not run.

I have noticed starting cold and backing out of the garage lately I back out close the door then pull forward a bit then back to get out since a SUV is parked behind me and when I put it in reverse the idle drops then comes back up , does not do this in forward gears and it only happened 3 times 2 backing out of the garage and 1 backing out of the parking space on the 20 round trip .

Sometimes I need to cycle the key 8 times to prime the system so it starts other times 5 times depending on how long it sits, so I need to at least check the pressure running.

It's possible I got a crappy gas last fill up since 1/3 of the tank was 89 octane and maybe it mixed yet that seems like a stretch . Since I installed the new MPS I was using 89 octane . Here at high altitudes 87 seems enough.

If it were not so damn hot out in the garage it would be easier to work and think .

All I can do now is check the MPS and TPS and trigger connectors and the grounds and tighten them and see if this affects a change then go from there . Also I need to feel the engine while running to see if this is the vib source . I did find a small piece of paper in the generator near the upper brush and pulled it out so maybe it was sucked in the fan and made it's way up there.

It does not seem to run different than before . I hate these sorts of issues that come out of no where.

Just an update.

I checked the cylinder head temp sensor and @ 93 * it was 1900 ohms I can't seem to find the temp chart to tell where it should be at that temp. What I did find was since the plastic connector is black with age and I can no longer see if the terminals are connected and it seemed to pull out easy I found a double one I had and could see through it and found it was really difficult to push the two terminals together so I opened the female one up a bit and now it's tight . It seems the contact was only between the plastic cover pressing the terminals together. It seems to be close to back to where it was before. I may have got the connections to tight yet I feel I can pull the female one out if I have to .

Mon Aug 01, 2016 10:53 am

I drove it today and it seemed better now that the HTC connector is tight .

I don;t know what the HTC reads when it's hot .

One other question. In the Bentley they show a tester for the fuel system . Is this tester they show and the tests that follow for the vw tester that plugs into the test plug on a 73 or is it one you plug in series with the ECU plug ?

Mon Aug 01, 2016 11:19 am

blues90 wrote: I drove it today and it seemed better now that the HTC connector is tight .

I don;t know what the HTC reads when it's hot .

One other question. In the Bentley they show a tester for the fuel system . Is this tester they show and the tests that follow for the vw tester that plugs into the test plug on a 73 or is it one you plug in series with the ECU plug ?

The Bentley shows two different testers. Which one are you asking about?

Bosch EFAW series:

VW1218:

Mon Aug 01, 2016 11:48 am

KTPhil wrote: blues90 wrote: I drove it today and it seemed better now that the HTC connector is tight .

I don;t know what the HTC reads when it's hot .

One other question. In the Bentley they show a tester for the fuel system . Is this tester they show and the tests that follow for the vw tester that plugs into the test plug on a 73 or is it one you plug in series with the ECU plug ?

The Bentley shows two different testers. Which one are you asking about?

Bosch EFAW series:

VW1218:

They list 3 in the text EFAW 193 uses plug adapter , not sure if this is for plugging in the cars test connector . The 243 was the one that the Bentley states VW dealers used the most and the 1218 was the latest one out from photo's is see of the 1218 it looks like it plugs between the ECU and test unit. Don't know about the 243 .

The only reason I asked is that I was hoping I could use the test plug to do tests like read the HTC cold without pulling the plug .

Mainly I'm trying to find out if there are any FI connections that are not well connected .

Seems right now I need to check the terminals on the TPS and MPS and trigger points and if no change then I need to pull the ECU and check from there .

Since I got the TS2 terminals or Head temp sensor in a clear plastic holder I now see a difference . Also sometimes I wonder if the ECU see's the TS2 proper. I know the connection to the ECU is good because if the TS2 is unplugged the car will not start or will quit if I unplug it. What I wonder is if the ECU changes the mix from hot to cold.

I recall trying a 250 ohm resister in line with TS2 and it didn't seem to change anything yet this was at idle yet something should have changed at idle or it could be a change that is not drastic enough to hear or feel. It may be something one needs a exhaust sniffer to know. I do recall back in 97 I had a variable resister on TS2 and had a sniffer on it at work trying to lean it out to pass smog and you could see the sniffer see the change yet I didn't notice it running any different.

Mon Aug 01, 2016 12:18 pm

The test plug has nothing significant to do with the EFI.

As for testing the connections......that is the lroblem with using any of the fuel inje tion testers. They are only as good as the wires and connections of the system they are plugged into. Even modern systems are hamstrung by this fact.

The best way to make absolutely sure that all of your connectors are connecting properly....is to assume they are not due to 40 years of vibration, oxidization and heat cycling.

Spend an hour......with a pin out tool....and pull each connector one at a time....from each female plug. Test fit it on a male pin....and if its loose.....lightly crimp/tighten the side rolls of the terminal with small pliers.
If the wire joint is frayed or corrodex....snip off the end and with a real crimper tool....crimp on a new one.

Does the ECU change rich to lean from hot and cold.....from the CHT?.....absolutely! Thats all it s there for.
The ECU read resistance to ground. The CHT is a ground.....with a thermal resistor or thermistor between the ground of the threads on the CHT and the wire going to the ECU.

As temperature rises......the resistance drops....and fuel mixture gets leaner.

Plugging in a resistor of about 200 ohms....should do very little at cold idle. This is because the resistance of the CHT when the car is cold is roughly,2300 to 2500 ohms. An extra 200 ohms means nothing when cold because it pretty much puts total resistance beyoned the range that the ECU can react to.

Its alreay as rich as it can get at idle when cold. Howeverm....once warmed up....when the CHT resistance has dropped below 300 ohms.....that 200 ohm resistor makes a difference. Ray

Mon Aug 01, 2016 12:56 pm

If I remember right, the Bosch 228 was just the old 193 with the "late TPS adapter" (part 243) built in. It does nothing you can't duplicate with a VOM. It does make diagnosis faster, though. It hooks up between the ECU and the rest of the system. You can run the engine with it in place.

The VW1218 actually tests the ECU itself, as well as wiring and sensors. It hooks up in place of the ECU, and you NEVER want to run the engine with this tester in place.

As said, the VW Diagnosis connector is not connected to the EFI in any way.

You can hook up your VOM to the connector pulled off the ECU, and then wiggle the component connectors and gently tug on the wires to see if the reading jumps, indicating a poor or broken connection. This may not catch all near-failures, though.

As posted, you can help the system reliability by taking the connectors apart and GENTLY tightening up the two roll edges.

Mon Aug 01, 2016 1:01 pm

Buy an 02 sniffer & adjust your MPS/air fuel ratio/tailpipe emissions, so you'd Know you were actually gonna see/feel a difference. :idea: