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Wed Aug 07, 2024 10:55 am

Just to add to the possibilities, condensors and coils can fail when hot, too. :roll:

Tue Aug 20, 2024 10:04 am

I had to top off the battery after sitting for a bit. Fuel pressure was too high at 33.5 psi (if my cheap gauge was to be believed, I have another so I may try to verify that.) Adjusted that back down to 28 PSI.
Let it run for a while and didn't have any issues. Will take it out for some short drives soon and see if it pops up again.

Wed Aug 21, 2024 10:20 am

nogoodwithusernames wrote: I had to top off the battery after sitting for a bit. Fuel pressure was too high at 33.5 psi (if my cheap gauge was to be believed, I have another so I may try to verify that.) Adjusted that back down to 28 PSI.
Let it run for a while and didn't have any issues. Will take it out for some short drives soon and see if it pops up again.

The high fuel pressure can cause your original symptom. In these fixed pressure systems (actually it goes for ny EFI system) every 1 psi = 3.57% of your total fuel mixture (100% / 28 = 3.5714% for each 1 psi).

So, running 33.5 psi = running 19.6% richer than normal at any rpm. When you are just idling, two ports tend to run a little wet because of the out of time injections in this system. The injected fuel spreay against a closee valve so the ports get wet and excessive fuel builds up. Its not an issue once you are over about 1500 rpm.

This is why more modern "batch fire" systems tend to have a fuel curve that runs fairly lean at idle to partly compensate for this issue.

The other question is why is your fuel pressure that high. You note that you had to top off the battery. You may be running voltage that is too high or too low.

Voltage can cause two issues with D-jet.

1. On one hand, low voltage...say below 10 volts....causes rich running because of issues it causes in the ECU.

2. On the other hand, high voltage can cause over run/over speed at the pump. That can cause high fuel pressure. BUT....the fuel pressure regulator "should" be able to compensate for that and keep pressure stable.

A related issue with stalling and high fuel pressure. The low impedance injectors used in D-jet have a notorious issue. They do not seal up well at pressures of 35 psi and higher. This means at low rpm they may be leaking because they have a hard time reseating. The reseating issue is more of aproblem at high rpm/cycle rates.
The other issue is that at pressures above 35 psi the angle of the pintle causes the spray pettern to degrade to a stream instead of droplets. This makes the "wet port" thing more of an issue at idle.

You noted that your pressure gauge may not be accurate. If your fuel pressure is actually higher than 33.5 psi...this may be part of the issue as well.

So, just for the heck of it, check your voltage on the EFI system. The battery being low may have nothing to do with anything but its worth checking.

This is probably one of the better "cheap" gauges I would use. You should look at the 0-60 psi model. Its +/- 1.6% of the full scalle accuracy. Its not "graded" buit is equovalent to a class 1A.

http://www.mcmaster.com/#3845k5/=y6zqxj

If you have a bit more in your budget...I reccomend this one. Again, slect the 0-60 psi range. This is +/- 1% full scale accurate. Class 1A graded.

http://www.mcmaster.com/#4240k7/=y6zsm0

If you really have the money and have other things to work on and need a GREAT gauge. :D

This is what I have now....its little bigger...but is grade 2A. It has 0.5% accuracy of full scale and is liquid filled and has grad marks in 1/2 psi increments.....and very importantly...its good to 212F...which means I can leave in in the engine compartment for a little while tuning without damaging it....which is something most people do not realize about basic gauges...is that they are generally not designed for high temp. Most are maxed at 125-150F. Leaving them in the engine compartment makes them inaccurate fast.

http://www.mcmaster.com/#4063k23/=y6zvtw

Ray

Wed Aug 21, 2024 1:42 pm

Ray, as always the level of detail you put into your posts is appreciated.

I did test voltage already, knowing it can cause issues with D-jet. It held steady at 12.5 volts while running. Did not change more than a few points when reving. I do get a slight glow in the Gen light especially at night with headlights and such on.

I'll check fuel pressure again with another gauge, I'll see if we have a better one at work I could borrow for an evening.

I am not sure why fuel pressure would have changed, I cannot remember if I checked it after changing out the fuel pump back when the original one went out. That was something like 7 years ago now. It's very possible that it's been too high since then.

raygreenwood wrote: nogoodwithusernames wrote: I had to top off the battery after sitting for a bit. Fuel pressure was too high at 33.5 psi (if my cheap gauge was to be believed, I have another so I may try to verify that.) Adjusted that back down to 28 PSI.
Let it run for a while and didn't have any issues. Will take it out for some short drives soon and see if it pops up again.

The high fuel pressure can cause your original symptom. In these fixed pressure systems (actually it goes for ny EFI system) every 1 psi = 3.57% of your total fuel mixture (100% / 28 = 3.5714% for each 1 psi).

So, running 33.5 psi = running 19.6% richer than normal at any rpm. When you are just idling, two ports tend to run a little wet because of the out of time injections in this system. The injected fuel spreay against a closee valve so the ports get wet and excessive fuel builds up. Its not an issue once you are over about 1500 rpm.

This is why more modern "batch fire" systems tend to have a fuel curve that runs fairly lean at idle to partly compensate for this issue.

The other question is why is your fuel pressure that high. You note that you had to top off the battery. You may be running voltage that is too high or too low.

Voltage can cause two issues with D-jet.

1. On one hand, low voltage...say below 10 volts....causes rich running because of issues it causes in the ECU.

2. On the other hand, high voltage can cause over run/over speed at the pump. That can cause high fuel pressure. BUT....the fuel pressure regulator "should" be able to compensate for that and keep pressure stable.

A related issue with stalling and high fuel pressure. The low impedance injectors used in D-jet have a notorious issue. They do not seal up well at pressures of 35 psi and higher. This means at low rpm they may be leaking because they have a hard time reseating. The reseating issue is more of aproblem at high rpm/cycle rates.
The other issue is that at pressures above 35 psi the angle of the pintle causes the spray pettern to degrade to a stream instead of droplets. This makes the "wet port" thing more of an issue at idle.

You noted that your pressure gauge may not be accurate. If your fuel pressure is actually higher than 33.5 psi...this may be part of the issue as well.

So, just for the heck of it, check your voltage on the EFI system. The battery being low may have nothing to do with anything but its worth checking.

This is probably one of the better "cheap" gauges I would use. You should look at the 0-60 psi model. Its +/- 1.6% of the full scalle accuracy. Its not "graded" buit is equovalent to a class 1A.

http://www.mcmaster.com/#3845k5/=y6zqxj

If you have a bit more in your budget...I reccomend this one. Again, slect the 0-60 psi range. This is +/- 1% full scale accurate. Class 1A graded.

http://www.mcmaster.com/#4240k7/=y6zsm0

If you really have the money and have other things to work on and need a GREAT gauge. :D

This is what I have now....its little bigger...but is grade 2A. It has 0.5% accuracy of full scale and is liquid filled and has grad marks in 1/2 psi increments.....and very importantly...its good to 212F...which means I can leave in in the engine compartment for a little while tuning without damaging it....which is something most people do not realize about basic gauges...is that they are generally not designed for high temp. Most are maxed at 125-150F. Leaving them in the engine compartment makes them inaccurate fast.

http://www.mcmaster.com/#4063k23/=y6zvtw

Ray

Wed Aug 21, 2024 1:49 pm

Charging voltage is low. Should be high 13s to low 14s. This needs to be addressed before going any further.

Wed Aug 21, 2024 2:11 pm

Tram wrote: Charging voltage is low. Should be high 13s to low 14s. This needs to be addressed before going any further.

Copy that, will check out the alternator and regulator. I have a known good of each in my Squareback (T4 motor) that I can swap out to test. Hopefully just the VR as that's a much easier and cheaper job.

The battery is a bit old and like I mentioned needed a quick charge. It did start once without a charge but didn't have enough juice to start up again after it died. (Too rich, forgot to hook up the CHT sensor after testing that :oops: ) Battery should only really affect starting though, not once it's running.

Thu Aug 22, 2024 6:30 am

nogoodwithusernames wrote: Tram wrote: Charging voltage is low. Should be high 13s to low 14s. This needs to be addressed before going any further.

Copy that, will check out the alternator and regulator. I have a known good of each in my Squareback (T4 motor) that I can swap out to test. Hopefully just the VR as that's a much easier and cheaper job.

The battery is a bit old and like I mentioned needed a quick charge. It did start once without a charge but didn't have enough juice to start up again after it died. (Too rich, forgot to hook up the CHT sensor after testing that :oops: ) Battery should only really affect starting though, not once it's running.

No, the battery is between the generator/alternator and the efi system. If it's affecting voltage while driving, that can affect fuel mixture if it drops low enough.

Having low voltage while driving....say below 10 volts....can cause rich running. And, it can cause poor coil output.
And.....while voltage does affect how the fuel pump runs, the engine should never see the variation because the D-jet system puts out roughly 10X to 12X more fuel than the engine can use. If that went to 8X-10X or 12X to 14X.....the regulator can "regulate" both situations.

And ....low voltage, would cause slower pump running......which would be leaner not richer...but it does not matter at the level of fuel the pump provides . And high voltage would run the pump faster....which does not matter because the regulator will vent excess to return. It all stays the same.....or close enough.......from the fuel pump point of view.

If your fuel pressure was properly adjusted last time the car was driven...and you did not change it....then Something changed either at the check valve in the pump (not bypassing as much....maybe partially stuck or has a clog or corrosion)......or something changed at the regulator (same thing, maybe corrosion plugging the outlet port downstream of the metering plate)......or.....maybe the return line between fuel pressure regulator and the tank is partially plugged.....either a metal line got dented or a rubber line got kinked.

Ray

Thu Aug 22, 2024 8:10 am

Swapped the voltage regulator out with no change, idles at 12.5v. If I hold it around 2500 rpms it will rise to 13.5v. A quick blip of the throttle doesn't change anything. Guess I'll pull the alternator soon.

Sat Jan 04, 2025 2:28 pm

Yet another loping idle concern. Bought the car non running. Replaced all the HP lines in the engine compartment (to the injectors as well), replaced injector seals, swapped to a 2 port pump, replaced vacuum lines, replaced head temp sensor, adjusted point gap and valve clearance, fuel pressure is at 28psi.

Full scenario. Initial cold start she idles great for about one minute. After about a minute she starts to idle erradic with a bit of a lope. Seems to rev out just fine. Ive read many posts on here and none have really helped. looking for a little insight from the gurus.

Sat Jan 04, 2025 5:55 pm

michaelmike wrote: Yet another loping idle concern. Bought the car non running. Replaced all the HP lines in the engine compartment (to the injectors as well), replaced injector seals, swapped to a 2 port pump, replaced vacuum lines, replaced head temp sensor, adjusted point gap and valve clearance, fuel pressure is at 28psi.

Full scenario. Initial cold start she idles great for about one minute. After about a minute she starts to idle erradic with a bit of a lope. Seems to rev out just fine. Ive read many posts on here and none have really helped. looking for a little insight from the gurus.

Questions:

1. Do you have a cold start injector and is it operating during that one minute?
2. Is your AAR working? Is it open when cold...and how much and is it closing once it warms up?

3. So you have a two port pump. What did you do with the return line and you note 28 psi, is the pressure gauge needle stable/steady or rattling back and forth. If so, how many psi?
Does the gauge needle dip when you rev it? How much?

4. When you shut down, how fast does the pressure on the system drop?

5. What about seals and hose (vacuum hoses)?

6. Have you checked the MPS to see if it holds vacuum?

7. What is the voltage feeding both the fuel pump relay and the main relay that feeds the injection system?

8. What is your timing at idle?

Ray

Sat Jan 04, 2025 7:47 pm

I do have the cold start.

I will look into testing the AAR.

I plumbed the two port pump as referenced on every post on thesamba. PSI holds steady with no fluctuation through all rpms. Have not viewed how quickly it drops.

All fuel lines and vacuum lines were replaced.

Testing the mps, im assuming it would be a leakdown test?

Havent checked voltage at these points, whats the location of the FI relay.

Will check timing tomorrow.

Sat Jan 04, 2025 8:37 pm

Ok,

I got manic and went to investigate things in the rain and dark. The AAR in the car (included in the photo) seems to do nothing as its still drawing vacuum when the engine is warm after running 10min. I observe is it doing little when I pinch off the line to the air cleaner. I suspect i should at least replace it for good measure?

Now the interesting part. After messing with stuff I questioned if it was idling too low instead of "struggling" to idle. Grabbed a 15mm wrench and screwdriver and with an 1/8 of a turn she was idling. Like the steadiest idle i've ever had in a vw. Ill take it.

The new issue is the it stumbles and hesitates right off idle so now im going down a new trail it seems. Thoughts?

Sat Jan 11, 2025 5:33 am

You should clean the aar and adjust it to make it work

Sat Jan 11, 2025 10:10 am

Yes, I did clean the aar and it appears to function. I believe I need to clean adjust the TVS as the car runs better with it unplugged leading me to believe its rotated too far and enriching it at idle.

Sat Jan 11, 2025 2:11 pm

michaelmike wrote: Yes, I did clean the aar and it appears to function. I believe I need to clean adjust the TVS as the car runs better with it unplugged leading me to believe its rotated too far and enriching it at idle.

Yes, good plan. KTPhil went through his recently and outlined how to do it, right before the Invasion if memory serves.

Mon Jan 13, 2025 10:48 am

Tram wrote: michaelmike wrote: Yes, I did clean the aar and it appears to function. I believe I need to clean adjust the TVS as the car runs better with it unplugged leading me to believe its rotated too far and enriching it at idle.

Yes, good plan. KTPhil went through his recently and outlined how to do it, right before the Invasion if memory serves.

I have cleaned my AAR, but that was years ago. That pot metal distorts with heat and so I spent quite a while filing/deburring, polishing the moving parts, then was careful to not overtighten it. I adjusted it a couple of times, but since the coil was aged, it was never a simple "fully opened/fully closed" deal... kind of a compromise; then I adjusted the idle air screw on the throttle body to compensate at warm idle.

By the way, I've noticed that the flange of the AAR interferes with the newer cases, and if you don't notice it, you will bend or break one of the "ears" on the mounting flange. I filed away to make clearance and now it sits flush and doesn't leak.

It was the TVS that I went through right before the T3 west coast Rally. Contact cleaner, degreaser, lube... it took a while but it cleared up my bucking problem.

Mon Jan 13, 2025 11:05 pm

KTPhil wrote: Tram wrote: michaelmike wrote: Yes, I did clean the aar and it appears to function. I believe I need to clean adjust the TVS as the car runs better with it unplugged leading me to believe its rotated too far and enriching it at idle.

Yes, good plan. KTPhil went through his recently and outlined how to do it, right before the Invasion if memory serves.

I have cleaned my AAR, but that was years ago. That pot metal distorts with heat and so I spent quite a while filing/deburring, polishing the moving parts, then was careful to not overtighten it. I adjusted it a couple of times, but since the coil was aged, it was never a simple "fully opened/fully closed" deal... kind of a compromise; then I adjusted the idle air screw on the throttle body to compensate at warm idle.

By the way, I've noticed that the flange of the AAR interferes with the newer cases, and if you don't notice it, you will bend or break one of the "ears" on the mounting flange. I filed away to make clearance and now it sits flush and doesn't leak.

It was the TVS that I went through right before the T3 west coast Rally. Contact cleaner, degreaser, lube... it took a while but it cleared up my bucking problem.

Yes, the TVS is what we were talking about. :D

Sat Feb 01, 2025 9:51 am

Just wanted to come back and update. I must reiterate the importance of voltage that everyone speaks of. After poking around I found my charging regulator was poorly functioning, kinda working when it wants. Replaced it with a Bosch SS one and have a smooth 14v. Now the dang car runs like a Swiss sewing machine! When all else fails check your voltage! Now on to other things.

Tue Feb 04, 2025 2:16 pm

Howdy,

Is there an off-the-shelf noid light for D-Jet testing?

If not, does anyone know the part numbers (DigiKey, etc…) to make one?

Thanks!
Robbie

Wed Feb 05, 2025 12:45 pm

airschooled wrote: Howdy,

Is there an off-the-shelf noid light for D-Jet testing?

If not, does anyone know the part numbers (DigiKey, etc…) to make one?

Thanks!
Robbie

From what both Tram and Ray tell us, the noid light wouldn't flash long enough to see. Most of us use a VOM (we've already got it for testing the rest of the FI system). You might catch part of the needle swing if you're watching it. You can also test the injector for voltage that way. Keep in mind this IS old tech, and these cars use a VOM for testing and diagnosis of any part of the FI system. This is because the FI system is resistance based.
There are 4 things to keep in mind about the FI system; One is resistance, two is stable voltage, and three is stable fuel pressure, the fourth thing is NO vacuum leaks are allowed.
I hope this helps.