TDI Conversion--Troubleshooting Apparent Electrical Problem

[HBB]

I've got a 1990 Syncro powered by an TDI ALH, and am looking for some help troubleshooting.

Specifications: This vehicle was set up as an mTDI at one point; apparently due to the complexity of controlling a VNT turbo, it was configured with an AHU exhaust manifold and KKK03 turbo. It was later converted to an eTDI, and is currently set up with an AHU ECU. I understand the van mostly sat for a few years before I acquired it. I've worked out a few bugs, but for the most part the engine has run well. I am not impressed with the wiring harness, and would like to start over from scratch at some point.

Symptoms: The engine died just a few blocks from home this morning. Very hard to get started again, took probably 20-30 seconds of cranking. When it did start, it ran at 1200 RPM, with no response from the accelerator. Took a peek in the engine compartment to see what was going on, no obvious problems , so I put it in gear and slowly limped back home.

I have a Scanguage in there, and while limping home it was showing an intake air temp of 270 (it was about 65 degrees out at the time) and an engine coolant temp of close to 500 degrees (the block was cold to the touch). I was also seeing a slight negative intake manifold pressure.

VCDS is showing 5 new codes that reappear after clearing:

00533 Mass Air Flow Sensor (G70)
48-10 Supply voltage - Intermittent

00522 Engine Coolant Temperature Sensor (G62)
30-00 Open or Short to Plus

00777 Accelerator Position Sensor (G79)
27-00 Implausible Signal

00527 Intake Manifold Temperature Sensor (G72)
30-10 Open or Short to Plus - Intermittent

00539 Fuel Temperature Sensor (G81)
30-00 Open or Short to Plus

In addition to those codes, I get a 00626 for Glow Plug Indicator Light Open or Short to Ground - Intermittent, but this code is always present (the glow plug light is not hooked up).

What I've Done:

1. First step was to inspect the engine compartment to make sure that I hadn't thrown the timing belt or anything catastrophic like that. All belts and hoses look good, no visible leaks, nothing looks, sounds, or smells like its wrong.

2. Second step was to see if I could get accelerator response bypassing the accelerator pedal. I'm not sure on the terminology here, so bear with me. There is a cable that runs from the accelerator pedal to the engine bay, where it is hooked up to what I think of as a accelerator position sensor. I manipulated this by hand to eliminate the possibility that the accelerator cable was bound up or broken. No response.

3. Third step was to hook up VCDS and see what codes were present. I then tried clearing the codes repeatedly, but they come back every time.

4. Fourth step was to disconnect the battery for a bit and then re-scan after hooking it back up. Codes still came back.

5. Next I tried firing up the engine again to see if there was any difference in the codes while running. Very hard to start, cranking for 10-15 seconds. I tried this a few times, and sometimes it would fire up with just a bump of the starter (which is how this engine usually operates), other times it would take quite a bit of cranking to get it to catch. No change in the codes when idling, still idling at 1200 RPM.

6. I then hooked VCDS back up to see if pedal input was registering. Acellerator position was registering properly, showing 0% with no input, and 100% floored. Brakes were registering as well.

7. After all that, I took a closer look at the engine wiring harness. I did find one spot where two ground wires had worn through the insulation. I separated the wires taped over the worn spots, and then checked to see if this made any difference in operation or codes. No change. I also noticed that the positive terminal of the battery has been making contact with the battery compartment cover (battery is under the passenger seat). This will need to be shielded in the future, but for now I made sure the positive terminal wasn't in contact with anything.


I know that I am getting a limp mode due to the wacky sensor inputs, but I'm not sure what is causing the problem.

If I had a spare ECU, I would hook that up so I could eliminate the possibility of a bad ECU.

Any ideas on how to identify the problem?

[?Waldo?]

I'd put the mTDI pump back on. There's no advantage to an eTDI unless you're running the VNT turbo.

[HBB]

I don't have the mTDI pump--it was swapped out several owners and many years ago.

Sourcing a pump and converting the engine back to a mechanical set up strikes me as a pretty complicated and expensive project. I hate to throw that sort of time and money at a problem that could be as simple as a loose connection or a bad ground.

[tjet]

Troubleshoot is this order:

00533 Mass Air Flow Sensor (G70)

00777 Accelerator Position Sensor (G79)

Then the temp sensors

[hans j]

Sounds like a wiring issue. I had a van come in last week with an AHU. One shop said they needed a new pump due to all the fault codes. First glance at the engine I saw a burned wire that started at the N75 and went all the way up to where the black/yellow clump of wires starts. I added in a fuse when I rewired it! There was quite a bit of vibration in their setup and the wire wore through and grounded itself on the intake manifold.

According to the wiring diagram: http://vwts.ru/electro/g3/g3_wd99_1z.pdf ALL of your faults are related with a ground wire. Double check continuity on the grounds and fix any wires that might be worn through.

At first I was thinking you had a bad CTS and maybe a bad power to the MAF, but after checking the wiring diagram, it's easy to see they all share the same ground wire somewhere. Fix that and your van should run just fine.
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1986 Canadian Syncro Westy TDI - 1989 Syncro Single Cab - 2001 Audi S4 - 1981 VW Caddy ABA - 1980 VW Caddy EV - 1973 VW T-181

[HBB]

Thanks for the responses, I appreciate all the help.

hans j, that sounds like the culprit. I was planning on tracking down a wiring diagram tomorrow, but you've saved me the trouble. I'll look into that ground first thing in the morning and report back.

[Vanagon Nut]

I agree with wiring issue. Likely at the engine portion of the harness.

Does the TDI have that giant round connector between the engine and ECU portions of harness? If so, I'd look there. Clean the connectors well.

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[MarkWard]

The throttle potentiometer is not weather proof. The ECU is programmed in such a way that if there is a fault in the system, the ECU goes into limp mode, which would be no throttle response and a steady idle just above normal idle. It is so you can safely move to a safe location.

Did you mention you have VCDS software? If so, you should be able to see the throttle pedal working in the software.

The temp sensors going way out of normal assuming the ambient is cool and the engine is not overheating could indicate some sort of short. The stock ambient temp sensor is also the boost sensor for the ECU. Coolant temp is for the gauge and ECU. Sensors out of parameter, could also cause the limp mode condition.

You'd probably get better info at the TDI club website. I would also suggest moving the throttle potentiometer into the cab. Look at my gallery and there are a couple pictures how I adapted the TDI all in one pedal to the Vanagon pedal using no cable.

As far as hard starting, if the ECU is getting the wrong temp, it won't crank fast enough to let the fuel be delivered. Look up Hamman mod on the TDI website. There are a couple work arounds for this hard start hot problem.

It sounds like you have a combination of parts. At some point it might make sense to standardize your setup to something VW sold. Mix matching parts, can work, but you need to really understand how the systems work.

My N75 valve got some dirt in the vent side and the symptom was van would move out from a light and then as the boost exceeded the limits would go into limp mode. Cycling the key would clear the fault temporarily until it sensed and overboost condition. A stuck VNT will also do the same thing. Good luck. Bid fan of the TDI flybywire in the vanagon.
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☮️

[HBB]

Well, upon further inspection, I am absolutely amazed that this van hasn't already burned to the ground.

Since what I was seeing in the engine compartment didn't match up with either the AHU or ALH wiring diagrams, I started tracing out wiring from the sensors that were throwing codes. I very quickly discovered this:

That burned up red wire is the other end of one of the ground wires that had worn through mentioned in my first post.

The blue/red wire didn't match up with what I was seeing in the wiring diagrams, so I unravelled the friction tape holding everything together, and found this:

The blue/red wire is connected to 8 black/yellow wires of varying gauges, along with two black wires. This isn't consistent with anything I'm seeing in the ALH and AHU wiring diagrams, so I am stuck chasing these out to see where they go. Since I'll end up pulling apart most of the engine wiring harness just to make sense of what is going on in there, I'll probably just start over from scratch and build my own wiring harness.

I plan to search here and the TDI conversion Yahoo group, but if anyone can steer me toward some good resources that would help me out in putting together a new wiring harness, that would be much appreciated.

I'll also give some more thought to going back to a mechanical set up, but I still think it will be cheaper and easier to re-wire the engine. I just don't have the fabrication skill set needed to put together a mechanical IP pump on my own, and the prebuilt units seem pretty spendy (~$1800 for the non-Prothe units).

[HBB]

[hans j]

That looks like the 109 relay ground? What number is on top of the relay? Similar circumstances at the one I looked at. You will need to open the harness all the way back to where the burned wire stops. The wires might not match because the relays plugged into the fuse box originally and the leads could have been changed a few inches away from the relay.

You can look at the CTS reading while wiggling wires and possibly watch the changes where wires are rubbing together.

Ok, yes that is the 109 relay. Listed as the J317 on page 5 of the link I posted. it should get power from key on (I used my original coil wire on the gas engine) and then main power can come from the alternator or battery.

On my ALH, the factory had three fuses coming off of that relay, so I powered a small fuse block with the 109 relay and distributed power that way.

On the AHU, there are no fuses. Yours suffered the same fate as the one I worked on. I placed a 15 amp fuse after the relay in the blue/red wire (yours is burned) and that goes to the black/yellow clump that provides power to everything.

I still feel there is a ground issue, but you have to also fix the obvious burned stuff. All of you faults have a common ground issue, not a common power supply issue.
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1986 Canadian Syncro Westy TDI - 1989 Syncro Single Cab - 2001 Audi S4 - 1981 VW Caddy ABA - 1980 VW Caddy EV - 1973 VW T-181

[Vanagon Nut]

If you're comfortable opening these up, check your ECU circuit board and components for burns and inside the 109 relay for failed solder joints.

If I recall, my Jetta gas swap uses a 109 relay to carry power to the ECU and a main positive buss. Over time, solder joints on it failed. I highly doubt the guts of the relay could fail bad enough to cause a short, or that your ECU was damaged, but checking these parts doesn't take much time.

Just recently, I found that my ECU had taken quite a hit from what was likely a major short. Likely due to PO.

edited for clarity.

Neil.

[HBB]

[HBB]

[Vanagon Nut]

Ya for sure. Wasn't suggesting reusing the power supply relay. Just suggested looking inside it to help determine what caused the short. i.e. failed solder joints gone too far. Though that is a far fetched concept. I guess the short could be on "either side" of the 109 relay.

I can't see the diagram Hans j kindly linked to but from what I've read in this thread, it seems your power supply relay isn't fused in the OEM application. I know this is true of my OBD1 109 relay. IIRC, the gas Motronic OBD2 has fused power to the main positive buss for injectors etc.

I know little of the TDI so will bow out at this point.

Just for laughs, and point of reference, pics of my ECU.
I'm impressed that the engine still ran "ok" in spite of the burned components. If you want, I'll remove the pics from your thread.

ECU PCB and underside of PCB frame rail:

birds eye view

_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[costal_cat]

[Vanagon Nut]

FWIW, my ECU, and the 2 I bought, have a plastic "plate" on the bottom of the PCB to protect it from connecting to the metal shield inside the case. That said, I did see what may be heat marks at that shield. I think that in my case, what happened with the PO of the donor car was a major short. i.e. jumper cables put on reversed (polarity)

My thought was that in HBB's situation, a short in the harness causing the power supply relay to fry may have done damage elsewhere.

_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[HBB]

[HBB]

I think my favorite part of the engine wiring harness so far has to be the coolant glow plug wiring.

Whoever wired this thing up went through the trouble of mounting the coolant heating element relay (G325) in the Vanagon engine bay and incorporating all the associated wiring into the harness. This engine, however, doesn't have coolant glow plugs, presumably it was from a vehicle with an automatic transmission.

[Vanagon Nut]

Thanks for posting what you found.

I ain't no expert, and I'm sure if someone looked closely at some of wiring QC, they might wonder, but twisting wires together? Even though each has a casing, old wires, cracked casings..... BTDT when I inspected and repaired the harness for my swap.

Good news is that a used ECU shouldn't be too much money. That said, yours may be fine as you suggest.

Would you mind posting the diagram you're using? Partly morbid curiosity on my part I guess but I am curious of the interface between the Vanagon 15 circuit and TDI harness.

In its' OEM form, my OBD1 gas swap 15 buss wire to ign. coil and ECU is larger than a 1981 Vanagon ign. coil wire.
I highly doubt this was the case, but if the Vanagon OEM wire was too small a gauge for your TDI ECU etc., maybe that's something to look at?

Thanks

Neil.
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN