Relay, ECM, Puff of smoke, 98 TDI

[Drooque]

Hello,
Just registered and first post. I just purchased a 98 Jetta TDI for $750. The story from previous owner is:
Ran great but started hard when cold. Drove it into his garage. Installed the new relay (I assume for glow plugs). Turned the key and there was a puff of smoke and everything was dead. Checked all the fuses and all were good. All wiring looked good. Decided it was the ECM. Bought a used ECM and another relay. Got old ECM out from under cowl. Decided he was too sore to work on it any more (had a serious work injury). Never went back.
It's sat for over two years now without being touched. The guy is a friend of my fathers who worked as a mechanic all his life. The car looks great otherwise. Any advice where I should start?
Thanks,
Andrew

 

[hskrdu]

I wouldn't have started with the ECM, but maybe he went through more troubleshooting than described. Do you have a scan tool/VCDS? I would start with the basics, fluids, filters, fuel system, battery, air/vacuum, leaks, timing, etc. We have a great no-start thread, but it's MkIV. Many of the principles will apply, but not all the specifics. Keep posting with updates and specific questions here and others will chime in. I haven't had a MkIII since 2010, and that was a gasser.

Car won't start troubleshooting

Please note that this is a work in progress. If you can help fill in the blanks that I note, please PM me or post here. Thank you. So, your car will not start. This is probably the second most common problem discussed on TDI club, second only to glow plug problems. I will try to outline...

forums.tdiclub.com

 

[Drooque]

Thank you. I agree about the ecm. I haven't tried changing it yet.
I've checked most the fuses and everything seems good. I read the thread about the relay being plugged into the wrong port, which sounds probable. I looked at many wires and checked continuity and everything has checked out this far.
I replaced a fuse that was pulled and laying on the floor, and dash lights now work.
I haven't put the relay back in yet because I am worried it is problematic. Maybe I'll try to test it outside the car.
Question: will the car run if it's hot, without the relay?

 

[hskrdu]

If you are talking about the glow plugs and any fuses/relays in that system, the gp's do not come on until the ambient temp falls below a certain threshold (at least for the MkIV), and it's fairly low. IOW, if the disconnected relay is only gp's, it won't impact the car starting except in really cold weather, and have no impact in temps above that (again, for the MkIV). If the gp's are original, they might not even be firing up when cold. Bottom line, the gp's are not an issue in the summer.

Again, if the car has been sitting, start methodically through the basics, and be clear about the situation: Is the car cranking but not running? Is it failing to crank? Was there a biocide added to the fuel tank as it sat for two years? Maybe drain and add fresh fuel? New fuel filter installed? Is fuel getting to the engine? Is the battery good? All fluids good/changed? New filters? Vacuum lines? When was the timing belt (and all parts in the system) changed, and who did it/set the timing? Etc. Any of the above can contribute to a no-start, and replacing items without a plan can be problematic. Read through the thread I linked, it has a lot of Q&A.

 

[Steve Addy]

Familiarize yourself with this thread and then make sure that no one has installed a glow relay in position #12 where no relay should be for Mk3 TDI cars.

Steve

 

[Drooque]

Thank you both for the attention to this. It means a ton.
I read that entire thread reguarding glow pug relays (which I mentioned in my earlier post), and I suspect that yes, he may have put the relay in socket 12. He said their was a puff of smoke like a burnt wire. I cannot find any burn marks on anything. Every fuse through out the entire car is good by for continuity. I have been proceeding cautiously so as to not fry more if something is shorted some where. Below is a picture of the my fuse box. The relay he said he relpaced was 180 (it was removed from the car when given to me). So far the only thing I do not know it does is no instrument panel lights - oil, battery, temp, glow, etc. ever come on as expected when the key is turned on.

PXL_20230715_032245557.jpg

• Drooque
• Jul 14, 2023

 

[hskrdu]

Turned the key and there was a puff of smoke and everything was dead.

I read that as a puff of smoke from the tailpipe, but you mean from the relay box?

 

[Drooque]

Sorry, I wasn't more clear. His words were a puff of smoke from under the dash. He was certain there were electrical problems and a new, used relay and ECM were needed.

 

[hskrdu]

Ok, well the lead on a problem with the relay/fuses is helpful. I wouldn't put too much stock in other diagnoses unless you have VCDS and have done some troubleshooting step by step. If the car has been sitting there are a lot of basic items to look at.

 

[burpod]

i'd be more worried about smoking the ce2 fusebox than the ecu. ecu is almost guaranteed to be fine. hopefully you have the wiring diagrams, you'll need that. lots of room for issues in there. i've rewired (completely and not stock) a couple of my ce2 wired cars..... the factory wiring is a bit of a rats nest. one reason i redid it in my own fashion

 

[Steve Addy]

i'd be more worried about smoking the ce2 fusebox than the ecu. ecu is almost guaranteed to be fine. hopefully you have the wiring diagrams, you'll need that. lots of room for issues in there. i've rewired (completely and not stock) a couple of my ce2 wired cars..... the factory wiring is a bit of a rats nest. one reason i redid it in my own fashion

My suspicion as well....

I would have to pull the fuse box and check all connectors and see what it looks like, maybe replace it with a spare.

Steve

 

[Drooque]

UPDATE: Had car running today, with some rigging.
Current known issues:
1. No communication through OBDII
2. No power to fuel cut off
3. No indicator lights on instrument panel
Have not been able to find any burnt wires, bad fuses, etc. I decided power was likely not coming from relay 109, and I was correct. However, the relay works properly. It is activated by ground and never receives the ground. By jumping power across the 109 relay socket, I can pull codes. By jumping hot to fuel cut off while 109 socket jumped also, the car starts and runs easy and well. The only codes are p0380 and p1617, both related to glow plug circuit.
So my primary task right now as I see it is to figure out what sends ground to relay 109.
Thank you all for all your thoughts.

 

[Steve Addy]

UPDATE: Had car running today, which some rigging.
Current known issues:
1. No communication through OBDII
2. No power to fuel cut off
3. No indicator lights on instrument panel
Have not been able to find any burnt wires, bad fuses, etc. I decided power was likely not coming from relay 109, and I was correct. However, the relay works properly. It is activated by ground and never receives the ground. By jumping power across the 109 relay socket, I can pull codes. By jumping hot to fuel cut off while 109 socket jumped also, the car starts and runs easy and well. The only codes are p0380 and p1617, both related to glow plug circuit.
So my primary task right now as I see it is to figure out what sends ground to relay 109.
Thank you all for all your thoughts.

Bentley Manual...which I do not have at hand ATM.

Steve

 

[burpod]

i can look it up tomorrow. i know in my mk1/mk3 i have an ground interrupt to 109 as my safety kill. iirc it goes to the ECU. in my mk1, i have my safety kill (stealth no-steal) switched on the mfa switch on my mk2 stalk but i am fairly sure i just took that wire and put it up there and it goes to ECU. just need to look it up in the diagrams

 

[Drooque]

Thanks again for all the help.
So I have three different wiring diagrams that I have been going back and forth from. It appears the 98 Jetta has some things different than the 97, but some things different than the 99 and 99.5. Quick side question, where is the best place to get relay 180?
Anyway, I have not made any more progress. I am confident the ECU is not the problem because I have two of them and the car is identical with either, and I know they function at least well enough to log codes and run the car.
Please tell me if I am correct in my following assumption:
ECU has some hot and ground all the time; Ignition is turned on which sends signal to ECU -> ECU sends ground back to Relay 109 -> Relay 109 energizes 12V to a few different components including back to ECU -> ECU runs fuel injection -> Car runs
I believe something is not working in the very first step where turning the ignition on communicates with the ECU. But how does that tie into instrument panel not working or is it a coincidence.

 

[Drooque]

I know the odometer and clock work. Not a single warning light ever illuminates. I checked continuity from the 3 pin on instrument panel ground and it was good. Checked the 13 pin to respective fuse in fuse box and it was good. Also. There are two plugs into the instrument panel that are same pin configuration but wiring diagram only mentions 1.

 

[Drooque]

It sure would be nice if any of the half dozen wiring diagrams I have found actually matched my car.
There should be a connection (at least one) to the ECU that is hot when ignition switch is in on position but not always hot. On both the 97 Jetta and 96 Passat wiring diagram, it appears it should be a black wire attached to pin 38. that is not the case for mine, and I cannot find any other wire that is hot only when key is on.

 

[Shoveltrev]

pull your steering column covers an check your ignition switch , sounds like it has a dead leg on it

 

[Drooque]

I have inspected the ignition and it seems fine, but more suggestively, the DRL come on when key is in on position so I think it is between the fuse/relay box and the ECU, and not the switch. I am going to recheck anyway. I have a list of things I'm going to try this evening and I will add that to it.

 

[Drooque]

Found the problem, but not sure how to proceed. There is apparently melted contacts between the layers of the fuse panel. Once I narrowed down where to look, I found a wire with a little evidence of getting hot, it had continuity through it's plug, but not through the relay panel, and there was no evidence of the burning on the plug or the panel where it connects. When I was trying to examine it, all of the positive circuit became closed to ground (knew because I had multi-meter attached at the time. So I guess jiggling it around jostled and shorted inside the panel. I played around with stuff and couldn't resolve the short until I pulled a fuse. Coincidentally, this fuse and the bad wire are right in line with the relay 12 position.
So now I don't know if I should find a replacement panel and swap it in, try to bypass the bad area, try to repair the current panel, or rebuild it with a universal panel. A quick peruse of ebay did not turn up any correct panels, some mk4 and some mk3 but none that look like this end of line mk3s.
One question I don't know, is if the relays above the normal panel are detachable, so I would only have to get the basic panel?
Any thoughts?

 

[Abacus]

Yes, the relays above the panel are detatchable, they have small safety catches on them but do come off easily once you figure one out.

The fusebox should be same on any Mk3 car, which includes the Passat. Unfortunately there are none near me in the local junkyard, nor do I have a spare.

Is the plastic on the fusebox melted? if not, you may be able to remove individual wires with a terminal removal kit.

Here are some of the B4 TDI fuseboxes, for comparison.

 

[Steve Addy]

The fusebox can come from
Mk2 (89-92)
Mk3 (93-99)
B3 (90-95)
B4 (95-97)
and I think Cabrio (95-02).

Steve