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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old February 9th, 2012, 17:06   #1
Join Date: May 2011
Location: Sunny Neenah, WI
Default 97 Passat TDI - Random Stalling, Won't Shut off with key -LONG-

First off, let me extend my heartfelt thanks to this community for all the advice I have gleaned over the years. You guys are the best.

I am having a weird electrical problem. Here are the symptoms and my diagnostic process thus far...

My car is a 97 Passat TDI. 280,000 miles. Rebuilt head and headgasket ~20,xxx ago. When I bought the car 2 yrs ago it would not shut off with the key. The car started fine, ran and drove fine, but you had to snub it out in 5th gear to get it to shut off.

When I turned the key to "OFF" all the electrical accessories would shut off (radio, dashlights, fan, ect) like normal, but there would still be power to the fuel cutoff solenoid.

I replaced the ignition switch and Relay 109 at this point. No change in behavior. I replaced the fuel cutoff solenoid. No change in behavior.

Here is the interesting part. When I would stall the car out, the power to the fuel cutoff solenoid would disappear.

Also I noticed that when I would first start my car the dashlights were dimmer than usual. If I were to blip the throttle to ~2500 rpm, they would get brighter and stay there. Sort of like how a GM 1 wire alt has a kick-in speed.

I noticed that if I started the car and did not raise the throttle past 2500 rpms the car would shut off normally with the key. If I took it past 2500 rpms it would continue to run when shut off and need to be snubbed out to stop the engine.

At this point I suspected something rotten with the alternator. I cleaned the brushes and contacts and had it tested. It tested good. My alternator is a Bosch 120 amp unit without the clutched pulley. I replaced the alternator and scratched my head.

So, I added an inline switch to the wire powering the fuel cutoff solenoid. and used that to shut the car off. It works fine.

Car has performed flawlessly and has been very reliable until last week Monday.

We were loaded down making ~70mph on the interstate. The roads were clear. The temp was ~15 degrees Fahrenheit. I noticed the tach begin to tweak out. It was jumping around a little bit, then it would return to normal.

Not 5 minutes later the car lost all power and stalled out. I threw it in neutral, keyed the car off and restarted, it started fine. 2 minutes later it stalled again. Now the growplug light and check engine light were flashing. Again, neutral, key off, it restarted fine.

I suspected the fuel may be gelling, as my previous fillup had been in TN and I was back in WI (gotta love a TDI) I pulled into a gas station, topped off the tank, added some anti-gel, and pulled the codes with VAG-COM.

While I don't remember the exact number of the code pulled, it was something to the nature of "Fuel cutoff solenoid short to ground"

I immediately suspected my fuel cutoff solenoid switch and removed it from the circuit.

Got back on the interstate, 5 minutes later the tach began to tweak out again. 2 minutes after that, the car stalled out. The car consistently restarted, so I just continued on like that for another 600 miles. The stalling was inconsistent. Sometimes it would be fine for 10 minutes, other times it would immediately stall after restart. But it always restarted. Glowplug light was flashing at me again.

Got home. Pulled codes with Vag Com. Again, I don't remember the exact numbers, but there was the "Fuel cutoff solenoid short to ground" code and a "Glowplug Monitoring" code.

I pulled and tested all the glowplugs. They were good. Checked the wiring. It was good. Replaced the Fuel cutoff solenoid and Relay 109.

Again I removed the alternator and had it tested. It tested good. I had it the guys test it on the bench 15 (yes, 15) additional times and it always passed. I replaced the alternator, cleared the codes and went on my way.

Car did the same thing. 15 minutes of driving, Tach would tweak out, 2 minutes later, car would stall.

I noticed that from a cold start, it would take about 10-15 minutes before the car would stall. The Tach always would begin to tweak out before it would stall ~ 1-2 minutes later, though the time between the tach tweaking and stalling was now getting shorter. Sometimes on restart the car would immediately stall.

The car would always restart. The Glowplug light would flash. "Fuel Cutoff solenoid short to ground" code would be thrown.

At this point I removed the factory wire from the fuel cutoff solenoid. I isolated it to prevent shorting and then ran a wire directly from the battery positive to the fuel cutoff solenoid.

No change in behavior.

Car ran ~13 minutes, tach began to tweak, car stalled. It restarted immediately, glowplug light flashing, CEL illuminated. I haven't checked the codes yet, but I suspect the same.

I have cleaned all the grounds I can find. I replaced the battery. (Old one was 10 yrs old)

At this point I am pretty well stumped. I am beginning to suspect the computer. ($$$) On my old diesels (1.6 NA's) a failing alternator would cause an erratic tach, but would a failing alternator cause the car to stall?

Any suggestions?
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Old February 9th, 2012, 17:51   #2
Veteran Member
Join Date: Sep 2010
Location: Oakland, CA
TDI(s): 1997 Passat

Start with an easy but important one. Check all grounds. Remove the battery and you'll see a main grounding junction. Clean all you can find, and even run a fresh ground strap from the battery to the frame and from the frame to the engine if you have to. Poor grounds can cause all kinds of hard to isolate grief.
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Old February 10th, 2012, 08:07   #3
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Join Date: Nov 2007
Location: Nobleboro, Maine
Fuel Economy: And the miles just keep ticking away

Check out this thread and what I found on mine. It turned out to be a break in the wiring harness from chafing.

Let us know what you find.
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Old February 10th, 2012, 14:42   #4
Join Date: May 2011
Location: Sunny Neenah, WI

Abacus, today I unraveled the wiring harness all the way back to the firewall. While I was in there I took Yblocker's advice and cleaned the ground points. No shorts or bare spots to speak of.

Car was still up to its old habits today. Stalling and the tweaking tach.

I did notice an interesting thing though. Above I mentioned the alternator "kicking in" at ~2500 Rpms. Just for giggles I drove the car around all day without revving it past 2500 rpms. The car ran and drove perfectly. Heck, it even shut off with the key. The tach never fluctuated, car never stalled.

I'm curious, do any of your cars have an alternator "Kick in" speed?

I'm really wondering if there may be some kind of fault with the alternator. I'm going to try to source a known good unit and do some further testing.
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Old February 10th, 2012, 15:19   #5
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Join Date: Feb 2000
Location: Santa Barbara, CA

The tach is not driven by the alternator "W" terminal on TDIs as it was on TDs and IDIs, its driven by an ECU RPM signal. Disconnect the wire from that terminal and I suspect you will still have the same symptoms. I suppose you could measure charging voltage, but I doubt that incorrect voltage is the issue either.
- Chris
'15 GSW SE 6MT, '01 Golf 5MT
'97 Passat sedan, '96 Passat variant
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Old February 10th, 2012, 16:03   #6
Join Date: May 2011
Location: Sunny Neenah, WI

Thanks Chris! I was wondering why I had a tach signal with no alternator on the motor...
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Old February 14th, 2012, 15:17   #7
Join Date: May 2011
Location: Sunny Neenah, WI

Sourced a used alternator today. The alternator kick in speed must be a VW thing. Car doesn't start charging until it gets revved above 2300 rpm. Once the alt kicks in, car will not shut off with the key. Weird.

Car has not acted up yet with the new alternator. Ill keep y'all posted.
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Old February 16th, 2012, 17:11   #8
Join Date: May 2011
Location: Sunny Neenah, WI

Solved it! I found that the blue connector coming from the alternator was hooked up to the plug for the reverse light switch! I included a picture, there is enough lead on these connectors to easily mix this up.

Now the blue connectors are attached to each other, and the black connector goes to the reverse light switch. Car runs better than it ever has. No more stalling, tach tweaking or weird charging system kick-in speed. Car also shuts off with the key now. Thanks guys.
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Old February 16th, 2012, 18:35   #9
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Join Date: Sep 2005
Location: Tucson, Az
Fuel Economy: A5: 36mpg Avg / A6: 39

Great find!

It's the little details that will get you every time!

Diesel fleet: '15 Jetta TDI SE; '06 Jetta, TDI, DSG-5sp Conversion; '06 DC Cummins, CC/LB/DRW; Past Project car! Troubleshooting Links: Trusted TDI Mechanics IP Timing Timing Belt FAQ A3/B4 Low Power Cyl Head Repair Fault Codes What you have just read is an opinion...take it as you see fit!
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