Help! Injection problem ? while on a long drive

Hi, I hope someone can give my friend a clue what is going on with his 02 Jetta TDI 5 speed. He is driving from LA to Phoenix and called me from Blythe. As he is driving down the road the tach will suddenly go up and down, with no change on his part. He hears a kind of thump-thump-thump coming from the engine, and the tach continues to race up to 4 or 5,000, then way down. He then pulls over, turns the car off, restarts the car, and all is well... for about 10 minutes, when it all happens again. I sold him the car about a year ago; it only has 60,000 miles on it, and is generally in great shape. No problems at all in the past year.
Injection pump issue? ECU issue?? Clues? He's staying overnight in Blythe but hopes to be in Phoenix in the morning.....
Thanks for the help!
Ken

Faulty serpentine belt or alternator pulley.

MOGolf said:

Faulty serpentine belt or alternator pulley.

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The only guess I have as to why is that the tach is run off of the alternator and belt/pully is causing fluctuating alternator speeds.

Now, could you tell us that I'm wrong and why cuz I"m confused.

Clue: thump thump thump but no mention of vehicle jerking (which would indicate actual engine changing speed)
Clue: if injection pump, then engine would be changing speed
Clue: no mention of CEL

Therefore alternator is fluctuating in speed and tach goes wacky.

Possible causes of alternator fluctuating: bad belt (sections missing?), bad freewheel pulley (most likely because "it works for 10 minutes"), it is falling off the engine (not likely based on the "it works for 10 minutes"), loose wiring connection (not likely due to "thump thump thump" but I had this on my other vehicle about 1.5 months ago).

My first thoguht was clutch, but I have never personally experienced a slipping clutch, I was wary to say anything. So why don't they run the tach off of the coil?

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whitedog said:

So why don't they run the tach off of the coil?

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Coil? On a diesel?

On my LR it fires a coil on the compression stroke and exhaust stroke (which is a compression stroke for another cylinder). Alternator is more reliable than a coil that could fail yet the other three coils on my LR can keep the engine running.

Coil? On a diesel?

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Yeah, the one that fires that injection glow thingie.

OK, maybe not. Sorry for the poor joke.

Thanks much for the quick replies. One more bit of information that my friend didn't mention the first time, or that I didn't hear. When the car is in this 'state' of random tach-waving, he says he doesn't seem to have any control over the throttle, or, more specifically, there is power loss. It goes for a few seconds 'under its own control' then they can control the throttle again. The tach goes up and down, settling eventually at idle. The last time it happened they stopped the car, stopped the engine, restarted it, and it was fine. He just told me now that he drove it around at low speeds in Blythe, doing some shopping, and it was fine. So now the worry is just getting it to Phoenix in the morning...

How would serpintine belt/alternator belt lead to loss of power?
Thanks again...

Now that you're mentioning power loss, forget what I previously posted. It is important to give all the known facts to get a proper diagnosis.

MOGolf said:

It is important to give all the known facts to get a proper diagnosis.

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Doggie hangs head in shame.

You also mentioned earlier about the CEL - the light's been on for the past six months but it has only been on because of a glow plug issue. Of course, since it is already on, no way to know if it threw another code...

I would suspect a problem with the throttle control. It is done by wire and as such sometimes encounter problems with sensors etc. Drivebywire has done an excellent write up on how to clean and fix. http://forums.tdiclub.com/showthread.php?t=32884&highlight=throttle+control+RPM
Good luck

Canadian_Grizzly said:

I would suspect a problem with the throttle control. It is done by wire and as such sometimes encounter problems with sensors etc. Drivebywire has done an excellent write up on how to clean and fix. http://forums.tdiclub.com/showthread.php?t=32884&highlight=throttle+control+RPM
Good luck

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Unfortunatly the pictures now point to a Job finding site or something.

Perhaps Drivbiwire is making a commission? Thanks Dog your always on alert. I'll pm Drivbiwire and see if he can update the links...although the post itself contains alot of great information.