'97 TD AAZ - Weird stumble. Any ideas?

[iggi]

Hi guys,

I've got a problem: I'm 500 miles from home, don't have my bentley with me and my car is running really weird.

Started running odd after a long, slow downhill.

- heavy smoke at idle or part throttle
- misses or stumbles while under part throttle at light load
- runs fine whie under load/boost
- seems a bit low on power

Flats or downhills are almost undriveable unless I keep the RPM's above 3K.
Driving in town is a supreme pain in the butt.  I either have to have my foot off the pedal or have to give it nearly 1/2 throttle.
Basically if I drive it like I stole it - it's bearable...  but I really don't need the tickets.

If it was a gas turbo engine I'd say it was a vacuum leak.
No experience diagnosing diesel so I'm a bit flummuxed.
Not sure whether it's going to be ok to drive home or if I need to park it and take the bus home.

Any ideas?  I'd much appreciate any help!

[SMOKEYDUB]

what colour smoke? are you overheating? are you leaking fuel ? do you have much fuel?

[jtanguay]

hmmmm yea how much fuel did you have going downhill? maybe your pump sucked up some crud?  could be clogging the filter

[iggi]

thanks for the quick replies.

Lots of diesel - had 3/4's of a tank when the problem started.
Thought it might be a bad tank of fuel but had 280K on the tank before I had any hiccups at all.

Not overheating
No visible leaks
Smoke looks (and smells) just like normal diesel smoke.
No apparent change in fuel economy
Oil looks (and smells) fine.

1 pre-existing problem.  Doesn't like to start cold.
Other than that it's run great the least two weeks.

[burn_your_money]

How did you go down the hill? In gear using the engine to slow you, or in nuetral using the brakes?

[iggi]

In gear.
Is that bad?

I noticed the engine temp dropped quite a bit  (from middle of the gauge to the lower third)

How did you go down the hill? In gear using the engine to slow you, or in nuetral using the brakes?

[burn_your_money]

In gear.
Is that bad?

I don't know. I was just asking incase it is important. Basically just throwing ideas out there

[bert]

My mates AAZ in a transporter had a sudden problem like that,the crank bolt come loose and the timing gear turned a bit,i found this just before it went altogether,check crank bolt for tightness???
Bert

[QuickTD]

My mates AAZ in a transporter had a sudden problem like that,the crank bolt come loose and the timing gear turned a bit,i found this just before it went altogether,check crank bolt for tightness???
Bert

My money's on this.

[iggi]

check crank bolt for tightness???
Bert

Well..  it would really suck to have it come loose on the way home.
I don't have the repair manual with me.
Does anyone have an online description on how to check the bolt?

Anything else I should check?  I took a look at the belt and it looks fine  (it's coming on 200K and I'm booked to get it replaced in Nov.)

[QuickTD]

You can check it for tightness with a 19mm 12 point socket wrench, if it moves at all it's way too loose. If its running poorly, the crank pulley key probably has significant wear already so tightening it won't do much good.

[iggi]

Thanks!

Good thing I brought my tools with me.
If the bolt is tight will it probably be ok to drive home?  (740K - through rogers pass)   Or should I be calling a tow truck?

Another clue:
I just got back from a test drive.  At idle it runs much better with the choke pulled out.  Pushed in it smokes and stumbles.

Thanks again.

You can check it for tightness with a 19mm 12 point socket wrench, if it moves at all it's way too loose. If its running poorly, the crank pulley key probably has significant wear already so tightening it won't do much good.

[QuickTD]

The "choke" is not a choke, its a timing advance to assist in cold starting. If the idle smoothes out when its pulled then my diagnosis is confirmed. The timing has become retarded due to the crank bolt loosening and the crank pulley key wearing. If the bolt is replaced with a new one and torqued to spec (66ft/lbs + 90º) you might make it home, I'm inclined to think not though... If the pulley key shears completely, which it usually does within a few miles of showing symptoms, the cam goes out of time and bends the valves.  

 The bolt won't stay tight if the key is worn, the pulley shuffles around and quickly loosens it again. The only real fix is to pull the engine, remove the crankshaft and have it welded and machined to take a TDI crank pulley.

[iggi]

hmmm..  now I'm worried.
Especially since I've gone over 500K since the problem started.

PS  Yup.  I know the "choke" isn't a choke, but thanks for clarifying.
It certainly does highlight the timing issue.

Thanks,

The "choke" is not a choke, its a timing advance to assist in cold starting. If the idle smoothes out when its pulled then my diagnosis is confirmed. The timing has become retarded due to the crank bolt loosening and the crank pulley key wearing. If the bolt is replaced with a new one and torqued to spec (66ft/lbs + 90º) you might make it home, I'm inclined to think not though... If the pulley key shears completely, which it usually does within a few miles of showing symptoms, the cam goes out of time and bends the valves.  

 The bolt won't stay tight if the key is worn, the pulley shuffles around and quickly loosens it again. The only real fix is to pull the engine, remove the crankshaft and have it welded and machined to take a TDI crank pulley.

[ricosuave]

answer to your pm sent on clubveedub

also,
http://tech.bentleypublishers.com/forum.jspa?forumName=volkswagen.a.a3