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Author Topic: 98 AHU problems... Won't rev  (Read 383 times)

February 03, 2018, 03:10:03 pm

Smoker

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98 AHU problems... Won't rev
« on: February 03, 2018, 03:10:03 pm »
Well I'm stumped. I just picked up a mk3 jetta. The car itself is in really good shape, and completely unmolested. 248k miles.

When I got it: it would start up and idle perfectly. It would rev to about 1800 rpm smoothly, and anything above that it would break up/misfire/etc and blow all kinds of white smoke. Not coolant, but white smoke that would indicate a fueling issue. Previous owner replaced the turbo, cleaned intake manifold, got frustrated and decided that it had a blown head gasket because of the white smoke.

I have vag-com. No codes except glow plug monitoring.

What I've tried:
-looked at all wiring I could find. No apparent issues.
-unplugged maf. It might run 5% better unplugged, but still very bad.
-checked static and pump timing. Cam was a bit retarded, but pump was within spec. I adjusted static timing to spec. Result: no change. Still no codes.
-eliminated cat converter to make sure it wasn't clogged. It wasn't. No change.
-swapped ecu with a known good one. No change. Still no codes.
-swapped pump with a known good one and re-timed. No change. Still no codes.
-swapped all 4 injectors with a known good set. No change. Still no codes.
-removed intake manifold to make sure intake ports in the head weren't clogged. Clean as a pin.
-removed downpipe to check for something silly... Blockage or gasket installed backwards or something. It wasn't.

I'm not a diesel expert, but I'm not a newbie either. I'm 99.9% sure this is an electronic issue, not fueling or compression.

I'm out of ideas! Any chance a bad dbw unit could cause this??


I'm about to throw in the towel, get an accelerator pedal and cable from an AAZ car, and try out this Rover pump I've had sitting on my shelf!

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Reply #1February 03, 2018, 03:35:00 pm

Smoker

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Re: 98 AHU problems... Won't rev
« Reply #1 on: February 03, 2018, 03:35:00 pm »
One thing I've noticed: timing and iq values seem to 'jump around' more than others I've seen.

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Reply #2February 03, 2018, 08:22:27 pm

ORCoaster

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Re: 98 AHU problems... Won't rev
« Reply #2 on: February 03, 2018, 08:22:27 pm »
Electrical connection as in grounds?  Make sure the battery, the trans and engine contacts are clean and maybe even run a few extra to the body.
Now Own 1981 Caddy as the NEW DISTRACTION to all that is around me.  Project Away!

Reply #3February 06, 2018, 07:44:24 pm

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Re: 98 AHU problems... Won't rev
« Reply #3 on: February 06, 2018, 07:44:24 pm »
I checked and cleaned all grounds.

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Reply #4February 10, 2018, 05:59:42 pm

burn_your_money

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Re: 98 AHU problems... Won't rev
« Reply #4 on: February 10, 2018, 05:59:42 pm »
Is it MK3s that have an issue with the wiring for the timing advance solenoid being rubbed off by the corrugated wire wrap?
Tyler

Reply #5February 13, 2018, 12:19:59 pm

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Re: 98 AHU problems... Won't rev
« Reply #5 on: February 13, 2018, 12:19:59 pm »
Is it MK3s that have an issue with the wiring for the timing advance solenoid being rubbed off by the corrugated wire wrap?
Hmmmm... I haven't heard of this. But they sounds plausible.

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