# 8V GTI bogging/low power issues.



## bluetoes591 (Apr 3, 2009)

I have an 85 GTI engine in my 90 Fox. I spliced the wiring harness from an 86 GTI into the Fox harness. I have two years and 30,000km on this swap, so while it is possible that it is my wiring causing the issue, it isn't super likely at this point.

My car is low in power everywhere in the rev range, particularly if hard on the throttle. If I accelerate gently the engine revs more freely. It run best on a cold start and worst on a hot start. After a hot start the first couple blocks it barely runs, sounds like vapour lock on a carburetted car. Runs out of power beyond 4,500rpm. Hesitates badly off idle or at about 2,500rpm and recovers somewhat by 3,500rpm.

I have replaced my fuel filter, my transfer pump and my O2 sensor. I have been over the engine several times for vacuum leaks. I do not yet have a fuel pressure gauge, though I will be buying one soon. I have done every electrical test in the fuel, ignition and emissions sections of the Bentley.

The only test that my car does not pass is the total timing. Doing the test from the Bentley, knock controller vacuum disconnected I'm supposed to get 16° advance at 3000 rpm. I get 22° advance. Same with the controller connected to the vacuum hose, 22°. Vacuum hose has a decent vacuum.

For some reason this harness does not have the test connector for the knock controller. There is no conductor at pin 4 of the harness connector, so I can't check for fault codes.

What are the chances that this could be my issue? Is there too much advance and then under load retarding too much? The problem didn't happen overnight, used to be more subtle and has gradually gotten worse. It also seems to be somewhat better the first time driven after disconnecting the battery.

Any ideas? I'm running out of patience with this thing.

Edited to add that if I disconnect the throttle switches it runs much better, but then idles at 1,400rpm.


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## bluetoes591 (Apr 3, 2009)

Does the ICU play a role in ignition advance or does the knock controller do all of the timing variation?


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