Boosting problem

arnebret · 03-28-2002, 01:17 PM

Very strange...

My car was doing great. Just had new clutch etc. engine running fine, but on full throttle the boost comes on (gauge shows 1.8bar) but the engine seems to stall and then pick up again, very bumpy. When i stay just below the full throttle, like 80-85%, no problems at all, fine boost etc. Any thoughts?

dogslovetrucks · 03-28-2002, 01:23 PM

I pulled this from the Porsche FAQ site- hope it helps:

8.7 I'm experiencing a random power loss in my Turbo, what's up?

This appears to be a common problem, especially on the 89 Turbos. The normal boost is 1.2 bar. If everything is operational, it will go to slightly above 1.8 bar. The most common problem is a bad connection due to corrosion on the throttle position switch (located on the throttle body, forward of the intake manifold). On one side is a cable that controls the throttle opening, and the other side is a black plastic device that reads the throttle position. The connection to this device can become corroded. Typically moving around the connector a bit will fix the problem temporarily. Disassembling the connector, cleaning and putting on a coat of dielectric grease on it will fix it semi-permanently.

Good luck

arnebret · 03-28-2002, 01:24 PM

Well, it looks like i just found the answer... I browsed around a bit in some of the 944 Faqs around, i found this:

8.7 I'm experiencing a random power loss in my Turbo, what's up?
This appears to be a common problem, especially on the 89 Turbos. The normal boost is 1.2 bar. If everything is operational, it will go to slightly above 1.8 bar. The most common problem is a bad connection due to corrosion on the throttle position switch (located on the throttle body, forward of the intake manifold). On one side is a cable that controls the throttle opening, and the other side is a black plastic device that reads the throttle position. The connection to this device can become corroded. Typically moving around the connector a bit will fix the problem temporarily. Disassembling the connector, cleaning and putting on a coat of dielectric grease on it will fix it semi-permanently.

Seems to be my problem, and is i can recall i have been messing around with my throttle body. I'll disassemble the complete unit tomorrow and see how to fix it. I'm 99% sure this is it.

Thanks anyhow!

arnebret · 03-28-2002, 01:27 PM

HAHAHA!! We just posted the EXACT same part at the EXACT same time... well, thanks for your help anyway!

dogslovetrucks · 03-28-2002, 01:32 PM

Cool- hope that gets it for you.

arnebret · 03-29-2002, 09:06 AM

Strange...

I did some factory tests to see if the throttle switch was ok. All results showed everything was functioning fine. I drove with the switch detached and the boost was 1.2bar, as it should be. When i attach the switch the boost is 1.8bar and stays there, but the car isn't smooth at all at max acceleration.. Boost stays 1.8 steady but the engine is just surging, picking up, surging, picking up etc. very annoying. Something seems to hold the fuel or air back causing the engine to stop accelerating as it should.

Might this be a wastegate related problem?? Or has some sort of valve (blowoff valve or any other) failed? I can't really find a logical reason...

Maybe someone out there?

Goku · Goku's Garage

Well if when you are at full boost it feels as if you hit a brick wall (as in feels like someone hit the brakes REALLY hard) then you are overboosting. If you have shimmed your wastegate or put on a banjo bolt or the sort without a chip then you'll have the problem. If you are overboosting without chips this will happen. It's the factory safeguard of having a maulfunction and having the engine blow up due to overboosting =)

arnebret · 03-29-2002, 11:25 AM

Hmm, it doesn't slow down suddenly, but just jumps and bounces a bit in full acceleration. It's certainly not due to overboost, i have all things standard. No special chips, wastegates or banjo bolts...

bogomili · 03-29-2002, 02:18 PM

Well, for what's it's worth. . . I had a similar problem yesterday when trying to pass somone on the way up the hill (the 8000 ft. on I live on). I thought overboost as well until it just finally died at after a first gear stop light launch blew it all the way off - rather embarassing by the way. Up till then, it was very rough when I let off the throttle in higher boost ranges.

It turned out to be the purocil connection to the throttle body sucking unmetered air (I have the stock flapper box w/ custom hard IC pipes, hence the purocil hose).

Try all your hose clamps and boots both pre and post intercooler. Might be an easy fix and sounds just like my problem.

Matt
Big Bear Lake, CA