GS-T Jerks Under Boost

[DuvalGs-t]

I have a '95 GS-T that i bought from a guy that lives down the road from me. He only had it for about three weeks before he sold it to me. The guy i bought from the car, bought it from another guy who had it in his garage as a project car. To get to where im going, i dont know exactly what has been done to my car. It has a Turbonetics turbo with a blue backplate, fmi with Greddy piping, aftermarket rims, aftermarket front bumper, TurboXS RFL BOV, NGK plug wires with NGK Iridium plugs, Apexi 3" N1 exhaust, aftermarket boost gauge and narrow band. Thats all that i know of that has been done to the car, so i didnt think it was a bad deal for $1700. So this is what the car is doing and i dont know why, ive been looking for about three weeks and i still cant find anything. The car runs fine out of boost, but when i hit about 6psi, it starts bucking real bad and blows black smoke. After i do that a few times, i guess the car goes into limp mode or something but it starts sounding like a Subaru. The car only does this with the MAF plugged in. When i unplug the MAF, the car stumbles up to speed, but after the car builds boost, its fine. I thought that maybe a dirty maf would cause it to make the ECU think its running lower boost and hit a fuel cut, but even with the MAF being cleaned, it still does it. Im lost to what to do to fix this car. Help would be much appreciated, thank you.

 

[GSTurbo1]

Either too rich or a boost leak or both. Black smoke = unburnt or partially burnt fuel. I would say boost leak. Sometimes I can drive through it on mine but i'm going to BLT test soon. You should do the same. If you have wideband or some sort of AFR monitoring device keep it between 11-12 under hard boost.

go to the search bar and put in boost leak should solve your problem

 

[DuvalGs-t]

Thank you for the fast reply, but why would the car only do this with the MAF plugged in? It has a narrow band, but thats useless to me.

 

[DuvalGs-t]

Are you talking about like the plumbing from the turbo up to the intake mani. or the intake manifild itself? I had the car running 20psi daily and the rubber line from the turbo to the wastegate melted and spiked to 30psi one time. I forgot to mention it has an external tial wastegate on the factory exhaust manifold. Would that crack make it buck and jerk like that, but stop when i unplug the MAF?

Well on my way to work today, i ripped on the car a few times and watched my narrow band, when the car starts to "jerk" , the narrow band pegs lean.

 

[DuvalGs-t]

I have been riding around without the maf sensor, the car runs better top end without it, i still dont know what it could be.

 

[Paintballaa5]

Best thing to do is not get on it for now until you know if your AFR's are suitable.

 

[thaibxr]

I had a similar problem with my 98 GST. The car would drive around the city fine but as soon as it would start boosting the car would feel like it was missing or sound like a "lesbaru". I troubleshot a bunch of sensors and even replaced a few but nothing seemed to change. I put a new AEM in it, new FPR, Injectors, fuel pump etc., but it still missed. Finally, after researching, I decided to pull off the valve cover and right there in front of my face I saw the problem. One of my HLAs failed and the rocker arm fell off one of the intake valves.

I bought a new set of HLAs, installed everything, and after re-tuning the AEM my car ran like a champ.

It's simple enough to pop that valve cover off and inspect everything underneath it. Changing the HLAs isn't that bad but it takes some time.

 

[bryanwheat]

I have been riding around without the maf sensor, the car runs better top end without it, i still dont know what it could be.

Quit driving the car without the maf plugged in. You are going to blow the engine up doing that. You like have a boost leak or something along the lines of that. Test for boost leaks, take those iridium plugs out and get it running right. Do you know what the maf sensor does?

 

[DuvalGs-t]

I have just done the headgasket and intake/exhaust gaskets on it about two weeks ago. While i had the head off, i replaced and lapped all the valves and installed new valve seals. re-assembled and started driving. The car started doing this before i done the head gasket. When i pulle the valve cover then, everything looked fine to me. Now on top of all of that, my tag starts going crazy like it's dancing everywhere and dropping to 6 o'clock and loses all power no matter how much gas i give it. i replaced the cam position sensor the power transistor pack the coil pack the crank angle sensor and the knock sensor about a month and a half ago. So the car is jerking around and pegging lean when i start hitting boost and occasionally it starts doing the crazy tach deal. I have an EPROM ecu in the car, so hopefully it isn't shot out. I'm about to start the BLT now, but a boost leak shouldnt make it lean out i wouldnt think? Maybe it's sucking in unmetered air after the MAF? It has a Dejon tools intake.

 

[DuvalGs-t]

I have fixed the problem by buying a 2002 Audi A4 1.8t Quattro with Revo stage 2 tune fmic and apr tuned exhaust. This car runs so much better. Thanks for yalls help.

 

[filabob1]

What happened to the GST?

 

[DuvalGs-t]

Its sitting in my driveway about to be for sale. It only gets like 8mpg rolls what looks like brown smoke, not black, not grey, not white or blue. The car screams when it runs right, but that only happened once and hasnt since. I couldnt figure out what was wrong with the car.

 

[wicked98gsx]

wait... you stopped working on the car because you couldn't figure out you have a major Boost leak? You should have just took the I/C piping and looked for a rip in the couplers.

man I wish I lived in Florida still. Id buy it off of you now

 

[DuvalGs-t]

Ive checked over everything at least 30 times. I cant find a boost leak. Could it be a bad turbo making it do that? Could it be pushing my rfl bov open?

 

[bryanwheat]

Ive checked over everything at least 30 times. I cant find a boost leak. Could it be a bad turbo making it do that? Could it be pushing my rfl bov open?

Did you actually pressurize the system, or did you just open the hood and look for things that might be leaking.

 

[DuvalGs-t]

Just looked, i dont have anything to pressurize the system. The shop i work at dont either.

 

[filabob1]

http://www.dsmtuners.com/forums/art...-boost-leak-test-how-boostpro-net-tester.html

Check this out. Boost leak may not be your ultimate problem, but this may help you out. I hate to see you get rid of the GST.

 

[bcjjones]

What a joke. Get a small air compressor from harbor freight for 40 bucks and build a BLT for 15. You'll find your, what sounds to me like a pretty major boost leak, and you'll have a much better running car.

Then you could sell it as a running car. Instead of a brown smoke blowing pos.

 

[MrwillyJ]

Its like 5 bucks to make a BLT..

 

[bcjjones]

Or better yet keep the GST and sell the Audi

 

[FLASH1970]

You need to pressure test the system. It costs maybe 10-15 bucks to make a boost leak tester from stuff you can buy at Home Depot. Search this site, I know it's on here somewhere. Or Google "How to make a boost leak tester". Plug in all your sensors, get a boost controller and a wideband. The narrowband is useless. It sounds like you've thrown a bunch of time, money, and parts at things that won't fix your problem and now are fed up. Find out what injectors you have, what fuel pump you have... If you have the EPROM ECU, get DSMLink and use it to datalog and tune your car. When you were beating on the car, how much boost was the gauge showing?

Post up under hood pics, closeup pics of the fuel injectors... maybe some people here will chime in and help you identify what parts are on the car.

 

[bcjjones]

Lowes must be a little more expensive here then! Cost me right around 15

 

[DuvalGs-t]

The car has stock 450's on it and it was on 12 psi off the wastegate and ran 20 on the controller. The car has been problems since i got it, i think its just one of those problem cars. If its not one thing, the next day it will be another. Ill try doing a blt out of curiousity even though im selling it. But if its a boost leak then wouldnt the narrowband peg rich instead of lean?

 

[GSTurbo1]

Check to make sure are all of your injectors are firing... when it sounds like a subaru. Could be something pulling a wire apart while under hard boost. Just a theory.

 

[DuvalGs-t]

It use to sound like a subaru. Then i found two bent valves and replaced them. Now it only sounds like one when i drive for 30+ minutes. It loses all power like it just quits giving fuel. I can let it sit and cool down, then its fine for another 30 minutes.