Cant figure out whats wrong with my car

[bigbro6785]

I have a 97 GST that i bought 1 year ago. Ever since I bought the car it has ran really slow and I cant for the life of me figure out what the problem is. I installed a boost gauge and noticed that my boost would drop from 10 psi to 7 psi almost instantly once I would get to about 4500 rpm (which i think is really wierd). I did a boost leak test and fixed them all but I still had the same problem. I installed a MBC and that fixed the pressure drop problem, but my car still ran the same and still felt slow. Since then I have changed the plugs, wires, checked the timing, changed the oil and even the fuel filter but the car still runs horribly slow. For the mods that I have (intake/uicp/dp/exhaust/mbc@13psi) the car should have some kick to it but it doesnt. I got a compression test done and they said that it was within the service limit, but barley (around 130 on all 4 cylinders). This is low, but i dont think it would have such a drastic effect on my performance. Anyone have any ideas for me because I am completly out. Thanks for anything.

 

[95AWD6Bolt]

That compression shouldnt have such a drastic affect on your performance. I would get a boost leak test done. You might have a massive leak somewhere. That would definately affect the performance of your car.

Also, assuming that you have the stock 14b or t-25 turbo, it does drop a few psi when at WOT.

 

[bigbro6785]

I have done a boost leak test and fixed them all. The car now runs at 13 psi and drops 1 or 2 psi slowly at high rpm. It use to drop 4 psi instantly right at 4000-4500 rpm (dont remember which one). So im thinking that had something to do with the ecu dropping boost for some reason. And yes I have a stock t-25

 

[Bender]

Sounds to me you have a broken exhaust stud or a cracked exhaust manifold. Take off your heat shield and look around. Look closely thought because some hairline cracks are hard to see, yet still let exhaust creep w/ no noise.

 

[bigbro6785]

Thats the thing, there are no leaks at all. The turbo spools up fine and now it holds boost fine since i put a mbc. It was only with the stock bcs that the boost would drop instantly. Thats what i find so wierd.

 

[bling5tatus]

are you knocking at all? Won't the stock ecu when connected to a bcs open the wastegate and retard timing if it sees too much knock?

 

[adidalax]

Thats the thing, there are no leaks at all. The turbo spools up fine and now it holds boost fine since i put a mbc. It was only with the stock bcs that the boost would drop instantly. Thats what i find so wierd.

He is saying exhaust leak. Boost leak test will not check for this...

My stock T-25 runs about 15psi on its own w/ only the BCS restrictor removed. If you put an MBC on there and are still only getting 13psi out of her, you probably, like Bender said, an exhaust leak either before or after the exhaust housing.

Try stuffing a shop rag in the muffler outlets and seeing if you have any leaks upstream around the turbo.

I'm assuming your car isn't smoking or anything crazy, right? Also, when you checked the timing, you remembered to ground the timing wire, right?

 

[alex99gst]

You could run some seafoam or carb cleaner through your car to check for exhaust leaks. It helped me accidentally find one at the turbo.

 

[bigbro6785]

From what I understand, if the exhaust manifold has a leak it is alot harder for the turbo to boost. But my car hits full boost at about 3000rpm. It is only getting 13psi because thats what I have it set at. I can try the sea foam thing just to be sure tho. I didnt check the ignition timing, i checked the cam timing. And lately there has been a loud grinding noise that i think is coming from the flywheel area (im thinking the starter is rubbing for some reason?). Also when I take the car on the freeway, once i start slowing down and let off the gas the car shuts off. My mom said there is also alot of black smoke coming from my exhaust when i take off. This is so frustrating.

 

[Bender]

Sorry I havn't gotten back to you sooner. From personal experience, if you have an exhaust leak before the turbo (cracked manifold/broken stud), the car will spike up to whatever you have the boost controller set to, then drop off to however much boost it can sustain with the leak. The psi you have after the initial spike is determined by the size of the leak.

 

[nytescion]

I'm thinking it something more internal of the motor....

car boosts to 13psi fine
there is grinding noises
black smoke
and car dies at highway speeds when you let off the accelerator

symptoms don't sound like a boost leak to me......or exhaust for that matter.....

 

[Black_Bullet]

From what I understand, if the exhaust manifold has a leak it is alot harder for the turbo to boost. But my car hits full boost at about 3000rpm. It is only getting 13psi because thats what I have it set at. I can try the sea foam thing just to be sure tho. I didnt check the ignition timing, i checked the cam timing. And lately there has been a loud grinding noise that i think is coming from the flywheel area (im thinking the starter is rubbing for some reason?). Also when I take the car on the freeway, once i start slowing down and let off the gas the car shuts off. My mom said there is also alot of black smoke coming from my exhaust when i take off. This is so frustrating.

Do you have a logger? If not you should get one.
Black smoke is unburned fuel.... Only thing that would cause that is if your running
way overly rich OR if you have a boost leak. Running way to rich will cause a lose of performance. Make sure your ignition timing is on, if you find you have an exhaust leak fix it, and how do you have the boost controller hooked up. The waste gate vacuum line goes into the side of the boost controller, the other vacuum source goes into the bottom. And are you venting your blow off valve? Also do another compression test yourself to make sure and do it right after running it when its hot. For a 2g 130 is horribly low and I wouldnt consider that in service limit considering your compression ratio should be up more in the 170s. 130 would make your car smoke and burn oil.. Does it...... After you do all that you shouldve narrowed it down a good bit.

 

[Bender]

Then you may be running lean. If you dont get enough fuel upper end, the car isnt going to make as much boost. I was able to stop my car from dropping from 23 to 18 just by richening my upper end.

edit: just reread your post. If your rings arent sealing like they should, you will get blow by. This will cause black smoke and poor boost. How many miles are on the engine? It may be time for a rebuild.

 

[Black_Bullet]

Then you may be running lean. If you dont get enough fuel upper end, the car isnt going to make as much boost. I was able to stop my car from dropping from 23 to 18 just by richening my upper end.

edit: just reread your post. If your rings arent sealing like they should, you will get blow by. This will cause black smoke and poor boost. How many miles are on the engine? It may be time for a rebuild.

????

 

[Cobrasatellite]

I think he was talkin to big bro black. I think bender may be right if all the leaks are gone (i wish i could acomplish that) and the exhaust all checks good and the compressions that low... ever thought of doing a 6 bolt swap its alot les work then that rebuild.

 

[bigbro6785]

turned out my car spun a rod and ended up messing up the whole engine.

 

[Black_Bullet]

Sorry to hear... I think half of us on this forum has been down that route.
Well if money permits, a rebuild with forged internals would be nice...