i had 4/6 exhaust bolts in and i took the turbo/manifold off and fixed the corner one and it was running rich and then i took a trip to chicago (not far) it runs lean im at 9psi daily driving, it was like this before. im getting worried because summer is around the corner and street racing is aproaching i checked the boot and ideling is fine untill start up it jumps 500-750 19psi vaccum. any suggestions
By "4/6 exhaust bolts", I'm guessing you mean the exhaust manifold studs. How do you know it was running rich or lean? Do you have wideband? Or did you just assume this? Idle at 750 RPM is normal for our cars. A slightly rough idle is normal. At idle you say you have 19hg of vacuum? That sounds pretty good to me. 9 PSI daily driving...hmm. Do you floor it everywhere you go? Why don't you do a tune-up and simple maintenance. If you think you're idle is really jumpy, check all charge pipes and vacuum hoses for cracks. Remove every charge pipe and visually inspect for cracks. If everything checks out ok, re-install and check your vacuum hoses. I would say to start with the vacuum hose leading to your bypass valve first and follow it back to the backside of the throttle body and check those hoses. With the car running, you can take a length of hose and hold it against your ear and carefuly move it around the engine bay to listen for hissing sounds. This would indicate a leak. Around the intake plenum, you will hear a slight hiss. This is normal. You should be able to tell if you have a leak. As for street racing....everyone here will flame you for it. I was going to, but I decided not to. I used to do it. I understand. It isn't the smartest thing you can do, but i've been there. Also learned from it. So, i'm not going to comment on it anymore. I hope I helped you out some. Good luck!
The exhaust studs wont affect running lean or rich, thats either a tune up problem or a vacuum leak problem.
Exactly. The only problems with snapped manifold studs would be squealing at startup and under acceleration until the engine is warmed up, causing the leak to seal a little. That and maybe a tad less of response from the turbo. Would this loss of exhaust cause the o2 to read slightly different at all? I have a crappy narrowband gauge and I noticed after I fixed the studs, it would read a bar richer. I know I can't rely on it while just cruising, or even for REALLY tuning, but it does read one bar richer than it ever used to.
My old Nissan Pulsar EXA Turbo was a shocker, the studs would stretch and break constantly, at one point it blew a whole corner section off the manifold, it warped the next manifold... aaaaah typical Nissan engineering. I'm glad I got rid of that particular turbocharged nightmare.
If I gave my MX6 as much attention as I gave my Fiero, I'd be around here far more often!
An exhaust leak will cause the car to run very slightly rich. Remember that the O2 doesn't work under WOT. So what ends up happening is the turbo will spool slower (less air volume) but the same amount of fuel is being dumped.
At least I found this to be true. I actually dumped fuel out the exhaust on WOT, until full boost. Then when I fixed the leak, it went away.
the idling i fixed i put a new clamp on the tb boot.. it would jiggle off sometimes. but i have a narrowband o2 sensor and i know it wont be accurate but i just want it to be safe to boost to 13-14.and i dont punch it very often i enjoy the gas in my tank. if i take it to a dyno will the a/f number help with fixing the problem? will it narrow it down.
thanks
Over here when you put the car on the dyno they usually hook up a A/F sensor on the exhaust (name escapes me at the moment), so they will have a very accurate reading of your A/F.
We also have engine analysers that will test the spark, timing, etc. In combination of these things they will definately be able to at least give you more information.
This is what we have on the other side of the planet. Not sure if it is the same for you, or the cost involved.
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