I finally drove my car on the streets for the first time this year about a week ago. When I first took it out it stumbled pretty bad at a start vibrating a little bit too. Now its a little smoother off idle, where its really rough is 1500-4500 rpm at about 1/3 throttle. If I open it up more it smooths out. It also gets very close to stalling if im rolling and clutch in, brakes in.

Currently my fuel pressure is about 30-36 psi during normal driving. It is very often at 30. A/F fluctuates from low lean to high stoich, never to rich.

Before storage fuel pressure would range from 30 to maybe 40ish. The only time it would be at 30 would be decelerating, no throttle, mid rpms. cruising wouldnt drop below 32. A/f would fluctuate from low lean to mid rich.

I changed the fuel filter. The pump has about 10k on it. The regulator is obviously varying pressure, but could it do that wrong? Maybe a bad injector? I could switch my a/f guage to the other o2 sensor and if it will flucuate to rich on that side I guess that would confirm that.

Any other suggestions?

 

What is your pressure at WOT?

 

I havent gone WOT yet this year, 3/4 at the most and I dont think it has gotten above 36 at that. Im a little nervous about going WOT when Im not sure Im getting the fuel I need.

 

No big... take the vaccum line off the FPR and see what it is. Taking the vaccum line off while the car is idling will similate WOT.
Keep the line off and drive around and do a few short blips to see what happens to your fuel pressure.

 

Good idea. Ill give that a shot tommorrow.

 

Just did the simulated WOT. At idle it stayed at 42, when I actually opened it up, still only at about 3/4 throttle it would go down to a low of 36. A/f still only fluctuated between low lean and mid stoich. I still got that vibration in the mid rpms which leads me to belive a bum injector.

 

In no way is your fuel pressure supposed to go down when accelerating.

 

My fuel pressure going down when I accellerate obviously is not optimal, but I dont think thats the problem because pressure is staying up at idle but the a/f is not fluctuating as much as it should. It will do this when it has first started up so I have ruled out some sensors that would only affect it when it has warmed up.

 

Who did the tuning? I don't think what you described can be blamed on only one injector...

 

bad gas?

 

The tune was done by MadZ28. It worked well last year, before I drove the car this year I had him change a couple things like tire size, got rid of cps, but nothing major. I sent him an email to ask if there was anything he changed that could cause this.

Bad gas is an idea, thats why I put in a couple bottles of techron and filled up at a busy station. When I pulled the cap the tank smell like old ***. But I dont think bad gas would make the a/f not go rich...

 

I just disconnected the O2 sensors and took it for a drive. No vibrations like that. I find it hard to beleive the 02 sensors are bad since im not getting an ses light for them. Maybe Ill replace them anyway. They are cheap from GMPartsdirect.com.

 

Don't be too quick to blame the 02's. Once you disconnect a diagnostic sensor your PCM reverts to open loop so basically all sensors are bypassed and your fuel maps/spark curve will go to a default setting.
What you need to do is get the PCM scanned to see what's happening while in closed loop.

 

My first thought was "what could be screwing up to cause it to run better in closed loop". As far as I know the only sensor not used in closed loop are the o2 sensors. So if it runs better without them then the MAF must be running well as well as the MAP. I know its not the coolant temp sensor because it will barely run when that is screwing up. If I did have bad gas is it possible my knock sensor was retarding timing more at part throttle?