Ive been having low idle issues, seems to be to rich. Just added a B&M fuel gauge. 2 questions though. Is the gauge supposed to flicker at idle. My pressure is at 55psi at a cold idle and the needle flickers between 50-60 psi. Second question, I havent tried to drive it yet, but I followed the DIY gauge install in the stickies. The guage seems to be awful close or even touching the hood liner when closed. Is this normal? I am afraid that it will really touch when the motor shifts.

 

With the vacuum line disconnected, the pressure should be 47-54 PSI. With it connected, it should probably be about 7-8 PSI lower.

How are you measuring the pressure? Vacuum on or off? As for the pressure changing, with vacuum disconnected, I'd expect it to be rock steady. With the vacuum on, it'll vary with the vacuum.

Idle problems are normally dirty throttle body or IAC. Idle speed is completely under ECU control through the IAC.

I'd hook up a vacuum gauge and see how it looks. If the vacuum fluctuates then you might want to find out why. A good scanner will tell you right away if it's rich or not. You look at the short term fuel trims while it's running.

 

I measured with the vacuum on, which line shoud i pull off? Is it difficult to check the IAC?

 

If you measured with the vacuum on, then your fuel pressure's 8-9 PSI too high OR you have a bad vacuum leak. You don't have a 255 LPH pump in the tank do you? Having too big a fuel pump can sometimes cause the pressure to build up because the FPR can't bypass enough back to the tank.

Pull the hose off the FPR then plug it. You should see the fuel pressure go up 8-9 PSI when you disconnect it. The numbers I mentioned are "vacuum line disconnected" numbers right out of the shop manual.

Make sure there IS a vacuum on the line you disconnect., If there's no vacuum on that line, the fuel pressure will be high except under acceleration. I can disconnect and reconnect that vacuum line and see the pressure jump up and down.

 

Ill give it a shot, Im running the comptech fuel pump. I did notice an abnormal hissing sound coming from under the intake manifold. I couldnt narrow it down to anything though.

Thanks for the help, Ill let you know what I find.

 

Comptech Fuel pump with an NA engine or FI? You know that Comptech also sells a special fuel pressure regulator (FPR) too? I'm going to guess that pulling the vacuum line makes no difference and that the problen is the your fuel pump is dumping so much fuel into the rail, the regular FPR can't divert enough to the tank so, it can't relieve the pressure. That'll make it real rich at idle and cruising when the fuel pressure should be reduced.

When I foolishly installed a 255 lph on one of my car's I had to get the AEM adjustable FPR to tame it. You can change the internal bypass size on the AEM to adjust for large fuel pumps.

 

I pulled the vacuum and the pressure goes up a little past 60, still flickering.

Im sorry should of gave a little background info. Comptech s/c 7 psi emanage only adding fuel in boost, all values at zero otherwise. If had this setup for over 2 years with no issues.

Where else could the vacuum leak be, whats under the intake manifold because I do hear some hissing from under there?

 

I know NA, when you're talking FI, I'm not experienced. I'd expect stock fuel pressure at idle and when you have no boost so, I'd say you have a fuel pressure problem.

How's the fuel pressure increased when you're in boost? Somehow or other you get more fuel under boost, either fuel pressure, increased injector sizes or more duty cycle.

I don't remember any vacuum lines under the manifold. The fact you pull the line and pressure goes up even more suggests, the FPR's reacting to vacuum like it's supposed to, you're just about 8 PSI high. Who knows the ECU might compensate for that automatically. If you're not getting mxture CEL's it can't be that wrong.