yeah my car's beginning to **** me off, here's some symptoms, I'd like to hear some ideas, theories, or tests I can execute.

1) car is hard to start and sometimes won't hold an idle for first few seconds
2) high rpm missfire (anything above 5100rpm basically it starts to break up) and according to the dyno was running lean
3) car was going very lean on the nitrous even on smaller shots
4) when motor is cold if I lift off the throttle while cruising rpms will jump below 1000rpm mark and then return to normal after a second or so

now here's some things I have done so far
-brand new opti with cam swap
-new ngk tr6 plugs
-checked all plug wires

I'm beginning to think my fuel pump is taking a ****, if so what psi would I look for with key at on position, idle, and wot? also do I use the schrader valve to read from? or maybe I have some faulty injectors how would I test for a lean injector?

 

Stock FP should be at or near 40psi with all the vac tube hooked up to the FPR. Yes you tap the schrader valve in back of the intake.

 

should it be constantly at 40psi? (on position, idle, and wot?)

 

If you disconnect the vacuum line to the fuel pressure regulator, then the vehicle's fuel pressure should not fluctuate regardless of the position of the throttle (or more importantly, engine vacuum)

 

close to it...43 i think.

key on engine off should have 40+

should have 40+ with vac. off running

 

The fuel pressure regulator is vacuum controlled. The higher the engine vacuum, the lower the pressure and the lower the engine vacuum the higher the pressure.

If you have a fuel pressure gauge installed on the engine and simply use a pair of pliars to squuze shut the vacuum hose to the regulator, you'll see the pressure increase a lot. That's because you've shut off the vacuum source which keep the FP low.

So, at idle, when engine vacuum is HIGH, and the vacuum hose connected to the fuel pressure regulator, the reading at idle should be at, or very near to what the FSM (Factory Service Manual) says it should be.

The actual pressure differs for different year engines; The 86 L98 is somewhere around 43 psi while in later years, GM raised it to around 47 psi.

As you floor the throttle, engine vacuum drops off (becomes lower) which caused fuel pressure to increase.

When I check to see if the FP is holding at WOT, I remove the Schrader valve completely and screw on the FP gauge (you know the one with the long hose, like the one TPIS sells).

I tape the gauge to the outside of the windshield and continue the glance at it as the car blasts down the road. If the pressure begins to drop, I then know I have an area of concern.

That's the procedure I've found most often recommended.

Hope this helps.

Jake

 

thanks man

 

LT1 "standard" fuel pressure is 43.5psi. Factory tolerance on the "no vacuum" fuel pressure is 41-47psi. It has to be able to hold that pressure at WOT/max engine load/RPM.

The vacuum line to the LT1 FPR is so easy to remove that there is absolutely no reason to risk crushing it with pliers. It is plastic, not rubber, and will crack easilly.