OK, still having all these stumbling problems. Replaced the fuel pump, and still runs bad. Question is... what pressure should I have at the motor? We had like 40psi and then it would go down to lkike 30 or so. The gauge may be messed up so we're getting a new one, but could the regulator be bad? If it messes up, will the pressure at the rails be wrong? I'm assuming it would be. I appreciate any help! TIA

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

A good base line is usually 40-45 psi with the vacuum hose off of the regulator. Didn't mention if your psi was with hose off or not.
A bad regualtor may exhibit any number of signs.
Not holding correct pressure, maybe.
Pressure not flucuating with manifold pressure, should go down about 10psi when the vac. hose is connected back on.
But will usually, never hold pressure once car is turned off. It should hold the pressure for about 10-15 minutes minimum.
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And is its not holding pressure, it could be other things besides the regulator though.
Test by using a pair of vice grips, and lightly pinch off both the supply and return line where they are a rubber hose, immediately after cutting car off, may need a second person.
If it still looses pressure quickly, then you have a leaky injector. If not, then release the return line, if you loose pressure, you have a bad regulator.
If not, and you release the supply line and you loose pressure, then you have a bad check valve in the fuel pump or a leak around the pulsator or hose in the tank.


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Rob
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[This message has been edited by 2QUIK6 (edited March 11, 2001).]

 

Ok thanks! It was doing this stuff before we put the fuel pump in, so I'm gonna rule out the leak at the pulsator... and we removed the pulsator anyways. I guess we'll try pinching those lines and seeing what it will do. I'm assuming that my car should have about 40psi and should hold this for quite awhile after shutoff... right? Well, I guess we'll try and see whats wrong then. How do I check for a leaking injector? Would this cause all these problems? It seems as if all fuel supply is cut off momentarily causing a "bucking" of the motor. VERY VIOLENT also! We thought that maybe a bad FPR was causing a lean/rich condition and when the ECM was trying to compensate it was putting to much fuel to the injector (and voltage) and then shutting off the injectors momentarily. Think this could be possible? TIA

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

To check for the leaking injector, you'll have to pinch off both lines and see if pressure drops.
Forget to mention, the pinching off of the lines is done with engine off, key on to energize the pump for 2 seconds, or just turn engine on, then turn it off and immediately clamp the lines.
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It would have to be a really bad or stuck open injector to effect it like that. Pull the spark plugs and that may tell you which one is bad if it does fail the pressure test.
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I would suggest getting a scan tool to bebug any further, it may not be the fuel system causing it. Could be weak coil, bad IAC, bad wiring somewhere.
Is the stumble at take off like a normal take off from a stop sign, or a WOT take off?
Maybe IAC not properly set or bad if at normal take off, could be coil if at WOT.
Again, scan tool needed.

 

We're borrowing a scanner this week. I understand that! I NEED ONE! It does it just about any time, so thats the big problem. The coil is... we've swapped them out and I swapped IAC's and no change. Well, guess I'll have to hook up the scanner and see. May swap out ECM's too. THANKS!

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'91 GTA:
www.fbody.com/members/91WS6GTA

 

Was the IAC reset after you installed a new one?
But IAC will only effect initial tip in of throttle from a dead stop.
What chip are you running? Maybe a bad chip, or wrong timing/fuel tables programmed in. ECM swap wouldn't hurt either if you have one readily available to try.