Before the mod, I tested the fuel pressure at 44psi or 46psi for about 2-3 second when turning on the ignition, then droped about 2psi, but stayed. However, after installing the new fuel pressure regulator (set at 48psi), it would drop to "0" after reading 48psi (the needle moved to 48psi then drop to 0). While replacing the new regulator, I did remove all the injectors. No leak was found. Car's running fine. Any idea?

 

You mean it dropped to zero after you shut the car off? If it went down instantly, then you have a fuel pressure leak somewhere. It would have to be a significant leak to make it drop instantly though. I had an adj. FPR on my '96 and it would go down to zero after about 5 minutes. Examine your fuel injectors really well with the car running and check for a leak there. If there is a leak, obviously it's gotta be at the regulator or the injectors. Did you notice any loss in power?

 

I have an adjustable regulator on my 96 as well. Before I installed it, there would be pressure in the line for days after the car was turned off. After installing the adj. one, the pressure drops off pretty quickly after shutting the car off. Also noticed it take a little longer to start the first time, I think that's because the fuel lines need to pump up first.

Flynn :reddevil

 

GMs Service Manual shows a procedure used to isolate the cause; but like most their procedures is somewhat complicated.

Assuming no exterior hose/line leaking, it is either at the pump or at the engine.

Memory tells me that it could be an injector (which you say you've eliminated as the cause) the regulator itself or the return hose at the pump.

I've seen all kinds on posts on this issue. Some say their pressure holds for days, others say for minutes.

I timed mine once and posted the times it took for the pressure to fall off, which was in the minutes. Even now, some days I can pop my hood and my pressure gauge will still be at 40 of psi after the car has sat in the garage overnight; other times, it will be at zero.

Since I have no dirveability problems, I quite worrying about what the gauge shows me.

If I recall, if you remove the vacuum line from the regulator and fuel leaks out, you've got a regulator leak.

The tank problem can be checked by squeezing the rubber return line to the tank. If pressure holds while you're squeezing the hose but drops when you release the pliars, it's the line on the pump itself that's allowing fuel to return to the tank. If pressure drops while holding the return line in the pliars, then the cause has to be up front.

You can use the rubber hose attached to the block near the mechanical fuel pump boss (lower passenger front)

Hope this helps.

Jake

 

Mine did this exact same thing. The fuel pump would not hold the pressure in the line. It could either be a loose hose on your fuel pump or the pump itself. At least it is easy to fix. My car ran fine for a month or so while this was happening then one day all it would do was idle. It could no longer hold pressure above 6psi. Good luck.


[Modified by C4-Wolf, 4:28 PM 2/7/2002]

 

So, you think it's the pump or the pump line? As I mentioned above, it was OK till I removed all the injectors and replace a new adjustable fuel pressure. I forgot, I also replaced a new fuel filter, but I don't think the filter is the problem. I am thinking about replace the stock fuel pressure back and see what happen.

 

If it is going down to 2psi quickly, something is wrong or going to be soon. You might want to look at ( I believe it is a noise supressor ) that is attached directly to the outlet on the pump. It can be less than a snug fit at times so maybe fuel is leaking back through that. Or if the pump is old it could just not be up to holding pressure any more. Either way if the car is running fine now you have no immediate problem. But like I said mine did the same thing for 2 months ( good psi at startup then dropped rapidly to little or no pressure ) but right when I was 150 miles from home it completely failed. Had to hitch a ride home and then get a ride back just to replace it. Anyway, just be aware that it could go. Maybe it never will, but with the pressure dropping off that quickly, it may be on its last leg. Hope you figure out the problem.
Jeff