AJT84

92 LT1 completely stock. I was checking my Fuel pressure tonight and idling it was around 38 psi. As I opened the throttle body the pressure sat around 38-36 until the rpm got around 3500 or so, NORMAL? Then it began to come up. Now, idling with the vacuum off the FPR it made 48psi. And when I'd snap the throttle quickly it would come up into the low 40s. I realize 41-47 seems to be the operating range for this engine. Does this pressure seem on the low side to anyone?

My real oddball question is I noticed while the car was running that the FPR was ticking, as if opening and closing quickly, though pressure was pretty steady. Is the ticking normal? I know that's a weird one but I'm inclined to replace the FPR due to it and to see if it raises the operating range of the pressure before considering the pump.

Sorry for the amateur questions. Car starts and Idles great, just has some part throttle weakness I cant figure out. Also at WOT just before shifting from 1-2 (automatic) it sometimes coughs just before the shift. Wondering if that's fuel starvation.

Eduardo L98 1991

with the vacuum hose disconected you wil read about 40-45

cardo0

Best just to set it to stock which is 41psi with the engine off. Now if you have an adjustable regulator and the pressure is to high when you turn the key (but not to start) then you of course need to bleed off some press before readjusting. Finally I would start the motor then shut off to measure the fuel pressure one last time engine off to verify you got it right.

Yea so the function of the vacuum operated regulator is to keep the pressure differential across the injector constant as manifold pressure changes. As the throttles open the engine vacuum does go down but that is really absolute pressure going up - as manifold pressure is moving towards atmospheric pressure. That means there is greater pressure resisting injector flow. So the vacuum operated regulator will increase fuel pressure to the injector to maintain the desired flow rate.

When you have are at idle the vacuum inside the manifold is very high but the absolute pressure is very low and there is less pressure to resist injector flow. The vacuum operated regulator adjusts fuel press to lower fuel pressure to the injectors and maintain desired flow.


Well if you change fuel pressure you need to change the injector constants too. That means a new tune and in a '92 that would take a new ECM chip.

Hope this helped.

AJT84

Didn't mean to imply I was going to install an adjustable regulator. I would replace with OE part. Now speaking of tuning, isn't the factory flow rate of the injectors based on a 43.5 psi system? That I'm not sure of, and I'm not trying to retune anything. i just thought the ticking in the regulator seemed strange. Still no feedback on that. I understand how it's supposed to work just was looking for thoughts from anyone who had real world experience with this.

bjankuski

You are fine, leave it alone. The fuel pressure should only be checked with the vacuum disconnected and since yours read 47 with it disconnected and 38 connected the regulator is working fine and as far as I can tell your pump is fine. If you quickly mash the throttle to the floor the fuel pressure should jump up, if you slowly open the throttle the pressure will not jump up because you still have vacuum in the intake. If you drive the car and floor it and the pressure should hold around the 43 to 47 PSI range, if that happens the pump is fine.

DVNCI

Correct, 43.5 is what most injectors are rated at. With vacuum hose disconnected, that's what you should see. (and therefore that's what you should be seeing at WOT)