pifo1964

1993 Lt1, 14.000 miles.

With ignition on, fuel pressure around 37psi, five minutes later 32psi and still dropping slowly.
With engine running at idle, keeps at 34psi and when I disconnect the FPR jumps to 41. Accelerating smoothly, the pressure stays stable and when I accelerate suddenly, the pressure rises rapidly.
Despite little fuel smell at the vacum hose (no leaks at all) I think my FPR is working fine, but mi mayor concern is if the pressure readings are a little low.
Despite the few miles but many years submerged in fuel, the pump is not giving the correct pressure and not holding it (already tested injectors for leaking)

Could be the fuel pump?
FPR?
Or despite what the FSM tells, those readings can be consider normal?

BTW, car is running fine but maybe could run better….

Thanks!!

whalepirot

I recall FP spec is 41 or so, pump running, no vacuum on the FPR. At idle, the higher vacuum regulates the pressure lower, due to low engine demand. Under accel, the FP rises to meet demand, via low vacuum to the FPR. Without the engine running, key ON then OFF, the FP shuts off after a short spell, so FP may bleed off slowly. How slowly is key as it may indicate a leak in that pressurized system, perhaps an injector or one of the O-rings.

Then, if it ain't broke, don't fix it!

JoBy

With fuel pump running the pressure should follow engine vacuum
.

Sid.123

When I got my 86 vette I was concerned at the low fuel pressure so I changed the pump and filter.. the result is exactly the same...at idle Fp is about 37psi rising slightly with throttle..there is talk on the forum in other threads of having 50-60 psi but I think your only need this if you have bigger injectors fitted.

bjankuski

Your pressure readings are fine.

Purple92

Before you get too concerned - you might just want to check the fuel pressure with a different fuel pressure gauge. Some of the gauges they are selling these days are HORRIBLY inaccurate.

If the car runs fine at higher RPM @ WOT, I wouldn't worry. If you are getting misfiring at WOT - lift immediately - you want to fix the problem. It takes very little time for a lean condition at high load to do SERIOUS damage.

If you need to diagnose a low fuel pressure problem - you can block the fuel return line to see if the pump is able to supply higher pressure - but I'd recommend doing that with the engine off. Alternatively - if you can tape a fuel pressure gauge to the windshield, and go for a short run - if the fuel pressure holds steady as you accelerate at WOT from say 2,500 to 5,700 RPM - the fuel pump is fine...

pifo1964

[QUOTE=Purple92;1594622230]Before you get too concerned - you might just want to check the fuel pressure with a different fuel pressure gauge. Some of the gauges they are selling these days are HORRIBLY inaccurate.

That is the first thing I'll check, I have already spoken to a mechanic that will lend me his pressure gauge which surely is more reliable than my chinese made.

Thank you all for the responses!!

pcolt94

[QUOTE=pifo1964;1594622745]Your pressure reading are fine. You can get 5 different gauges and they all may read slightly different. If you have a slight bleed down over time it's normal and there is a window of acceptance. It's an older car but as long as the pressure doesn’t drop to zero right away when key is off of pump stops, there's no real problem. The running pressures are in a normal range.

You also never stated an actual problem you had but only focused on the fuel pressure for some reason.

pifo1964

You also never stated an actual problem you had but only focused on the fuel pressure for some reason.[/QUOTE]

Thanks for your answer.

I asked the forum because lately I 'm feeling my car with less power and as FSM mentions higher fuel pressures than taken by me, I thougt there might be a problem related.
But reading all you answers, maybe it's the gauge, or maybe it's me and nothing is wrong... or maybe it's the fuel it self.
Here it happens that sometimes the fuel does not mantain homogeneus quality an perhaps, after the last load I 'm running a fuel with less octane and the ECM is retarding timing a little bit.
The car is running fine and accelerates firmly without hesitations but I feel it weaker than a a couple of weeks ago.

pcolt94

Make sure your air filter is in good shape. Pull off the bellows and look at the air induction system and make sure there are no obvious restrictions.

Check out the EGR and just check for any codes. Something may turn up and engine lights (SES) don’t show all.

Or, could you just be getting use to the power?