Thread: Fuel pressure?

So ive been trying to hunt down this slight misfire im having on all cylinders for a little while now. Pretty much everything in the car has been changed.Plugs( al 606), wires, maf, icm, fuel filter a year ago, o2 sensors, no cat, no egr, lim.

So ive pretty much narrowed it down to the fuel pump. Last time i checked my pressure was a year ago when i got the car and i thought it was 62 psi with key on engine off. Well i just checked it and first cycle it was at 50 psi and started to drop slowly. Second time i tried it was at like 54-55 and same thing dropped slowly over ide say 10 second about 5-10 psi loss. I tried with car on and it read 62.

So i believe the pump is bad. Opinions?


Oh forgot to mention this morning the car hesitated to start. the first turn of key. Second time it started fine. And when i went out today a few hours later it started fine.

Pump sounds fine to me.

It should ever be lower than 45ish, and you are in the 50's and at near 60 while the pump is running.


You can tape the fuel pressure gauge to your windshield and take it for a drive and see if the pump loses PSI over time.

Well the series 3 and series 2 are also different

What does GM say for the 04+ returnless fuel system?

I wanna bet because the 04+ cars dont have a FPR on the rail, that pressure bleeds a tad after the prime.

no alldata atm ima have to search google a bit more

Also sucks my fuel pressure tester i have the hose is like 2 feet long so i cant drive with it on dash

If you have a no-start condition because there’s no fuel, the first check would be fuel pressure. On a Series II 3800 engine, fuel pressure should be 48 to 55 psi with the key on and engine off. GM does not provide a fuel volume test spec but, as a rule, a good pump should deliver about a quart of fuel in 30 seconds.
On a Series III 3800 engine in a Buick Lucerne, the returnless EFI system has the fuel pressure regulator mounted in the fuel tank with the pump instead of on the fuel rail. There is no fuel return line from the engine back to the tank. The fuel pressure on these engines should be 56 to 62 psi with the key on and engine off.

Yup i just checked it again to make sure and it measured 50 psi 3 times key on engine off and after pump turned off it would drop to 48 and stay there so ima try replacing the fuel filter cus i replaced it a year ago but who knows with these filters i sell at the store how good of quality they are.

So i replaced fuel filter and went from 50 psi to 56-57 and i def noticed a power increase. But now im misfiring more. Think maby i just need to d/c the battery to reset the pcm? idk why i would misfire more for more fuel

Ok so just a quick recap of things done to car and whats happening in hopes someone can figure this out.
Car is throwing no codes. Car misfires on all cylinders randomly and does so bad at wot keeps the car from shifting into the next gear.

parts replaced/removed

Egr removed
Cat removed
Maf replaced
O2 sensors
plugs al 606
wires al
icm
fuel filter
seafoamed
Injectors have been taken off and cleaned and sprayed good
vac is good
fuel pressure good

idk if i left anything else out. only thing i can think of is maby a cam or crank sensor?

Anyone?

Check compression?

Down the plug gap to .055?

Well just a little follow up. I figured even though i changed everything ignition related within the last year and even though the misfire is across all cylinders, ide test the resistance on my wires and coils. What i found was one of my wires were cracked and im thinking well that might have something to do with it but that it actually the only wire i can get readings off of. Every other wire i get nothing from with my mult meter. I even tried a different meter with nothing. So i ordered a set of delphi wires for tomarrow. But i took a set of cheap ones i had on the shelf just to make sure i was getting correct readings and every wires testing perfect. Ill post back when i put them in to see if the misfires are gone.

Ok so again a little follow up. I put on some new delphis and warrenteed the **** al one i had. Misfire still there but car is running a little better. Im starting to think injectors. Ima test them tonight. I didnt really think about them because i was getting misfires across all cylinders, but i remembered when i took them out cleaned them and replaced the orings, one of them was broken on the bottom a little bit. So im thinking air is leaking threw. I was reading that if one injector is bad it can follow to other injectors aswell, explaining why im getting it across all cylinders.

Found my misfire






**** hmmm..... Now at my work i get brand new stock ones for 27 a peice or i can upgrade them now concidering im replacing all 6....

4 broke and no idea
I imagine this will cause misfire from air leaking threw hense why its not picked up by pcm and its so small and it worse at wot

Them little plastic things always break, I have removed them all on my car.

The injector orings will seal them.

Originally Posted by Ginseng

4 broke and no idea
I imagine this will cause misfire from air leaking threw hense why its not picked up by pcm and its so small and it worse at wot

at wot your making boost so it would be hard to have a vacume leak that would let in air in there as there would be air trying to escape, as ffdp said the o rings do the sealing and those plastic retainers just keep the o rings in a proper postion so its hard to mess up a install.

by lookin at your pictures it looks like your injector nozzels are getting plugged (cant really tell). I would do a injector balance test on the car and that should tell you all you need to know.

ac delco fuel filter. misfire gone... let this be a lesson. Dont settle for filter besides ac delco