Mechanics

CHEVY LOW FUEL PRESSURE POOR RUNNING

2000 Chevrolet Express

Engine Performance problem
2000 Chevy Express V8 Two Wheel Drive Automatic 70,000 miles

Engine would occasionally barely run as if running out of fuel. Turning off and then re starting would clear problem. There are some hesitation problems during acceleration. A lean fuel mixture code was occasionally triggered. Pressure test of fuel system revealed low pressure. Replaced fuel pump, pressure regulator. Pressure is 62 at initial key on then drops to 54 or 55. Jumps back up to 62 at key off. Engine still hesitates on acceleration though fuel pressure rises to 62. When throttle punched or vacuum disconnected. Interestingly I forgot to re-connect the electrical connections to the MAF at one point and the engine runs better without hesitation though fuel pressure remains arond 54, reconnecting MAF decreases performance. Any Ideas?
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Thomascarr
June 9, 2010.




Ok with that said I would get some mass air flow cleaner from you local parts store (do not use anything else) and clean the mass air flow unit. Let me know if this fixes it. If not then you will need a digital multi meter so we can run a couple of tests on it to see if it is bad and needs replacing.

Racefan966
Jun 9, 2010.
Sorry I forgot to say I already cleaned it with the maf cleaner with no improvement. I'll get a multi-meter. So I can do the testing. Thanks for the reply. Also already replaced fuel filter and it recently had the oil pressure sending unit replaced cause it was leaking.

Tiny
Thomascarr
Jun 9, 2010.
Forgot to mention before That I already cleaned the maf with no improvement. I have a multimeter to test it with. I should also mention that the oil pressure sending unit was replaced not to long as it was leaking but I don't think there is any relation to the current problem. The fuel filter was replaced before the pump or regulator. Something of interest that I've noticed is that the fuel gauge flutters very quickly and and isn't even noticable unless you look carefully. This was happening before I replaced the fuel system parts and after.
Thanks.

Tiny
Thomascarr
Jun 10, 2010.
Ok when you have a multi meter and it don't need to be an expensive one just one that will do volts and ohms ok, get back to me and we will do some testing.

Racefan966
Jun 12, 2010.
I got ahold of one tested the pos and neg to maf both good apprx 12 volts. The other lead reads.04 steady and doesn't move with rpm.

Tiny
Thomascarr
Jun 12, 2010.
I would like to check both the MAP and MAF sensors ok. First the Maf, I need to know that the black wire with the white stripe has low resistance (ohms) to ground. Now check that the pink wire for battery voltage. Now the yellow wire is the reference wire to the computer so this voltage should very and to check that you back probe the wire with paper clip and hook up you meter and then start the van, as you increase and decrease the throttle and air moves past it, it should send a signal back to the computer that varies in voltagae. Now the MAP sensor is a simple test what I need you to while the van is at idle just unplug the vacuum line to it and let me know what it does ok.

Racefan966
Jun 15, 2010.
Hi, I have exactly the same problem as you and am getting exactly the same readings as you on my 2000 v8 express, Did you ever resolve your problem and get your fuel pressure up? I am in england so nobody has a clue about these vans!

Tiny
Jcramphorn
Apr 2, 2011.
So have you tried to adjust the pressure regulator? Inside the vacuum port there is a tiny screw to adjust the pressure. This does mean that you will take off the upper plenum a couple times but if there is no leak or crack in the lines to the injector unit thats all I could think that would pick it up.

Racefan966
Apr 2, 2011.
Hi, thanks for the reply, No havent tryed that yet, didn't know you could do that on this van. Il go and investigate this further. Theres no leaks or cracks in the lines and according to the fuel pressure gauge the pressure doesnt go down when the vehicle is left, the pressure just stays at around 54 on idle and up to 62 when you kick it down, the van runs great most of the time, just loses power when hard accelerating up hill and you have to turn the key on and of twice in quick succession to get the pressure up enough to start it. Hard to find information on this van in the u.K but think the fuel pressure should be 60-66?

Tiny
Jcramphorn
Apr 2, 2011.
Yes teh pressure should be 65 psi at start up and 58 to 60 running so tell me how old is the fuel filter?
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Racefan966
Apr 7, 2011.

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