Fuel pressure spec


#1

i have a 1998 chevy blazer 4wd v6…i like to know what is fuel pressure spec for this blazer i test fuel pressure it was 58psi when i turn key on.when i start car it’s at 56 psi


#2

Spec is 60-66, what leads you to ask?


#3

i wasn’t for sure where it should be at.when i chk it it was 58 psi .so now i know fuel pump is going bad


#4

when i give it some gas psi drops down a little bite.


#5

Sounds pretty normal to me. Me thinks you should look elsewhere for your problem.


#6

i just test it agin and the neddle moving like crazy between 54psi and 58psi when the car is running


#7

“Sounds pretty normal to me. Me thinks you should look elsewhere for your problem.”

I agree with Bing.


#8

i just got back from my shop and thay said 58psi is to low.it should be more like 66 psi.


#9

Sounds pretty normal to me too. Low end of spec is 60 psi and you have 58. A few psi low shouldn’t be noticeable when driving. What exactly is the symptom you’re trying to fix?

And don’t assume the fuel pump is bad. There is also a pressure regulator, and it’s a lot less expensive to replace than a fuel pump. If fuel pressure is even the root if your problem, which I doubt.

You’ll get better results here if you start by posting your original problem and ask for people’s input. 2 psi low fuel pressure is not your real problem. So…what is the real problem?


#10

it’s been running routh and it takes little long to get up to speed when driveing it.when i hit 44 mps car likes sputting and when i push on gas padle hard car don’t go.i know thay test drove it and said its sputting when you hit 44 mph and he hock up fuel pressure gaueg and said yea its to low 58 is to low it should be more like 64 to 66 psi


#11

Rough running and severe loss of power are not caused by fuel pressure being a few psi low. I would suspect something like a plugged catalytic converter. Have they checked the exhaust system for blockage?


#12

i already have that done and new tune -up


#13

Well then something else is going on and you may need to find someone else to diagnose it correctly.

Rough running and poor power could also be symptoms of timing belt slipping a tooth, burned valve, broken valve spring, etc. Has anyone done a compression test on the cylinders? I’d start there.

Also, if the engine is running that poorly, there should be trouble codes stored in the computer. Has anyone read the codes?


#14

The fuel pressure is too low.

Your engine has the central port fuel injection system. This means it has a central port injector called a spider assembly.

https://www.rockauto.com/catalog/moreinfo.php?pk=1053753&cc=1314133&jnid=503&jpid=13

This spider assembly has injectors called poppet valves. These poppet valves rely on the fuel pressure to blow them open to introduce fuel into the cylinders.

If the fuel pressure drops below 60 PSI, the poppet valves don’t get blown completely open to inject the proper amount fuel into the cylinders and the engine runs rough.

Replace the fuel pump.

Tester


#15

thanks Tester for your help man.ill get that pump replace soon


#16

If replacing the fuel pump doesn’t fix the symptom, that spider mechanism has been reported here as the source of problems sometimes too. Or the fuel filter could be plugged up. One way to test for that is to hook up the fuel gauge, place it somewhere you can see it, and take the car for a drive. If the fuel pressure drops considerably when accelerating, going up hills, esp if this drop in fuel pressure is associated with the symptom, that could mean the fuel filter is plugged.

One more idea, if your engine has a separate fuel pressure regulator, then there will be a vacuum hose going to it. Remove that hose and see if there is any gasoline in the hose. There shouldn’t be.


#17

I would try changing the fuel filter after I checked for a restricter exhaust with a vacuum gauge.


#18

I tend to agree with jesmed1 about an exhaust system restriction. The fuel pressure may be a little lower than spec but should not cause a problem unless you’re flooring the pedal at 100 MPH. Even that is debateable. Eight PSI should not make much if any difference.
There’s also the possibility of some gauge error.

My youngest son has purchased 3 of those dashboard vent temperature thermometers from different vendors to keep tabs on A/C performance and all 3 were off by a country mile. The norm was 15-20 degrees error and one was almost 30 degrees off.


#19

Before doing anything else, make sure that your pressure gauge is accurate. If others are sharing the gauge, that makes it even more important.


#20

Just had a Blazer around 1998 come in that I worked on about a week ago. It was a no start with 55 PSI fuel pressure. Replaced pump, had around 65 PSI KOEO and it was no longer a no start. Fuel pressure being within specs on these vortec motors is very important. The injectors will not function properly if pressure is low.