No start: Fuel pump runs but 50psi

[erubin]

1996 4.3L P/U 2wd.
Truck stalled a few times yesterday. Today wont start. A squirt of starter fluid gets it running a few seconds. All the injectors have power.
I can hear the fuel pump go on.
Hooked up a pressure gauge to the test port. measured 50psi with the return line pinched off (same reading without pinching off the return).
Will this slightly low pressure prevent the truck from running and starting?
If so i guess I will change the pump and filter while at it. Need to siphon out half a tank of gas which is a drag. At least it's a CA car so no rust under there. There is a strap in the front part of the tank that appears straight forward but the rear strap also has a steel member bolted to the frame that appears more difficult to remove. I will do this alone so lifting off the bed is not an option.

[MT-2500]

Yes even a couple of lbs low will keep the injectors from squirting on a cold start.

Unless it is a 7.4 the specs are 60/66
Hard to start cold.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

[Indy Tech]

If you have the 4.3 L CSI system you will need 60-66 psi as MT said or it will not start .
if you have the SFI system you need 56 psi.
With you having the 4.3l and have the CSI system make sure you do a leak down test as these motors are known for bad fuel regulators
If i remember rightly if your 8th Vin # is a W then it has the CSI system.
Remember when testing you fuel pressure be Careful not to exceed 75 psi when testing with the return hose blocked ( on thr CSI system)
That will kill you fuel regulator(if its not already leaking)
One more thing, when you tested the pressure you had 50 with and without return hose blocked check your fuel filter
Indy

Edit -Just noticed wasted my time on this one its bloody years old

[erubin]

Thank you for your insightfull suggestions.
the 8th caracter is a "W" so the pressure spec is 60-66psi and I measured 50psi with the return line pinched. Without it pinched the presuure varied from about 44 to 50psi (did the test a few times) and in the few moments of the testing I didn't notice significant pressure drop.

I can buy an OEM Delphi pump. It's just the pump (not the assembly so it doesn't include with level sender, etc) is that usually good enough? I read a TSB that mentioned low pressure problems caused by a ruptured fuel pump pulsator (the flexible connector located between the pump and the metal fuel line in the tank). Hopefully if that is the problem it will be visually apparent.

As for a clogged filter i guess the only way to really check it is to replace it; correct? BTW, the day the problem started although it stalled a few times it otherwise accelerated properly, would that rule out a clogged filter?

[MT-2500]

To check a fuel filter I always remove it and see what runs out like rust or water or black stuff and try blowing threw it.

Not sure it has a pulsator.
But I always go the complete pump module because of the old plastic lines and bad fuel sending units and electrical connections.

Some even have a rewire kit with them.
To take care of wiring problems.
Good luck
MT

[erubin]

dropped tank and replaced the pump. Truck starts right up. Replaced the filter and all is well so far.

Fuel pressure with new pump and filter (both the inline and the in-tank replaced). 56psi
Pressure with return line pinched. 90psi.

Maybe the regulator is on the way out? I was expecting 60psi. In any case the truck runs fine for now.

At the old pumps outlet is a metal oval device with rubber internals. It is called a fuel pump pulsator. Anyway a mechanic friend who has done these jobs before said he always replaces it with a fuel hose since they are know to leak. Interestingly my pump kit came with the perfect length and diameter hose to replace it.

[blazergirl63628]

i have a 98 blazer it wont start,new fuel pump new filter. pour gas down it starts runs fine. will sart fine if the temp. is above 40 degrese outside.once you get it started. will run and start the rest of the day just fine next morning the same thing unless warm out what could this be please help going nuts

[erubin]

Somebody with more experience might pinpoint right away the problem based on your fuel delivery problem only when cold starting. A lot mention the fuel regulator. I wonder if an experienced mechanic would need to go through a pressure test to pin point the problem given the syptom. I would measure the pressure during cranking. Assuming it was too low I'd test again with the return hose pinched temporarily. If it then starts the regulator would be my bet, if not I'd wonder about other possibilities.

[MT-2500]

Originally Posted by blazergirl63628

i have a 98 blazer it wont start,new fuel pump new filter. pour gas down it starts runs fine. will sart fine if the temp. is above 40 degrese outside.once you get it started. will run and start the rest of the day just fine next morning the same thing unless warm out what could this be please help going nuts

Welcome to AF
This post is old and was started by someone else.
It is best to start a New Thread on your problem.

The decription sounds like a fuel deliver problem.

You need to run a full fuel pressure test.
Watch and check cold start cranking presssure.
You need 64-65 cold starting pressure to squir injectors on a cold start.

For 4.3 engine.The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.
MT

[blazergirl63628]

Originally Posted by blazergirl63628

i have a 98 blazer it wont start,new fuel pump new filter. pour gas down it starts runs fine. will sart fine if the temp. is above 40 degrese outside.once you get it started. will run and start the rest of the day just fine next morning the same thing unless warm out what could this be please help going nuts

changed the fuel regulator problem seems to have gotten worse.changed throttle position sensor still no change can some one out there please give me some ideas the might be helpful willing to try anything at this point!!!!!!!!!!!!!!!!!

[erubin]

You're wasting money and time by replacing parts without testing. Did you pinch the return before replacing the regulator? If not you threw money away without performing a needed test. Finally you must borrow or buy a fuel pressure gage to test as per MT-2500. If you just want to guess and keep replacing parts without diagnosing first maybe someone else can suggest the next part to throw at the car. Good luck.

[blazergirl63628]

finally got someone to do pressure test it was only a 20 and bleeds off to 0 in seconds.

[j cAT]

Originally Posted by blazergirl63628

finally got someone to do pressure test it was only a 20 and bleeds off to 0 in seconds.

replace fuel pump and fuel filter. try to keep gas tank more than 1/4 as low fuel in tank damages fuel pump..........measure fuel pressure after pump r/r just to be sure pump is operating properly. delphi pump is best others have problems.......if after this it starts hard when below 40deg f the ECT sensor should be checked for resistance.