2000 4.3 won't start, but fuel pump comes on...

[Surfnbiker]

I've had this 2500 Express for approx. three years and already had the fuel pump replaced once. Then it just quit working entirely.

This time around, it started slowly. Just hard starting when cold, usually in the morning. Have always been able to hear the fuel pump. Once started it would run fine all day.

Fast forward a month or so. Problem getting worse, now it will be hard to start throughout the day. Until finally, today. Fuel pump comes on, but no start. Just a little sputter, but it will not fire off. Haven't really done any diagnostics except for one thing, pulled off the doghouse, found the fuel lines going up to the manifold, and found a schrader valve there. In some other posts that I read, there should be fuel there. Boy was there ever! Shot a two foot stream towards the rear of the cab. It's a work truck, so no worries.

Next I shot some carb cleaner into the air box, and it fired right up, and continued to run without so much as a cough. I know there has to be a specific component that isn't doing its job.



Anyhow, the issue seems to be when I let the truck sit for a hour or more, it was hard starting but now it just won't start without "priming it" Any suggestions? Thanks!

[Surfnbiker]

Okay some progress has been made. I picked up a fuel pressure gauge and found out that despite being able to hear the fuel pump and smell gas, the pressure that I got when cycling the key was only around 40psi, and dropping. Then I started the engine via some carb cleaner, it bumped up to 50psi. Still not the recommended minimum of 60psi. Then when I stepped on the pedal a bit to raise Rpms, the needle on the gauge starts to drop. Looks like I'm getting a new fuel pump.

[MT-2500]

Originally Posted by Surfnbiker

Okay some progress has been made. I picked up a fuel pressure gauge and found out that despite being able to hear the fuel pump and smell gas, the pressure that I got when cycling the key was only around 40psi, and dropping. Then I started the engine via some carb cleaner, it bumped up to 50psi. Still not the recommended minimum of 60psi. Then when I stepped on the pedal a bit to raise Rpms, the needle on the gauge starts to drop. Looks like I'm getting a new fuel pump.

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.

[Surfnbiker]

MT,
Thanks for the great info. What I ended up doing is putting a pressure gauge on the fuel line, and finding out that when I cycle the key before starting, I was only building approx. 40psi. and would drop RAPIDLY. Then after a shot of carb cleaner to get the engine started, pressure increased to 50 psi, but when you raised the RPMs, the psi. would start to drop. So, I decided to replace the fuel pump. I got an OEM unit, and managed to install it in just a couple of hours. I even tended to some long overdue exhaust leaks, while I was under there. Knock on wood, for the past two days it has started and run like a champ. Thanks again for the advice, it's definately going in my file for future reference.

[MT-2500]

You are welcome.
And Thanks for posting back how it went and the fix.
Glad all is well and running and starting good.
Good luck
MT

[Surfnbiker]

Just thought I'd drop a note and say it has been a few weeks now and "knock on wood" the van is still running well. Starting right up, hot, cold, whenever.

[MT-2500]

Good News.
Thanks for posting back
Good Luck
MT