2001 Blazer 4.3L Fuel Pressure

[bigj-dog]

Hi, working on a friend's '01 Blazer with a 4.3, he's complaining of poor mileage, about 12mpg or so, and sometimes dieing right after cold start, but then starting again right away. He was wondering about the pressure regulator failing, but there are no driveability issues whatsoever. I replaced the cap and rotor, not in too bad of shape, and started checking fuel pressure in hopes of finding the problem. Here's the stats, running 52 ft/lbs, after prime w/o starting 60ft/lbs, pinch return line while running, 52 ft/lbs, hooked up gauge to 'out' side of filter and plugged adapter (ie. dead ended line at gauge) 60 ft/lbs. I'm assuming the pump is weak or heading out, anyone think of anything else? The filter is newer, but I'm going to swap it anyway and recheck dead ended pressure. Oh yeah, pressure drops about 10 lbs in 15 minutes after shutting off truck with gauge hooked to test port. Pressure also drops similarly with gauge at filter and dead ended. Thank you very much. Jared

[MT-2500]

Originally Posted by bigj-dog

Hi, working on a friend's '01 Blazer with a 4.3, he's complaining of poor mileage, about 12mpg or so, and sometimes dieing right after cold start, but then starting again right away. He was wondering about the pressure regulator failing, but there are no driveability issues whatsoever. I replaced the cap and rotor, not in too bad of shape, and started checking fuel pressure in hopes of finding the problem. Here's the stats, running 52 ft/lbs, after prime w/o starting 60ft/lbs, pinch return line while running, 52 ft/lbs, hooked up gauge to 'out' side of filter and plugged adapter (ie. dead ended line at gauge) 60 ft/lbs. I'm assuming the pump is weak or heading out, anyone think of anything else? The filter is newer, but I'm going to swap it anyway and recheck dead ended pressure. Oh yeah, pressure drops about 10 lbs in 15 minutes after shutting off truck with gauge hooked to test port. Pressure also drops similarly with gauge at filter and dead ended. Thank you very much. Jared

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.

[euromech]

The only true fuel pump test is to use the proper gage attached to the test port( on the driver's side of the throttle body for that model). A gage is available at NAPA or A to Z etc for about $50. The pressure for that car should be 60 to 66 psi according to GM Specs.

[bigj-dog]

Yeah, I checked it with the proper gauge at the test port and the results are listed in my first post. I also checked the pressure at the out side of the fuel filter with a dead end at my gauge and it only read 60 ft/lbs. What I'm wondering is if anyone could verify that my pump is weak before I spend $350 on a new one. Thanks for reading and for your time.

[old_master]

If there are no external leaks, your "dead end" fuel pressure test should show a bare minimum of 75psi.

[bigj-dog]

That's the clarification I was looking for, just needed someone to reassure me. Thanks. I'll order a fuel pump tomorrow.