Air in Fuel System
 

This is my first post. Great forum!

My son has a 1998 LT 4x4 4 Door with Plastic Fuel Tank

• Engine randomly dies
• System won't hold pressure when key is off and there is air in system when I depress pressure valve until sytem is re-primed
• If I prime system by turning key on/off several times, pressure returns and it runs fine until next random engine stall
• Symptoms started after mud got in tank (son went mudding with no gas cap!)
• Fuel filter has been changed twice
• No black smoke
• Engine is throwing no codes

I have some ideas but all the fuel system parts are pretty expensive and I really don't wanna start randomly throwing parts at the problem. Can you help? Thanks

First step is check fuel pressure and leakdown. Most auto parts stores rent/loan/sell fuel pressure testers. Connect the tester to the service port. When the ignition is initially turned to the RUN position, (don't start the engine) the fuel pump will be activated for ~2 seconds and then shut off. Pressure must be checked while the pump is running. Must be 60psi to 66psi and it must remain above 55psi for at least 10 minutes after the pump shuts off. The results will tell if there's a problem with the fuel delivery system. It will not tell what the problem is, only if a problem exists. Post your results.

Thanks for the reply. I guess I wasn't clear in my description. The engine rus fine until it stalls or it sits for a long while. Then it needs to be primed by turning key off/on several times. The system holds ZERO pressure very soon after the pump stops running. I figured I didn't need a gauge to check for pressure drop since pressure is ZERO. LOL

You do not know the pressure is zero if you have not checked it... :)

OK. I guess I technically do not know the pressure is absolutely zero. When I depress the valve, however, no fuel sprays out until the key is cycled several times. The engine will then restart and everything works normally until the next episode.

In order to properly diagnose what is wrong with your fuel system there is a certain set of steps that are needed to go through in order to isolate what expensive part of the fuel system is failing.

If you don't get the numbers all we can do is guess at what is wrong and have you throw parts at it because the fuel and electrical systems are very fussy about pressure and parts on these trucks. And we don't want to guess because it gets expensive fast and diagnosing is practically free.

If you don't have a fuel pressure tester most auto parts stores have a tool rental program and all you have to do is put a deposit on the tool and you get it back when you return it.

OK. I will rent/borrow a pressure gauge and post the results. It will probably be Saturday before this is possible.

I'm still having trouble understanding why the numbers are necessary. I'm not wanting to be rude, but I just like to understand how things work if someone would be kind enough to explain it to me. If absolutely no fuel is even trickling out of the valve when depressed, how is that not sufficient evidence that there is pressure leakdown?

I know I am the one who is obviously wrong here because everyone is agreeing the gauge numbers are necessary.

Thank you all for trying to help so far.

There's no doubt you have a fuel delivery problem, the question is what's causing the problem. We need to know what the pressure is when the pump is running, (engine off) and what the pressure is 10 minutes after the pump shuts off. If it passes both parts of the test, fuel delivery is good. If it fails one or both parts of the test, it means that a problem exists, but it does NOT tell us what the problem is. From that point, we need to do more testing with the pressure tester to pinpoint the problem.

OK. Thanks!

i got dibs its the pump. regulator can leak,but wouldnt cause 0 pressure,usually 50ish then drops. if u buy pump,make sure its dealership. YES there is a different for these blazers.