Won't Start - Fuel System?

99 Suburban, 5.7 Vortec, 4L60E auto trans, 91,000 miles, no engine repairs to date.

Vehicle was running fine and now won’t start at all. This happened twice before in the past 2 months, but would start after “resting” for 10 minutes on previous incidents.

I see plenty of spark at the plug wire, so am guessing fuel supply problem.

What should I expect as far as the service life of the in tank fuel pump? At 91,000 miles should I anticipate that this is the source of my problem?

Is there an easy way to determine if adequate fuel is being provided to the induction system? Where would I disconnect the fuel line? How can I judge if adequate volume and pressure of fuel is being supplied without having specialized equipment? I’m looking for some simple, observable, things like “fills a 12 oz beer can in 15 seconds of cranking” “pressure to squirt fuel from end of line a distance of 10 feet”. I know, not very scientific or quantitative but enough to help me diagnose problem and focus in from there.

My understanding is that there is a relay that runs the fuel pump for a few seconds to prime the lines when the ignition is turned on, then the fuel pump is powered by a relay from the oil pressure indicator as long as a defined psi is maintained. (I’ve seen people state values ranging from 4 psi to 15 psi). I do not hear any pump sounds upon turning on the ignition. Cranking the engine for up to 10 seconds does not have any effect (achieving sufficient oil pressure to activate the oil pressure sensor relay).

What is the location of these relays? How do I diagnose if one of the relays is not functioning or if the problem is the in tank fuel pump? Can I jumper these relays to provide power to the pump to diagnose without causing problems? Can I simply jumper 12 volt power from the battery to the pump to see if the pump functions?

What other things should I be looking at to solve this problem?

Now that is what I call a post!
With all that information and all those questions you have earned Merlins GM truck no start diagnostics 101.
Open your hood and look on the drivers side. You will see the electrical center. The F/P relay is in there. It should click when you turn the key on.
If it doesn't, check the ECM-B fuse.
On the fuel rail there is a schrader valve...depress it...does fuel spray out?
If the fuse is good, the relay clicks and no fuel comes out the schrader valve.....its a fuel pump.
If the fuse is blown....99.9% chance its a fuel pump.
If its a GM truck and it won't start .......you got it.......fuel pump.
And replace the filter when you replace the pump.

I'll send you my bill :evillol:

Thanks Merlin. I have now got the tank dropped. How do the fuel supply line fittings work? It looks like some sort of push and twist operation, but so far I can't get them undone.

There is a special tool to release them..it slides between the white plastic line and the fitting.
Since you are replacing the pump module, grab the fitting and break the pump (white) side off the pump , then you can work on getting the plastic line off the fitting with the tank out of the way