''02 Suburban 5.3 starts but won't stay running

My brother's '02 Suburban with a 5.3 died on his way home last night. He said it cut off, then on, a couple times before dying completely. Then it wouldn't crank, the starter solenoid would just click. I ran him out a new alternator. We swapped it out, jumped the truck, and it started right up. But then the idle would drop, it would sputter and back fire, and die. Opening the throttle just makes the back fires worse and kills it quickly. I could not find any air leaks, but it acts as if the intake is disconnected. There is no check engine light- not even when it is supposed to light with the key on and engine off. I think that usually indicates an ECU fault. I'm headed back out there today, what should I check?

I'm bringing a scan tool.

I'll check the fuel pressure.

I've heard that a bad battery could cause these symptoms? The truck cranks over strong- much stronger than it should if the battery had been drained. I charged it off my truck, but not very long.

I read that there is an anti theft system that may need to be reset, which causes the same symptoms? Sounds odd, but I'll give it a shot.

Anything else?

Thank you.

Drive it for a bit and see if it can relearn. Possible a bad battery cause the alternator to go out?

In reply to Stampie:

It's not driveable, it won't even idle. Runs for a couple seconds and dies.

Hit the fuel test port schrader valve and see if you have pressure, sounds like a dead/dying fuel pump

Sounds fuel pressurey to me too, but ask the computer what's wrong first.
I know there are grounding issues that cause absolutely bizarre issues on the later trucks but I can't say for certain with this vintage.

Yep, i agree, sounds like low Fuel pressure, likly pump issue.

I looks like the fuel pump. Only 25 psi with the key on, drops quickly when the engine starts. Stalls out around 10psi. It also bleeds down when sitting- could it be a regulator issue? Drops to 20 pretty quickly with the key off, and slowly drops from there.

Battery voltage was low, 11.5, but jumped to high 13's when running.

Couldn't connect the scanner to the ECU at first. Replaced blown cigar fuse and could connect, but couldn't get it to run long enough to get any codes or useful data.

To add insult to injury, some shiny happy person smashed the window overnight. Stole his baseball equipment. Left a couple very expensive bats in the bushes but kept his cup.

Kick the fuel tank or beat it with a hammer while trying to start it. That sometimes makes a dying fuel pump work long enough to move the vehicle to a more convenient location. Knocks the brushes loose, unsticks them from a rough-worn commutator.

Is the red security light on when trying to start? The fuel pump will not power up if the BCM doesn't recognize the key. You can jumper the fuel pump relay to verify that the fuel pump can supply pressure on its lonesome, but the computer will also cut fuel injectors when in security mode so you can't run the engine this way. If the fuel pump can supply good pressure, turn the ignition on and leave it on for 20 minutes or so. I think (not 100%) this is all you need to do to retrain VATS to relearn the key. It's either one time for 20 minutes or three key cycles at 20 minutes before attempting to start.

Beating the fuel tank with a hammer while trying to start is more immediate, and also more satisfying in a primal sense. "American car, Japanese car, ALL MADE IN TAIWAN!"

Knurled wrote: "American car, Japanese car, ALL MADE IN TAIWAN!"

That made me laugh. Is it weird that I actually know what movie that is loosely quoting?

Do i get a cookie for guessing correctly?

Seriously, hopefully they have an access panel unlike the silverados of the same era, i had the misfortune to make my own access panel in the middle of jackson ms to replace the pump on my brothers truck. At least its an easy repair otherwise.

Sucks stuff got stolen but at least they left the more expensive stuff, really weird they kept his cup...

Thanks guys, I'll try all of the above. I don't think the security light was on, but I'll check.

Before going after the pump look at the regulator on the manifold. Notorious failure point if you have one ( search YouTube). Otherwise dropping the tank sucks. I did it on my 05 Tahoe and it wasn't fun as there is no access panel.

And its cheap and easy to replace. A common fail point

Thanks, I'm suspicious of the regulator since pressure bleeds off pretty quickly. I'll check that first.