1998 suburban won’t stay running

[oldschool18]

Ok last weekend I worked on my suburban and Sunday night it fired right up and pulled it outside and parked it. This morning I went to pull it in the garage and the battery was dead, tried to jump it and it wouldn’t start and thought it might be out of gas. Went and got 5 gallons and put it in and still nothing. It fires up but would only run for a couple of seconds....... so I put a new battery in, checked fuel pressure and had 62 psi at the rail, had spark at least he coil and wires, checked all fuses and they were all good, swapped the cap and rotor and ignition control and the PCM. Thought there might be a problem with the passlock so I swapped that out and reprogrammed that and it still did the same thing. And I swapped the MAFS and cleaned it, I could not find any vacuum leaks or bad wires and me and my father are confused. He’s be a mechanic whole life and has been in business for almost 50 years and he was a little stumped. I haven’t changed the fuel filter cause it’s outside in the dirt and didn’t want to jack it up while it was raining but we had good pressure. Since I bought the thing it hasn’t missed or sputtered or anything and all of a sudden it won’t start. It acts like something won’t let it start, anyone have any ideas before I rip the top of the motor off?

[Palf70Step]

My guess is the fuel pump. Once your rain quits I would try the fuel filter first though.

[speedygonzales]

In this order

What is the pressure while you're cranking the engine?

Squirt fuel or starting fluid in the intake and see if you can keep it running.

Did you crank it over with the cap off to see if the rotor is rotating?

What do the plugs look like now that you have cranked on it several times and it ran like ass? It only takes 3 dead holes to keep the engine from running.

[oldschool18]

I believe it was in the 50’s when cranking and we did pour gas in and it ran until gas burned up, I didn’t check the plugs or see if rotor was spinning cause it fires up and runs then shuts off..... like something is telling it to shut off. I checked passlock and even swapped out another passlock module and reprogrammed it and same results.

[speedygonzales]

Then it's not getting enough fuel. Easy as that. Now figure out why.

Have you scanned it for any codes? Note there are codes that do NOT set a CEL.

FPR could be stuck not allowing pressure to rise high enough. Pressure has to be 60 to 66 PSI. One thing you can do is pinch the return(where it is plastic) line to temporarily bring it up and see if it fires up.

Next thing to check is the injectors firing? Noid light time.

[oldschool18]

We tried two different scanners and they wouldn’t link up, I had 62 psi when we did the initial check and that is in spec. But from what I remember the fuel relay is only used to start the car and the the fuel pumps power come from some where else and I believe it’s the oil sending or something so if it loses oil pressure it shuts the fuel off. So yes it gets fuel on initial crank but then loses it like it is being told to do so. Just checking to see if anyone else has had a problem like this in the past since I can’t get data from the pcm. I might have to jump a plug under the hood to see if I can get anything from the computer

[speedygonzales]

Originally Posted by oldschool18

so I put a new battery in, checked fuel pressure and had 62 psi at the rail,

Originally Posted by oldschool18

I believe it was in the 50’s when cranking and we did pour gas in and it ran until gas burned up,

Originally Posted by oldschool18

I had 62 psi when we did the initial check and that is in spec.

It's 62, it's 50, now it's 62 again. ?????????


62 I'm betting was during KOEO (initial pressure) It seems that you answered a few questions when you replied it was 50 during cranking.

The first question you answered was it was too low. So the initial pressure spurt causes a fire up but the lower pressure during cranking can't support it.

The second was that oil pressure has nothing to do with the pump running. Otherwise why would it be 50? If the oil pressure function were present, it would be an On/Off function. But that function is not used. Understand?

Now bring up the pressure like I suggested by restricting the return line and stop over thinking this.

[oldschool18]

What you suggested didn’t work either, and from what I could remember the initial pump turn on is from the key through the relay but if the oil pressure drops it shuts off the fuel...... but that might not be right on this model, when the rain stops I will get some more diagnostic checked out

[oldschool18]

Bad PCM was the cause.