1988 tbi 350 not starting on own..

[vr1967]

Working on an 88 for a church member.

Truck has new fuel pump and filter, rebuilt TBI, tune up (plugs, wires cap & rotor) new oil pressure switch and a few other odds and ends.
Truck will run if started with starting fluid, but will not start on its own. Injectors are pulsing, good spray of fuel, looks to be a white spark. I am trying to find my fuel pressure gauge setup, but pinched off return line with no starting. Sprayed starting fluid around engine while running and no vacuum leaks detected.
Plugged off egr valve, as it was stuck open and diaphragm ruptured.

Waiting on an adapter to use my OBD2 scanner on OBD1.

Short of finding my FP gauge (I’ve seen new pumps go bad) and scanner, what am I missing?

I will not just throw parts at it

Thank you

 

[GMCTruck]

Is your timing correct?

 

[vr1967]

Thanks, Will check it when I get my timing light back from my buddy.
Truck was running fine, then the next morning, he said it wouldn’t crank.
Been a while since I’ve worked on a tbi system. Need to find my manuals and receive the scanner adapter

 

[VIKING_MECHANIC]

How long will it run with starter fluid? From the way you described it, I suspect a fuel issue. When you turn the key on, can you hear the pump prime?

Possibly a fuel pump DOA right out of the box.

 

[Schurkey]

I suspect a fuel issue. When you turn the key on, can you hear the pump prime?

Yep. I want to know if the pump primes. If it doesn't prime...suspect the fuel pump relay, wire harness, or ECM.

Possibly a fuel pump DOA right out of the box.

Injectors are pulsing, good spray of fuel

He says that the injectors pulse and fuel sprays. He's got a pump that runs; although the actual pressure hasn't been verified.

Wild Guess: Failed fuel pump relay, relay wire harness, or failed ECM section that controls the relay. Fuel pump runs only when oil pressure is high enough to bypass the relay via the oil-pressure switch. The engine fires on starter fluid, builds oil pressure, and runs until shut off. The oil pressure goes away, and the engine doesn't start quickly next time.

The engine should start if cranked long enough to build oil pressure. But that could take awhile. Especially if the engine is tired, or the oil is contaminated so as to have unusually-low oil pressure. Why was the oil pressure switch replaced?

 

[vr1967]

Update:

Ok, due to family health issues, just got back on the truck.
Checked fp, it was 10psi at the throttle body.
Checked map sensor feedback and it was giving sketchy readings, so went and pulled the one from the 90 S10 I inherited. Numbers were spot on what they should be with the one from the S10, so hit the key and it fired right up.
Drove it a bit around the yard. Several cranks etc.
Will order a new map sensor, and he asked the other day if I would completely go thru the brake system, so plan on doing that as I can.

 

[vr1967]

Checking the MAP sensor on a tbi engine, and probably most others too. (Am at work, so don’t have wire colors, etc in front of me)

There are 3 wires going to the sensor. 5v hot, a feed back, and a ground. The feed back is the middle wire.
With a multi meter, check that you have 5v going to the sensor. Plug it in, and tap into your feed back wire. I used a straightened paperclip.
Turn the key on, and you should have right at 5v on the center wire. Connect a vacuum pump to the port, and for every 5in of vacuum, you should lose app 1v (with no vacuum, should be 5v, with 5” of vacuum, should read 4v, 10” of vacuum, should read 3v, etc)

That will let you know if your map sensor is good.

Will clean it up, and try to get some pictures when i get home from work this evening.