1988 Chevy Truck Engine cranks but wont start

We Checked the spark plug and there was enough spark so I don't think that is it. And the fuel pump and filter and also putting out enough pressure.

Ok, just a few minutes we're trying to find a fuel pressure gauge.

Is there any other way to check the fuel pressure with out a fuel pressure gauge? It turns out we don't have one

Ok cool thanks. What should the fuel pressure be on a 4.3L Vortec 6cyln. 1/2 ton truck

Ok thanks, no not right now not ill we get a fuel pressure gauge. Thanks a lot tho. I'll get back to you once we check it and hopefully it will work.

Do You have TBI (Throttle Body Injection)? 88-94.
The TBI uses 10-14 lbs pressure. When you first turn key to run the fuel pump runs for 2 seconds. Then the fuel pump continues to run IF there is oil pressure.

My wiring shows the Oil Pressure Sender having 3 connectors. With Tan: Orange: Gray wires going to the OPS. The tan goes to the gauges. The Orange and gray are part of the fuel pump switch. If there is pressure the switch is closed and you should read 0 ohms (use a volt/ohm meter) across the orange and gray. The ALDL connector (the plastic connector under the dash near the fuses. You normally short Connectors A and B pins and it flashes the engine error code. Pin G is Fuel pump relay bypass. Use a fused wire from 12V to it and try to start the engine.

Ping G is the lower left.

If it runs with fused +12V into pin G (assuming pin G is connected) I feel the oil pressure sender is bad or the wiring. You stated the engine runs for 2 seconds, hence the fuel pump relay works.

Dunno how many psi needed to activate the OPS/FP switch. Around 4 would be at the low end I guess.

By putting 12V to pin G of the ALDL it powers the fuel pump directly. Which tells you everything is OK except how the fuel pump is powered, (if the engine runs)

Look at it this way. The fuel pump is normally energized in two different ways. 1) Start circuit. 2) Run Circuit

To start an engine GM uses a 2 second only circuit from the ECM to power the fuel pump. This circuit energizes the fuel pump relay. It is just wired differently, than the run circuit (ie not using the oil press sw).

The run circuit passes power through the oil pressure/Fuel pump switch. The Oil Pressure switch is just a switch between the 12V power source and the Fuel Pump relay. Bad switch and the relay does not work, and no fuel pressure.

If the switch tests good, connectors and wires have a habit of going bad for no particular reason.

Ok so we got a fuel pressure gauge and this is what happened. When I turned the switch on the on position and while you hear the pump running it goes to 60psi. As soon as the pump stops running it goes back to 55psi. Then when you try to start it, it drops from 55psi to 50psi but still doesn't start. While the gauge is on.

How do you check if the injector/s are pulsing providing the fuel to the cylinders?

Ok so it turns out that may not be the problem this is our new suggestion.

The ignition cylinder lock was locking in position sometimes and sticking. Could this engage the security system and cut off fuel to the engine?

I'm not trying to disagree or anything cause I'll defiantly check the valve and ignition timing, but I've heard that if the ignition key switch is being messed with like if someone was trying to break into it, it could cause it to stop working. Which actually happened last summer my truck got broken into and the ignition key switch had to be replaced, because it was torn apart. But it didn't start sticking and taking a few times for it to start until about two months ago, and I would have to jiggle it really hard for it to go back in the off position so I could turn it all the way again to start it. But I actually took out the ignition key switch this morning and some of the springs were stretched and bent. Also the part that covers the springs was bent which I think was causing it to get stuck. The person that was telling me this said I would most likely have to replace the ignition key switch, and then take it to a GM dealership so they can scan it to get to back to normal.