88 350 TBI Fires but won't stay running
 

Hello everyone!

I am new to the forum and I have a very frustrating issue with my 88 350 TBI.

The issue is that the engine will crank fine, fuel sprays, and the engine fires up but immediately dies when I let go of the key. If I keep the key in the start position the starter will obviously continue to turn but I can rev the engine up with the throttle until I let go of the key again. As far as I can tell fuel is being cut off after initial start up when the key is released but I could be wrong on that.

Here is what I have confirmed:

1) I have strong spark, timing is accurate
2) Fuel pressure is 30 lbs at the throttle body from the pump and fuel sprays strong from the injectors

Possible issues I'm considering but would appreciate further guidance on:

1) Bad ignition control module
2) Bad fuel pressure regulator in the throttle body
3) Bad computer
4) Bad Coolant Temp Sensor (I tried unplugging it and starting it, same issue)

Oil pressure switch is new and the distributor, cap, and rotor have less than 1000 miles.

Any help would be greatly appreciated! thank you

Re: 88 350 TBI Fires but won't stay running
 

With the sensor and all it could be quite a few things, including those your mentioned. I am also thinking a bad crank sensor. Hopefully one of the better mechanical guys/gals will come on and give you some ideas.

Re: 88 350 TBI Fires but won't stay running
 

The spec is 9 – 13 PSI
My guess is you put a gauge on the end of the fuel line.
The fuel pressure is tested by using fittings to Tee in a pressure gauge.

There are instruction on testing fuel pressure in this link.
http://67-72chevytrucks.com/vboard/s...d.php?t=375132

My guess is it has a bad ignition module in the distributor like you suspected.

The computer needs to receive a distributor reference pulse from the distributor module to trigger the injectors.
It is possible for the module to produce spark without the computer getting a reference pulse. A bad distributor module or wiring between the module and the ECM/PCM can cause this.

The distributor module has a startup mode, which it runs on up to 400 RPM, and a run mode above 400 RPM. When these modules are failing sometimes the ECM does not receive the signal it needs to trigger the injectors in 1 or more of the distributor module modes.

Many stores like NAPA in my area will test the distributor module for free if you bring it in.

The test results from these stores are not always accurate, and some times the will say the module is good when it is not, but for a free test that may find the problem it is worth a try.

Make sure when you install or reinstall the distributor module that you use heat sink compound under it. The compound helps dissipate heat from the module. Without it, the module will fail.

Welcome to the board!

Re: 88 350 TBI Fires but won't stay running
 

Would seem to me, the switch is loosing contact and not supplying it's output when you let off the key. I think you should look at that with a volt meter to see what it's condition is when KOEO.

Does it cycle the pump when you go to KOEO? Is voltage getting to where it needs to be at that time?

Re: 88 350 TBI Fires but won't stay running
 

Here is a little information to help you understand fuel pump circuits.

The ECM controls the fuel pump relay.

The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.

When you turn the key on without cranking the engine, you should hear the fuel pump run for a few seconds.