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Old 07-30-2018, 08:40 PM   #1
docrock
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1988 wont start

I am posting this because I just don't get what is wrong.
Its a 1988 c30 with 5.7 throttle body. My son was driving it and ran it out of oil. He was driving on the freeway, it made no sounds, it just stop running. We had it towed home and started to diagnose. I changed the oil sensor and now the gauge works. still no start. changed the coil pack, distributor cap, rotor. When I turn the key on I hear the pump. The motor turns over. The engine will start on starting fluid. I put a noid checker on it and it does NOT pulse. What should I do now?
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Old 07-30-2018, 10:12 PM   #2
95 S_Trucker
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Re: 1988 wont start

It sounds like the pick up in the distributor failed. The ecm gets a rpm signal from the distributor and the ecm controls the injectors. The injectors will not pulse unless it gets that rpm signal. I am going to guess that you don’t have spark at all either.
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Old 07-31-2018, 09:26 AM   #3
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Re: 1988 wont start

Test to see if it has spark.

My guess would be the distributor module.

As Trucker stated, if the distributor does not send a reference pulse to the ECM then the ECM will not trigger the injectors.

Many auto parts stores will test the distributor module for free if you bring it in.

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.
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Old 07-31-2018, 09:29 AM   #4
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Re: 1988 wont start

If it was the module, the injectors would still pulse, because the ecm would still see the signal from the pick up coil.
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Old 07-31-2018, 09:41 AM   #5
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Re: 1988 wont start

The pickup coil connects to the distributor module not to the ECM.

The reference pulse comes from the module.

It is also possible for the distributor module to produce spark without sending a reference pulse to the ECM but this is rare.
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Old 07-31-2018, 10:22 AM   #6
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Re: 1988 wont start

Quote:
Originally Posted by ChevyTech View Post
The pickup coil connects to the distributor module not to the ECM.

The reference pulse comes from the module.

It is also possible for the distributor module to produce spark without sending a reference pulse to the ECM but this is rare.
I looked up a diagram. I see it now. You are correct.

On most of the cases I have seen first hand, when there is no spark and the is injector pulse, the module has failed. Or when there is no spark and there is no injector pulse, the pick up failed(mostly due to a worn distributor).
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Old 07-31-2018, 12:39 PM   #7
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Re: 1988 wont start

I forgot to mention I changed the module. I reinstalled the old module. Same problem I have spark but no pulse. I am going to clean the ground points in the distributor, and reinstall the new module. See what happens
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Old 07-31-2018, 01:53 PM   #8
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Re: 1988 wont start

Quote:
Originally Posted by docrock View Post
I am posting this because I just don't get what is wrong.
Its a 1988 c30 with 5.7 throttle body. My son was driving it and ran it out of oil. He was driving on the freeway, it made no sounds, it just stop running. We had it towed home and started to diagnose. I changed the oil sensor and now the gauge works. still no start. changed the coil pack, distributor cap, rotor. When I turn the key on I hear the pump. The motor turns over. The engine will start on starting fluid. I put a noid checker on it and it does NOT pulse. What should I do now?
I've got to ask since no one else has said it. Aren't you afraid this engine is a boat anchor now? Chevy engines are pretty robust but if it was run without oil then it was happening for some time. I was driving my old car and got stuck in traffic in 100 degree weather and my engine was running hot and blew off a radiator hose. I reconnected it and added water and drove it home. After that I was using about a quart of oil every 300-400 miles. I can't imagine how an engine running without oil *didn't* make any noise.
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Old 07-31-2018, 02:58 PM   #9
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Re: 1988 wont start

I was thinking the same thing. I was told that if oil pressure gets too low the oil pressure sensor shorts the signal to the distributor, which makes it not run. I am also thinking that their has to be ware on bearings, pistons, rings, valves, lifters, and oil pump. the engine holds 5 quarts we added 3 to get it to full. I am just hopeful because it runs on starting fluid.
I swapped out the module, same. Put the new back in with clean grounds, same. Checked the noid again still no pulse. I pulled the coil plug wire off and turned over the motor it arced to two pair of wires going from the coil to the distributor instead of to the top of the coil.....weird.
So does that mean I should replace those wires as I seem to be loosing energy there? I tested the wires with an ohm meter and they read zero, but with voltage loss maybe not enough for a pulse. I am going to replace the wires. Also seems weird that it arced to the wires instead of the coil. Maybe coil is not grounded...
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Old 07-31-2018, 03:40 PM   #10
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Re: 1988 wont start

Fuse? I had a similar problem of intermittent start. The fuse to the ECM also goes to the fuel pump, temp sender, and oil sender, so power gets cut before the engine fries. On my truck, the fuse socket was sprung, so the fuse didn't always connect. It had a new radiator, so I assume the PO had overheated. His fix was to wedge the fuse panel so the fuse wouldn't wiggle loose.
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Old 07-31-2018, 04:50 PM   #11
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Re: 1988 wont start

First of all thanks for the great comments. I tried the fuses by pulling them out checking them and putting them back, all in good condition. I decided to plug in my obd1 reader to see if it had any codes....ecm not responding. turned the key on it says ecm not responding...decided to start it and it fired off. It is running great. Not sure why the ecm has a read problem but who cares its running. Could be those fuses could have had some funk on them or whatever. I still think the one wire that has some cracks needs replacing but again thanks for the help
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Old 07-31-2018, 08:08 PM   #12
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Re: 1988 wont start

Glad you got it running!

Quote:
Originally Posted by docrock View Post
... I was told that if oil pressure gets too low the oil pressure sensor shorts the signal to the distributor, which makes it not run....
Not true for your 1988. Some earlier GM trucks had this but never on this body style truck.
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Old 07-31-2018, 08:43 PM   #13
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Re: 1988 wont start

It actually is G30 Van. But good to know. I am glad something happened to kill the motor
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