Cranking Problems
Thread Starter
Intermediate
Joined: Feb 2007
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Cranking Problems
I Have An 88 Vette That Starts And Runs Great But Soon As You Stop And Turn Off The Engine I Have To Disconnect The Battery Terminal For About 10 Minutes And Then It Will Start Until I Stop Again Then The Same Problem. If Any One Has Any Ideas On This Matter Please Let Me Know..thanks
Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
When it won't start, that is the time to look for the source of trouble. All engines require spark and spark at the right time, fuel and air and in the correct ratio. First use your timing light to test for spark and correct timing while cranking. Pull a plug wire and crank a few revs, the spark must be able to easily jump 1/2 inch. Next, measure the fuel pressure at the shrader valve at the end of the fuel rail by turning the ign to run for longer than 2 seconds, it should be about 40 psi. Watch how long it takes for the pressure to drop with the key off. If it drops rapidly, you may have a leaky fuel injector making it too rich to start. Next, use a noid light (available at parts houses) or a low power 12v lamp like a side marker lamp and connect it across the socket of an unplugged injector and crank the engine. The light must pulse showing that the ECM is pulsing the injectors. Let us know what you find.
Thread Starter
Intermediate
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i have tried everything that i possibly can and still no luck, like i said before once i get it cranked i can drive for 300 miles long as i keep it running but if i turn it off then it only turns over it shows to be firing and the fuel rail is full but still want crank until i disconnect the battery for 10 minutes to reset the computer then it fires right up again until i shut it off again...
Thread Starter
Intermediate
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i put a test light to the injectors while it runs and they pulsate when it turns over only they do not pulsate, soon as i unhook the cable and put it back they will pulsate and it cranks right up..
Last edited by lawnmowerman160; May 3, 2007 at 11:47 AM.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
When it won't start, you need to see if you get reference pulses from the distributor. The ECM pulses are determined by the reference pulses from the distributor. I'm at work,so can't tell you which wire this is from the distributor. I'll post that when I get home.
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Le Mans Master
Joined: Oct 2003
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From: seattle WA
Do you have the factory service manuals? doesn't sound like a ICM, but I'd be taking a look at the pickup coil, you can test it with an ohm meter. I'd also be wondering about the injector fuses. First time I've heard of this type of problem.
The pickup coil is where the ecm gets its signal to fire the injectors, it's located in the bottm of the distributor.
The pickup coil is where the ecm gets its signal to fire the injectors, it's located in the bottm of the distributor.
Last edited by rick lambert; May 3, 2007 at 12:18 PM.
Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
The injectors receive 12v pulses (actually grounding pulses) from the ECM. The ECM pulses the injectors according to the reference pulses from the distributor generated in the HEI spark module. Since you installed a new distributor which has a new spark module, it is unlikely that the spark module or the pickup coil which drives the spark module are defective. Aged spark modules will fail hot, but work cold. One experiment is to run the car until it quits and then get a can of circuit cooler (available at Radio Shack) and spray the ECM board and see if the engine starts running. This will prove it is the ECM getting hot. Spray the power transistors on the ECM board, they do the injector pulsing. If no luck, then look at the pulses on the purple/white wire out of the distributor when running and when it won't run (during cranking) and see if they are alike. Do this with an oscilloscope. Let us know what you find.
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ok heres what i done i pulled the ecm down and took the door off to the eprom and laid the ecm in the floorboard where it would stay cool and it cranks every time,,does this mean the ecm is bad? thanks
Le Mans Master
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From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
no-start
try just pulling the fuse instead of dancing with the computer, the prom, and the battery.
If it starts right up, I would seriously look at the ECM computer.
You might try the injector fuses, etc.
If it starts right up, I would seriously look at the ECM computer.
You might try the injector fuses, etc.
Team Owner
Joined: Mar 2001
Posts: 54,124
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From: Cincinnati, Oh USA
VATS compares the resistance of the pellet in the ignition key with its stored value. If the resisitance is within about 4% of the stored value, VATS closes the start enable relay allowing the starter motor to crank and it tells the ECM to pulse the injectors. You don't have a VATS problem, you have a defective ECM!