PFF - Pennock's Fiero Forum, PDA Edition

No spark no injector pulses- Question for the wiring experts (Page 3/3)

Dennis LaGrua

JUL 03, 06:53 PM

quote

Originally posted by phonedawgz:

The ECM is not required for the HEI to produce spark. At cranking speeds the HEI controls the spark internally. At over 400 RPM the HEI sends the spark signal to the ECM, the ECM controls the advance and sends it back to the HEI. But again at less than 400 RPM, ie cranking speeds, the ECM does not control spark.

You are getting no injector pulses and no spark. The HEI isn't getting proper power, or is failing internally.

Are you measuring power at the distributor with the distributor still hooked up and with the engine cranking? Testing for voltage with the load disconnected can give you readings that will send you in circles when troubleshooting.

I completely understand what you are saying but at this point either something in the distributor isn't working right or as you say power could be the problem BUT if the 12V feed at the cream plug tests OK then the only item that can reduce that voltage is something inside the distributor but we already replaced the coil and the ICM with a GM part. We have a new distributor on the shelf and we will install that tomorrow.

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greenturnedblue

JUL 03, 08:07 PM

quote

Originally posted by Dennis LaGrua:
we already replaced the coil and the ICM with a GM part. We have a new distributor on the shelf and we will install that tomorrow.

Remember parts can be dead on arrival especially control modules like the ICM which can further add to the confusion. If there is no spark at the ignition coils there will therefore be no spark at the dizzy. I would first use a test light or voltmeter to find out exactly where the signal to ICM cuts out. the ICM itself is probably fine especailly since you just replaced it but it obviously isnt getting the signal to fire the spark plugs. then verify the ICM is actually sending the command to fire the injectors. If the ICM is indeed sending the command to fire then the issue is somewhere along the line between the ICM and injectors

[This message has been edited by greenturnedblue (edited 07-03-2022).]

sanderson231

JUL 04, 10:05 AM

Try testing for power at the distributor with a test light instead of a voltmeter. I had a Chevy Aveo where the headlights quit working. I had power with a voltmeter and was baffled why the headlights would not come on. I tested with a test light and it did not light. Turned out to be a corroded connection under the dash.

phonedawgz

JUL 04, 11:04 AM

Are you testing it under load? Testing it with no load can give you a good reading that will turn bad when testing it under load.

Backprobing a connector lets you test under load. Basically you slide a pin up the backside of the connector while the connector is still plugged in. Search for youtube videos to see the procedure.

A poor electrical connection between the dist and it's power source can be the cause of voltage dropping under load.

quote

Originally posted by Dennis LaGrua:

I completely understand what you are saying but at this point either something in the distributor isn't working right or as you say power could be the problem BUT if the 12V feed at the cream plug tests OK then the only item that can reduce that voltage is something inside the distributor but we already replaced the coil and the ICM with a GM part. We have a new distributor on the shelf and we will install that tomorrow.

olejoedad

JUL 05, 08:55 AM

The 4.9 uses the coil in the distributor cap, and requires grounding.

Is the ground strap in the cap connected with the screw?

Dennis LaGrua

JUL 05, 08:05 PM

quote

Originally posted by olejoedad:

The 4.9 uses the coil in the distributor cap, and requires grounding.

Is the ground strap in the cap connected with the screw?

All looks OK . Will put in a new distributor but it will need to wait until Monday. If that doesn't work it will probably be the harness but it did work before we replaced the tranny. Maybe the harness was bent it or pulled something.

greenturnedblue

JUL 05, 10:18 PM

It "looking" OK doesnt mean much. you should probe it with a ammeter and see if there is continuity between both ends. Then you will know if it is actually grounding or not.

Dennis LaGrua

JUL 06, 10:35 AM

quote

Originally posted by greenturnedblue:

It "looking" OK doesnt mean much. you should probe it with a ammeter and see if there is continuity between both ends. Then you will know if it is actually grounding or not.

Already tried a band new coil and a GM branded ICM. No change. I believe that something in the distributor or wiring may be open. Suspect the reluctor and pickup . I'll just replace the distributor on Monday with a new one that we have on the shelf and see what happens. If that doesn't work then the next step is the harness as we have 12V going to the distributor. That will be double checked under load before the new distributor goes in.