I have a 4.9L swap and the engine started and ran fine with the harness. Discovered that the transmission was bad so we pulled it out and had it rebuilt. Put everything back together, engine cranks but no spark and it appears that there are no injector pulses as well. Scan tool says defective neutral range switch so we replaced it. Still no start. I suspect that the ECM /system somehow is not getting any power. Could be a ground or power problem so I could use some tips to troubleshoot. What a PITA.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Both Ignitions at crank time is "dumb" and under ICM control. ECM doesn't start ignition control till see 500-600 RPM.
------------------ Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should. (Jurassic Park)
Both Ignitions at crank time is "dumb" and under ICM control. ECM doesn't start ignition control till see 500-600 RPM.
I hear what you are saying but it looks like the ECM may be without power. Tomorrow I will check all of the switched 12V inputs that supposed to be there. The engine uses a distributor but inside is the ICM and the cam sensor.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
the ECM provides the CEL right? So if the ECM is uncommunicative the CEL wont come on when you turn the key to ACC
Thank you. Thats a very good point . The CEL light goes on when the ignition is turned to on but then turns off. To make sure we will double check to see that the power and ground feeds are all good. It could also be that the power is not getting to the ignition module or the ignition module has failed. I just wish this was OBD2 as the diagnostics are better but the solution right now seems to be to check the power sources to everything
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Always check power and ground circuits. Is it possible a ground wire didn't get hooked back up during transmission installation?
Its on the to do list. But since I work on the cars P/T it may be a week or so before I get to it.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Hook up a scan tool and see if the TPS reading changes when the gas pedal is pushed. That will show if there is power to the PCM. However it could be that there is no power to the ignition module.
It had a no start problem on a 3800 that sat for a few months. It had spark, fuel injector pulses and good fuel pressure. There were no codes set on the scan tool. Out of desperation, I changed the crank position sensor and cam position sensor and the car started. I theorized that the PCM was getting bad signal from the crank position sensor and the timing was way off.
Hook up a scan tool and see if the TPS reading changes when the gas pedal is pushed. That will show if there is power to the PCM. However it could be that there is no power to the ignition module.
It had a no start problem on a 3800 that sat for a few months. It had spark, fuel injector pulses and good fuel pressure. There were no codes set on the scan tool. Out of desperation, I changed the crank position sensor and cam position sensor and the car started. I theorized that the PCM was getting bad signal from the crank position sensor and the timing was way off.
Been away for a few days now back. Focusing on missings grounds an power right now. The crank position sensor on the 4.9L is in the distributor. There is a probably a way to check it with an ohm meter but haven't gotten that far
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The power to the distributor comes from the ignition switch through E3 of the C500 connector. After it passes through the C500 connector there is a 0.5mm fusible link ("H") on the way to the distributor. If this fusible link is blown there is no power to the distributor or ignition module.
Easy to check power to distributor on a 4.9, just unplug the tan connector on the cap. That is the coil power. The plug on the distributor body pin provides communication with the ECU.
Easy to check power to distributor on a 4.9, just unplug the tan connector on the cap. That is the coil power. The plug on the distributor body pin provides communication with the ECU.
Did the Battery Junction Terminal get hooked up?
Got to do those checks. As for the junction terminal this is how it looks now. 10 AMP fuse is good.
[This message has been edited by Dennis LaGrua (edited 06-19-2022).]
Easy to check power to distributor on a 4.9, just unplug the tan connector on the cap. That is the coil power. The plug on the distributor body pin provides communication with the ECU.
Did the Battery Junction Terminal get hooked up?
Checked the cream colored connector on the distributor. We are getting 12V to the distributor. The connection to distributor power and ECM at the junction block appear to be hooked up. Now I suspect that it could be a ground problem somewhere, the ECM itself or even a bad ignition module, pick up or coil. Not sure how to test the module . Its the GM 7 pin unit. Working with OBD1 can be a real challenge. Next thing is to first try to test the distributor, then disconnect the ECM connectors and measure for power and grounds there. On second thought the tach doesn't move when cranking and the injectors are not getting pulsed.. That points to a bad ignition module but only if the module is getting power and ground. The module is the current focus but I've been told aftermarket modules vary widely in quality. . Update 6/22/22: Replaced the ignition module with a new older genuine GM part, cap, rotor, & rotor contact. The previous owner had replaced the module with an unmarked Chinese piece of crap. He also chipped the module connector so I put a dab of red silicone on the exposed area. We will let that dry and will try to start the engine tomorrow
[This message has been edited by Dennis LaGrua (edited 06-22-2022).]
Replaced module and no change. Back to wire tracing. Could be the coil. Now to check if the coil is getting power.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
To confirm whether there are injector pulses you need to unplug an injector and test with a "noid" light. May be able to borrow at Autozone et al but they are not expensive and worth having in the tool set.
Have you confirmed the ICM is sending the pulses to fire the injectors and plugs? Icm handles all ignition under 400rpm or so
ICM has been replaced with a new GM unit. Still believe that we may have a wiring problem. Next up to see if the ICM pulses are being sent to the coil using a test light on the coil 12V and ground inputs. If it doesn't blink while cranking then we test the magnetic pickup
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
UPDATE: Still checking, Coil and IGN module replaced. Still no spark. Grounds seem ok. Only thing left to check is the ECM itself, the rest of the harness and might try replacing the distributor as it could be the pickup coil but I can check that with an ohmeter. Scan tool shows nothing which may be common for OBD1.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 07-03-2022).]
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.
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.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
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).]
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.
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.
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.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
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.
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.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
