No spark no injector pulses- Question for the wiring experts (Page 2/3)
olejoedad JUN 16, 08:59 AM
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?
Dennis LaGrua JUN 19, 03:39 PM

quote
Originally posted by olejoedad:

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).]

Dennis LaGrua JUN 20, 06:26 PM

quote
Originally posted by olejoedad:

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).]

Dennis LaGrua JUN 23, 04:39 PM
Replaced module and no change. Back to wire tracing. Could be the coil. Now to check if the coil is getting power.

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" 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 "

olejoedad JUN 28, 03:50 PM
greenturnedblue JUN 29, 04:50 PM
Have you confirmed the ICM is sending the pulses to fire the injectors and plugs? Icm handles all ignition under 400rpm or so
sanderson231 JUN 30, 01:23 PM
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.
Dennis LaGrua JUN 30, 04:11 PM

quote
Originally posted by greenturnedblue:

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 "

Dennis LaGrua JUL 03, 04:25 PM
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).]

phonedawgz JUL 03, 04:35 PM
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.