Picture of a 7 Pin Ignition Module, common for OBD1 EFI System.
dave w
Electronic Spark Control.JPG
Picture of a 7 Pin Ignition Module, common for OBD1 EFI System.
dave w
Electronic Spark Control.JPG
Thank you Dave, this is what I am looking for. Is this in the 89 or 90 emissions/fuel manual? I only have the B, C and G, W posts on my ICM.4pin.jpg
Using the 4 pin module works for a "Fuel Only" TBI system, meaning no spark control from the ECM.Originally Posted by Dlxman
Likely, if one injector is working, the 4 Pin Ignition Control Module is working fine.
The ECM has two injector drivers, maybe one of the injector drivers is bad?
dave w
Thank you, I was hoping the Ignition Control Module was bad. 3 months ago, I removed it and had it tested at a parts store and it was fine. I also heard that it could be bad and still test fine... (word on the street). I would like to test the circuit as noted in the manuals, but I would only guess which wire is sending the reference pulse. How, or where would I check for an "injector driver"?
BTW, I also believe this is a "fuel only" TBI now that you mention it. This is also a Howell TBI If I have not noted so earlier.
Thank you so much for your time. I have a new ignition control module to add to my parts list.....unfortunately.
I also replaced the ECM, if the "driver" is a software driver, and had the same issue. Since then, I put the old ECM in since apparently it was okay (since no change, now I have two ECM's ... good or bad I do not know. Too much diagnosis by wallet, I desired to go a bit more high tech and found this forum. I am really thankful for all the support, and am now over my head. I am an engineer, so can handle a bit of technology.
The steering column was removed, and harness from the ECM was inspected as OK. Continuity checks proved good. All the grounds are new, as well as the frame. Using a test light to D16 and D14 proved I had a light at D16, but not D14 with ignition on.... Hmmmm. This led me to an open circuit on on 468 LT GRN (which was included in the steering column drop and pulling the ECM connectors out for inspection. Again. No issues, breaks, bends.. Going to Injector circuit diagnosis, I can not tell with the system I have if I am getting a reference pulse from the ECM.
The injectors are powered by the ignition switch, both "On" and "Start" positions. The computer Pulses Ground (measured in milliseconds) to the injectors. The more milliseconds ground is sent to the injectors, the more fuel to spray out of the injectors. So 25 milliseconds of ground will spray more fuel than 15 milliseconds of ground.
Schematic below is 1989 TBI, other years are very similar or identical to the 1989 schematic.
dave w
1989 Chevy Truck K 1500 Truck 4WD V8-350 5.7L_04.jpg
which injector IS working the one at D16/BLU (injector 1) or D14/LT GRN (Injector 2)?
ALSO, i think it's time to ditch the test light. Do you have a DMM? I like to see what the actual voltage is. Even using continuity tester on DMM will register up to 50 ohms which can be a large voltage drop...
Last edited by tayto; 09-15-2021 at 08:11 AM.
Hi Tayto, The injector D16/Blu is functional. I do have a DMM and can check the voltage. The reason for the test light was per the manuals as a quick test to check for power to ground and rule out a circuit issue, if yes >>> if no>>>.
Do you desire that I check the voltage at each connector with "key on", "Cranking", both?
Thank you for clearing some of this up. I apologize, however I still have some questions concerning this. So with the initial "key on", I should be able to have a DMM on the ground side of the ignition control module to see a pulse? I am trying to find the circuit from the ECM to the ignition control module to validate that circuit. I had thought it would be the ECM B5 ppl/wht ckt 430, but cannot locate that to my distributor.
Perhaps there is something else I should be checking.....
so with your DMM referenced to ground, negative lead on battery or chassis, you want to see if you have 12+ volts on the WHITE and RED wires with key on. you can then check continuity to ground on the BLUE and GREEN wires. with the engine NOT running you should have no continuity to ground. should only have pulsed ground when the engine is running if my thinking is correct. you can then check the ground with engine running and see what its doing. i am wondering if you have a poor connection at the injector or a bad #2 injector driver in ECM if all the wires rang out OK... keep us posted
EDIT; not sure how Howell has setup your system, if the 430 wire isnt there and ran before i would expect it to not be the problem.
EDIT 2: I SWARE i've seen each injector fused separately by GM in the past but i may be remembering wrong, i assume Howell has an auxiliary fuse block and you've verified all the fuses are good there?
Last edited by tayto; 09-15-2021 at 04:53 PM.
Posting Permissions
Reply With Quote
Bookmarks