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Thread: Help understadning my CJ7 SBC datalog

  1. #31
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    Quote Originally Posted by dave w View Post
    Using the 4 pin module works for a "Fuel Only" TBI system, meaning no spark control from the ECM.

    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
    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.

  2. #32
    Super Moderator dave w's Avatar
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    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

  3. #33
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    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.

  4. #34
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    Quote Originally Posted by tayto View Post
    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...
    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?

  5. #35
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    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.....

  6. #36
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    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.

  7. #37
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    this is the test light gm is referring to. also called a noid light

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  8. #38
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    Quote Originally Posted by tayto View Post
    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?
    Only to clarify, I do have a color deficiency, so I call for support to find the correct colored wire. Sometimes it takes me a bit. I have two pics, one of the distributor and one of the harness replacement for the plugins to the distributor.
    I got twelve volts at each wire on the B & C (brown? & red?) side of the Ign Ctrl Mod. 0V at the green and white shown. I have 12V at each injector connector. Started and the opposite injector is firing (lt grn). I know you say no way. I put tape on the connector that was good to not get confused. I am going to check or tighten each injector connector terminals.

    I agree to give up on the ckt 430. Yes, there is a separate fuse box near the ECM, and various other fuses that all check OK.

    I'm also going to start it and fuss with the connector wires push/pull to see if I get juice while running...
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    Last edited by Dlxman; 09-17-2021 at 09:36 PM.

  9. #39
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    looks like an "old school" gm big cap HEI to me... not familiar with how Howell does these setups. they must be picking up a distributor reference somewhere to fire the injectors? any wiring diagrams or literature supplied when you got it?

  10. #40
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    The howell system uses the tach lead off the distributor to signal the ECM to fire.

    Update.. The injectors do not fire simultaneously. Using the timing light on number one, I could only see one cone, and the other a bit of a mist. I did a slo-mo video being back lit and could see a good cone out of both injectors. perhaps one injector is 180 deg apart. I fussed with the connectors, pulled out the lead of the connector and checked for fit, voltage, continuity... put it together and they both fired.

    Ran awful one day, pulled the tack wire, and with key on, momentarily touched 12v to the wire, and both injectors fired.. Put the connectors back on, air cleaner etc. Went down the road just fine with all sorts of power. no misses, stumbling..

    I have not found any reason why the stumbling occurred, nor why it is gone today. It may come back on a longer trip, which has happened in the past.

    I have attached the log file from this trip, along with some spray cone back lit pics. The videos are nice, but at 55 to 100mB, I feel they are too big to post.

    I am curious why my 02 sensor is bouncing up and down eratically. Is the ECM still learning? Is this normal? Seems to smooth out at WOT.
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  11. #41
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    normal the o2 voltage is changing like that @ idle/light cruise. i have a feeling you've fixed the problem during this process. i normally would reset the ecu by disconnecting the battery after a repair like this. i have had an ecu "learn" to run poorly and after you repair something it still doesn't run right until a reset. it's also not uncommon for the ecu to need a few days or even weeks of driving to "settle in". Again I have no idea how close Howell got the tune, but I would think it is pretty generic. Glad it's running hopefully problem does not come back.

    EDIT: was distributor new or rebuilt when did this swap?
    Last edited by tayto; 09-22-2021 at 03:23 AM.

  12. #42
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    I sure hope the problem is corrected. We will see if it randomly pops up as it had in the past. I did have the battery disconnected while messing with the wiring and ECU, so thank you for this tip. I also agree to let it drive for awhile to have it learn more (hopefully learn to behave!!). If the problem does come back, I will know what to look for. This post and website has been a tremendous wealth of information and help. I sure do thank you for your time, efforts and patience with me through this problem.

    BTW, I am not sure if the distributor was new, or rebuilt in 2014 I'm thinking new. I have my old points dist, original 69 QJ, and 69 cast iron intake as a back up (too many times I thought about reverting).
    Thanks again.

  13. #43
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    in my experience, i have always had no run issues with distributors. have also seen where a vehicle will run for awhile then shut off and not restart until cold. I recently got a reman'd distributor for a 92 GMC from Autoline. I had my own GM performance distributor in there so the vehicle was drives le. When I swapped it, it ran like crap and even my timing light was doing weird things. I messed around with it for over a hour before deciding to throw my distributor back in and truck ran good again. I tried replacing the module with a GM one i had and the reman dist still ran bad, so thinking maybe the wrong pickup coil was installed? I guess what I am saying is maybe it's worth replacing the dist with a known good one next time. GM HEI's are generally solid so no need to reinvent the wheel.

  14. #44
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    It ran well on Sept 20th. Granted it was only briefly. A couple days later, not changing or adjusting anything, a longer drive resulted in worsening performance. The next day, on a longer trip, same thing. Returning home, after a longer ride, I decided to log a run.

    I THINK I FOUND THE SMOKING GUN.

    I attached 4 files, two datalog files, and 2 excel (open office *.ods) files. The 920 is when the jeep ran WELL, the 926 the jeep ran POOR.

    Looking at the excel files, I organized the data as I needed to see it. I saw the column for the ALDL enabling. On the running well file, the ALDL was enabled. On the POOR running file the ALDL was disabled. Plus all sorts of wierd numbers up and down...

    So, if the smoking gun is the enabling of the ALDL, then I need to trace down where the short is to turn this on and off. I suspect ignition to ECM somewhere.

    Would you think that an ALDL not enabled would perform this way? Gas only TBI...

    BTW, I do have an oversized Novak Jeep radiator which keeps it running cool if that may be a problem of the engine never getting warm enough... just a thought...??...
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    Last edited by Dlxman; 09-28-2021 at 08:57 PM.

  15. #45
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    i'm pretty sure ALDL mode when there is a 10k resistor between terminals A & B on the ALDL connector. Not sure what datalogging cable you are using but my Moates one has a switch to toggle resistor or no resistor.

    you can take your meter and measure the resistance on your datalog cable between pins A & B
    Last edited by tayto; 09-29-2021 at 03:08 AM.

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