Shorbagon Posted January 31, 2016 Share Posted January 31, 2016 I picked up a 1989 Comanche Pioneer for $500 a few months ago and I'm loving this project. I'm having a parasitic draw issue. It's drawing 4.35 when everything is off. All fuses and relays have been tested with no success. Issue: electrical power loss and then engine stall. Battery tested and good. Alternator tested and good. Here's a list of what Ive completed. Gas tank and pump. Tail light wires spliced cleaned and reconnected. Ignition key cylinder replaced. Headlight switch replaced. Battery cables replaced. Spark plugs and wires replaced. Engine ground wire upgraded and replaced. Any suggestions for finding the issue? Link to comment Share on other sites More sharing options...
Dillithium Posted January 31, 2016 Share Posted January 31, 2016 Did you check the starter? Link to comment Share on other sites More sharing options...
Shorbagon Posted January 31, 2016 Author Share Posted January 31, 2016 When the battery is fully charged it starts with no issue and will continue running until the battery is drained. What should I do to check the starter? Link to comment Share on other sites More sharing options...
MJCARENA Posted January 31, 2016 Share Posted January 31, 2016 When the battery is fully charged it starts with no issue and will continue running until the battery is drained. What should I do to check the starter? Sounds like your alternator is not working. Link to comment Share on other sites More sharing options...
Shorbagon Posted January 31, 2016 Author Share Posted January 31, 2016 When the battery is fully charged it starts with no issue and will continue running until the battery is drained. What should I do to check the starter? Sounds like your alternator is not working. That's was my first thought too. I was confident that the alternator was the issue. I pulled it inspected it and had it tested. The alternator is in good working order. The alternator wires were inspected as well. The 4.3 amp pull is now what seams to be the problem. I see the alternator wire runs to the ignition "relay" before heading to the battery. Could that cause this problem? Link to comment Share on other sites More sharing options...
Gene Posted January 31, 2016 Share Posted January 31, 2016 Hi Shorbagon, Do you mean that there is a current draw of 4.35 amps? That is a HUGE current drain. I agree the alternator is the most likely suspect. If the diodes short, the alternator output will be greatly reduced, and the shorted diode will act as a short-circuit, causing the current draw. Try disconnecting all the wires to the alternator, and see if the current draw is still there. Otherwise, this is plain old electrical troubleshooting. Put a meter in place for measuring the current draw, and disconnect things one at a time, disconnect the fusible link wires, pull fuses, and so forth to isolate the pathway of the current draw. Once you have a clue, you can track it down the rest of the way. Again, though, I think the alternator is most likely. Perhaps the testing was not accurate. Good luck! Gene Link to comment Share on other sites More sharing options...
Shorbagon Posted January 31, 2016 Author Share Posted January 31, 2016 Hi Shorbagon, Do you mean that there is a current draw of 4.35 amps? That is a HUGE current drain. I agree the alternator is the most likely suspect. If the diodes short, the alternator output will be greatly reduced, and the shorted diode will act as a short-circuit, causing the current draw. Try disconnecting all the wires to the alternator, and see if the current draw is still there. Otherwise, this is plain old electrical troubleshooting. Put a meter in place for measuring the current draw, and disconnect things one at a time, disconnect the fusible link wires, pull fuses, and so forth to isolate the pathway of the current draw. Once you have a clue, you can track it down the rest of the way. Again, though, I think the alternator is most likely. Perhaps the testing was not accurate. Good luck! Gene This is a good plan. I disconnected the alternator wires and it dropped to 3.0. Then I disconnected the wires in the attached images below (right passenger side engine bay). this dropped the output to 0.2!! Any idea what these connection go to? https://www.flickr.com/photos/shorb/shares/14Nj23 Link to comment Share on other sites More sharing options...
Gene Posted January 31, 2016 Share Posted January 31, 2016 Good work! You're probably 90% done! Perhaps one of the guys who knows these jeeps inside and out, such as hornbrod, will reply and tell you not only just where these wires go, but what's most likely to have failed. He, and a couple other forum people, are walking encyclopedias about these jeeps. However, I'd probably just take a flashlight and roll underneath and look. I would look particularly around the exhaust pipe, and around the oxygen sensor, to see whether a wire may have gotten too close and melted into the exhaust system. You're almost there! Gene Link to comment Share on other sites More sharing options...
Gene Posted January 31, 2016 Share Posted January 31, 2016 This may be connector C103, which is listed as "Engine to ECM" Disconnect a battery cable first. Then reconnect the C103. Disconnect the connector at the ECM. Reconnect battery cable and see if the current draw persists. If it is gone, then ECM may be shorted. If the draw is still there, may be a shorted wire. All of the above is assuming that this connector goes to the ECM. Gene Link to comment Share on other sites More sharing options...
87MJTIM Posted January 31, 2016 Share Posted January 31, 2016 The connector looks like C103. It connects the engine and ECU. Here is the '88 electric manual to help guide you. http://comancheclub.com/topic/12083-electrical-manual/ Link to comment Share on other sites More sharing options...
87MJTIM Posted January 31, 2016 Share Posted January 31, 2016 You guys beat me to it! Link to comment Share on other sites More sharing options...
tugalo Posted January 31, 2016 Share Posted January 31, 2016 looks like C103, if so, it goes to pin B7 on the computer, the automatic transmission, and to the fuel pump relay............... Link to comment Share on other sites More sharing options...
Gene Posted January 31, 2016 Share Posted January 31, 2016 The more I try to read the wiring diagram, the more confused I get..... As tugalo said, it appears that connector C103 serves a lot of stuff, including the engine computer, fuel pump relay, auto trans controller, and ?power latch relay. Perhaps you can try pulling the relays, one by one, and see if any of these make a difference.... Gene Link to comment Share on other sites More sharing options...
Shorbagon Posted January 31, 2016 Author Share Posted January 31, 2016 I pulled the ECU (Bendix) and hooked the alternator back up. With the ECU completely removed I'm down to 1.5 draw. From what I can tell C103 continues along the back engine bay wall and drops down through the firewall to the ECU. I opened up the ECU and everything looks visually good. What does the ECU control? Link to comment Share on other sites More sharing options...
Shorbagon Posted January 31, 2016 Author Share Posted January 31, 2016 The connector looks like C103. It connects the engine and ECU. Here is the '88 electric manual to help guide you. http://comancheclub.com/topic/12083-electrical-manual/ Thanks for the link. I will look through it. Great reference for future problems as well. Link to comment Share on other sites More sharing options...
tugalo Posted January 31, 2016 Share Posted January 31, 2016 The ECU or ECM controls the engine fuel management, injector firing times/ pulse widths, and most other engine functions. If the truck is running, i don't think the computer is bad, may be a chafed/shorted wire in the harness. Link to comment Share on other sites More sharing options...
Eagle Posted January 31, 2016 Share Posted January 31, 2016 Unless I'm missing something, it would seem that the ECU can be eliminated or indicted by simply unplugging the connector from the ECU under the dash, then check the draw again. If there's no draw, the drain must be either in the ECU, or downstream from it. If the draw is still there, there's either a cross connection upstream of the ECU, or the problem is in some circuit that has nothing to do with the ECU. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 1, 2016 Share Posted February 1, 2016 Unplug the 2 wire plug on the alternator while checking for a draw and see what happens. Link to comment Share on other sites More sharing options...
87mjdriver Posted February 3, 2016 Share Posted February 3, 2016 i just recently fixed a parasitic draw on my MJ. for what its worth I got on youtube and followed Eric the car guy. he does a good video on how to track down the draw safely. eric mentions that you should first check any added on circuits, turns out that was my issue and i checked it last, doh! Link to comment Share on other sites More sharing options...
Shorbagon Posted February 3, 2016 Author Share Posted February 3, 2016 This is a little frustrating. I pulled the ECU which dropped the draw and I followed the wires with the diagram in the link above for c103. I put everything back together and the parasitic draw seams to be gone. I can't pin point what stopped the draw. I installed a new belt and tested the voltage when running. It tested at 14.5 volts. I expect this problem to come back and I will keep you posted. Thanks again for the great insight. Link to comment Share on other sites More sharing options...
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