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Bad ECU? How do I check my brainbox...

2478 Views 18 Replies 10 Participants Last post by  Gypsy_Botanist
I was driving the other day and shortly after I got fuel, my tac, speedometer and all of my gauges went dead. I thought/hoped it might be a loose fuse & continued to drive her for about an hour and then I started to loose a little power, she just couldn't maintain 75, I was driving on the highway, and slowed to about 60 with the same amount of throttle on level ground. Then all of a sudden she starts kind of chugging or gives a shudder, a few seconds later she backfires and I lost all power. She died when i took her out of gear, or maybe I turned the key off. After I got her stopped I tried to start her up, and got nothing. The fuel pump turns on and the engine cranks and turns over but no fire (I've not checked the plugs for fire yet so only 90%). I also have no check engine light, not even when you turn the key or for the few seconds it turns on after starting. I tried turning the key thrice to see if she is throwing any codes but I got nothing. So i think the brainbox is dead I just don't know how to test it. I thought I could plug an OBD computer into it but I don't know where to plug it in at, or any other ways to diagnosis it. I'm going to get a relay checker and check all the relays and fuses under the hood. If anyone has any other ideas about whats wrong or how to check your brain box please let me know.

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I would not condemn the brain when you stated that all the guages, etc. went dead. You should not trust the CEL when the rest of the cluster does not work.
You did have the end of the plug grounded when you checked for spark? Right? I am not trying to insult your intelligence but have to question how you do things based on this thread and your posts. If you missed the most simple of things it could sidetrack your diagnostics and results. Your lack of common terminology or acronym knowledge leads me to believe that your knowledge is basic but yet some of your other observations are very encouraging that we can all get on the same page and accurately diagnose this problem.

Remove the coil to distributor high tension wire at the distributor end and check to see of spark will jump at least a half inch if not close to an inch to ground. You can do this with a spark tester or by installing a Philips screwdriver in the end of the coil wire and holding the metal blade of the screwdriver at least a half an inch from a good ground surface. It will probably require a buddy. A reasonably insulated handle on the screwdriver is wanted and it will probably require a helper.

If have spark going to the distributor cap but not coming out to the plugs it can indicate a few things. Water or moisture in the cap, a burned through rotor, a distributor that does not turn, a carbon tracked cap, a messed up rotor to cap connection, lots of bad plug wires or at least where you tested. etc.

If you do not have spark from the coil wire you need to test for power to the coil, and a pulsing negative coil circuit, preferably with a test light.

It really does not sound like your ECM is dead in the way that most of them go dead. You were able to do things and bring your cluster back to life after the fact. You were able to flash codes after the fact. The ECM does control ignition timing and pulses in this engine but other basics have to be covered. The majority of ECM failures that are documented involve no Check engine light and not fuel pressure... They come down to bad capacitors and the ECM never really powers up for a few minutes.

I believe that we have crossed that basic bridge.
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