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

2482 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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Just to confirm, you're still having trouble with the engine not starting?

It's hard to tell what the right next step might be without being there. A blown fuse under the dash and a drain on the battery suggest a problem with wiring or with another electrical component. Whether or not that's related I won't guess.

With the ecu able to "talk" again you could work on diagnosing the no-start. If the engine has compression, spark, and fuel at the correct time it should start. You could check for spark first. That's a biggie. No spark means moving to check for power at the coil, then check for the coil negative signal as the engine is cranked over.

If you have spark the next step might be to check for fuel. If you have starting fluid you could try spraying a little bit into the throttle body then cranking the engine. If it starts and stalls you should try to determine why fuel isn't getting into the cylnders. Are the injectors firing? Check power and ground circuits at the injectors for proper operation. If you have spark but starting fluid won't start the engine shut everything down and pull the plugs. Are they wet? Covered in black carbon? Do they smell like gasoline? Is the stuff you put into your tank not really gasoline? If the plugs are wet try cleaning or replacing them (do not clean plugs with a wire wheel) and try starting the engine again. If you have fuel and spark and the plugs are good I think diagnosis is going to be a little tougher. You may have a sensor giving wrong information to the ecu so you're getting bad spark timing or wrong fuel. Or you may have a mechanical problem.
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