AMC Eagle Den Forum
The Shop => Electrical => Topic started by: JayRamb on March 24, 2015, 10:45:51 PM
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How to tell if the 'computer' on the Eagle is working or not?! How do you tell? Is there a simple way?! I hope. I need answers! Jayson
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I'm guessing your Eagle still has its original Carter BBD carburetor.
For starters, does your Eagle start and run? If it starts and runs, try this: Take off the air cleaner. Now look down through the carburetor throat for the two little plungers. Have someone start the engine while you're watching the little plungers. They should move forward and backward and then settle somewhere near the middle of travel.
CAUTION: Be sure you protect your face against carburetor backfire while you're looking down the throat!
Post up the results of the above and let's go from there.
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And that also begs the question "Why do you think its not working??". Symptoms??
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If your computer is working, you might just need a blast of carb cleaner or the bowl may need cleaning. They love to attract dirt.
If it's not working do the ECM Test Bypass. Unhook the computer from the back of the carb, use a pair of needle nose pliers to slide the 2 pins back a bit.
The good thing about the ECM Test is that you can always reverse it quite easily.
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the computer also controls timing from the fuel ratio, and a knock sensor. the knock sensor is on the front portion of the intake manifold. I circled it in red on an attached picture. if you tap on the intake near the intake sensor, the computer will attempt to change timing to stop the knock noise that it hears. I have found out that the Snap-On scanners have the ability to show a data stream for the 258. if you select jeep, then the model year of your eagle, 258-4.2L, and trans and A/C option. it will show you what the computer is, or isn't doing, and the various inputs from sensors. I haven't spent enough time with it to understand how the system works, and my car is missing the pulse air and solenoids that control it.
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More than once the ECM test bypass has fixed weird problems in an Eagle for me. It is quite easy to do, but remember to reset the timing after doing the work, as it is no longer controlled by the computer, and timing will be retarded. If you can find an old Eagle to harvest parts from, you can make a plug-and-play wire harness so no factory wires need to be cut or spliced. I think I did a thread somewhere here years ago, but don't remember where......Rich
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I will be following this closely. I am trying to get a response from my ECM as well. It does not initialize and I've tried multiple steppers and two ECMs. Oxygen sensor is brand new and all switches are tested and working. I have it bypassed currently but would like to return it to stock, minus the air injection. I would love to see a thread where someone troubleshoots and repairs the stock system instead of ditching it.
This article is a big help as the Jeeps of the era are nearly identical:
http://home.sprynet.com/~dale02/ (http://home.sprynet.com/~dale02/)
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Do you need the ECM in your part of the country?
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I should add that the computer is located behind the passenger side kick panel. I would recommend taking the package tray out when removing the kick panel. You also will want to be careful with the vacuum solenoids bolted to the valve cover. Perform an ohm test before you hook them to the computer, as I have found they will go bad, and draw more current than they are supposed to. That is not good for the computer, and can risk damaging it.
I'm not sure what the ideal resistance specification is off the top of my head, but I have found it before.
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The set of valve cover solenoids I have ohm out to about 73 ohms each.
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from what I can find, that sounds OK. I created a new page in the eaglepedia pertaining to the operation and diagnosis of the Computerized Engine control based off of the 82 TSM that IowaEagle added. hopefully this will be helpful.
http://amceaglesden.com/guide/Computerized_Engine_Control_Diagnosis (http://amceaglesden.com/guide/Computerized_Engine_Control_Diagnosis)
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OK, I unplugged the computer cable and now it pings. I unplugged my other Eagle's computer and NO difference. Still runs the same and still pings. :( So, one I think is shot and one is working. Hmmmmm
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Which cable did you unplug exactly? Mine pings badly under acceleration too when the computer is connected but unresponsive. I believe it has to do with the computer not retarding the timing correctly (because it isn't working).