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87 Comanche 2.5L EFI Running Rich


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Hi All, first time here so excuse me if I ask dumb questions!

 

At work, a customer of mine has an 87 AMC/Jeep Comanche 2.5L with the Renix TBI EFI system. It runs pure rich ALL the time. We have used our scanner and gotten into the ECM and the only sensor that was out of range was the O2 sensor, so we replaced that as well as did a full blown tuneup including plugs, wires, cap, and rotor. None of this helped. My co-worked thought that maybe the ECM was misinterpeting signals from sensors, but showing everything OK on the scanner, so we got a replacement ECM from the junkyard from another 87 Comanche 2.5L. No change. So looking deeper, still not finding anything, we replaced the coolant temp sensor since these have a tendancy to make the engine run rich if they fail (this one was reading a good temp and voltage, but we did replace it anyway). No dice... so we still have a 2.5L AMC motor that is running full rich. We are running out of options. We have checked vac lines and intake manifold for leaks to no avail...

 

any help would be greatly appreciated by us and the nice old guy who owns this truck...

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I wish i could help But have have the same exact year and motor and setup and mine does this to and it has since i got it. Even when i first got the truck i replaced all gaskets on from the head gasket up and all sensors and plugs and wires and it still has don't it. So i hope someone can help you with this since it might help me to. I just gave up on it along time ago so i havent researched it ne more. Also let the guy know about this site maybe he will be interested.

 

Cole

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Its TBI so theres one to check and its easy to access this is one thing i have yet to check for some reason. :grrrr: :dunce: But i have heard using a timing light you can see if its misting or not properly. :dunno: might try it tomorrow.

 

Cole

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The o2 sensor was just telling you it was rich, as if you didn't know. Check for vacuum at the MAP sensor. It is a small line and it is easy to plug. No or low vacuum at the MAP is interpreted as WOT by the ECM and it goes full rich. It also needs to have manifold vacuum, not ported. Lots of time the rubber plug at the TB swells up and allows vacuum leaks to the line.

Also, after it has been running, shut it off and watch the injector to see if it drips. You can also check for drip while it is running. Should be a nice cone spray with no dripping. How many wires did the coolant temp sensor have that you changed?

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The o2 sensor was just telling you it was rich, as if you didn't know. Check for vacuum at the MAP sensor. It is a small line and it is easy to plug. No or low vacuum at the MAP is interpreted as WOT by the ECM and it goes full rich. It also needs to have manifold vacuum, not ported. Lots of time the rubber plug at the TB swells up and allows vacuum leaks to the line.

Also, after it has been running, shut it off and watch the injector to see if it drips. You can also check for drip while it is running. Should be a nice cone spray with no dripping. How many wires did the coolant temp sensor have that you changed?

 

we have vac at the map sensor, and have even swapped in a new map sensor to be sure... still no change.

 

did not check the fuel injector yet.

 

the coolant temp sensor had 3 wires, the single wire unit should only be the sender for the temp gauge on the dashboard (or light if you have the base dash)

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I don't mean to be a little off topic, but does this have coil packs versus a distributor?

 

I had the iron duke in a 88 Grand am with coil packs. I made a mistake and ran 93 Octane in it. The computer compensated for the higher octane fuel and would advance/decrease the timing throwing the performance way off. It would run rich and then run lean.

 

It took about 3 tanks of 87 Octane to get it back normal.

 

Hope this is helpful.

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