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Old 07-07-2014, 08:16 AM   #1
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oil pressure gauge reading 5 psi at all times

Hello everyone! I just did a transmission swap in my 99 sport. I went from a 32rh to an ax15 using the 99 manual ecu. But now I am having issues with my oil pressure gauge. it's only reading 5 psi at all times cold hot even when the key is on but engine is not running. I changed the sending unit and it didn't make a difference. Every time I search I can't find anyone that has had the same issue as me. The gauge worked fine with the auto setup. Could it be a short in the computer or cluster? Any input would be much appreciated.

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Old 07-07-2014, 08:34 AM   #2
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Not sure where you got the sending unit but I would return it and go with a Mopar unit along with checking the condition on the wires and connector to the unit.

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Old 07-07-2014, 09:06 AM   #3
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Nothing involved in the 32RH/AX15 swap affects the oil pressure, I swapped from my AX15 to the 32RH with no oil pressure issues.

X2 on what Wattapunk said, I'd go with a Mopar oil pressure sender. It took 3 trips to my local Autozone one Sunday to get an oil pressure gauge sender for my son's Grand Cherokee before I finally got one that worked properly.
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Old 07-07-2014, 09:39 AM   #4
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I was thinking about the mopar sensor and the only thing changed in the swap that I could think that would affect it was the ecu
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Old 07-07-2014, 09:48 AM   #5
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The PCM (ECU) is the only other likely but still less likely source of the problem. Try removing all three connectors and reseating them to see if that changes anything. Or you could even temporarily swap the original PCM back into place to see what happens to the oil pressure gauge.
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Old 07-07-2014, 10:16 AM   #6
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I have the same problem and am watching this thread hoping to see a fix. My 99 manual 4.0 also reads 5 psi no matter what, just like the OP. To add my experience to other posts, I have the original ECU in the jeep and it runs like a top with no issues whatsoever. Prior owner installed a mechanical oil gauge and oil pressure is running in the proper range. Also, I have tried the mopar sender as well as a number of aftermarket units with no difference.

To the OP, I don't think it's the ecu if everything else runs fine. The fact that the oil pressure gauge needle moves at all when the ignition key is turned on means that the Jeep is getting SOME signal from the sender (a disconnected sender will show a dead gauge). As to recommended fixes I am stumped at this point. I toyed with the notion that either (1) the instrument cluster was swapped by the prior owner and is not compatible with the sender (2) there is a frayed wire somewhere from the sender to the instrument cluster which is not allowing a full signal to the cluster, or (3) a loose connection behind the instrument cluster. Due to laziness I never checked on these things.

Maybe check on these things related to wiring or the cluster and let us know if that fixes it.
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Old 07-07-2014, 07:10 PM   #7
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Ok so I just plugged the auto ecu in and the gauge works I am going to swap the computer with my friend (98 4.0 sport) and see what happens. I will update when I get results... but in the mean time does anyone have access to the pinouts for the auto and manual computers?
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Old 07-07-2014, 07:19 PM   #8
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Di you try reseating the connectors on the original ECU?
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Old 07-07-2014, 08:36 PM   #9
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Jerry the auto ecu I tried is the original and what exactly do you mean by reseat? And I plugged my manual ecu into my friends tj and his oil press gauge did not work. So I guess I'll spend the money on a good computer instead of another Craigslist deal for $70
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Old 07-07-2014, 09:46 PM   #10
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So odd that the ECU could work in all other ways except just the oil pressure gauge. Does anyone know the reason why?, and also if the auto ecu and manual ecu would work differently in terms of the oil pressure gauge? Since I have the same issue I would hate to have to buy a new or used ecu just to fix the oil gauge!

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