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PCM fault?

Kilroy08

NAXJA Forum User
Location
DE
I have a 1992 Laredo with the 4.0 and auto trans.Last summer I swapped a new motor in and have been having all sorts of issues from day 1.This is what it does:The cooling fan will not come on when the engine temp goes over 210* F, but it will come on when the A/C clutch cycles.My CB will make the jeep go nuts when I try to talk to someone: misfires, backfires, you name it.This is what I did:Checked my harness, the temp sensor to PCM circuit is fine, as is the PCM to fan relay circuit.Replaced the fan relay, cooling fan, pickup coil, temp sensor, MAP sensor, crank sensor, and put in a rebuilt PCM. None of this changed anything. I pulled the PCM out and opened it up, there is a loose capacitor on the circuit board and where they dug out the dielectric goo to fix the board, it looks like they did a shoddy job patching it up. This could possibly lead to moisture intrusion.I'm leaning towards partially brain dead PCM. Anybody else have any thoughts?
 
Well you don't want a loose capacitor, but you mentioned that you already replaced the computer and it didn't change anything. That would probably rule out the computer, assuming it is the right application.

But if they did a crappy job on fixing the one you bought, you could request a replacement.
 
Well the rebuilt one is a Cardone, and they have been known for shoddy QC. And the old PCM was turning green and funky inside.
 
The engine installer may have left a ground cable or 2 off. That would my first place to look.
 
I am the engine builder AND installer. All grounds were cleaned and checked.


So I guess that rules that out.

You said the CB make the engine go 'hissy fit',...where do you have the CB cables connected? Disconnect them and see if that changes things. What I am saying is, What do the CB and the engine have in common? My feeling is, the CB is drawing too hard in the power that the ECM or other electronics are connected to.
 
The CB is on its own circuit, I put in a seperate fuse block drawing power direct from the battery for any stuff I may want to add in. The ground for that is a body ground, and I'm drawing 10 amps max for the CB.None of these issues were present before the motor swap last summer.The CB stuff is not that big a deal right now, my jeep doesn't need that to function properly to prevent overheating. Just thought I'd mention it since it occured with the rest of my problems.
 
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