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Screwed Up PCM...I Think

C

CMK4425

NAXJA Forum User
Location
Baton Rouge, LA
I was changing out my battery terminals and when I went to start it it all went south. I turned the key to the on position and the fuel pump turned on like normal but also the electric fan started turning on and off, and the a/c compressor clutch started clicking on and off, also the check engine light came on. I hooked up my code reader and it didn't show any codes. It wouldn't start either just turn over. I unplugged the PCM and turned on the key and it was normal. Anybody know if the PCM is screwed? Can it be repaired or just replaced? Does a 1998 and a 2001 PCM interchange?:bawl::bawl:
 
98 and 01 will not interchange... sorry to be the bearer of bad news.

That being said this sounds like you probably have an intermittent connection, not a bad ECU. You never connected the battery up backwards did you? How did you make the connections for the new terminals?
 
I used the enamel coated terminals from Oreilly Auto with the screw down connection where the wire gets smushed down. And by backwards do you mean positive to negative or negative first then positive? I ask because I read about power surges from hooking positive up second.
 
there will be no power surges either way... either one completes the circuit the same. I was talking more about accidentally hooking the positive to the frame and the negative to the electrical system, that can fry all sorts of expensive things.

Those screw down connections really aren't that great, I have seen multiple vehicles with horrible electrical gremlins from them. In fact a friend of mine with a 92 XJ couldn't get the damn thing to stop dying on him and thought it was the NSS, he thought I was a magician when I opened the hood, touched the battery terminal, and it came back to life.

I use the big copper crimp-on terminals (you need a hydro crimper to do them properly, though they can be done in other creative ways... just not the usual "mash it with pliers" method) and solid brass terminals with a wing nut and a stud. Never had a single problem with that setup.
 
No battery has been hooked up correctly since I have owned it. I might go pick up some of the marine style terminals and copper lugs tomorrow. Could a bad battery cause this issue? My battery seems to drain pretty quick. Thanks for the input.
 
bad battery could definitely cause it - without a good battery there, the voltage will fluctuate a lot as the alternator field coil cycles on and off (controlled by the ECU.) I'd bet on either that or the terminals, but probably the terminals.
 
If it is not the battery, I would suspect the wiring at the ignition switch and the ignition switch itself are fried, melted, shot, at least if it was an older jeep I would. Not sure if the 2000 solved the the weak wires and switch problems the earlier XJs had. I would also suspect a bad battery ground post, or busted battery post internally to the battery. Check the cranking voltage at the battery, if it is under 10 Volts the battery is toast. Check the starter ground for less than 1 ohm, if it is higher than 1 ohm the starter current may be back feeding into other devices, acting like ghosts turning stuff on and off.
 
Cool I am going to swap out the terminals and get the battery checked. I really like these terminals but they will have to order them
tz620.jpg
 
Where and how does the cable attach?

CMK4425 said:
Cool I am going to swap out the terminals and get the battery checked. I really like these terminals but they will have to order them
tz620.jpg
Click to expand...
 
I have those terminals. They are great, they came with my 1 guage primary wire upgrade. You can add as much extra stuff as you want, I have the starter, PCM, amps, winch and upgraded headlight harness. They are called military terminals I believe.
 
Are you sure the wires are not bad. I upgraded mine because they were corroded inside the jacket. Just putting new ends on might not fix it if they are really bad.
 
What year is the jeep you're working on? As for the ecu interchange, The 2001 ecu is a Jtec+ with 3 coil drivers (waste spark) so if you reflashed it with a 99 calibration (Jtec+) it would run a 98, but since the 98 is a Jtec with only 1 coil driver (distributor) it won't run the 2001 motor.
 
I have those wing nut terminals from A-zone.

The negative had to be reamed out some because it wouldn't fully seat on the battery post.

Kept hitting my hood when shut.
 
I am not impressed with the surface area, contact area on that bolt/nut set up at all. I prefer the brass ones where I can lay the loose wire out flat over a larger surface area.
 
I have some of those brass ones but apparently need to spread or ream them significantly to fit on a normal battery post, so they're still in my junk box until i can find some more tools that aren't extortionately expensive. The reamer I have won't cut the brass and I don't have a spreader tool.
 
sidewaysstarion said:
What year is the jeep you're working on? As for the ecu interchange, The 2001 ecu is a Jtec+ with 3 coil drivers (waste spark) so if you reflashed it with a 99 calibration (Jtec+) it would run a 98, but since the 98 is a Jtec with only 1 coil driver (distributor) it won't run the 2001 motor.
Click to expand...

Side question, since you seem knowledgable in these things: can I get a 98 5.9 zj ecu reflashed to be a 98 5.9 dodge 2500 MT ecu? Or is that completely impossible?
 
Yes you can, Physically the ecu's look different because one is a Motorola Jtec and the other is a Huntsville Jtec. The hardware is physically different but the software that runs them in the same. So what you need to do is change the part number of the ECU, flash in the calibration for the 2500 5.9 MT and set the VIN to match the VIN on the 2500.
 
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