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New PCM

Ben H

Ben H

NAXJA Forum User
Location
Fresno
I have done all the trouble shooting for a no start/no communication with the PCM. It looks like it needs a new computer. Is it necessary for it to be programmed by a DRBII scan tool or can I program it with a snap on scanner. I ask this because I am 40 miles from the dealership and towing will be very expensive. I have started a couple of other post that relate to my problems. What do you think should I just take it to the dealer and have them fix it? I think its that time. Any input from anyone will be greatly appriciated.
previous thread link: http://www.naxja.org/forum/showthread.php?t=87103

2000xj, 4.0, AW4, ignition rail not distributor.
 
Replaced PCM and got it running. Took it directly from the dealer to a good spot for a little wheeling. When and only when I was wheeling it, it stalled. The symptoms are very similar to an IAC, but that was just replaced and I have troubleshot that sensor. I have a code that says that my new O2 sensor is bad, it is a hard code for a heater circuit. Can an O2 sesnor cause intermittent stalling?
 
I replaced the IAC and the front O2 sensor. Still stalling and now no Check engine light. I drove it about 180 miles today, and it is acting like an absolute turd. Couldnt keep it over 60 up a grade that I usually fly up. No throttle repsonse at all and it overheated 1 time on the grade and 2 times on flat ground with the cruise set. I have replaced the following:
Both O2 sensors twice!
cam sensor
crank sensor
oil pump drive
radiator, hoses, t-stat, and fan clutch
PCM
Flushed all fluids
TPS
IAC twice
MAP
new spark plugs
ASD relay

I am running out of money to fix this thing. I have the thinner head on it as it is a 2000xj, there is no sign of coolant or oil contamination. I have not run a compression test, but other than a cracked head, or blown head gasket, what could cause this sudden power loss? I have checked for vaccm leaks, and a plugged cat. I just dont know where to go next. I hate to be a pest about my junks problems but I am running out of options.

Edit: I also had a huge decrease in MPG. I Got about 160 miles on a tank>
 
Last edited:
Fuel pressure regulator?? Just a guess but your description matches similar symtoms I experienced, and fixed with a new fpr.
 
I will check into that. Do you think that syncing the fuel to the ignition after replacing the oil pump drive was done incorrectly? But it doesnt feel like it is out of time, like when a rotor screws up.
 
Since you've changed so many items, here's one area that certainly can cause poor throttle response: catalytic converter; although a muffler could do it to. I experienced an "no power" symptom like you describe ("couldn't keep it over 60---") as soon as my XJ warmed up. Turned out the tubes in the CAT would deflect and basically cause huge amounts of back pressure, there by reducing the amount of air able to flow through engine--results the same as limited throttle.
 
just blockage of the cat or the cat breaking apart? I tapped on it the other day and heard no rattle in the cat or the muffler. The cat would also cause me to overheat. I will do the backpressure test today. thanks bubba. I am in Santa Maria a lotl, so if you get the urge to wheel hit me up.
 
The flow out of the tail pipe is normal. Little more condensation than I remembered, but not gas or coolant smell. Just clear clean condensation. I took it out for a test drive again today. I payed attention to every little detail.
It is still sluggish, progressively more sluggish as it reached operating temperatures. I noticed about a half second of throttle hesitation occassionally while accelerating from a stop. The bummer of it is that it wanted to stall out at a stop light, just like it does when an IAC is bad. The lack of power and throttle hesitation makes me think it is still sensor related. Possibly the MAP sesnor? I still have no CEL showing. Quite frankly it has been performing poorly since I fixed the forward O2 heater circuit. Maybe a computer reset is in order. Im running in circles and I am so freakin lost.
 
Ben H said:
But it doesnt feel like it is out of time, like when a rotor screws up.
Click to expand...
The computer controlls the timing.

You may try re-indexing the distributor. If the dist. is off one tooth one way or the other, it could be the cause.
 
Hmm. I remember, back when I got my "kolak" header that he sold an O2 sensor, and was adamant that it had to be this particular type, as many people had had problems running off-the-shelf sensors. I actually fried the wires to that sensor and just picked up a bosch from NAPA, which seems to work okay (well I am currently having hesitaion problems, but I don't *think* it's the O2).

I'd hate for you to spend another unnecessary $100, so it may be worth seeing if anyone else chimes in about the O2.

kolak said:
"I always recommend only the genuine Mopar O2 sensors, especially with 1996 and later, OBD II Jeeps. They offer best compatibility. NGK makes the sensors for Mopar, by the way."
Click to expand...
 
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It's not likely that a bad O2 sensor will cause stumbling or stalling. A bad O2 would certainly set a code and check engine light on an OBDII truck.
My CAT didn't rattle when it failed--just the "no power" thing. It didn't hesitate or stall either. But disconnecting the CAT for a test ride doesn't cost anything, and may be your problem.
 
logdog said:
The computer controlls the timing.

You may try re-indexing the distributor. If the dist. is off one tooth one way or the other, it could be the cause.
Click to expand...

that is what I am thinking. It has the coil rail and an oil pump drive/cam sensor in its place. I found it very confusing as to what the correct procedure was to install the oil pump drive. I will hook up the scanner to sync the injectors to the time. I am hoping that this is the issue.
 
I swapped out MAP sensors to double check and still nothing. Kind of weird that it started to run correct after I ran it through a carwash. Later on this morning I gunned it out of an intersection and the intake coughed slightly and the CEL came on. Hooked up the scanner and no codes to be found. There is some wierd mojo going on here. It was running good with the CEL on. After I cleared the CEL it was running poorly again.
 
Ben have you checked the coolant temperature sensor? Its an important one, but I havent, unless i missed it, heard you mention it. Check reference voltage to it, then check resistance cold and hot. Normally this sensor is what your computer uses when in cold starting condition, then upon warming up, hands over the duty to the O2 sensor. Just a thought.
 
Thanks for the heads up on the coolant sensor. You know I havent even given it a thought. I did replace it about 3 months ago when I did my 3 core swap.. I will definately check it out tommorrow.
 
The coolant sensor seems to have been the problem for the sluggish, stalling, and bucking. Got all of my power back. It was a relative new sensor. I will hope to see an improvement in gas mileage. Thanks to all those who threw info this way.

Ben
 
stoked indeed.

Thanks Tim it would have taken me a while to even check that. I didnt think that sensor had that big of an impact on fuel to air mix.
 
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