NMJeep01

Okay so im replacing my pcm in hopes of fixing a backfiring issue through my intake, first off i believe its the pcm because the cps wires are getting correct voltage its also a brand new cps, second has a new timing chain compression is great and accurate for all six cylinders, fuel pressure is perfect, idles great but the second i hit the gas at all it backfires through the intake and sounds like a popcorn machine. The fly wheel is also perfect, no cracks or bends, and has brand new spark plugs new distributor and new distributor wires, sense all of these things are in check thats why i believe its the pcm, now i was going to get a remanufactured pcm so i went about getting the model # of my pcm and it is 05010397ab this is for a 97 jeep cherokee 4x4 with a manual transmission, i gave the dealership my vin # "1j4fj27f4vl540042" and they had informed me that this pcm is no longer supported by Chrysler and no dealerships in the entire country carry this pcm, so what i was wondering first off sense this one is no longer supported is there a pcm that will interchange with mine and maybe it just has a new model #? If anyone knows about either my problem with the xj and thinks its something other than the pcm please let me know what you think it could be and also if you know much about pcm's and how and know if there is a substitute pcm that i could use for my model, then that would also be very helpful, please feel free to correct me on anything if you think i may be wrong, thanks! Oh yea and the cps is a mopar one.

captainwoot

Not to second guess you...but are you sure the firing order is correct? Fuel pressure stable under load?

Usuall popping though the intake would mean a timing / valve or a lean issue...I have never seen a pcm cause this.
Good luck!

tjwalker

Anything is possible, but at the end of the day, I don't think you are going to find that the computer is the root cause of your backfiring. In my garage, replacing the computer is a "diagnosis of exclusion", meaning every possible other possibility is ruled out by a methodical testing strategy before swapping the computer.

Backfiring through the intake is often caused by an imbalance in fuel/air ratio. I'd test the map sensor for starters as that sensor is directly involved with fuel/air. And be sure that the vacuum line leading to that sensor is pulling good vacuum. That sensor can be tested with a manual and a meter.

Have you verified fuel pressure with a fuel pressure gauge? For a 97, you should have 49 psi, plus or minus 5 psi.

I would also recommend that you put a scan tool on your XJ and monitor all engine management sensors to be sure they are operating within correct parameters before springing for a different computer. Money well spent to have a shop do this if you don't have a scan tool and the knowledge to use it and interpret the data. In one instance, I found a valve issue in the head to be the cause of serious backfiring.

Good luck and keep us updated!

NMJeep01

Thanks for the info, i forgot to include an important part to everything, there is one error code that comes up that normally has to do with the cps or distributor timing, although the distributor is perfectly timed, the cps is also brand new, i have also used two different brand new cps's that were from auto zone so im pretty confident it isn't the cps, also all circuit readouts for the wiring for the cps has come out right. Both the fuel pressure and the each cylinder has the right readouts, in fact very impressive readouts, i had recently put new injectors and this caused for a very impressive readout for fuel pressure, also each cylinder has the correct compression, if it was the map sensor i would think that it would probably show up on an OBDII scan although maybe there is a short in the circuit, i will check it out and give an update, the new pcm should be in on wednesday, and for anyone that may run into the same issue that i did for the pcm being interchangeable i found some info that may be helpful, the pcm that i have is a 05010397ab, as stated in my post, i found out that this one was not produced or available anymore, i ended up talking to a shop in flordia that deals with strictly pcm's they informed that the pcm with the model # 56041274ae is interchangeable for my pcm and also interchangeable with many other pcm's.
Ill put an update on my xj once i try out the new pcm, thanks for the replies and information everyone, every bit helps!

NMJeep01

The map sensor checked out good on all readings both in the OBDII scan and voltage and resistance of the sensor and wiring.

tjwalker

This IS important. Very important. The fact that you have a code and symptoms is not likely a coincidence. How long have you had this code? Did it start before or approximately at the same time that your backfiring symptom began?

What is the exact code number? Need the exact code as with OBD, the devil is definitely in the details.

OBD isn't perfect, but I religiously use any and all codes as a roadmap when troubleshooting. I know you have some new parts installed but your OBD is telling you that something isn't right. Always chase and resolve every code without exception.

salad

Sounds *like* your cam position sensor is toast, let's see what DTC you have!

At any rate I agree the tjwalker, most PCMs are replaced out of frustration and lack of understanding, NOT because thorough and complete troubleshooting points to them as a problem. Your list of things checked is far from complete.

NMJeep01

Thanks for the input guys, what else would you recommend checking? And everything that has to do with the code has been checked out, i believe i checked just about everything that i could possible think of, if there is anything you think i should add to the list than it may be very helpful in finding the problem, the only last thing that i could possible think of is maybe the fuel filter? but then again im getting perfect readings for fuel pressure, im honestly not sure at this point because everything is checking out good, that has anything to do with timing or sensors or basically anything that could cause my backfiring, that last thing i can think of is the pcm, and it is my last thought, i have checked everything that i know of, but maybe i missed something, anything else that i should check just post and let me know, cause the pcm is my last ditch effort.

tjwalker

Post the code! We can't help you without it.

NMJeep01

Hello everyone, i would love to update my status of the jeep to running, running great actually, the pcm fixed my issue and its ran better than ever, thanks everyone for the input it has helped alot, and im hoping this thread helps someone else in the future too!