96 Jeep Cherokee runs fine then rough, then fine

[rockfangd]

could you give me an idea of which numbers should match. Out of all the sets of numbers, 2 sets match. the large number and one of the shorter sets.
I figured if solder joints were so common that I would repair it before I install it to make sure it is not still the same problem.
MAybe I could just try it.
I want to replace the CPS also just to rule it out.

 

[greg92jeepxj]

The original PCM that my '92 jeep was manufactured with had an eight digit service code number with the manufacturer date next to it. I currently have a reman unit that begins with an R followed by seven digits. I only know of one place online that can match the service code number to application and that is Rockauto but I am certain there must be more. I respect you trying to rule out any problems and correct them before hand but I think the first thing is to make certain your wiring harness does not have any short to grounds that will feed back to the PCM and cause an internal short on the PCM's circuit boards. I don't have the correct wiring diagram for your jeep , only a 1992 but there are input and output on the PCM connections that correspond to injectors , ignition coil , sensors for power steering , a/c , courtesy lights , etc.
Basically , with the battery disconnected and PCM unplugged , you can check for continuity with an ohm meter and look for short to grounds with a self powered test light using the wiring harness plugs . It would be best to have the correct diagram . Autozone's website may possibly display this . Once you've declared the wiring ok , I'd say you can try the replacement PCM . If a problem still exists and you want to try your hand at computer repair , then would be a good time. But ask yourself , " if I just checked the wiring harness and it's ok , why is a replacement PCM having the same issues ? " . Start with a good visual inspection of the engine wiring harness and determine if repair is needed . Ohm test and short test is a good idea but first check sensors with jeep running for 5 volt reference and feedback signal to PCM to determine communication between sensors and PCM . Make certain computer safe equiptment is used . A computer safe test light to look for voltage with any wiring that connects to a PCM is imperative and a 10 mega ohm impedance DMM as well . We want to fix problems , not create more. If you feel that the CPS may be causing an intermittant hard/no start , follow the manuals procedure to diagnose a CPS . Before cracking open that PCM , diagnose the jeep first , If there is a problem with the jeeps wiring or component(s) , it will cause a problem to the replacement PCM. It's like putting in a new fuse without fixing the short and blowing out a new fuse , it would accomplish nothing if there is in fact a problem and not found. I realize your trying to find why this problem exists but diagnosing the jeep first before parts swapping will be cheaper.

 

[rockfangd]

Hi all. I have some news.
Today I swapped out the pcm for a used one. Note this morning it did the spell twice before I did the swap.
Tonight I drove it and I noticed 3 things right off the bat
It seems like the engine spins and starts faster
It runs smoother and lights all over seem brighter.
Check engine light did not come on.
I dont know if the first 2 things could be related or not but It definately different.
On drive home it ran good, didnt do the usual, it even seemed to shift smoother. I also notice that it has noticable increase on takeoff and seems to come down to idle smoother when slowing down. I dont know if it is all coincidence or not but I dont often see any noticeable change.
I pray it did resolve the problem but the luck she has had with the jeep just doesnt make me all that hopeful.
I will update this in a week or so unless the problem continues. If it does I will be changing the CKP sensor

 

[greg92jeepxj]

Really happy for you that after so long since this problem began that now you can finally enjoy your jeep that it is running well without fear of a sudden drivability problem . I am as hopeful as you are that all goes well and continues so for good and that the previous problem never returns , just a good running and reliable jeep ! We will probably wonder what the initial cause was for diagnostic purposes but for now I'm with you , let's leave well enough alone and enjoy the jeep in its good running state ! We all know that the less we tamper with the better but if we ever must , let us all tread carefully with our computer safe test equiptment in hand. I agree with you that best thing now is just to drive it and just see how it acts and be happy with it as it is serving you well which is what you waited a long time for . Just curious though , without laying a glove on the jeep , was there any work done on it before this problem began ? Sometimes the littlest things cause problems . Sometimes strange things happen after jump starting another vehicle . Just wondering. But I am sure you'll want to be extra careful that no one causes harm or performs any detrimental acts to your jeep now in its good running state. Well , reall happy for you , good job ! Greg

 

[rockfangd]

Well guys. the run like shit switch is still happening.
The pcm definately did help other things though. Now the ses light doesnt come on anymore, all monitors cleared, Starts easier and runs smoother.
But when you are driving down the road all of a sudden it starts bucking and jerking for about 5 seconds then all good til it does it again. I am going to try the CKP sensor anyway. The jeep runs great other than when the spells occur. nothing else out of the ordinary.
I have to say I am glad that swapping out the pcm was not a waste though.
You know I have to ask in case it could be related. could egr problem cause this ?

 

[greg92jeepxj]

Well , if this were a '89 or older , I would say to check your EGR valve and solenoid but after 1990 , when Chrysler rewrote the book on four wheel drive , for jeeps anyway , the RENIX system disappeared and the EGR along with it. Camshaft dynamics , cylinder head design and compression ratio increase are to thank for that eliminated the need for EGR. So it won't be that but good call since that is a driveability symtem that causes such a hiccup. Cam and crank sensors ought to be checked as per service manual procedure to rule in or out either. Glad it's running better and happy your narrowing it down by process of elimination . I would say check for faulty oil pressure sending switch for intermittant , cannot remember if you did so already . This seems to be something that may be triggering the auto shutdown relay , but again , only a possibility. Intermittant at best. Cam and crank sensors are a better bet. Oil pressure sending switch is less likely though possible.

 

[greg92jeepxj]

Ok , read back a few posts and saw you already addressed the oil pressure switch and wiring , was wondering of the canister purge solenoid ? How did that check out ?

 

[rockfangd]

Where exactly is the solenoid located?
I figured that on the EGR because I figured if it had it I would have addressed it when I have looked at it before

 

[carnuck]

No EGR to worry about. Have you run any GOOD fuel system cleaner? (I use AMSOIL PI) How old are the cap, plugs and wires? IIRC, the MAP sensor is on the side of the throttlebody and not on the firewall anymore (the hose would crack) Have you checked the ground wire isn't loose on the motor or body?

 

[greg92jeepxj]

Where exactly is the solenoid located?
I figured that on the EGR because I figured if it had it I would have addressed it when I have looked at it before

Your canister purge is probably operated by engine vacuum and not an electronic solenoid .
Try disconnecting the hose that comes from the OUT connection on the canister but disconnect it where it goes into the intake and plug it and plug the intake as well . See if you notice any difference in the behavior of the jeep while driving . If this improves the driveability problem your experiencing , then the problem is the vacuum motor on top of the canister. They are usually not serviceable separate so the canister would have to be replaced.

 

[rockfangd]

No EGR to worry about. Have you run any GOOD fuel system cleaner? (I use AMSOIL PI) How old are the cap, plugs and wires? IIRC, the MAP sensor is on the side of the throttlebody and not on the firewall anymore (the hose would crack) Have you checked the ground wire isn't loose on the motor or body?

complete tuneup recently
Have run several treatments
Removed and inspected the hose to the MAP sensor. Good. Map is located on side of TB unit
engine grounds seem to be solid and tight

 

[carnuck]

clean the connections on the coil and look for arcing tracks. Were the plug wires replaced?

 

[rockfangd]

Ok to update this. Today I removed the line from the canister to the intake and capped both ends.
This setup has 2 ports on the canister and a vacumn solenoid seperate with 2 lines and an electrical plug.
I plugged the line that plugs in right by the MAP Sensor.
The lines go, tank line to canister
canister to solenoid.
solenoid to vacumn source. the one I disconnected
Anyway I started the jeep and let it run. About 3 minutes of it running and same thing. IT keeps cycling from stumbling to running good, after about 1 minute it was running like nothing ever happened.
Pulled one code for B1S1 o2 sensor heater which came up yesterday. The 0420 code never came back after replacing the ecm. fuel economy seems better also.
I told her to drive it for 1 week and bring it back with results to what I did today, I honestly have my doubts

 

[greg92jeepxj]

While having success with the PCM swap , this problem is still testing you . Time to test the O2 circuit . Since you are getting a bank 1 error code , the O2 harness to check would be the up stream O2 . With the ignition on and engine off (KOEO) , use a computer safe test light to probe the harness side of the O2 wire . This test light can read positive and negative voltage so must be hooked up accordingly . Test for 12v on the O2 power wire with alligator clip to negative . Test ground wire with alligator clip to positive . The heater circuits (remaining two wires) are checked with alligator clip to negative. If 12 volts , ground and heater circuit are ok , O2 is most likely defective. Strange this code just came up now. I expect with the new PCM that readings will be ok but check wiring harness to O2 sensor for any breaks . We must be sure if wiring is good or not if this problem is intermittant . Possible the O2 is damaged. Don't want to send you to the parts store until we're sure. Using a computer safe test light is the quickest way I know to get those readings and you can back up the 12v reading with a DMM to be sure your getting 12 volts.
Im sure you have a level of diagnostics to some degree or you would not have gotten this far so I'm sure you are well aware to be cautious around computer feedback circuits which is why is I stress to everyone to use computer safe test lights and computer safe dmm's . I wish not to treat anyone like a novice when I know they are not but when these problem test us this way we tend to move too fast and make errors . I have once and it costs me a PCM because I was in too much a rush to finish and get back to work and did not get to the parts store to buy the proper test light. Should have waited until I had more time. I wish to pass on my knowledge through trial and error so someone else will not committed the same. I am not ASE certified but I take my curb side diagnostics serious. Tread careful and always trust yourself first. If I do not have the knowledge to proceed , I will try to get it if in my scope. Last resort is to take it to a mechanic . You know the story there. Some great , some should shine shoes. Wishing best of luck .
Want to see you conquer this too . Greg

 

[rockfangd]

I swear you have been a huge help. Although the problem has not been resolved it helps alot. I am very careful with probing anything. I changed both o2 sensors. B1S1 about 2 years ago, B1S2 about a year ago. B1S1 was bad .B1S2 I replaced in hopes of resolving this issue, and I figured they do get out of range over time. I will check wiring next saturday. I wouldnt be one bit surprised if sensor was bad again. I wouldnt be surprised if the vibration from all of this issues may have damaged it

 

[greg92jeepxj]

Thanks for your kind words brother . I , like you , just would like to see your jeep run again as it should . I tend to take these diagnostic things a bit personal since I take an interest in them and also like to learn from them as anyone does. I trust myself before a mechanic as I have gone the extra mile when I can when they don't wish to devote the time. You know they cannot through no fault of their own , the boss wants all the cars done . I just got one at a time. I try never to throw my hands up and admit defeat but always hope to come back another day rearmed with a new plan. You know this problem your having is right under your nose and you will find it . I hate the time it takes , winter closing in , but when all is done and done right , it's a great , warm feeling to know you did it yourself but most important you did it right ! You'll bust it , I know you will . Sorry it takes so long. Glad you got sense others don't when taking care to not wreck something while trying to fix something. Glad to hear it. If you can keep your head and not get overwhelmed , your a better man than me. But I'll keep trying .

 

[rockfangd]

Ok so I will be replacing the o2 sensor thursday. I have asked her on 3 occasions since I plugged the vacumn to the purge valve and all 3 times her response was the same. She said the problem still occurs but it is not nearly as bad as it was before. I guess I will find out after the o2 sensor is done. At least there arent any other codes/ Thanks all

 

[rockfangd]

Ok guys wonderful news.
o2 sensor replaced, light went out same day, hasnt come back on. runs good without spell, passed NYSI yesterday.
So there was 2 problems, 1 being the pcm, once I swapped out the pcm and the light came on for the o2 sensor I knew where to go with it.
I will say I am not one to just change parts and this is one of the extremely rare cases I have had that the pcm made a difference. I imagine fuel economy is better now. Thank you all for your help. I cannot wait to contribute all I can to help our fellow members. Happy Holidays

 

[greg92jeepxj]

Really happy to hear you beat this one down ! The great news is that you only had to change what parts were really necessary and did some really good diagnosing ! Makes you feel good when you knock something out the right way , systematically . Job well done and your contributions will always be welcome . Really glad everything worked out and will always look forward to your experience and assistance . Good job ! Greg

 

[griffo]

my son in law has a 96 Cherokee that died up the beach we fitted a new crank sensor and a new coil it ran fine for about ten minutes than it died again anyway to cut a long story short it was toed back to my house and sat in the yard for a few weeks then i got my mate around hes an auto electy to check the sensor but it was fine then he noticed the brand new coil was not working so we plugged in the old one and it started straight up.i ran the car at idle for about ten mins and then took it for a run were it back fired and died on the side of the road again so then i wiggled the wire going into the coil and it started.that i then got some zippy ties and firmed up the wire harness to the coil and we have not had a problem since try that it worked for us hope this helps griffo .