97 jeep grand cherokee problems

[Kj413]

This jeep is the straight 6, 4.0 motor. All of a sudden, at 1500rpm, the motor started to fumble or miss and the tach jumps to 2000 then back down. Did a full tune up, distributor cap (which had a hole in it), rotor, distributor switch plate, throttle position sensor & ignition coil. Still fumbles and sounds even worse now. Guy at parts store says it might be computer. The check engine light is not on. Any suggestions or anyone have this issue before? Jeep has 204,000 miles on it and runs great if not at 1500rpm. No loss of power at all.


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[greg92jeepxj]

Welcome to Jeepz.com . Thank you for your post . I,will try to address this with some ideas but have not had this problem . Hoping someone who has can add . No check engine could be good or bad . You may or may not have a computer related symptom. We always stress to,start simple like clean all electrical . Battery terminals , chassis grounds , starter connections , O2 and PCM grounds , etc. . If any glitches are caused by dirty or corroded connections , you can diagnose every sensor or part on the jeep and still it find the cause simply because everything continues to be a suspect. This is general maintenance but in this case , a good start to eliminate bad connections as a possibility. If 5 volts reference is found at a sensor , say the TPS , the PCM is likely good and signal feedback to PCM Is normal then things like a dirty idle air control motor or vacuum leak can be liked for. There are emmissions items that cause rough idle or stalling but first these items ought to be check to rule them out before moving on. This is a good start but yes , if anyone has ever had the same symptoms , there post will be helpful.

 

[Kj413]

Thanks! ok, it finally threw a code. it's P0443 and the explanation is: P0443 Jeep EVAP Purge Control Circuit OBDII Engine Light Trouble Code | Engine-Codes.com. i'm really hoping it's the purge solenoid and an easy fix. I really don't want to buy a computer for it. Any have this issue before?

 

[SteelHeadz]

It's possible that the purge solenoid is causing the issue. Theoretically, if the purge solenoid stays open or intermittently opens, it's a vacuum leak... There's still a multitude of possible scenarios like what Greg92jeepxj has mentioned. Since there is a logged failure to that purge solenoid, check the connections and vacuum lines attached to it. If it checks out good, replace the solenoid and retest.

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[Kj413]

It's possible that the purge solenoid is causing the issue. Theoretically, if the purge solenoid stays open or intermittently opens, it's a vacuum leak... There's still a multitude of possible scenarios like what Greg92jeepxj has mentioned. Since there is a logged failure to that purge solenoid, check the connections and vacuum lines attached to it. If it checks out good, replace the solenoid and retest.

thanks for the info. ok, doesn't look like any connections, hoses or wires are compromised. put a new solenoid on it and still doesn't run right. we tested the solenoid connector, it has power on the positive side, but on the ground side, there is no power. hooked the ground directly to battery and could finally hear the solenoid working/clicking, but still missing when running. starting to think it's the PCM. :roll:

 

[greg92jeepxj]

Just want to say , yes , your on to something and I believe your correct . Good diagnostics work on your part:shades: . As you may know , the PCM grounds the solenoid as it does all solenoids , I.E. , fuel injectors , power is always supplied steady on when ignition is on but PCM decides when to activate the solenoid by applying ground. Well , theory aside , having once dealt with this issue on an auto , EGR solenoid would not ground and scan tool showed "off" at all rpms and under load. It seems that your next check should be PCM diagnostics IMO , what say all ? It's sad that a PCM is to be condemned for one error , but I say a complete scan . A diagnostics session on the treadmill ( as I call it) would confirm this but pricey $$. Guess we'll have to settle for a hand held scanner ?

 

[Kj413]

Ok, I will have my buddy scan today and see what I get. Thanks for all the help, will report later.


Kj

 

[Kj413]

Well, I ordered a new computer and it won't be here for a week. The wait continues.


Kj

 

[greg92jeepxj]

Guess we'll hear more of the verdict in terms of what fault(s) were found when the replacement PCM arrives. I've replaced ecm's before but when the sequential port fuel injection systems were being introduced on production vehicles starting in the '90's , faults were rare to my knowledge on PCM's
unless someone "spiked " an electrical component that fed back to the PCM , I.E. , relays or solenoids or even improper jump start or charging , PCM swap is not too common. PCM's and the former ecm were supposed to be durable and last the life of the vehicle. I'd still have my original in my '92 if I didn't (stupidly) use a 12 volt test light on a relay circuit that fed back to the PCM and cause a "spike". Computer safe test lights are always safe to use on most circuits except for high amperage circuits such as starter or alternator. It only takes a quarter of a volt to power the diode in the computer safe tester therefore eliminating the threat of over draw . Everyone who does their own diagnostics ought to own one of these Jim dandy items to grace their tool box.
There use to be a procedure to check via an ohm test of the harness connections to the ecm's ( battery disconnected) to verify proper resistance of a computer circuit such as a sensor.
I haven't done one to a PCM equipped vehicle but there should be one for these.
I usually verify continuity but this isn't enough as you'll want to be certain there is no short to ground which most certainly cause damage to sensitive internal components of the PCM and or its PROM , EPROM or EEPROM chip ( depending on model year). I suppose you can get away with using a self powered test light ( battery & PCM disconnected) on the PCM harness if the correct printed procedure is available but this is highly technical and of course better left to a certified tech of course . We diyer's can pull it off if careful and possess the documentation procedure but self confidence must be assured. Why do I mention all this ? As I stated , PCM's just don't wear out or just blow like a fuse , something "spikes" them , like an over current . Don't want to frighten or cause doubt at this stage but I'm certain your aware of electrical parts policy with regards to return and exchange . While I don't think you'll run into any problems since the jeep can start and run with the existing PCM , there is likely no problems in any harness or sensor that can cause damage to the PCM but always good to be sure so diagnostically a good idea to check.
Trusting that the scan taken produced readable results which are helpful to diagnosing PCM health and vehicle electrical to some degree. As long as you and your assistant are confident that it is likely that no vehicle wiring that feeds back to the PCM has been tampered with thereby compromised , trusting the PCM swap,will go well. I personally get too cautious around computer circuits since from experience I ( just that once ) shorted the regulator circuit in the PCM of my jeep and caused low output to charging and ignition system . I also found only a few years ago a poorly repaired dash wiring job of the blower resister circuit that the a/c thermostat was bundled with that fed back to the PCM that was probably not helpful. Repaired those and eliminated that possibility . This is grief waiting to surface but if at all possible , please at least check if any wiring does in fact short to ground that shouldn't. A wiring diagram is an asset but I believe none of the actual wiring from the PCM should ground except the PCM ground itself which ought to be found with the O2 ground and battery negative ( usually). Solenoids that are grounded by PCM are done internally to the PCM ground but won't show up on a test light procedure since the PCM isn't actually grounding it as the vehicle isn't running. Sensors don't run with the vehicles continuos ground circuit , they only feed back to PCM except for a battery powered circuit. Internal drivers handle the switching . Just simply note any wire that may ground and research later . Use the ground connection that the PCM actually uses since it's native to the PCM. Don't use battery - or body ground . Realizing this post is a long , lengthy lullaby but I have learned to question why did the PCM fail and would not want the replacement to as well. If anyone has a simpler approach , I welcome it but this method was used by me when I did my jeep several moons ago and with the help of a wiring diagram it worked for me . Hope this serves to help . Greg

 

[Kj413]

ok, so my remanufactured PCM came in, we put it in and could tell right away that the purge solenoid was working. it wasn't with the other pcm, so we know it wasn't sending the signal. not sure why the old pcm failed cuz it happened out of nowhere, while i was driving. well, when i tried to start jeep with "new" pcm, it would start, then die, like there's no fuel pressure. tried this numerous times with the same result, it would not stay running, but the solenoid was working properly now. so we put the old pcm back in, jeep starts right up, but still has problem with sending signal to solenoid. so at least i know now that it was the pcm. sending the one i bought back and going to a junk yard to see if i can find one. if not, guess i'll be forced to buy new. the saga continues.

 

[greg92jeepxj]

Happy that the uncovered fault was cured but as I once found out that the wrong service number which results in the wrong application for engine management and so forth is most likely the problem . If the replacement PCM service number matches the I guess we can say its just a dud.
Sorry your dealing with this the hard way and I realize your well aware of the faults and remedies and doing really well diagnostic wise but this is really getting testing , isn't it !
I just hope this will not cost a mint to correct this problem. Like you , it still has me wondering what caused the fault but at this stage , one step at a time. I'm sure you've done the best visual inspection of wiring and all entailed . We appreciate your posts as your hard work will help another member that may encounter this fault but sorry the it's somewhat grueling .
Looking forward to your posts as we all whom are following this thread and most certainly wishing you well. Greg

 

[Kj413]

ok, so totally frustrated here. the new computer fixed the problem with the purge solenoid but still having the main issue of fumbling or misfiring and the tach jumping. it's really weird cuz it was fine at 35mph, but started messing up at 50mph. going to just take it into a shop and see if they can figure it out. if not, it's going up for sale or to the scrap yard. so over it!!

 

[greg92jeepxj]

I'm feeling bad that your so upset , can't really blame you though. Computers do that to us.
Praying that this works out big time , hate to see you lose a nice jeep. It seems that more scanning is in order to see how the PCM is viewing feedback from the sensors and its output as well. I agree , this isn't making sense how the original worked fine save for the purge solenoid control. Now a replacement won't even run it right. Hoping a salvage yard has a good PCM that matches your service code . I think you must feel at this point that a used PCM will do better than a Reman unit. Just wondering if anyone in our forum may have a good PCM for you. Wish I did , I'd gladly give it to you rather than see you lose your jeep........

 

[Kj413]

I called all of our local salvage yards and can't find one jeep! That's why I had to buy a reman one. Gonna try a few more things on it tomorrow and see what happens. I'd gladly take some TNT if you have any! LOL!


Kj

 

[greg92jeepxj]

Begging you not to give up because of the PCM . I'm sure you got a real nice jeep. I think its time we put the word out on our forum if anyone has got a factory unit that's in good shape. But the scan session is a must. No TNT , even if Independence Day is approaching ! Please !

 

[Kj413]

I really do love this jeep. It's super clean and runs great except for that one glitch. It has 204,000 miles on it but had tons of people tell me the motor is the best one jeep made. This is the luck I have with any vehicle, though. If all else fails, taking it to a shop.


Kj

 

[greg92jeepxj]

Not going to stop praying for you ( and your jeep ) , I like things to work if there is hope. Assuming the jeep ran fine for the most part ( except for the purge solenoid ) , I would hope the wiring harness under the hood is in good shape and no shorts but the scan readings will help viewing what the PCM is doing or not. Almost sounds like the knock sensor is not doing its thing but you did not say there was any pinging. I can make a list of sensor glitches but the scan reading will have to confirm. I know something about luck with vehicles. Just would yet want you to give up on yours. Super clean jeeps of that era are a rare commodity around here.

 

[Kj413]

Ya know, when we bought it, it had a ticking until it warmed up. Whoever had it took great care of it. Would live to drive it for years if it will let me! Off to bed. Will update later. Thanks


Kj

 

[Kj413]

Just a few pics of her before I go to bed. Lol


Kj

 

[greg92jeepxj]

View attachment 19668View attachment 19669View attachment 19670
Just a few pics of her before I go to bed. Lol


Kj

Oh , she's a beauty ! Live on you beautiful ZJ ! Woman always pick the good one ! Birds of a feather I guess .
Yeah , bed time . Leave it to me to rob a woman of her beauty sleep. Just didn't want you to pull any locks out over it. Tomorrow is another day , another plan of attack. Well , nite nite and pleasant jeep dreams . Lol