Jeep Cherokee Grand Cherokee Engine and Performance Problems



  • lunghdlunghd Member Posts: 61
    Flex in motor was allowing the CPS to be shorted out & causing the ECU / engine to lose timing. CPS is a very, very common issue for these engines. Someone must have had this motor out in the past & not torqued it back correctly.
    Flexplate bolts coming loose are a common problem but not the motor to tranny bolts.

    Motor & tranny mounts are ready to be replaced after that many years... not too hard of a job and there are alternatives to the stock mounts.

    For a detailed "how to" on changing the mounts you can check out my On-Site Tech index at Another Freakin' Jeep Cherokee Website
  • lundelllundell Member Posts: 6
    well i removed the valve cover and none of the springs are bad it looks like it is all going like it should but on second cylinder back the clank is going with the second valve from the front on on the cylinder it is the only one that goes with the clank so are you still sure that it could be the flexplate bolts being loose and to be honest i am really not quite sure what you said like i dont know what the CPS is or the ECU or Flexplate. i am only sixteen so i am not sure what it all is but i have some clue to what is what but if i ever get this fixed i would like to learn more about you cheap lift kit that you did on that jeep of yours i think that is perfect for me if i get through this prob
  • lunghdlunghd Member Posts: 61
    Ok - I think I missed a few posts along the way but let me see if I am following you... Sounds like a hammer on the inside of the engine?

    This sound goes along with just one of the #2 cylinder's valves? If it is ONLY following ONE of the two valves is is more than likely a stuck lifter and not so bad... could also be a leaking exhaust manifold gasket...

    Hammer-like sounds imply a bad rod bearing. If it is a seriously solid 'CLANK / KNOCK' sound then it is likely to be a bad rod bearing or piston pin. It's hard for me to tell based on what you've described above so let's try this:

    Does it become more pronounced at higher revs?
    Does it get worse or diminish as the engine gets warmed up?
    Is it a solid 'clank/knock' or more of a 'tick/tap' sound?
    If you have an oil pressure guage... what's your pressure cold / hot? (Don't run it to get hot if it's really bad.)

    If it is more of a 'tick/tap' sound then you can try running some Marvel Mystery Oil in your engine oil plus a small amount mixed with your gas as well. (Just follow the label directions.) Marvel Mystery Oil is a great product - been around for ages & will help loosen a stuck lifter / valve. I had a stuck lifter on my 90 XJ when I got it about 7 years ago and a few weeks of running this freed it up never to get stuck again. It may take a couple of times using it with your oil changes to free up a badly stuck lifter. If your lifter has collapsed completely it will not fix it... Post back & we'll go from there!
  • lundelllundell Member Posts: 6
    ok yeah you have read what all that i have put

    It stays the same with higher reves but they are more constant with the motor , But i just started it today and it wasn't as loud of a tap now it is more like a combination wrench is being hit on the inside not a hammer
    And it starts go away at about 1 and 3/4 rpm but by 2 it is gone and when it hits three it starts to have this kind of whining sound and i haven't gone above that
    and the pressure gauge is at about 60
  • lunghdlunghd Member Posts: 61
    Sounds like a combination wrench? :P ( A ratchet??? ) I think I get ya. If I'm not understanding - please correct me!

    " SOUNDS LIKE " a sticky lifter but get a second opinion from an old neighborhood wrench you may know just to be sure.

    Assuming it's a sticky lifter: IE, if it's NOT a hammering/knocking sound that has a deeper sound... but is more like a ticking / tapping then try the Marvel Mystery Oil per directions on the bottle.

    SO LONG AS THE ENGINE ISN'T ACTUALLY KNOCKING... run it a few weeks, change the oil & filter & do the Marvel Mystery Oil thing again. You may have to repeat this again but it usually clears it up in a few weeks of running the motor.

    I did this a few times & it cleared up my sticky lifter. MMO is great stuff - glorified tranny fluid but does the trick!

    If your oil has been neglected in prior years the MMO will cause the oil to get dirty faster as it loosens up the varnish build up so be prepared to change the oil a few times in the next few months depending on your miles driven.

    AGAIN - if you have a knocking rod... this is NOT the way to fix it! Get that second opinion from a friend or neighborhood wrench...


    Link to my site:
    Another Freakin' Jeep Cherokee Website
  • lundelllundell Member Posts: 6
    when i said combination wrench i mean the wrenches that have a box on one side and then an open end on the other

    And for this MMO i have to drain the oil in it now put that in and then just run that and you think that it will stop and if it doesn't just change the filter and do it again

    But i will still go ask someone that knows what they are talking about also and if he thinks it is a sticky lifter i will try it
    but i will get back to you and tell you what he says and the prob might get figured out
    thanks a bunch for given some knowledge this way most people would just say what ever
  • lunghdlunghd Member Posts: 61
    Glad to help if I can! Just hope I can save you some $ with a cheap fix instead of having to open the motor up.

    Yes, definitely get that second opinion on the sound just to be sure. The sound you're describing sounds more of a metalic 'tank' sound, like a wrench striking the block than the 'tick-tick'tick' a lifter makes. Lifters can be pretty noisy - pushrod can be flopping around a bit if it's fully collapsed (which MMO will not fix...).

    No, you don't have to drain the oil now unless it's already past time to change it.

    Get that second opinion on the sound first... but if it's a lifter you just add the MMO to your oil now & run it until your oil change is due... THEN change it. It's all on the bottle.

    If you still have a sticky lifter, add it again. In my case it only took a couple of times adding it and no problem since.

    Again... have that noise confirmed as a bad lifter first.
  • ehuffehuff Member Posts: 4
    Thanks again. I'm out of town until Sunday but I'll be checking this out as soon as I return home.
  • jeepdramasjeepdramas Member Posts: 2

    my 4.0L jeep is running quite hot when idling (almost three quarters on dash) and stops going up when the AUX fan comes on. why won't it come on earlier? and when in motion drops down to under half (100 deg cel.). i changed the thermostate and flushed the radiator. i live in a hot climate is it just the radiator is to small for my missions.? or maybe this relay switch i read about. where do i find? is it a big job??
  • jeepdramasjeepdramas Member Posts: 2

    could be wheel bearing or hub. if you swerve the steering wheel back and forth like a mad man dose the noise come and go?
  • patdowerpatdower Member Posts: 11
    when i start my Jeep the oil pressure is a little lower than normal, as it warms the pressure drops, eventually to zero and the check guages light comes on. When I accelerate the check guages light shuts off and the pressure rises slightly, only a little bit! I have plenty of oil, and I had it changed 3000 miles ago. What is my Jeeps problem?
  • dsmansdsmans Member Posts: 10
    I have a 2000 Jeep GC and have just experienced the same problem. Today was the first time it dropped to zero however, and the check guages indicator came on. I was told before from Valvoline that a wire was off and they put it on, but the sending unit will have to replaced eventually if the problem persists. I will have to have the dealer confirm this week.
  • dsmansdsmans Member Posts: 10
    Ok, this is dsmans again. First I want to thank all that have commented on this particular problem.

    On 2/18 I wrote I had experienced the sensor problem. Since then, I have bought it to the dealer. They had the car all day and I called at 4:30 that aftrnoon only to find out that the sensor was checking out fine and that I had no pressure. What they then told me is the next step is to drop the pan and go in and assess the damage my engine has suffered. The beginning price to drop the pan began at $483. Secondly, most likely I was looking at getting a new engine. I said stop right there, I'll come pick it up and get a second opinion. After reading the comments here, I realized that my engine is fine, my oil is clear, I have no knocks, pings, or smoking, car running hot et al. I bought it to a AAA rated local autoshop and they replaced the sensor and the pressure was reading where it should be after idling. If it does go down again, they suggested, as long as the engine is fine, not to worry about it too much. I'd spend more trying to find out what the problem is.
  • jeeptsijeeptsi Member Posts: 8
    I have the same exact problem with my 97 tsi. I replaced the cap, rotor, crank position sensor, cam position sensor, fuel pump, sparkplug wires, sparkplugs, ignition coil 2 times, air filter, motor mounts and it still giving me the same problem.
  • jerry50jerry50 Member Posts: 6
    I have a 1995 6 cyc w 145k miles and had wide swings in oil pressure when driving and at idle. Pressure sensor internal membrane had tear and needed replacement, now working fine. Oil pressure test at 3k rpm's was fine but at idle was lower then factory spec, meaning some internal oil passage blockage. My mechanic recommended running some oil cleaner/flush thru engine before next oil change to dislodge internal debris which happens in every engine. Once a year this is what he recommends as routine way to keep clean.
  • rinomcbrinomcb Member Posts: 1
    So my oil pressure gauge on my '95 GC was doing much the same as many have posted here. Now I've replaced the sensor and my oil pressure gauge is reading zero - all the time! Do I need to reset a computer or something? Please advise.
  • cpb2cpb2 Member Posts: 6
    I have a 98 Jeep Cherokee 4.0L with about 85K miles on it. After starting normally, it runs and drives normally for about a minute, then it starts to misfire and won’t handle a load for about 45 seconds. After that, it drives fine until I shut it off. The problem happens even when the engine is fully warmed up, if there is a 15 minute or so cooldown period. If I stop enroute, say for gas, no problem. When the problem is occurring, I can rev the engine OK (manual trans), but cannot load the engine until it “clears”. If I watch the RPMs when I first start the engine and just let it idle, you can see the change from about smooth 1000 RPM to an erratic 250-750 RPM, then a surge to about 1200 RPM back to a smooth 750-1000 RPMs again. Almost seems like a timer-based mixture change or failed sensor bypass. If I attempt to “drive through it” there’s often a backfire-like sound under hood. My usual trips are very short, less than a mile, 3 or 4 times a day. I’ve run some fuel injector cleaner through it and changed the coolant, replaced rotor, distributor cap and wires, but that’s about it. Although I’m not a trained mechanic, based on symptoms, I think I may have ruled out coolant temp sensor and throttle position sensor. Any ideas before I submit to the mercy of the dealer? Thanks in advance!
  • tidestertidester Member Posts: 10,059
    You may also want to check out Grand Cherokee Shuts Off While Moving.

    tidester, host
    SUVs and Smart Shopper
  • daniemudaniemu Member Posts: 1
    I have a 1995 Jeep Grand Cherokee and yesterday the check engine light came on. I didn't notice any change in how the vehicle was running (the temperature and oil gauges were fine). I stopped at a shop to get it checked out, but wasn't able to get in. When I got back in my car, it didn't come on the rest of the way home. I wasn't sure if I should take it in, or if this was possibly a fluke.
  • jdchjdch Member Posts: 1
    When I start my 98 Cherokee, the check gauges light comes back on as there is about a 20sec delay before my oil pressure gauge begins to read any pressure. It used to begin reading immediately along with all the other gauges. This behaviour began after my last oil change. Once it begins reading I have normal pressures of 40-50 at speed and as low as 15-20 (warmed up) when idling. What would cause this delay and should I be concerned?
  • lvgm250lvgm250 Member Posts: 2
    Hi, Did you find out what the problem is? My Jeep is doing the same thing, it's also a 98. I have replaced the distributor cap, spark plugs, crank shaft position sensor, fuel injectors, fuel pump, fuel filters, fuel pressure regulator, and I cannot figure out what the problem is. It is still acting up. Please let me know if you find out. Also, my check engine light is not on and so I cannot get a diagnostic reading and the dealer says that it wouldn't be a computer problem or O2 sensor/catalytic converter issue if my check engine light isn't on. The dealer wants to charge alot to even look at it, just wanted to check and see if you could help me out or if anyone else has any suggestions. Thanks.
  • jeepowner1jeepowner1 Member Posts: 2
    Hey, have you found the answer to this problem yet! I have the same issues with my 96'GC, I've replaced the same parts as you. I do get a trouble light from the Crank shaft position sensor. It reads out a intermitant reading of piston 1. I also have violent back fires ever so often. Think I may have to replace my PCM.
  • cpb2cpb2 Member Posts: 6
    not fixed yet, but I have not invested any time or money yet; hoping for forum help, too. Like yours, no check engine light or diagnostic codes are set on mine. I don't see the cam position sensor on your list. I seem to recall my problem showing up about the same time I replaced the plug wires/dist cap and rotor. That was prompted by noticing arcing from plug wires after washing engine. Problem seems to be worse in the rain. Wonder if I got something wet or damaged a weatherseal?
    Mine does not die completely like the Grand Cherokee thread recommended by the host. Will keep forum posted if I succeeed.
  • smcgill10smcgill10 Member Posts: 2
    I have had a couple of problems with my jeep lately. Not sure if they are related or not. First, when starting sometimes it would sputter and miss, once i get on the road and get it enough gas it was fine. Well the other day it started and the check engine light came on. I drove it for about 15 min and the check gages light also come on, it was overheating. We changed the spark plugs and deleted the ODBII codes po300, po302, po305. Now check engine light is off and has not failed to start properly. Now it overheats at idle, the fan is on but seems to be spinning slowly. Sorry for such a long post!! Please Help!!
  • tuggajbtuggajb Member Posts: 646
    what engine codes are all eng misfire have you done any work on it?
    fan could be fan clutch bad
  • smcgill10smcgill10 Member Posts: 2
    The code po300 is misfire on random cylinders, po302 and po305 are the number of the cylinder. The only work i have done is change spark plugs and erase those 3 codes. By the way i have the 4.0 I6. Also, it doesn't seem to overheat evertime i drive it.
  • tuggajbtuggajb Member Posts: 646
    fan cluch could be on again of again first thing i would change is crank pos sencer if that is not working right would throw off timing and could cause overheating and miss fires
  • cmbmbspscmbmbsps Member Posts: 2
    Well, I bought a 1990 Jeep Cherokee just 2 Days ago. It's Automatic Transmission, 6 Cylinder Inline Engine 4 wheel drive. The previous owner told me he had just replaced the water pump and thermostat, but didn't mention anything about an overheating problem. When We got it home I did a complete tune up, changed all the fluids and filters and such. I noticed, after the drive home, that there was water in the coolant reservoir. I figured that it was just becuase he had replaced the water pump, and thermostat, and wasn't wanting to waste coolant. After we had finished our tune up, we took it on a drive to see how it was doing. It drove just fine for 15 minutes, and started to heat up gradually until it was in the red. We pulled over, waited for a bit, and drove to a mechanic. He told us that because it was a closed system, it's very easy to get a bubble in it, and that it doesn't work to just fill up the reservoir. So, we unplugged the heat sensor in the back of the engine, and took off the main radiator hose. We filled up the Radiator with coolant, directly through the hose until we had a steady stream of coolant coming out of the back of the engine, where the heat sensor was. We than filled the reservoir up, and let her run. After about 5 minutes of idleing, the reservoir had emptied some, and so we filled it a little past half way to complete, and we figured the bubble was gone, and our overheating problems were over. a 25 minute drive around town confirmed that. However, we drove it a distance of around 65-70 miles last night to be able to get home, and it did just fine until we got about 10 to 15 miles from the destination and it started to over heat again. We pulled over, and it spued coolant all over the place. So, in the end, something's wrong. So, to finish off, just some last things I noticed..... 1.) We found a pinched radiator line that goes back to the transmission (it appears the transmission is cooled by the coolant as well???) 2.) When it gets hot, the coolant seems to bubble back into the reservoir,and is usually boiling inside the reservoir. 3.) The coolant seems to be a rusty brown color whenever it overheats. However, it was a lot less rusty the second time. I have a feeling that it is just a bad, corroded Radiator. But, I just don't know. I want to change from a closed, to an open system, and don't know I sure would appreciate any help. Thanks!!!
  • rnadeaurnadeau Member Posts: 1
    I am replying because I have the same problem you are talking about. I have a 2000 jeep striaght six and replaced oil sending unit and finally oil pump which was very expensive and I still have the problem. I am looking for any suggestions or solutions. I was also having a problem with loosing radiator fluid. Thanks, Rick.
  • poconojeeppoconojeep Member Posts: 4
    I took mine to a dealer about a month ago. It also needed some other work, but I wanted to make sure that there was nothing seriously wrong engine wise before shelling out money for a new radiator and new battery. They were sure the problem was the sensor. So after paying $900 for the sensor, radiator, and battery I drove home only to discover the problem hadn't been fixed. When I took it back the next week they told me the problem was in the engine and quoted me $5000 to replace it, which obviously I wasn't going to do. My Solution: I'm trading it in and leasing a new Nissan XTerra. They gave me $3000 for the trade. Too bad I owe $6000. My guess is the engine they were putting in Cherokees and Grand Cherokees of this era was a complete piece of crap.
  • jeeptsijeeptsi Member Posts: 8
    I changed the pcm (engine control module). My mechanic advised that he got another jeep into his shop and was advised that the jeep would run if the center connection of his pcm was held up. seems that the connection would loosen up and cause the jeep to idle rough and then shut off. he advised that the circuit board in the pcm may be cracked and changed it. so far it's running great now. you can get a refurbished unit for $250- $ your local auto parts store.
  • jeeptsijeeptsi Member Posts: 8
    It could be any of these problems:
    1. emissions system not functioniong properly
    2. fault in the fuel or electrical systems
    3. faulty secondary ignition system (cracked sparkplug insulator or faulty plug wires)
    4. vacuum leak at the throttle body, intake manifold or vacuum hoses.
    5. valves sticking.
    6. crossed plug wires- check the firing order.
    7. valve timing incorrect.
  • jeeptsijeeptsi Member Posts: 8
    Try changing your crankshaft position sensor first. This senses crankshaft position (tdc) during each engine revolution. The pcm uses this information to to control ignition timing and fuel injection synchronization.
  • tuggajbtuggajb Member Posts: 646
    prob have pluged rad would put new one on heaveyduty

    trans has small cooler in side rad un pinch line for sure
  • tourprotourpro Member Posts: 1
    So I bought a 2000 grand cherokee on ebay (first mistake). IT has always run hot since I bought it about 3/4 or a little more on dash. So then one day it chimed and said check gages and it was almost on the red. I had the thermostat then we got into the water pump which was cracked. seemed to be fine after that. about 2 or 3 days later I was driving on the highway and overheated at 3/4 on the dash and the heat went cold. so I bled the cooling system to remove any air pockets, but now it still runs 3/4 or more on the highway... but in the city it runs just over 1/2. Any suggestions???? I would really appreciate any input.
  • cbeissercbeisser Member Posts: 1
    I have a 2000 Jeep Cherokee Sport, 93,000 miles. I had the same problem with my oil pressure; it's fine when I start up, but after driving for 5 minutes it begins to drop and will drop all the way to zero if I come to a stop. Last week I realized I was also losing coolant. Took the Jeep in for service, mechanic says I have a cracked cylinder head. This is my 3rd Jeep Cherokee, the others ran for 160,000 miles plus (my 99 is still on the road-no problems). I asked the mechanic why this Jeep engine failed since it's been carefully maintained just like my other Jeeps, he said "some of these heads just crack spontaneously". (???)
    Does this sound right to anyone?
  • poconojeeppoconojeep Member Posts: 4
    If you check the forum, most of the people having this problem have Cherokees or Grand Cherokees of about the same era. Clearly, whatever engine they were putting in these vehicles was sub-standard. My last Jeep was an 1986 Cherokee Wagoneer that ran forever. It was the reason I bought another. Now, I've got a Nissan.
  • commitcommit Member Posts: 1
    I have an 02 and had the same problem. The engine light would come on for about a week and then go off. If you have an AutoZone near you ask them to run their system on it to give you the exact reason the light is coming on. If it says slow emissions leak, which is what mine said, you can do one of two things. One, check your emissions hoses to make sure they aren't cracked, this is really simple, just open the hood and there are only two hoses. The guys at Autozone can show you where they are just in case you're not sure. The next thing, and this is what fixed mine, was replace your gas cap. Mine had a slow leak around the gasket. Hope all works out okay.
  • acewinduacewindu Member Posts: 1
    I have an 05 JGC, and it shuts off while slowing down. The dealer can't figure it out, replaces O2 sensors, etc. They say they don't understand the codes the computer sends, then they bring in Detroit. They are no help either. This leads to dangerous situations while driving. They termed it Parking Lot Manuever issues. It only happens while I'm slowing down. It happened again when I turned on the AC, and it idled up and down from 0 - 600 RPMs. Any ideas?
  • jcarlson0418jcarlson0418 Member Posts: 1
    I have a 2000 Cherokee Sport, 4.0L, 4x4 and have had an overheating problem since 2005. It began to overheat so I took it in...had the radiator, thermostat, and head gasket replaced. It worked good for about a year and started to overheat again, but was okay as long as I kept filling it with coolant. About two weeks ago it wouldn't run at all without overheating. Just finished replacing the head gasket, water pump, thermostat, thermostat housing (it had cracked), and the radiator. I did it myself and just finished last Saturday. It ran perfect, had put about 250 miles on it, until today, on my way home it overheated. I am at a it possible the engine is bad?? It shouldn't be running that hot, and I know there is nothing wrong with the cooling system now, I just replaced the entire thing. Any suggestions?
  • jc00jc00 Member Posts: 2
    My wife's 2000 cherokee 4.0L just started experiencing the issue.

    Which is strange because a co-worker just had his 2002 cherokee 4.0L have the issue fixed. He went to a dealer. They replaced the sending unit. It was good for a couple of days... then back again. The dealer then replaced the pump at the tune of $450.00+. His issue has not returned in 2 weeks. He also never experienced the engine running rough when the issue occurred.

    My wife's vehicle on the other hand was really struggling to keep idling. So, not having alot of cash, I decided to tackle the oil pump.... it is Michigan... 30 degrees and snowing in April.. NICE! I have been under the vehicle so far for about 8 hours across 3 nights. If I had a lift it probably would have taken me maybe 2 hours to get to this point. I am ready to put the new pump in.

    That being said, if it gets to the pump replacement stage with you, I would suggest paying the extra $300 to have it done for you.

    I will update this when the pump is in to say if it fixed it or not.

    At any rate.... We never had the issue until the wife took the Jeep to a Valvoline quick change. The clown over filled the engine. I am guessing two quarts. This allows the oil to be aerated by the crank. Also, to be noted we had used a semi synthetic the oil change before. So, this oil change took us from semi synthetic back to plain oil.... maybe this could pay its part in root causing this issue...

    more details to follow....

  • rllewisrllewis Member Posts: 2
    My 1994 4.0 Jeep Grand Cherokee started running terrible (bucking and stalling). I replaced the crankshaft position sensor, and it ran fine...except that afterword it started bucking after about 20-30 minutes after starting. It runs rough like this for about a minute...then runs fine again. It has done this without fail, every day for the last 6 months.
    It never stalls, and always starts.
    When it starts bucking, it slows down to around 40 mph, not fun when you are on interstate. Giving it more gas results in more bucking. It is definitely temperature related, during cold weather it takes longer to manifest.
    I have checked the coolant & manifold temperature sensors, MAP sensor, camshaft position sensor, and fuel pressure. I have replaced the spark plugs, rotor, wires, and fuel filter.
    I only get this problem for 1 minute, then it's gone.

    The onset of the problem is gradual (15 seconds), and it clears up over a 15 second period as well.
  • cpb2cpb2 Member Posts: 6
    FIXED! Turns out that it was the upstream O2 sensor, even though no diagnostic codes were set. Local shop put 2 hrs labor into diagnosing it an nailed it first try! Have driven it a dozen times now with no problem whatsoever. Go for it and post confirmation!
  • tuggajbtuggajb Member Posts: 646
    be sure to prime pump or you will have the same prob you have now
    i just fill it with grease befor i put them on
  • kkelley2007kkelley2007 Member Posts: 9
    I have an '05 with the same engine. I have 57,000 miles on mine and I've never had that problem. Nothing normal about that to me.
  • jeepowner1jeepowner1 Member Posts: 2
    After I changed the PCM, all is well.The funny thing about this is the dealer ship was just as lost! Great information on Edmunds. For all who are out there with a jeep crank shaft sensor or cam sensor Problem. If after changing the sensor and you still have problems you may have to change your PCM;that fixed my problem. I didn't have any luck with having the PCM checked by the dealership. GOOD LUCK!
  • thisaintworkinthisaintworkin Member Posts: 1
    I have a 91 jeep Cherokee with the 4.0 HO it starts and idles fine then I put it in drive and after about 5 minutes of driving it will just stop running, when I stop I can crank it over and it wont start but if I turn the key off for a minute It will start and do the same thing as soon as I start to drive. Rarely when it dies and I stop the starter wont even work but the radio and lights work.
  • bethjohnsonbethjohnson Member Posts: 1
    I have the same exact problem with my 1994 4.0 Jeep Grand Cherokee. Have you found a solution?
  • pgr40pgr40 Member Posts: 2
    My son just purchased a 2000 GCL 4.0L with 74K miles.
    While driving it home the temp gauge showed 240 degs.
    I checked it out and found that the fan relay is bad:
    AC engages, fan doesn't go on.
    Temp exceeds 210 deg., fan doesn't go on.
    Switched the 40 amp fuse in the PCM, fan doesn’t go on.
    Hot wired, fan goes on.
    Is the fan relay on a 2000 GCL 4.0L the same and in the same place as your 2003?
    If not do you know where it is located?
    NAPA part#?
  • 440jeep440jeep Member Posts: 12
    I have a friend who uses MMO and he swears by it. But my father is a die hard slick 50 guy. I was wondering about which to use in an engine I am building (all brand new parts). or is the MMO stuff just for lubing up older engines?
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