woody62 Posted November 23, 2007 Share Posted November 23, 2007 Hello all, I'm new at this so stay with me... I just got a 87 Jeep Comanche from CA by way of CO. I can't get it to run right. Took it to dealer and he is having trouble with it. It is the 2.5 throttle body, 4 spd. It will idle and go IF you take it to the floor and run but nothing in the middle. It falls on its face! No power in the mid range. Replaced a ton of parts and it idles really well but still no power. We cut off the exhust and ran stright pipe, still no power. It is like it isn't getting air? Or something wrong with fuel air mix? We replaced fuel filter and we have fuel presure. Maybe not enough under power? The Jeep dealer is Lou's Jeep in Geneva IL and they have been with Jeep since 1946 so I know they know what they are doing but sure would like some ideas from so of you. Need your help. Thanks,\Woody Link to comment Share on other sites More sharing options...
whowey Posted November 23, 2007 Share Posted November 23, 2007 First, thing. Howdy Neighbor!!!!!!!!! I'm out in lovely Ogle County. BOB(a part timer here) is right down the street from you. When you cut off the exhaust, did you remove the converter? One idea would be a plugged cat. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted November 24, 2007 Share Posted November 24, 2007 ...or it could even be classic "I downgraded to a 2.5" syndrome... they're underpowered motors. but, better than a 2.8...is it behaving worse than even a 2.5 should? Link to comment Share on other sites More sharing options...
feerocknok Posted November 24, 2007 Share Posted November 24, 2007 Straightpiping a 2.5 doesn't seem to work well, but getting rid of a clogged cat would be good. How's your air filter? Fuel injector? Spark (cap, rotor, plugs, wires)? 2.5s are slow, but not "fall on [their] face slow." Link to comment Share on other sites More sharing options...
Eagle Posted November 24, 2007 Share Posted November 24, 2007 2.5s are slow, but not "fall on [their] face slow." But this is a 2.5L 4-speed, which means it has 3.45 gears rather than the 4.10 gearing used on 2.5s with a 5-speed. I own two of these. The 2.5L mated to 3.54 gears IS "fall on its face slow." Link to comment Share on other sites More sharing options...
comancheon33 Posted November 24, 2007 Share Posted November 24, 2007 Mu 2.5 4 speed with 3.55s and 235/75/15 won't get out of its own way. It will hold speed once you finally get it there though. Decent gas milage also ;) Thats why it is still in there. Link to comment Share on other sites More sharing options...
Kenosha Warrior Posted November 25, 2007 Share Posted November 25, 2007 mine was on 205's and it got out of its way, and then some. Peppy little buggar. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted November 25, 2007 Share Posted November 25, 2007 mine's pretty peppy for a 4 cyl...it's the 4.10 gearing and 5th gear tho. it gets like 16-17mpg because I run 55mph to school and back every day. it's best mpg (21) is at 45mph and 2500rpm. Link to comment Share on other sites More sharing options...
woody62 Posted November 25, 2007 Author Share Posted November 25, 2007 I cut off all of the exhuast. No converter. We don't do emission test here. The little truck has power at start and if I put it to the floor but nothing in the middle. Have replaced throtal control sensor, crank sensor, rotor, cap, wires, pulgs, battery, all battery cables, starter. made another ground cable. I'm confident I have electric, gas and air but I'm missing something here. Just no power at all. I MEAN at ALL! in the middle. If I put the peddle in the middle the truck slows and will stall. It has to be on the floor or just touching it. Any ideas? Thanks, woody Link to comment Share on other sites More sharing options...
Confedneck Posted November 25, 2007 Share Posted November 25, 2007 sounds eerily like a bad MAP or MAF sensor or even tps sensor, or bad ignition control module... don't know which of these your jeep has, but test the ones ya got... Link to comment Share on other sites More sharing options...
JeepcoMJ Posted November 25, 2007 Share Posted November 25, 2007 it has all of those Link to comment Share on other sites More sharing options...
Eagle Posted November 25, 2007 Share Posted November 25, 2007 What about the oxygen sensor? I don't know too much about the Renix injection system (remember, folks, the early TBI was a Renix system, too). Is it possible that under normal cruise it isn't reading the exhaust correctly? I don't know if flooring the peddle overrides the O2 sensor to give a richer mix for maximum power, but it's possible. How does it respond when you FIRST fire it up on a cold day? On a cold start, instead of a choke the ECU operates in "open loop mode," ignores most sensor input, and provides a pre-mapped, extra-rich mixture for warm-up. In my '88 XJ 4.0L, the switch to "closed loop mode" takes place about 2 miles down the road after pulling out of my driveway. I have to back up and turn around before heading up the driveway, so figure about 5 minutes (approximately) in open loop mode. Try your MJ that way. Start it first thing in the morning, get on the road immediately, and see if it's running any different in the first couple of minutes. On cold days, I can literally feel the switch take place. The location happens to be a level stretch with a 35 MPH speed limit. I'll be cruising along in 4th gear, right at the speed limit, and I can feel the engine do a little stutter, bump, and then it smooths right out again. Link to comment Share on other sites More sharing options...
woody62 Posted November 26, 2007 Author Share Posted November 26, 2007 Eagle, You sounds like you have a good handle on this. They told me they replaced the O2 sensor too. But if you start the truck it runs fine and really well for a few miles. It really gets bad and looses power as it gets warm. Some thing else, if you stop, turn it off and let sit for a couple minutes and start again it seems to run fine for a couple minutes and then back to running like crap. So what sensor have I forgotten? woody Link to comment Share on other sites More sharing options...
JeepcoMJ Posted November 26, 2007 Share Posted November 26, 2007 the stop/shut off/restart thing is classic renix. what that does is clear the computer of any "trouble codes". a renix computer doesn't actually store trouble codes, it clears every time it's shut off. so, I would probably take it into someone with a scanner for the renix system and have them plug it in while it's running. from there you'll know if anything is faulty (most likely) Link to comment Share on other sites More sharing options...
Eagle Posted November 26, 2007 Share Posted November 26, 2007 Either it's getting bad data from some sensor, or it only runs "right" in open loop mode. If it only ran well for the first few miles after a cold start I'd say it was the latter. If it reverts to good every time you start, well JeepcoMJ is correct, the Renix system doesn't "learn" and store anything -- every start begins from the default ECU program. So, some way, somehow it sounds like there's a sensor that isn't sending the right data to the ECU. Don't be lulled into a false sense of security because various sensors have been replaced. There are defective sensors. I just changed out the CPS in my '88 MJ, and after replacing it the truck still won't start. It;s supposed to be putting out 0.5 to 0.8 volts a/c when cranking. It's producing 0.23 volts. I gave up, had it flat-bedded to the dealership, and a week leter they can't figure it out. Don't give up, but try to double-check everything. Have you found the link someone posted recently to an article on how to test ALL the sensors in the Renix system? In your situation, I'd say it is definitely recommended reading. Ah -- found it: http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted November 27, 2007 Share Posted November 27, 2007 Are you still having this problem? Link to comment Share on other sites More sharing options...
woody62 Posted November 28, 2007 Author Share Posted November 28, 2007 I haven't gotten a report from the repair shop. Almost a week now. Thanks to you all. This is OUTSTANDING information. I think you are probably right on. I had trouble getting it started at all when we got it. I put new battery cables on, new battery and added another ground cable. Started fine but ran like crap. By the way... remember this is a CA truck. So from what I have read this is an issue too. See Wikipedia info. RENIX. It must be the computer. I saw cost from $35 used to $300 new. What should I be paying if I need the computer? Are they had to get new? I'm afraid to see the repair bill at this point from Lou's Jeep. I'm going to tell them about the article on the RENIX system. Thanks again to all. I'll keep you posted. woody Link to comment Share on other sites More sharing options...
JeepcoMJ Posted November 28, 2007 Share Posted November 28, 2007 don't spend the $$$ on a new PCM, and if they did get you a new one, you need to demand their sources and to see the work order for it...they're sure to know that they can get them used in good order, so make sure you get what you pay for. not trying to scare ya just keepin ya on your toes Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted November 28, 2007 Share Posted November 28, 2007 Do you know what temperature your truck is running at? Link to comment Share on other sites More sharing options...
woody62 Posted December 1, 2007 Author Share Posted December 1, 2007 Okay guys. Here is the update. They finally got it fixed. It was the FUEL PUMP. I didn't have enough pressure. They said I had about 10lb? of pressure. Put the new pump in and it runs great!! I think the 2.5 4 banger has got a good deal of power. I'm keeping all the notes you sent me on the electric system. I'm sure I need it. I'm looking for a different rear end. I think the gears could be messed up. Any suggestions as replacement? This is more of a road truck so I'm looking for a road gear. 3.?? What Cherokee can I get rear from that will fit? woody Link to comment Share on other sites More sharing options...
feerocknok Posted December 1, 2007 Share Posted December 1, 2007 I'm looking for a different rear end. I think the gears could be messed up. Any suggestions as replacement? This is more of a road truck so I'm looking for a road gear. 3.?? What Cherokee can I get rear from that will fit? Road gear as in prodominately highway drving? 3.73 would be my suggestion for highway use on stock tires. For alot of city stuff, 4.10s. Cherokee axles need to have the spring perches relocated in the rear, do a search for that info, and make sure the gears in your front axle match that of your rear axle. Link to comment Share on other sites More sharing options...
ifixit8 Posted January 15, 2008 Share Posted January 15, 2008 glad to read about another northern Il mj owner. sorry to hear that you had to through alot of parts at it. that dealer should have figured it out sooner. hopefully they didn't bend you over. :eek: I had a 99 cherokee that i just gave up on. I ended up trading it in for the wifes current 03 suzuki xl-7. that thing, I almost started throwing major parts at it like the fuel pump and distributor. I am glad that I didn't have to deal with it. Link to comment Share on other sites More sharing options...
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