tugalo Posted October 26, 2016 Share Posted October 26, 2016 Friend of mine is working on a 95 Cherokee sport, 4.0L, automatic. When he got the Jeep, it would not run. He replaced the crank sensor and now it runs, but lopes badly at idle and backfires thru the throttle body and exhaust when revved up. Very sluggish pickup. He has replaced the crank sensor with 2 new ones from O'reilly (BWD brand), replaced the MAP sensor, the temp sensor, the coil, the computer, the entire distributor with cam sensor, and the plugs and wires with no change in symptoms. He has seen the timing change 30 degrees when revving the engine. Vacuum is good and the fuel pressure is 39 lbs. Once in every 30 or so starts it will crank and run perfectly. I advised him to try a different brand of crank sensor, but beyond that, i am out of ideas. Anyone care to offer an opinion? Any and all help appreciated. Link to comment Share on other sites More sharing options...
shelbyluvv Posted October 27, 2016 Share Posted October 27, 2016 No codes or check engine light? Link to comment Share on other sites More sharing options...
onlyinajeep726 Posted October 27, 2016 Share Posted October 27, 2016 Check that distributor again. If that's correct, pull the timing cover and check the chain, verify it hasn't jumped a tooth or two. Link to comment Share on other sites More sharing options...
omega_rugal Posted October 27, 2016 Share Posted October 27, 2016 backfiring almost always means valve timing is off, recheck distribuitor and timing chain as the previous poster says... Link to comment Share on other sites More sharing options...
tugalo Posted October 27, 2016 Author Share Posted October 27, 2016 I forgot to mention that it was not throwing any codes. He has checked the timing chain and it is okay. He has had the distributor in and out several times to make sure its right. He even deliberately set it one tooth off to either side to see if that made a difference. What's curious, is that once in a while, the truck starts and runs normally, idles fine, and will go to redline without a skip. The guy is a pretty good mechanic, i let him work on my MJ when i get lazy. We were talking it over last night and he told me that he found a water leak at the heater valve which is almost over the sensor ground point so i pointed him in that direction. I also suggested that he enlarge the mounting holes on the cps and remount it. We will dig at it some more this afternoon, Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 27, 2016 Share Posted October 27, 2016 He has seen the timing change 30 degrees when revving the engine.............. That's a bit high, but not excessive. It normally jumps about 25*. What is the timing degree reading at a steady 1K RPM? It will jump around some, but should read close to 16*-22* BTDC average. Check the voltage on the GRY/WHT coil connector wire with the ignition ON. It should be close to 12VDC. Check the 4-wire cable that comes out from under the distributor cap and make sure it fits in it's slot, not pinched, and check the wires to make sure they are not skinned. Link to comment Share on other sites More sharing options...
shelbyluvv Posted October 28, 2016 Share Posted October 28, 2016 Sounds like the TPS but they normally throw a code. Link to comment Share on other sites More sharing options...
tugalo Posted October 28, 2016 Author Share Posted October 28, 2016 The computer was changed out with one from the JY and made no difference. I'm beginning to wander if there are not some broken solder joints in the computer connector pins as shown on some utube videos. When the truck is running rough, there is a loud sucking noise from the throttle body, starting to wander about the IAC, but if the computer solder joints are bad, it may not be getting energized. Link to comment Share on other sites More sharing options...
Fernando87mj Posted October 28, 2016 Share Posted October 28, 2016 Wouldn't that be from a bad throttle body gasket ? Or a broken vacuum line which in return makes it run to lean if it's the throttle body gasket or to Rich if the vacuum line is messed up? Maybe I'm wrong but it seems like those things are worth checking Link to comment Share on other sites More sharing options...
tugalo Posted October 30, 2016 Author Share Posted October 30, 2016 The truck was built in Aug of 94 and all the wiring diagrams say that the crank position supply should be 8 volts. We have a 5V supply and a .02VAC output signal on a digital meter. Anybody seen an 8V supply? We did find a high resistance ground at the dip stick stud and fixed that but it still only runs good on occassion. Mostly it lopes, shudders, and backfires all the way from idle to full throttle. Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 30, 2016 Share Posted October 30, 2016 I don't know what wiring diagrams you are using but the reference voltage to the CPS for all OBD1 Jeep 4.0's is 5VDC. Follow the CPS harness up to it's connector, open it up, and clean it out real good. Dirty/loose pins on that connector can cause rough running for sure. Link to comment Share on other sites More sharing options...
tugalo Posted October 31, 2016 Author Share Posted October 31, 2016 Understood Don, My understanding was that all 4.0's used a 5V supply, that's why the reference to the 8V confused me. We have checked and metered the wiring and pins.. Also disconnected the plug at the computer looking for loose/corroded pins. Hooking a timing light up to a plug wire, you can see the signal dropping out, so in my mind it is definitly ignition and not a fuel issue. I'm leaning toward 3 hosed up aftermarket CPS's. will try a new one from NAPA tomorrow. Link to comment Share on other sites More sharing options...
HOrnbrod Posted October 31, 2016 Share Posted October 31, 2016 FWIW, I've has two CPS's go bad over the years. Both times I got an 11 fault code. :dunno: Link to comment Share on other sites More sharing options...
tugalo Posted November 1, 2016 Author Share Posted November 1, 2016 Well, after ANOTHER crank position sensor change, the truck does the same thing. If you hook a timing light to a plug wire, and rev it up, you can see the ignition dropping out. Just to recap, we have changed 3 distributors, 4 MAT sensors, 4 crank position sensors, 2 TBS's, 4 Iac's, 2 air temp sensors, and tried 2 different cam sensors. Every so often, the truck will start and run perfectly. If you re-start it immediately, it still runs fine, but if you wait 5 minutes and start it, it runs like crap. The wiring and the pins on the computer all look good. I think we are going to go to our friendly junkie and get another computer, but throwing parts and money at it is not working so far. I remember a topic on the forum detailing a Renix repair for splices in the big harness that runs along the firewall. i wonder if the 95"s had the same set-up. My thinking is that somewhere we have an intermittent loss of signal or ground. I looked up the 95 wiring diagram on my computer, and they all show an 8V supply to the sensors and we have 7.75V on that line. Link to comment Share on other sites More sharing options...
Tex06 Posted November 1, 2016 Share Posted November 1, 2016 Alternator wiring ok? My alternator pin was burned up giving me fluctuating voltage (caused by bad grounds I believe but made my problems much worse). Kind of a long shot, I know. Sent from my SM-G930T using Tapatalk Link to comment Share on other sites More sharing options...
tugalo Posted November 2, 2016 Author Share Posted November 2, 2016 Haven't looked at the alternator yet, but anything is worth a shot at this point. I am about convinced that it is an intermittent open in the ignition circuit wiring but nothing we've tried has helped, even cussing at it does not help !! What's really frustrating is the odd time when you start it up and it runs perfectly Link to comment Share on other sites More sharing options...
tugalo Posted November 2, 2016 Author Share Posted November 2, 2016 Well........I think we have a winner! Even tho this does not apply to our MJ's, I send it along for everyone's general fund of knowledge. After replacing everything we could imagine would affect the ignition, we have found that the alternator is intermittent. On the later model XJ's, the alternator is a part of the trigger for the coil. So, when it is not putting out, ignition is hit or miss. Another lesson learned about haphazardly replacing parts. Oh well, now there are several spares...... Link to comment Share on other sites More sharing options...
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