imtehbeef Posted April 20, 2011 Share Posted April 20, 2011 I finally got my 1992 Comanche on the road, but its got a hell of a misfire under heavy acceleration. List of new parts: Cap/Rotor Plugs Wires Fuel Pump Fuel Filter TPS All of which were changed by the previous owner. The weird thing is the engine computer isn't throwing any codes related to misfires. These are the codes I get: 12 - Battery disconnected within 50 key turns 35 - Cooling fan relay fault (Doesn't make any sense as I don't have an electric cooling fan) 33 - AC Circuit fault (Also doesn't make sense as I don't have AC) 55 - End of codes. Anybody out there have any ideas? Merging onto the highway everyday without being able to floor it is getting kind of annoying. :wall: Link to comment Share on other sites More sharing options...
jeepers Posted April 20, 2011 Share Posted April 20, 2011 A BAD IGNITOIN COIL WILL DO THAT ALSO but i also had a bad fuel ine in the tank( between the output of the tank and the pump ) check your fuel psi . should be between 28 and 42, at the fuel rail . if you have r12 ac guages you can check it out :wrench: Link to comment Share on other sites More sharing options...
imtehbeef Posted April 20, 2011 Author Share Posted April 20, 2011 Well, since the ignition coil is all thats left for old parts, I guess I'll go pick one of those up tomorrow. NAPA probably has the right gauge for the fuel rail, so I might as well check the fuel pressure tomorrow too. Thanks for the input. Link to comment Share on other sites More sharing options...
imtehbeef Posted April 25, 2011 Author Share Posted April 25, 2011 Checked the fuel pressure, 39 without the regulator, 31 with it. Bought a brand new coil. Still misfiring. I checked the resistance on the injectors, all are approximately 15 ohms. I'm out of ideas. Everything on the fuel/ignition system is new. Would a bad intake air temperature sensor cause this? The resistance at 60 degrees is only 5k ohms, the book says it should be above 10k. Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 Well, I checked the IAT sensor today with the truck fully cooled down, and its within factory specs. I ripped the catalytic converter off, thinking it might be a partially clogged cat, but that didn't fix it either. I'm runnin out of stuff to check here people. Anybody got any ideas at all? Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 27, 2011 Share Posted April 27, 2011 Auto tranny? My 91 stumbled under WOT until I got the kickdown cable adjusted right. Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 That sounds like a likely culprit. I've been trying to get this mother@#$%er to throw a code for 3 weeks now, and no matter how bad it "misfires" it won't throw a code. Did your 91 sound like a misfire when it stumbled? And how would I go about adjusting the kickdown cable? I followed some instructions I found online (can't remember where exactly) but it didn't seem to adjust the cable, only pull it really tight. Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 27, 2011 Share Posted April 27, 2011 If you don't have the factory FSM, you should get one. Here's a link that's close: http://www.allpar.com/SUVs/jeep/cherokee-transmission.html Mine did it after I swapped in the 99+ intake manifold, and it took a few tries to get the cable right. It wasn't exactly a misfire, but more like a 4-barrel carb loading up and going nowhere when I stomped it. I had no fault codes either. If adjusting the cable doesn't help, might be time to start looking for a substitute ECU to try. :( Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 Cable is adjusted, and its still doing it. Could the torque converter be the cause? The truck was run low on transmission fluid by the previous owner. It stumbles in every gear too. Any ECU from 91-95 should fit, right? My ECU does make a weird high-pitched whine when the key is on. Off topic, do you happen to know where I can get an FSM for a 92? I've been using the 93 FSM for a Cherokee I got from greatlakesxj.com Link to comment Share on other sites More sharing options...
HOrnbrod Posted April 27, 2011 Share Posted April 27, 2011 Cable is adjusted, and its still doing it. Could the torque converter be the cause? The truck was run low on transmission fluid by the previous owner. It stumbles in every gear too. Any ECU from 91-95 should fit, right? My ECU does make a weird high-pitched whine when the key is on. Off topic, do you happen to know where I can get an FSM for a 92? I've been using the 93 FSM for a Cherokee I got from greatlakesxj.com One more thing to try. Do you have a timing light? The timing is not adjustable on the HO engines, but the marks are there on the harmonic balancer and the timing gear case. Hook the light up to #1 cylinder and it should read about 12-14* advance @ 2000 RPM or so, and most importantly the strobe should be steady, not jumping around. If it's jumping around the distributor gear could be off a tooth or worn, a sloppy bad bearing, or a faulty stator sensor in the distributor. Easiest fix for this is a new/rebuilt distributor. Can't get parts easily to rebuild them anymore. Don't think this would cause the fault codes you are experiencing though. ECU? I would replace it w. the same one that's there now. But a substitute close year would work for troubleshooting if it clears the codes and corrects the symptoms. Jeep FSMs come up on Ebay all the time, prolly your best source. 91/92 FSMs are basically the same, both are early OBDI systems. Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 I won't have access to a timing light for another week and a half, when school gets out. I think it runs way too good for it to be a timing problem though. The truck accelerates like a madman at WOT until it gets close to redline, and then it starts to misfire. I'm not sure the exact RPM, I have the idiot light gauges :shake:. Occasionally the truck will go all the way to redline without misfiring, but its completely random when it does it. When I test drove it after adjusting the kickdown cable, it misfired 4 or 5 times on the first pass, once on the second pass, and then 4 to 5 times on the third pass. Link to comment Share on other sites More sharing options...
jeepsouth Posted April 27, 2011 Share Posted April 27, 2011 Rev. limiter? :cheers: Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 I don't think its the rev limiter. It keeps accelerating in between misfires. It does seem to be doing it less today, although I haven't had a good stretch of road to test it on. It's hard to test a misfire at the top of first gear in a 25 mph zone. :wall: Link to comment Share on other sites More sharing options...
jeepsouth Posted April 27, 2011 Share Posted April 27, 2011 Might be your cranksaft position sensor maybe. Do you have a rear main seal leak? :cheers: Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 Yeah, I do have a rear main seal leak. I remember reading somewhere that this could cause problems with the CPS, because the pickups get oily? Should I go clean the pickups and see if it helps? Link to comment Share on other sites More sharing options...
jeepsouth Posted April 27, 2011 Share Posted April 27, 2011 Couldn't hurt beef. Give it a try. good luck :cheers: Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 I couldn't pull the plate off of the transmission to clean the ring gear, because I don't have a wrench big enough, but I was able to take one of the small bolts off and pry the plate open. What exactly am I looking for to be covered in oil? The ring gear looked pretty dry. I also noticed that the high pitched whine that the ECU makes changes when I unplug the crank position sensor and the cam position sensor. I'll try to post a video when I get back from town. Link to comment Share on other sites More sharing options...
knever3 Posted April 27, 2011 Share Posted April 27, 2011 Maybe you have dirty injectors or a clogged EGR valve. Does it spark knock when loaded? Either pulling something or power braking it at low rpms? If an injector cannot get the fuel out it will miss. Link to comment Share on other sites More sharing options...
imtehbeef Posted April 27, 2011 Author Share Posted April 27, 2011 Thats the thing I don't understand. It doesn't knock or misfire at all until it gets close to shifting, and usually only at WOT. I can power brake all day long and it won't misfire once. I'll try to take a video of a 0-60 pass at WOT in a little bit. It's still not throwing a misfire code, either. Link to comment Share on other sites More sharing options...
jeepsouth Posted April 27, 2011 Share Posted April 27, 2011 Your ecu is making noise? I assume when you are in the cab with ignition on ,but not running the engine. That is strange to say the least. Link to comment Share on other sites More sharing options...
jeepsouth Posted April 27, 2011 Share Posted April 27, 2011 I won't have access to a timing light for another week and a half, when school gets out. I think it runs way too good for it to be a timing problem though. The truck accelerates like a madman at WOT until it gets close to redline, and then it starts to misfire. I'm not sure the exact RPM, I have the idiot light gauges :shake:. Occasionally the truck will go all the way to redline without misfiring, but its completely random when it does it. When I test drove it after adjusting the kickdown cable, it misfired 4 or 5 times on the first pass, once on the second pass, and then 4 to 5 times on the third pass. If you have no tach how do you know you are at redline? Does it misfire just before the auto trans shifts to the next gear when accel pedal held to the floor between all gears?My mustang will sometimes hit the rev limiter on the 1-2 shift I can adjust shift points with my handheld tuner to get out of this. Maybe you have slow shift solenoids in your trans. maybe from overheat when fluid was low? :dunno: Link to comment Share on other sites More sharing options...
imtehbeef Posted April 28, 2011 Author Share Posted April 28, 2011 Sometimes the misfire happens a good 1000 rpms away from the shift point. As for the ECU noise, I couldn't get it on video because my phone microphone won't pick up such a high frequency, but its just a faint high pitch whine that you can only hear when you're under the hood. I've heard the whine come from an ECU in one of my previous trucks that ran fine, but I can't remember if it was a Jeep or not. In other news, I decided to check the new TPS voltage just for kicks, and its only putting out 3.6 volts at WOT. My Chilton says it should be putting out over 3.9 volts. Did I get a faulty TPS unit? This would cause the engine to lean out at WOT and cause a misfire, right? Link to comment Share on other sites More sharing options...
imtehbeef Posted April 28, 2011 Author Share Posted April 28, 2011 KgOD78gnV6M If you listen closely you can hear it misfire 2 or 3 times in this video. I kept it floored until after it shifted. Link to comment Share on other sites More sharing options...
jeepsouth Posted April 28, 2011 Share Posted April 28, 2011 Can you adjust the tps to read the correct voltage at wot? I seem to remember this was possible by slightly loosening the screws. :cheers: Link to comment Share on other sites More sharing options...
imtehbeef Posted April 28, 2011 Author Share Posted April 28, 2011 Nope, the TPS on the 91 and 92 Comanche's are nonadjustable. Link to comment Share on other sites More sharing options...
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