shawn Posted May 26, 2015 Share Posted May 26, 2015 its so inconsistent i cannot tell what's triggering it but the one consistency is that when i pull up to a red light or stop sign the idle drops right down to 100 or it just stalls.but yet at all other times it idles perfectly . now a new motor has just been swapped-in and its doing the exact same thing - only a little worse. if I'm sitting still and put the brake on the idle doesnt change - but i have noticed this time that if I'm driving along and put in the clutch like I'm going to get ready to stop it will drop right down to 100 rpm for a second or 2, then go back up to normal idle. like i said it seems a bit worse after the swap and sometimes the only way to avoid stalling at stop signs ( especially ones that are approached heading down-hill) are to put the clutch in way earlier than i normally would and idly /coast up to the stop-line. I'm baffled once again ... thanks for reading. :) Link to comment Share on other sites More sharing options...
Rockfrog Posted May 26, 2015 Share Posted May 26, 2015 Sounds like a TPS issue. Link to comment Share on other sites More sharing options...
HOrnbrod Posted May 26, 2015 Share Posted May 26, 2015 Is this about your 91? If so check for fault codes, specifically a code 15. http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/ Link to comment Share on other sites More sharing options...
shawn Posted May 26, 2015 Author Share Posted May 26, 2015 yes. this one is my 91 (DD). also the mechanic that did the swap said that he thought it may be the tps too as that that was the one sensor that he swapped in from the old motor. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted May 27, 2015 Share Posted May 27, 2015 Cat/muffler got good flow through them? My truck did this when I got it and a piece of pipe and new muffler fixed it right up. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 27, 2015 Share Posted May 27, 2015 Got all the grounds hooked up to clean and shiny metal at the dipstick tube stud? Link to comment Share on other sites More sharing options...
HOrnbrod Posted May 27, 2015 Share Posted May 27, 2015 yes. this one is my 91 (DD). also the mechanic that did the swap said that he thought it may be the tps too as that that was the one sensor that he swapped in from the old motor. Check the codes before running wild. They are there to be utilized, and while not 100%, they are helpful at times. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 27, 2015 Share Posted May 27, 2015 yes. this one is my 91 (DD). also the mechanic that did the swap said that he thought it may be the tps too as that that was the one sensor that he swapped in from the old motor. Check the codes before running wild. They are there to be utilized, and while not 100%, they are helpful at times. Shoulda stuck with Renix. Much easier. Image Not Found Link to comment Share on other sites More sharing options...
HOrnbrod Posted May 27, 2015 Share Posted May 27, 2015 Just check the codes first OP. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 27, 2015 Share Posted May 27, 2015 Just check the codes first OP. Always the first place to start. Link to comment Share on other sites More sharing options...
shawn Posted June 3, 2015 Author Share Posted June 3, 2015 well it took a week but got around to this test. it's neat to have the option of this. i do get a code 15, as well as 12,33 and 35. i don't have air. i will be looking into a tps asap. thank you gentlemen once again :) Link to comment Share on other sites More sharing options...
shawn Posted June 9, 2015 Author Share Posted June 9, 2015 i thought i had it with the new tps but sadly it seems to have had no real effect. When i fired it up after the new sensor went in it idled high (1500) for a minute then immediately went back to normal and ran and idled perfectly -- until i went to stop fairly quickly. same symptom: idle drops right down to almost nothing and sometimes dies completely. Link to comment Share on other sites More sharing options...
shawn Posted June 10, 2015 Author Share Posted June 10, 2015 it is an old,, but high-flow muffler, and i see it still has the cat, so that's where I'm gonna focus my attention next. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 10, 2015 Share Posted June 10, 2015 well it took a week but got around to this test. it's neat to have the option of this. i do get a code 15, as well as 12,33 and 35. i don't have air. i will be looking into a tps asap. thank you gentlemen once again :) Since you are throwing a code 15 (no VSS output to ECU), this could be the cause of your stalling problem. The VSS sensor is mounted on the T-case since you have 4WD and feeds a signal to the ECU for engine RPM management purposes. Check the electrical connection for continuity from the VSS output connector to the ECU. Link to comment Share on other sites More sharing options...
shawn Posted June 10, 2015 Author Share Posted June 10, 2015 very good info and thank you. i will look into this asap. am i correct in thinking that the 4x4s speedo hooks to tc and the others hook to transmission? my speedo has never worked in this truck. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 10, 2015 Share Posted June 10, 2015 Yes, that is correct. Since your 91 electrical speedometer isn't working, I'd sure to pull it out and look for obvious stuff like a stripped speedo gear, speedo gear not clocked at the correct orientation, a rounded out square hole where the gear shaft plugs into, and/or obvious electrical connectivity problems on the cable to the ECU. The part number for the 2-pin VSS you need is 5252438. Rock Auto sells them as well as many others. Here's a how-to for the later 3-pin VSS, but the principle is the same: http://gojeep.willyshotrod.com/HowtoSpeedoGears.htm Link to comment Share on other sites More sharing options...
FrankTheDog Posted June 11, 2015 Share Posted June 11, 2015 If your speedo isn't working that's your problem. My 92 had an intermittent speedo and it would stall out at stops if the speedo wasn't working. It didn't stall when it was working. Changed out the sending unit on the transfercase output and has worked fine since. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 11, 2015 Share Posted June 11, 2015 If your speedo isn't working that's your problem. My 92 had an intermittent speedo and it would stall out at stops if the speedo wasn't working. It didn't stall when it was working. Changed out the sending unit on the transfercase output and has worked fine since. Frank, was your 92 MJ sensor 2 or 3 pin? My 91 is 2-pin, and I think the 92's went to a 3-pin, but getting conflicting info. Thanks. Link to comment Share on other sites More sharing options...
FrankTheDog Posted June 11, 2015 Share Posted June 11, 2015 Mine looks identical to the one in the picture minus the speedo output. My 92 XJ does too. It also had the same problem. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 11, 2015 Share Posted June 11, 2015 Mine looks identical to the one in the picture minus the speedo output. My 92 XJ does too. It also had the same problem. Thanks. Trying to track down when it changed from 2-pin to 3-pin. The parts manual is AFU. Link to comment Share on other sites More sharing options...
FrankTheDog Posted June 12, 2015 Share Posted June 12, 2015 Two MJ's I've seen with April of 92 build dates still have the two wire. Probably changed over about the time of the change to the 93 model year. Link to comment Share on other sites More sharing options...
HOrnbrod Posted June 12, 2015 Share Posted June 12, 2015 Noted, that helped. On digging deeper, the parts manual says the 2-pin speed sensor was used on XJ/MJ models up to build date 7-16-92, after that they went to the 3-pin. Little things like this just bug the hell out of me. :thumbsup: Link to comment Share on other sites More sharing options...
shawn Posted August 4, 2015 Author Share Posted August 4, 2015 This turned out to be one of the best pieces of advice ever. (thank you hornbrod). strangely enough, when i went to the parts store and picked it up i removed mine in the parking lot but when i got the new one i wasnt positive it was right so i figured that i'd just throw the old one back in and change them at home. on the way home it ran perfectly and didnt do the thing it had done for many years at the red light. when i was down there i noticed the wiring harness was quite rough and looked melted in one spot so will be changing that out asap. i think wiggling the harness and/or the sensor itself changed everything . i still have the new sensor and will just keep it in the truck and change it at the first sing of the problem showing up again. thank you again . i would have not thought of that on my own and i will pay more attention to the codes from now on. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 4, 2015 Share Posted August 4, 2015 It's good to have an HO. :yes: Glad to help. Link to comment Share on other sites More sharing options...
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