Jeepmmmj Posted December 27, 2016 Share Posted December 27, 2016 Ok. So My 91 mj 4.0 5 speed ax15 has got an issue. Basically it's got a high idle. Not all the time. It's only when it feels like it I guesse. Here is the strange part though. When it does have the high idle it's only as the truck is coasting in neutral and moving. It will idle all crazy anywhere from 1500 rpms to 2700 rims. Once the truck comes to a complete stop the idle will drop back downto a normal idle. Then as I take back off it will buck and backfire and spit out black smoke. It will do this as it please. Sometimes it will shut off and be completely flooded out and it will take a while to get it to starthe back up. When it runs fine it runs great though. I have not had a chance to have a scanner on it while it is acting up. When we did have a chance to put a scanner on it the tps and coolant temp sensor seemed to be acting normal. There is obvious black smoke comming out of the exhaust. I had the issue months ago and replaced the exhuast manifold because it was cracked. Drove 1400 miles on a long trip and it started acting up again. It seems electrical because of how it will come and go so sudden. Please help I want my baby to be happy and trusty but she has left me embarrassed in the middle of the road one to many times now. Maybe a computer? Harness? Please help any input will be highly appreciated. I've taken the throttle body apart and have cleaned it really well with no results Link to comment Share on other sites More sharing options...
gogmorgo Posted December 27, 2016 Share Posted December 27, 2016 Have you done cruiser's tips yet? www.cruiser54.com Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 27, 2016 Share Posted December 27, 2016 Check for fault codes: http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/ Link to comment Share on other sites More sharing options...
gogmorgo Posted December 27, 2016 Share Posted December 27, 2016 Herp-derp missed that it was a '91. Cruiser's tips won't be as useful to you. Link to comment Share on other sites More sharing options...
cruiser54 Posted December 27, 2016 Share Posted December 27, 2016 Check the vacuum line to the MAP sensor very closely. Link to comment Share on other sites More sharing options...
Tex06 Posted December 28, 2016 Share Posted December 28, 2016 I had issues with my 92. The main connector to the computer had corrosion on the pins...bad juju for the electrical signals. You have to pull the air filter housing but I would add that to the list of things to check. Or you can be like me and replace all your sensors first, then troubleshoot properly :D Sent from my SM-G930T using Tapatalk Link to comment Share on other sites More sharing options...
omega_rugal Posted December 28, 2016 Share Posted December 28, 2016 see if the stupid idle stepper motor is not stuck... Link to comment Share on other sites More sharing options...
Jeepmmmj Posted December 29, 2016 Author Share Posted December 29, 2016 Thank you all for the replies I'll be putting some hours in on it in the morning and will give an update :) Link to comment Share on other sites More sharing options...
Jeepmmmj Posted January 7, 2017 Author Share Posted January 7, 2017 Found this issue to be the coolant temp sensor! Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 7, 2017 Share Posted January 7, 2017 Found this issue to be the coolant temp sensor! That's an odd one. How did you troubleshoot and find that? Link to comment Share on other sites More sharing options...
desbennett004 Posted January 7, 2017 Share Posted January 7, 2017 I have a funny idle on mine, I have a temp sensor, haven't put it in yet. Now I will though.... Sent from my SM-N900W8 using Tapatalk Link to comment Share on other sites More sharing options...
Jeepmmmj Posted January 7, 2017 Author Share Posted January 7, 2017 Found this issue to be the coolant temp sensor! That's an odd one. How did you troubleshoot and find that? Finally had the scanner on it while it was acting up. The temp sensor was all over the place every time the truck acted up reading anywhere from negative 3 - 210 degreeS. The cooler the temperature reading the higher the idle. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 7, 2017 Share Posted January 7, 2017 Which coolant temp sensor? The one in the thermostat housing that feeds the ECU, or the one on the left rear cylinder head for the dash temp gauge? Link to comment Share on other sites More sharing options...
desbennett004 Posted January 7, 2017 Share Posted January 7, 2017 Which coolant temp sensor? The one in the thermostat housing that feeds the ECU, or the one on the left rear cylinder head for the dash temp gauge?I might be wrong, but I thought the one in the thermostat housing was for the electric fan? I think the ECU sensor is on the block, on the drivers side. Sent from my SM-N900W8 using Tapatalk Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 7, 2017 Share Posted January 7, 2017 You're wrong. The OP has a 91 HO, not a Renix. Link to comment Share on other sites More sharing options...
desbennett004 Posted January 7, 2017 Share Posted January 7, 2017 You're wrong. The OP has a 91 HO, not a Renix.My bad. Sent from my SM-N900W8 using Tapatalk Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 7, 2017 Share Posted January 7, 2017 No problem. It is a bit confusing. HO temp gauge: Sensor on cylinder head HO ECU: Sensor on thermostat housing HO aux fan: Off/on controlled by ECU Renix temp gauge: Sensor on cylinder head Renix ECU: Sensor on engine block Renix aux fan: Off/on controlled by sensor in the radiator Link to comment Share on other sites More sharing options...
cruiser54 Posted January 7, 2017 Share Posted January 7, 2017 HO temp gauge: SENDER on cylinder head HO ECU: Sensor on thermostat housing HO aux fan: Off/on controlled by ECU Renix temp gauge: SENDER on cylinder head Renix ECU: Sensor on engine block DRIVER SIDE Renix aux fan: Off/on controlled by TEMP SWITCH in the radiator Link to comment Share on other sites More sharing options...
Tex06 Posted January 7, 2017 Share Posted January 7, 2017 Tomato, tomato^^^ You two are great. :D Sent from my SM-G930T using Tapatalk Link to comment Share on other sites More sharing options...
cruiser54 Posted January 7, 2017 Share Posted January 7, 2017 Tomato, tomato^^^ You two are great. :D Sent from my SM-G930T using Tapatalk mOSTLY JUST TO PICK ON dON ANYWAY!! lol Link to comment Share on other sites More sharing options...
Jeepmmmj Posted January 9, 2017 Author Share Posted January 9, 2017 It was the sensor in the thermostat housing telling my ECU I was running all kinds of different Temps and confusing the ECU Link to comment Share on other sites More sharing options...
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