cz777 Posted December 3, 2012 Share Posted December 3, 2012 when my mj is colder than 40^ ....she is a real pain to start and run ......yes all sensors have been ohm out at different temps -all is ok all rest of the values are good ! damn she is like my ex wife a little chilly turns to be a b*@$£ ! this just started a few days ago !!! Link to comment Share on other sites More sharing options...
jimoshel Posted December 3, 2012 Share Posted December 3, 2012 Well warm her up first. Link to comment Share on other sites More sharing options...
jpnjim Posted December 3, 2012 Share Posted December 3, 2012 You might have gotten a hold of some bad gas, or maybe a little moisture in your tank. Slight fuel problems can cause bigger issues in the cold, especially when you need that richer mixture during warmup. Vacuum leak, missing factory air box/missing hot air line (pre-91), crusty injectors all make things worse when the weather gets cold. Link to comment Share on other sites More sharing options...
misfitmechanic Posted December 3, 2012 Share Posted December 3, 2012 Sounds like you could possibly have a problem with a coolant temp sensor. Your coolant temp sensor tells the PCM what the engine temp is during start up allowing it to adjust the air/fuel ratio. If your PCM is seeing that the temp of the engine is higher than it is during a cold start up it won't richen the fuel mixture enough to start easily or at all. I have ran into this on a 93 cherokee before. The sensor was out enough to make it impossible to start cold not enough to turn on a engine light. Link to comment Share on other sites More sharing options...
Eagle Posted December 3, 2012 Share Posted December 3, 2012 Sounds like you could possibly have a problem with a coolant temp sensor. Your coolant temp sensor tells the PCM what the engine temp is during start up allowing it to adjust the air/fuel ratio. If your PCM is seeing that the temp of the engine is higher than it is during a cold start up it won't richen the fuel mixture enough to start easily or at all. I have ran into this on a 93 cherokee before. The sensor was out enough to make it impossible to start cold not enough to turn on a engine light. Nope. unless he has an HO there is no PCM -- the Renix XJs and MJs have an ECU (Engine Control Unit). It doesn't control any other part of the power train. on cold start it runs in open loop mode, which ignores input from the sensors and uses a hard-coded air/fuel map. It doesn't enter closed loop mode (ECU control) until the coolant temp sensor sees around 165 to 175 degrees. For me, on winter mornings, that happened two miles down the road -- I could actually feel a slight hesitation then a surge as the transition took place. Link to comment Share on other sites More sharing options...
xjrev10 Posted December 4, 2012 Share Posted December 4, 2012 Nope. unless he has an HO there is no PCM -- the Renix XJs and MJs have an ECU (Engine Control Unit). It doesn't control any other part of the power train. on cold start it runs in open loop mode, which ignores input from the sensors and uses a hard-coded air/fuel map. It doesn't enter closed loop mode (ECU control) until the coolant temp sensor sees around 165 to 175 degrees. For me, on winter mornings, that happened two miles down the road -- I could actually feel a slight hesitation then a surge as the transition took place. Cool! I know what you are talking about in those last few sentences! I never thought about it I guess. Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 4, 2012 Share Posted December 4, 2012 Actually open to closed loop transition on OBDI models (91-95) starts when the O2 sensor starts passing traffic to the ECU. Real easy to see if you have an A/F meter. This usually occurs in less than two minutes; or up to three on a real cold start. After the O2 sensor passes traffic to the ECU (not PCM, that's OBDII) full transition to closed loop occurs within a minute or two max. Link to comment Share on other sites More sharing options...
cz777 Posted December 5, 2012 Author Share Posted December 5, 2012 sorry i left out she has TBI injection ....i think i found it tonight ...i will pull out her tongue out Wednesday .........will up date and do a total write up ...... Link to comment Share on other sites More sharing options...
cruiser54 Posted December 5, 2012 Share Posted December 5, 2012 Actually open to closed loop transition on OBDI models (91-95) starts when the O2 sensor starts passing traffic to the ECU. Real easy to see if you have an A/F meter. This usually occurs in less than two minutes; or up to three on a real cold start. After the O2 sensor passes traffic to the ECU (not PCM, that's OBDII) full transition to closed loop occurs within a minute or two max. Actually, Renix goes into closed loop real quickly also. I believe it's more related to O2 signal than temp. I've observed this more than once with my DRB hooked up. Link to comment Share on other sites More sharing options...
cruiser54 Posted December 5, 2012 Share Posted December 5, 2012 sorry i left out she has TBI injection ....i think i found it tonight ...i will pull out her tongue out Wednesday .........will up date and do a total write up ...... 4 cylinder then? Link to comment Share on other sites More sharing options...
cz777 Posted December 7, 2012 Author Share Posted December 7, 2012 update .. this started about 3 weeks ago the system went very lean like in backfires and hard to start .....i went with my fluke 88 the course of ohn and voltages all faired good ..what the moo?wiring good too so what is next ? yes she is a 2.5 liter TBI ... Link to comment Share on other sites More sharing options...
cz777 Posted December 28, 2012 Author Share Posted December 28, 2012 i have have them weird running times .....i caught it !!! damn gm tbi injector gremlin .....it stated to spray badly and stutter ....CRAP to caught them do this one and clean up its act ....damn !!!it will drive you nuts at times ! Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now