engine running funny

[92xjlaredo]

okay anyone ever have your 4.0 just run like shit every so often, seems to run worse as the motor gets hotter until you hit a maintained speed of around 30-40. almost as if its misfiring on a few cylinders. replaced the ignition coil, that really helped but still doing it from time to time, it doesnt have a consistent symptom or time to do this which is why it puzzles me. theres nothing that triggers it and nothing that really makes it do this. was down about an hour south of home the other day and it just refused to start in a parking lot, we unplugged the coolant sensor and cranked it over. it started but barley ran. shut it off plugged in the sensor and fired right up. does that temp sensor (thermostat housing one) really affect the motor THAT much or does it sound like i have something else going on? thanks gents

[CumminsJeep]

You seem to be in the right ballpark because it does sound like a sensor issue. 4.0s are known for crank sensor issues so it can't hurt to swap that out. Just do yourself a favor and get a dealer one. aftermarket parts store ones are sometimes garbage right outta the box. Its rough throwing parts at an issue like this but sometimes its what you gotta do if the problem can't be seen 100% of the time or with a good scan tool like a Modis

[ninetysix-ex-jay]

To answer the question about the coolant sensor : yes. It does effect it that much. When mine was going bad the jeep wouldnt run at idle and would break up around 2000rpm. To get it to start i used to put the gas to the floor and crank it over and never let it idle.

[92xjlaredo]

Just put a brand new one on order from the parts store today. Hopefully this clears it up. Did some research and now I know why it affects it so much. Lol I've had them read wrong at the gauge but never die on me like this before.

[92xjlaredo]

Okay. So its still acting up I'm at Cayuga lake with a few of my friends, we stopped to get drinks and whatnot at a convience store...went to start it up and it was running.on maybe 1 cylinder. It only does this when the temperature gets to around 210 Anyone have anything like this happen? And if Sivan you gimme a suggestion here, system has a 180deg thermostat, fresh coolant 50/50 mix withing a month or so now, and a brand new coolant temp sensor. Thanks gents

[hoggie101]

This is a long shot but did you check your cap and rotor maybe when it heats up it expands bc somethings wrong with it cracked/boltmissing

[92xjlaredo]

Well both bolts are there....can't tell for cracks yet because I'm still at the lake once I get home ill see about cracking.or any other damage

[92xjlaredo]

This is a long shot but did you check your cap and rotor maybe when it heats up it expands bc somethings wrong with it cracked/boltmissing

no cracks or other damage, thanks for the suggestion though. its too late now but it seems as though i have a bad crank sensor. ill need to run some tests in the morning....

[justtorchit]

Okay. So its still acting up I'm at Cayuga lake with a few of my friends, we stopped to get drinks and whatnot at a convience store...went to start it up and it was running.on maybe 1 cylinder. It only does this when the temperature gets to around 210 Anyone have anything like this happen? And if Sivan you gimme a suggestion here, system has a 180deg thermostat, fresh coolant 50/50 mix withing a month or so now, and a brand new coolant temp sensor. Thanks gents

it gets hot.... you shut it off... start it up and it starts to run on 1 cylinder? till you floor it and they slowly all come back???

sounds like alot of cherokees.

1 theroy is vapor in the gas line.... the fuel pump should have a check valve of some sort... these leak over time....
heat from your exhuast and engine bay creates the gas in the line to turn to a vapor as the fuel is pushed back into the tank. then when you start it up its pushing the vapor and choking on the little bit of gas actuallly going into the cylinder.

[92xjlaredo]

it gets hot.... you shut it off... start it up and it starts to run on 1 cylinder? till you floor it and they slowly all come back???

sounds like alot of cherokees.

1 theroy is vapor in the gas line.... the fuel pump should have a check valve of some sort... these leak over time....
heat from your exhuast and engine bay creates the gas in the line to turn to a vapor as the fuel is pushed back into the tank. then when you start it up its pushing the vapor and choking on the little bit of gas actuallly going into the cylinder.

just figured this out today, let it heat up until it was wayy too hot and barley ran. poured some cold water all over the intake and fuel rail and within seconds it perked right back up...gotta figure out how to keep the heat off of it until i can replace the header haha thanks gentlemen!