A week ago, my XJ (2001, 4.0, AT, 4WD) started running very rough on *every* hot start - so rough I could barely coax it through a parking lot. It did not go away if I gave it gas, like it would with heat soak. However, if I disconnected the battery for long enough to reset the ECM (~5 min) it started right up, no problem. I had no problems whatsoever on cold starts. It threw a few codes during this time, all misfires, multiple cyl and then #4. The problem occurred after a 700 mile drive to Nashville. Before that drive, we hadn’t been putting many miles on it, maybe 50 a week. We made it back to DC fine - I avoided hot starts when possible and used the disconnect trick twice. Other than this problem, the jeep was running fine. Three days later, the problem disappeared. It’s back to running like it should.
Background: bought it about 18 months ago. I had some intermittent issues with misfires, rough hot starts, and occasional stalls. The stall issue magically resolved itself last year. The rough hot starts seemed to be related to heat soak and went away when I installed some heat shielding on the rail and injector #4 this summer - but it’s hard to say exactly, because the issues have been so intermittent. Some of the misfire codes do not seem to be related to heat soak, and come up even when there isn’t a rough start or noticeable issue.
Relevant work done: did a compression test recently and it passed with flying colors. In the last year I’ve replaced the plugs (Autolite Copper Core) and cleaned the TB and IAC.
As best as I can guess, the problem is emanating from the ECM (otherwise, why would resetting fix it?) But reman’d ones go for $250 online, used on ebay is $100, and the junkyard isn’t a great option either (nearest pick and pull with a 2001 is an hour away, and there’s no guarantee the ECM would match or even still be in the vehicle).
But I'm not discounting the chance it could be something else entirely, which is why I'm a little wary spending money + time on the assumption it's the ECM. From what I've read, people tend to blame the ECM when they can't otherwise diagnosis a problem. And this Jeep has had enough misfire issues prior to make me think that the recent issue could be connected.
So while it’s working right now, I’d be nervous to take it on any major road trip until I figure out what was (is?) going wrong. But I have no idea how to diagnose a problem that isn’t happening anymore.
Apologies for the novel, I just wanted to put all the info up front.
I’ve searched the forums and google to see if anyone else was able to fix hot start problem with an ECM reset, but didn’t find anything. Anyone got any ideas?
Background: bought it about 18 months ago. I had some intermittent issues with misfires, rough hot starts, and occasional stalls. The stall issue magically resolved itself last year. The rough hot starts seemed to be related to heat soak and went away when I installed some heat shielding on the rail and injector #4 this summer - but it’s hard to say exactly, because the issues have been so intermittent. Some of the misfire codes do not seem to be related to heat soak, and come up even when there isn’t a rough start or noticeable issue.
Relevant work done: did a compression test recently and it passed with flying colors. In the last year I’ve replaced the plugs (Autolite Copper Core) and cleaned the TB and IAC.
As best as I can guess, the problem is emanating from the ECM (otherwise, why would resetting fix it?) But reman’d ones go for $250 online, used on ebay is $100, and the junkyard isn’t a great option either (nearest pick and pull with a 2001 is an hour away, and there’s no guarantee the ECM would match or even still be in the vehicle).
But I'm not discounting the chance it could be something else entirely, which is why I'm a little wary spending money + time on the assumption it's the ECM. From what I've read, people tend to blame the ECM when they can't otherwise diagnosis a problem. And this Jeep has had enough misfire issues prior to make me think that the recent issue could be connected.
So while it’s working right now, I’d be nervous to take it on any major road trip until I figure out what was (is?) going wrong. But I have no idea how to diagnose a problem that isn’t happening anymore.
Apologies for the novel, I just wanted to put all the info up front.
I’ve searched the forums and google to see if anyone else was able to fix hot start problem with an ECM reset, but didn’t find anything. Anyone got any ideas?