Few months ago check engine light came on and it was hesitating/misfiring. Took it to dealer and reported spark plugs bad. Replaced.
It continues to do the hesitation. It begins after approximately 10-15 minutes of driving. It will do it at idle or driving. Longer I drive the more it does it. It feels like a Buck or misfire.
For example driving on highway cruise at 105. It does the momentary Buck and cruise drops to 102 then immediately accelerates back to 105. Repeated over and over. No check engine light.
Took it back to dealer. They claimed it wasn’t doing it for them but had noted throttle body was dirty and could cause it. Had it cleaned. Still doing it.
Took it back for routine oil change and pressed this issue again. They said it was low on oil and the oil cooler was leaking and was the cause. I have to wait for part and it’s not super cheap.
However they did an oil change and it still does it immediately after. So even full of new oil it’s doing it. So why would low oil as a result of a leaking oil cooler be the cause?
They said without a check engine light it’s hard to diagnose. They did drive it for 18 km so they had to see and feel the issue but I’m not confident in their diagnoses.
If wouldn’t. They found the leak problem and are grabbing at straws hoping that will fix it.
This Jeep is 9 years old, why have it serviced at the dealer?
Find a local well rated independent shop. Try scheduling an appointment for a ride along with a mechanic equipped with a computer scanner so the problem can be identified.
Tester’s post for crankshaft sensor is a real possibility. Might even be worth just installing a new sensor. They are not usually expensive
The worse-when-engine-warm symptoms are definitely consistent with an ignition system problem. Likely possibilities are the crank sensor (as mentioned above), spark plugs, coil(s), or ignition module (if so equipped).
While there are no active current diagnostic codes, there could be pending codes, so make sure shop is checking for those too. Also
Ask shop if they have a way to disable cylinders one at a time to see if problem is occurring on only one cylinder? Modern pro-level scan tools are able to do this test probably.
If using that method they can ID the problematic cylinder, using that same method, it might be possible to determine if problem is the ignition system or fuel system.
Still no joy? Try to eliminate possibilities by using common sense. Any signs of an exhaust system leak? Intake air boot leak? Might try replacing any suspect -looking vacuum tubing, replace oil and filter, spark plugs, inspect coil and fuel injector connectors.
Intake manifold vacuum reading ok?
Engine compression test
Fuel pressure test
Transmission problems can mimic engine problems sometimes
These sorts of problems often require a lot of experimentation to solve. I had a similar problem on my truck a few months ago. Very bad misfiring. Ok, at first, but worsened as engine heated up, to the point sometimes it was barely drivable. I guessed ignition system for the same heat-related reason, and changed a bunch of stuff, no effect. So I formed another guess, experimented, with the fuel system, solved in less than an hour. Truck is much older than your Jeep, so can’t compare methods directly.
I appreciate the replies. I am going to press the issue some more.
One thing is they want me to have the oil cooler replaced and are convinced that is the problem. I am not convinced. They said they told me oil cooler was leaking in 2018. Implies I should have had to rectified then. I went back through service invoices and found august 2018 they did note oil cooler faulty and repaired it under warranty. Now want me to do it again.
That seems unreasonable to me. And also isn’t addressing the main issue. I am waiting a call from them to press the issue. (Going to have to go somewhere else I guess but I think I’d they replaced oil cooler in 2018 should they not fix it again now without charge?)
When the oil cooler was leaking, the engine oil mighthave gotten low enough to damage the engine internally, causing low compression. So imo as a first step it makes a lot of sense to ask shop to measure the compression in all the cylinders.
If compression tests ok, one idea for this symptom is a sticking EGR valve. Whether that would cause a check engine light depends on how the EGR function is verified. On my Corolla the computer knows when the EGR should be on, and it verifies that by measuring the temperature of the egr exhaust path. When the EGR is on, that path is open, so the temperature there should rise appreciably, from the hot exhaust gasses passing through. Suggest to research how the EGR function is computer-verified on your Jeep.
Things seem to be resolved. They did the oil cooler replacement first and then tech took it for a drive. Initially reported no issues other than a “flared shift twice”.
Techs notes:
Performed TCM adaptive reset and TCM relearn. While relearn in progress vehicle began to have intermittent misfire. No fault codes or MIL inspect OBD2 misfire data found.
#3 cyl randomly misfiring swap plug with cyl 1 and coil with cyl 5. Misfire followed coil.
Replaced ignition coil in cyl 5. Problem corrected.
And so far it appears to be corrected. Seems to have corrected a long standing (I was used to it and stopped paying attention) issue where occasionally it would hesitate for a moment on acceleration.
Not to sound like a sourpuss . . . did the shop give you an option or estimate to replace ALL the coils and plugs?
The other coils have been in there just as long, and there’s a fair chance they’ll also fail soon
A good shop will recommend replacing all, to avoid the scenario where the customer returns a month later to replace another coil and then comes back the month after that to replace yet another coil, etc.
I replaced spark plugs on one of my cars yesterday . . . as routine maintenance, not because of a misfire, btw . . . and noticed one coil had a crack on the underside
I’m replacing not just that one, but ALL of them
That’s a good point. They did not make that suggestion.
What started us down this was a spark plug replacement due to a check engine light and misfiring. Is it possible a tech could damage a coil while doing that?
This was done at the dealer. And while I do have an independent shop I like I went to the dealer because they got me in immediately and my local guy could not. And I was told I had to go to the dealer for a later alignment after blowing two tires on our crappy roads. So basically I was down the path of seeing the dealer.
At least it’s resolved. Coincidentally while they were finally repairing my jeep I was driving my gf’s 2013 ford focus and it felt like it misfired and gave a check engine light. Doh! Going in to our local guy next week….
