so my xj has been moved to reserve status, so it is driven infrequently. the last time i drove it at any good distance was 6 months ago. i noticed when i was almost home then, that it was obviously misfiring, and the CEL started blinking. it was due for inspection today and the battery was completely dead, so autozone replaced my gold series battery under warranty. on the way to the inspection (2.5 miles) i noticed it felt like it was missing. it being 20 years old now it is safety only here in NC. the cel wasn't on when driving there but was when i was leaving. on the way home the misfire was WAY more noticeable. i got back home, CEL still on, not blinking.

i waited a few hours, started it up, no misfire. i revved it a bit, still no misfire. i proceed to drive it around the block (<2 miles) it starts misfiring bad. and the CEL starts blinking.

so, is there a direction i should look for a blinking CEL due to misfire only when the engine gets close to operating temp and not at cold start?

spark plugs are new-ish 2 years ago or so.

thanks in advance!!

 

Here is a link to another user who is dealing with a misfire.
https://www.cherokeeforum.com/f2/how...isfire-256428/
First you need to read the code(s) and see if it is a multiple cylinder misfire or one cylinder.

 

If it is a P0300 (Multiple cylinder misfire) I would highly suspect clogged Pre-CAT. You've got to see what code you are throwing first. I've seen a lot of people start replacing plugs, coils, CPS, fuel pump and a laundry list of other items and still never solve the problem. My son's TJ did the same thing you are describing recently and both Pre-Cat's had broken loose and were clogging the exhaust. Replaced that and everything was fine. Not sure if the later model XJ's had that same pre-cat system or not, but I believe the 2000-2001 has that same system. There are more knowledgeable people here than me on the subject, only sharing my own personal experience. Unfortunately, the only way to verify that is to unbolt the pre-cats from the exhaust manifold and visually inspect them.

 

Obviously if you want to know what the CEL pertains to you need to know the code it has set.

 

P0303 and P0203. i cancelled the codes and changed spark plugs. runs way better, but the problem came back, this time just the P0203. cancelled the codes again, changed the coil pack, (after 177K it will need one soon anyway) problem came back, with both original codes. this time, it took a good bit more driving (2 miles-ish) before it started blinking again. there are no obvious breaks or frays in the number 3 injector wires, however the heat has disintegrated the wire loom that was once on there and bleached the wires almost white. i measured the resistance of injectors 1 and 3 while cold and showed both at 12.6. it starts fine and throughout this dance it always did while cold, and ran fine up until it starts misfiring. then it is obviously misfiring, like running on 5 cylinders.
im thinking of upgrading the injectors to the 4 hole units now.
please advise.

 

What are the resistances of the other injectors? You have to be very careful changing injectors, for one, do not get the chinese injectors off ebay. Been there, done that. Your reading sounds like it's within spec.

 

p0203 is injector circuit fault.either harness or injector i would say.

 

That being the case, look at the injector, wiring back the the pcm, check voltage on the injector, and lastly it could be the PCM itself.

 

Do you have a code reader where you can view live data?

Some other thoughts;
- Coolant temperature sensor that the computer would see.
- Fuel pump.

How does the car react on a "hot start?"

 

i cant read live data, i dont think anyway. it's my neighbor's code reader and its a MAC unit from years ago. the fuel pump can be heard priming to pressure when ignition is switched on, before starting. just curious, how does the coolant temp sensor come into play?
on a hot start, once it has been misfiring, it starts right up, but still misfires.

 

Fuel pressure should be around 50 psi. A pump that is / has warming up, might not deliver the necessary fuel pressure.
If you are able to view live data and look at the coolant temperature sensor that the computer sees, it would give you an idea if for example the coolant temperature sensor is stuck at a value of -40*. This would cause the computer to think the engine hasn't warmed up & would continue to dump excess fuel.

 

i am able to read live coolant temp, and it seems normal, starting out with ambient air temp and rising as engine gets warmer. i ordered rebuilt injectors today from ksuspension, and this...