CMI86

First issue is that here in the Minnesota cold my engine does not reach operating temperature. Has brand new Mopar 195* stat as of 8/2014. During the summer you could watch the gauge run up, lower and then run back up indicating the stat is functioning. Now I am lucky to get the gauge to go up over 150* while moving. If sitting still for a long time I can get to around 195* but see no action from the stat. This is a problem to me because my brand new heater core (did it myself !!) is producing poor heat and it is very cold here.

Second issue is an intermittent hard rhythmic miss at idle.Sometimes after driving the jeep for a while and I come to a stop you can hear and feel perfect bum bum bum bum miss in the engine. Any throttle application the miss immediately goes away. Never misses at speed only at idle. Sometimes throws a code sometimes it doesn't. Sometimes restarting makes it go away sometimes it doesn't.

Yesterday for the first time my vehicle started and immediately died which I understand to be a symptom of a crankshaft position sensor ? Could a dying CPS cause my odd miss ?

New cap & rotor, new plugs (autolite) new wires mileage plus. Ran techron fuel system cleaner symptoms still persist.

Thanks in advance for any ideas.

'90Cherokee

If the cold running started only after the thermostat replacement that's the place to start looking for the problem.

Is the code indicating which cylinder is misfiring?

Indicating what year and engine you have will help you get help.

Crazy 8s

The thermostat might be stuck open. It seems to be a common problem with some aftermarket parts.

The missing issue might be trickier to diagnose. You might try to isolate which cylinder is the culprit to make diagnosis easier... Could be clogged injector or its wiring. Could be worn rings, bent pushrod, damaged lifter, head gasket...it could be a lot of things...

tjwalker

1. Always post the year and engine when you start a thread. There are significant differences through the years, so accuracy in vintage provides you the best chance to get solid advice.

2. You mention that "sometimes it throws a code, sometimes it doesn't". The strategy for a check engine light is ALWAYS the same. Retrieve the code; use the technology provided to you on your Jeep. OBD isn't perfect, but it is by far the best source for clues and guidance on where to start troubleshooting. Once you get the code, post it here for comment. Be sure to post the exact code, not just a description. When diagnosing OBD, the devil is definitely in the details.

CMI86

Thanks for the replies. The cold running didn't start when the stat was replaced, it ran at perfect temp with the new stat up until a real cold snap set in up here and now it doesn't get to temp.

As for the miss the code is P:300 random misfire. I have not determined which cylinder but I would guess it to be the same as the rhythm and sound/feel are always the exact same. The odd thing is that sometimes the CEL lamp will shut off on its own, comeback on with a p300 when it seems to be idling just fine, ill clear it then sometimes it doesn't even come on when the miss is obvious.

Firestorm500

He said he had a MOPAR 195* stat.

OP: Try putting a piece of cardboard in front of the radiator or condenser.
Also, your water pump might be a little weak and not pushing water to the heater core. Your coolant might be low.

Use your on board computer and a scan tool to narrow down your miss. A lot of things can cause that. Find out before throwing parts and money at it *****-nilly hoping to get lucky.

CMI86

96 Cherokee Classic 4.0/Auto/231 284k miles

Crazy 8s

Chances are that the MOPAR branded parts are made in the same places the aftermarket parts are. I am a bit skeptical that the MOPAR name means much more than a bigger price tag.

In the 18 years since this chaps Jeep was made, the US has offshored most of its manufacturing capabilties...

CMI86

The funny thing is the radiator is pretty much junk to the point where prolonged driving at less than highway speeds in the summer would cause the temp to very slowly creep up and up to the point of mild overheating. I can only imagine how cold I would be with a good radiator.

I know the pump is good and fluid id topped off. The day I did the heater core it was about 50 degrees out. I started the truck and let it warm up. Thermostat operated perfect and it was idling at a tick under 210 within 10 minutes and blowing very acceptable heat.

Now at 10 degrees I can drive 30 miles and never get warm enough to even the stat a chance to open and start circulating hot coolant to the core.

CMI86

96 Cherokee Classic 4.0/Auto/231J 284K Miles

P:300 Random misfire code.

CMI86

It is just so odd that the new stat has been working just perfect in semi warm temperatures but now that we hit a real cold snap it just decides to get stuck out of nowhere.

Crazy 8s

I am not a pro at underheating vehicles, living in Arizona where the problem is usually in the other direction. I did read that some folks who have trouble getting their temp up have blocked up part of the radiator with cardboard and disabling the electric fan. It might just be really frickin cold where you are at and your cooling system is too efficient.

CMI86

Well I don't know if it is too efficient because in the summer it is not efficient enough lol.

Sails

With regards to the heating issue, I would test the thermostat.
To me what you are describing is an open thermostat and the coolant is circulating fully all the time. The thermostat's purpose is to remain closed allowing the engine to heat up to the desired temperature, if the engine isn't coming up to the proper temperature pulling the thermostat and checking that it is working properly would be the first step to trouble shooting the issue, at least to me.
It may be relatively new but even new things have been known to fail.
Just my nickel's worth!

Firestorm500

Even if it was made by a manufacturer that also makes other brands, the manufacturer will tailor their process to the customer's specifications.

Many people seem to have trouble understanding this business practice. Everything is NOT the same.