I have read and read and read pages of threads looking for the same issues I am having. With no luck.

It started with the typical misfire codes P0300, P0301, P0302, P0303, P0304. With a rough Idle.

First step I replaced the Spark plugs, wires, cap, rotor, and Crankcase Position Sensor. I took out and cleaned the Throttle body and injectors.

I cleared the codes and they came back only now it includes P0118 (M) ECT Sensor Voltage Too High Engine coolant temperature sensor input above the maximum acceptable voltage.

Also I went from 18mpg to 7mpg.

I did find a small crack in the exhaust manifold down hear the bottom.

Any and all ideas will help alot.... I'm lost.

 

Replace cracked manny. Clear and check codes. Possibly replace both o2 sensors. Does it ever pop (backfire) at manifold? If so, possibly running lean- check fuel delivery.

 

Also sounds like the sensor you mentioned may need replaced..

 

No backfires but it does feel like the exhaust is pulsing if that makes sense. I have another manifold, I will put that in today. Will a faulty ECT cause the bad fuel economy?

 

If you have a P0118, odds are high that the coolant temperature sensor itself is shot. I'd replace it and start there; it is a VERY important sensor and it could have a direct relationship to your crap gas mileage. They aren't expensive and are easy to replace.

More on the P0118:

http://www.obd-codes.com/p0118

 

And while you are at it..That little tube from the TB to the MAP sensor up on the firewall is crucial. Any crack, blockage ect will tank your mileage...I bumped mine messing with my injectors and it broke. Good luck, please keep us posted.

 

Hitting my head against a wall.... replaced both O2 sensors and the coolant temp switch and sensor. Cleared the missfire codes and try theP0118 it will not clear. Also having a hard time starting now. still running like SHart.... I checked all the vacuum lines and didn't notice any cracks, holes and disconnections.

I'm done throwing parts at it...

 

Supper easy check. Unplug the little rubber vac connector on the map there on the firewall and feel there for vacuum. The line might be plugged.

 

SO.... I checked the MAP sensor and vacuum lines and had good "suction" with the motor running.

I went ahead and reinstalled the temp switch/sensor at the thermostat housing back with the original one that was installed. I did this because I could not clear the code P0118 from the computer. Every time I cleared it, it came back on. I also notice the engine was running worse and had a very hard time starting. With the new sensor installed.

After this I also noticed I did not have a temp reading on the gauge on my cluster. I must have a bad temp switch that I had replaced as well. Back to auto zone with this as well.

All in all I drove it around about 40 miles between last night and today. With 4 cold starts I believe I'm past the break in stage for the O2 sensors I installed.

Its running better and I think my MPG are back to what it was before.

I will still replace the temp switch and sensor. I still have not had a chance to replace the exhaust manifold. With a three day weekend its on the short list.

Thanks for everyone's help and will keep you posted with my progress.

 

I don't know which years have what temp sensors where. My 90 has five. Gauge, at back of head,-engine, below manifolds,- fan, on radiator,- intake air on manifold,-ambient air, behind the front bumper. (is the best I can figure)

Did 96 combine the fan and gauge on the t-stat and the engine is below the manifolds?

My point is I hope you changed the right sensor. Glad it's better, tj "knows things"!

 

I have had the EXACT same problems, same codes I did my O2 sensors and it took a little more than a few starts but it cleaned up and no more codes, I never heard of that MAP vacuum line in all my searching, gonna check that tomorrow! just to be sure.

 

I know the one on my thermo housing controles the fan. The motor was hot, fan was running and when I unpluged it. My fan will go off.

 

I know the one on my thermo housing controles the fan. The motor was hot, fan was running and when I unpluged it. My fan will go off.

 

From reading your posts here i'm wondering if you mistook the sensor on the thermostat housing as the ECT sensor. I missed what year,model, engine you have, but on my 4.0L the ECT sensor is near the rear of the engine on the drivers side. Sorry if I misread

 

Well...I just spent a good while looking it over. After downloading your FSM I finally found under "fuel injection systems", that it looks that your sensor is indeed there in the T-stat housing.

I stumbled on an article suggesting you check the IAT sensor if your code comes back after changing the CTS. But that's not related to your gauge. I would think you need to get that sorted out next.

Ha! found a pic of TJ back in 09! http://www.jeepforum.com/forum/f11/1...e-time-930471/