My jeep is doing the same thing but runs perfectly fine no power loss no smoke but horrible gas mileage

 

Any progress on the diagnostics? I am eager to hear the cause of this before I start troubleshooting mine.

 

Same here. Did you ever put that new ECM in?

 

X2...........sounds like a bad sensor screwing with the pcm, you need to either test the sensors or have someone with a scan tool to read live data so you can see what the pcm is seeing. Maybe it would show something weird like an IAT sensor -40 degrees or something.......

 

Ok so I did have somebody scan and nothing came up. I checked everything, and nothing was bad. I did get a new ecm but the jeep would barely run. It was an early 00 that i got and was told it only had 2 o2 sensors but it runs like poo. So I have my original in.

 

I had to dig deep for this one.....page 39....lol.

Anyways, My XJ has been doing the same thing as far as the MPG's. I have the ford yellow injectors and a high pressure fuel regulator installed. 99+ intake, 63mm TB, free flow exhaust, CAI. I used to get like 20-24 hw. (that was when it was 2wd) I am running the stock (3.07) gears with 31's. I'm re gearing soon to 3.73. This is my DD. I checked all the sensors, except the o2 today, and all looked good per the Haynes manual. But I do have one question, In the manual it said that the "TPS for the black wire, to the center, (still plugged in with the key on, but engine off) closed throttle should read greater than 200 milli-volts, and fully opened should read a little less than 4.8 volts."

When I did this mine read -4.8volt closed and -1.012 volts opened? I'm guessing that the TPS is bad? and would this contribute to my gas mileage problem? Does the TPS have anything to do with air/fuel ratio?

Also wondering if 4.0Cherokee ever figured out his problem?

Thanks,
J

 

No i never figured out my problem. I actually think my tps is messing up now. Sometime when i am acelerating i will hold the pedal in the same spot and my jeep will just stop accelerating. It wont die. It will just all of a sudden stop going foreward. Sometimes I will hold the pedal in the same spot it might just take off all of a sudden. Anytime it does this I can either let off or punch it will fix the problem for a little bit. Does this sound like the TPS?

 

The O2 sensor has final say on the AFR. Indirectly, the TPS will transmit its position to the ECM for acceleration and baseline AFR for the given amount of throttle.

 

i found my coulpret the other day i think....IAT sensor was going bad, swapped in the new one and i never knew my Jeep had that much power

 

This sounds like your advance is screwed up. Have you thought maybe your timing belt jumped? Distributor off? Vacuum advance not working?

 

IT can't be that easy

Did you also reset the ECM?

 

I am having the same problem...literally. I just havent checked the sensors.

My uncle and his class at college will be checking it over soon. Hooking it up to the computer and all. Apparently there is a very good mechanic there too.

I shall report back.

My mileage has gone from 21, to 17, to 12, then back up to 14 as of right now. It has been at 12-14 for a few months now. No fun.

 

How often does the timing jump...

 

the Jeep 242 doesn't have a timing belt, it has a timing chain.

sometimes it honestly is.

I've never heard of it jumping, I've heard of people stretching their timing chain to the point it sounds like they have lifter tap really bad or even a mild rod knock. If your timing chain is bad then you'd know because it'd be making a horrid racket and the Jeep wouldn't be running right/

 

The timing chain can stretch on high-mileage engines and can produce symptoms such as lack of power, poor gas mileage, engine misfire, backfires, etc. Really all depends on how off it is - if at all.

Searching the net it doesn't seem like it happens often with this engine with some folks saying their chain has stretched with around 130K on the engine and others over 200K with no ill symptoms.

I'm just not familiar enough with this engine to tell you exactly what to do to test it other than pull off the timing cover and measure the slack. Search the net.

But I did want to point out that there are a few things left you could check without convincing yourself you are bats for tackling an imaginary problem