Before I spent any more money on parts Id run a compression check and a leak down test...
Ive seen a 4 cyl toyota 4x4 drop its mileage by half and it turned out to be low compression.

 

Yea I am going to do that tomorrow.

 

Ok on my results from the compression test and leak down FSM says between 120-150 with a deviation of 30 between all cylinders is ok

cylinder#1 153PSI 3% leak
cylinder#2 149PSi 5%leak
cylinder#3 151psi 6% leak
cylinder#4 145PSi 12% leak (Exhaust valve is not sealing completely)
cylinder#5 155PSi 6% leak
cylinder#6 152PSI 3% leak

My gauge said above 10% is a low leak. So Only one of my cylinders even can be considered a low leak and the others are at the top of there PSI....

I have a lot of carbon in my exhaust. You stick your finger in the pipe and it looks like you just stuck your hand in a chimney. Covers your fingers black. So I think it is still over fueling and it still runs the same. So... any ideas?

 

Sensors. You get to enjoy the fun of using a multi-meter to test all your sensors. If they're all good then I'm out of ideas

 

This what I have been saying.

And 4.0Cherokee you mentioned something about the computer/ECM. Are you going to swap it?

 

I wouldn't swap any more parts until I know all the sensors are good, Multi-meter's are cheap, easy to use and a great tool to have. Testing sensors is pretty much as easy as doing what the FSM or Hayne's manual tells you

 

I know that. He said he had a mechanic look at it and found nothing wrong. However it is cheaper to check the sensor's then what a ECM will cost.

 

What computer will fit in my 99? I dont know about the 00-01 becuase they are coil packs and i dont know if the computer controls that or not. Can somebody else chime in and help me out.

 

I skimmed through this thread and don't remember sseing anything about changing the o2 sensor. It maybe worth looking into.

 

What about the Gumout. Liquid you put when you about empty in your gas tank and fill up your tank with gas. Ive read that over time it will help you engine with performance, power, gas, and cleaning of the engine. Is this actually true? Has anyone ever used something like this and if so what was it and what was the result and would you recommend it?

 

Yes this has already been discussed.

I started a post that netted zero responses about tuning the engine computer.

My weekend toy has been tuned and the performance difference is amazing.

So does anyone tune their Jeeps?????

 

havent heard of anything, what did you do?

 

I've gotten the impression that you couldn't change anything unless you built you own adjustable MAP.
Can you change some of the tuning in the ECM?

 

on my last diesel you could put an inline resistor in the fuel electrical system, to fool the ecm into sending more fuel pressure. dont know if something like that is possible or not. but just to be safe, i wouldnt use anything other than a tuner or chip to avoid screwing something up.i havent had to price an ecm yet, but im sure there not cheap

 

The last 4 posts are total crap. Go somewhere else and jack someone else's thread. Messing with his ECM isn't going to solve the problem. If the ECM is bad he just needs to replace it. It probably isn't and there's just a bad sensor somewhere