hey i got an 88xj with a 4.0 auto, and ive been having nothing but problems with once i get one thing fixed its another, now when im driving it will bog down some and then come back and run fine, and it does it every now and then seems to be at lower rpms, and speed, but when your on the gas hard at higher speed it doesnt do it, also when you put it in drive or reverse and hit the gas it will stall sometime, and when parked it idles way down and stalls some times also and comes back when it doesnt stall, im running out of ideas and throwing parts at it, ive replaced the tps, iac, cps, cam sensor, fuel pump filter pr, cap roter plugs wires, all the grounds seem good too, also put new exhaust on and noticed inside the pipe was verry black and almost sooty, and checked the plugs and they were too, seems to me its getting to much fuel? any help would be grat thanks

 

While you're at it you might as well replace the map and Iat. They are the two sensors that would cause a rich condition

 

ok thanks i know the map and coolant temp sensor, have something to do with the air/fuel mix i was thinking about changing them but tired of guessing, and spending money on things that dont fix it

 

All the grounds "seem" good. That don't work unless you have the capability of seeing electricity flow.

Your generation of Jeep was notorious for an underdesigned grounding system. You must remove each end of the strap from the firewall to the head. Clean til shiny both ends and clean down to bare metal where they attach. Do the same with the connections at the dipstick tube stud.

 

sorry i should of been more clear with that, grounds have been removed and cleand also added one from the battery to the body, and ran a new gound wire to the tps from firewall, all was done after this problem started and made no changes

 

Start testing. Here's a link http://www.lunghd.com/Tech_Articles/...iagnostics.htm

 

yeah ive been avoiding doing that but im going to tonight.

 

Did you test the ground at the TPS for resistance before modifying it? Check the MAP sensor ground (Brown with White tracer) from the wire to the negative side of the battery. Must be less than 1 ohm. Check the same colored wire from the IAT while you're at it. There are some splice/crimps in that circuit that can vary the resistance to about 5 sensors and send you on a wild goose chase. Easy to fix if that's what you find.

 

so i havent had time to check anything yet but i was driving it today and and got to messing around with it. so the main problen ive been having is while your driving at any speed and in any gear it will all of a sudden bog down like your putting a break on in the motor, and then it will go back to normal, it doesnt seem to break up or run rough when it does it, and revs and idles fine in park. so when it did it i put it in nutrual and left my foot the same on the gas and it reved way up and then i pulled it back in gear and bogged back down and eventually want back to normal. i did it a few time and it did same thing, im thinking the trans is bad and locking up some how?

 

it does have a speratic ide sometimes but i think my new tps is bad so i got a knew one gunna put it in and see if it changes that

 

Ya that definitely sounds like tps and or map. The tps and map should have the same input voltage. Sure sounds like tps problems. Make sure to check the input voltage to both. Also use each sensors respective ground when testing. DO NOT USE A BODY GROUND OR THE BATTERY WHEN TESTING, you will get a different reading. This is where I'm confused, if you check for voltage at the tps ground it comes up with like .3. I have read up on this and found people saying that the ground is a "floating" ground coming out of the computer, separate for each sensor. This was done as a buffer to prevent voltage spikes. For this reason I was told NOT to run a separate ground to the body.....

 

when i was just putting the new tps in and adjusting it was spiking the voltage to 4.64v what is the same as the input and i adjusted the output to 3.85v what is 83% of input and still runs the same as befor so i cut the added ground and no changes, so i put in a knew map sensor and didnt change a thing either? smell like it running rich to me and seems to be loading up too

 

What do you mean spiking? And did you test the input to the map? Should be the same voltage as input to tps.

 

Ebay do out mean spiking? huh?

so i did some testing, the O2 needs 5-7 ohms, mine was at 16, the cts with the temp at 212 should have 185ohms, and so should the mat, at 210 my cts had .254, and my mat had .647, also the map has 4.99v input, and the out put was 1.7 wich is good, but my tps had 4.59v now not 4.64 like earlier, and tho output wasnt spiking since i cut that ground off, and the ground at the mat tps and map had o ohms so there good. so ia my o2, cts and mat all bad?

 

O2 is not a very good test. A better test is to warm it up and with it running back probe the connector to ground and output. The reading should jump up and down every second or two. The mat would cause a rich condition so sounds like that might be he cause... the cts also.. which did you measure? Back of head?