local dave

Hello every one this is kind of a long story so here it goes. I purchased my 3rd Cherokee the other day its a 1999 2 door gold 5 speed 8.25 with 302000. It had a hard time running had code p0108 map sensor voltage high. The old owner replaced the map sensor and the code didn't go away at this point it ran decent started right up but after a few minutes the idle would dip down very low and it would either want to die or die. So while driving it home I noticed that it would not rev past 3500 rpms and it would almost have a rev limiter effect. I have access to a mac tool scout scanner so I can see the values of all the sensors my map sensor was at 5 volts all of the time (running or not running ). When I back probed the center pin all of my readings where what they were suppose to be. So I did some testing and found out the my signal wire back to the ecm (green with red tracer) had no continuity from the middle pin to the 27 pin on the ecm . I could not find the break in the wire so I made a jumper wire. after that I plug my scanner in and now the values are 4.8 and vary while cranking. So I went to start it and it would not start only crank. With my scanner plugged in when I go to crank it looses signal to the jeep and says there a communication error. If I turn the key off and back on again it goes away but still wont start. Hopefully you guys can help me out im at a loss im a die hard Cherokee fan and I want to keep this one going thanks in advance.

jordan96xj

Crank-no-start diagnostic usually starts with determining which of the 3 following are missing: Spark, Fuel, Air. Then you work from there.

When the vehicle is ON (but not cranking), what does the fuel gauge and voltmeter show on the dash? If different, what do they show at the same time your scanner says that there is a comms error?

Cummins93

HF sells a hand vac. Great for testing map sensors. With key on engine off attach the vac to the map sensor while watching your multimeter or scan gauge. I've had many parts dead out of the box. Just had a new CTS tell me it was -40 in CT.

Idunno

The symptoms of starting and idling fine, then running poorly with a stumbling idle and no normal throttle response was fixed by replacing the IAC on my 98. Cleaning it did nothing because the stepper motor function was kaput. Then, the cold idle behavior seemed to deteriorate (or was marginal all along and my mind was focused on the hot idle/acceleration) until it warmed up and ran normally with the new IAC. The poor cold idle turned out to be the front O2 sensor. The OBDII system sensors are good for about 100,000 miles and should be changed regardless of condition.

On my 98 I changed the IAC and O2, as stated, to correct a symptom. Then I changed the TPS and back O2, taking the hint from the two I just changed suggesting imminent failure of the others. It seems to be running very well but not quite as smoothly as my 96. I'll be changing the CTS and ignition items in the coming days.

local dave

thanks for the reply Jordan so the battery gauge and fuel gage are accurate I can hear my fuel pump turn on I can also turn it on with the scan tool. Im not getting any ignition. I have a 99 four door auto parts jeep in my back yard I swapped the ecm and it does the same thing. its almost like when I turn the key to start it something shuts off like the ecm ? what could I start testing to determine what's wrong and hidden grounds or fusible links I may be missing there is no check engine lights no stored codes and all the gauges all work and are accurate. they jeep fired on the button before I made the jumper wire for the signal wire for the map it will only crank no start will not start on starting fluid after trying to crank it my scan tool tells me there is a connection error and losses all info

jordan96xj

Are your fuel gauge and voltmeter gauge still accurate when the connection error happens after attempted crank?

local dave

yes they are still accurate but the info on my scan tool gets wiped out the second I go to crank

jordan96xj

If you have a multimeter you need to read the system voltage while attempting a crank. With probes on the battery terminals, what is the voltage before the crank, and what is the voltage during the crank?

DCWinterXJ

Following...I have the same issue yet I have a 94 with a 96 engine. But the symptoms are quite similar. Wish mine had the obd2 connector and diagnostics. Many things were already replaced on my xj. Good luck. If you had my year I would advise you on what I had done so far but since you do not I dot know if I can help.

local dave

im going to verify this tomorrow after work the battery was a little low

local dave

yeah I think I read a little bit of your post have you gotten anywhere with it ??

DCWinterXJ

Not since yesterday. It is bitter cold in Jersey and now I am back in the work week. There is nothing I can do right now but more research. Personally(but I cannot prove this in any way) I think I have some shot wiring I need to locate. But in the interim I bought a few new sensors and what not...tps, iac, temp sensor....just because. Normally i dont do that but I had a couple bucks so it can't hurt. Anyway she is still in the doghouse. Drivin my car to work.

local dave

yeah im in ny its really cold here to and we just got a snow storm im going to wait until it warms up and than ill mess with my jeep

PatHenry

With the wind chill, -40 might not be that far off today.

jordan96xj

NY here as well. It was so cold today I went out at lunch and started the jeep up and let it warm, so that there would be no surprises when leaving work. Kid's Honda just popped a leak in the power steering line and its getting on the catalytic converter, so we are scrambling to figure out how to get that done quickly with it being so cold. What a drag.

PS. follow up on above. Got my butt handed to me by the Honda, worked on it till 1am. Lots of time spent on the 0 degree cement with water and ice everywhere. Had to take it into a shop the next day to complete the job. Haven't been defeated by my one of my 4-wheeled friends in a while, so I guess I had it coming. Took 3+ hours just to get the garage up to 35 degrees.