Runs then dies

[Tbates]

Have a 97 xj 4.0 l. I can start the jeep and leave it idling and idles good for 15-20 minutes then out of no where dies. I can restart it and runs good for same time, but after driving for a while it won't even hardly idle I have to do the classic drive with 2 feet to keep her running. It doe have a map sensor code stored I. The PCM but wasn't sure if that would give these effects. Key on voyage is like 4.5v and idle is like 1.4v. Is that voltage wrong or am I going the wrong direction all together with the running issue?

 

[greg92jeepxj]

Hey Tyler , sorry to hear about your driveability problem. Since the PCM has already logged a trouble code for the MAP sensor , it is best to proceed as you are doing . I do not have a reference to your '97 , but if the wiring color codes are the same for the '92 , I have that reference . The wiring diagram shows the ground as black/lt.blue tracer position A , signal wire as dark green / red tracer position B , and 5 volt reference wire as violet / white tracer position C .
Hope your using a computer safe volt meter , really important to do so . A meter that draws too much voltage to power its circuits will cause damage to the PCM . A computer safe test light should only be used as well with any PCM circuit on any vehicle. It's good your getting a full reference of 5 volts which tells us the PCM is putting out properly . The signal back to PCM is what tells the story whether the MAP sensor is working correctly . From idle , the reading increase with engine rpm . If not , either vacuum signal is poor to internal MAP diaphragm or an electrical problem with the sensor itself . Either way , warrants replacement . Verify vacuum exists at connection to MAP by pulling it off at idle and replacing quick . Idle will stumble and want to stall . Be sure that no vacuum leak exists from intake to sensor if you didn't already .
Back probe the B position ( weather pack connectors are marked with letters ) and take note to readings idle and during aceleration until highest reading is obtained and at what rpm .
The signal reading should reach almost reference voltage topping out at highest rpm by WOT ( wide open throttle ) . You will also want to look for any other vacuum leaks as well but this does sound like an intermittant driveability problem that can be caused by a faulty sensor , wiring and sometimes the PCM . We should not be quick to blame a PCM , but we want to be sure all else is good before we do . Wiring harness and grounds must be good to prevent PCM error or failure.
A good check for proper PCM activity is checking the TPS in the same manner , reference and signal , to verify PCM behavior as well as TPS condition . A diagnostic favorite. Hope this helps toward diagnostic check and hope it may solve your driveability problem . Post results as you can . Greg

P.S. - I should add that the air intake duct from air cleaner to throttle body be checked for vacuum leaks I.E. tears and rips as well .

 

[johnsjeep]

I would check the speed sensors and crank sensors if they have not been replaced already. Very common issue.

 

[White Buffalo]

If you need wire codes for your 97 I have the shop manual for the 98 uses the same wiring as the 97. It makes life easier for me to trouble shoot wiring problems on my wife's XJ

 

[Tbates]

I have not replaced any sensors and knew the crank sensor was a common problem on Cherokees just didn't know if they would throw a code or not or what symptoms they give. And yeah wiring schematics would be great

 

[greg92jeepxj]

To check the CPS , back probe the middle terminal on the harness disconnect with an ohm meter to battery ground ignition off . Should receive 5 ohms if no problem with wiring. Key on engine off , back probe with voltmeter middle terminal and either remaining terminal . Should receive 5 volts. Then , back probe the remaining terminal terminal that did not read 5 volts ( providing you did read 5 volts ) , crank engine and verify reading . Should read 0-5 volts with an average of 2.5 volts .
If any of these readings with good meter connections are not observed , CPS is not within specifications .
If trouble code is not logged , it is usually because the problem is intermittant and does not appear long enough to set a diagnostic code since the auto shutdown relay is not triggered. That is generally the case , but nothing in driveability problems are always to the book. You'll want to verify if any problems exist with wiring before we fault the sensor. A CPS does play a major role in feedback to the PCM to tell it that the engine is in fact running so fuel trim and spark advance can occur and be adjusted accordingly . This would lead us to suspect the CPS and why it is in fact a common fault . But we must be certain of where the fault is , as you are trying to do , before we just swap out a part and find it did not cure the driveability problem .
Please try this check as per the manual to obtain readings . Between the fact that CPS can cause this and the MAP error code logged , we need to be certain of which is at fault . Try to clear troubles codes . Usually a scan tool can do this better as pulling fuses and disconnecting battery negative don't seem to erase OBD 2 code well in my experience but scan tool does.
See if any come back . This is important . We want to know what continues to reappear .

P.S. - if satisfactory diagnostics are not gotten with MAP and CPS checks , it may be reasonable to go after the cam position sensor to rule in or out . Cam sensor is checked much the same way .