'98 Cherokee Starting Problem - JeepForum.com

 
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post #1 of 9 Old 05-10-2016, 03:36 AM Thread Starter
Droff
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'98 Cherokee Starting Problem

My son is a recent owner of a '98 Cherokee, 6 Cyl, Automatic that wouldn't start. For a couple weeks now, it has been a slow crank and then fire and start. As far as I know, it has ran fine with the exception of the night prior to the non-start issue. It was low on coolant and also the oil gauge was swinging between zero to some pressure reading on the gauge. Oil level reads good on the dipstick.

Yesterday the Jeep cranked and cranked and would not start, even with a jump it would not start. After a tow home and a little research, it sounded like it may be the CPS. I located it, disconnected then did an ohms check. Pins B to C read about 4 MEG Ohms, which doesn't sound like an open or a short. It's higher resistance than expected from reading a few posts so I'm unsure on a good or bad part.

I reconnected the CPS and pulled a spark plug boot to check for spark, which I had. When it was cranking, the Jeep started. Shut it down, put the boot back on the spark plug and it fired up again but it ran rough and I don't think it would get anywhere out of the driveway.
The below information is from a couple posts I found, which gives an indication of a bad CPS, sounds like what I had happen;
"-Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced."

So, an intermittent/faulty CPS?

Thanks for the help.

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post #2 of 9 Old 05-10-2016, 05:01 AM
irishlt
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http://www.cherokeeforum.com/f51/testing-cps-5563/

B-C pins are supposed to be open i believe

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post #3 of 9 Old 05-10-2016, 04:51 PM Thread Starter
Droff
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I got the CPS replaced and it fired up with no problem, idle was a bit rough (not sure if that has always been the case since bought) but it stayed running. It may have evened out after getting warmer.
It was fairly painless (20-30 min) but I did notice a fairly large opening on the bell housing, much larger than the sensor. Hadn't noticed it BEFORE I removed the old one.
It hasn't been driven yet but when I drop it in to drive, it sort of bogs then recovers, but when I go to reverse it coughs, sputters and almost dies before I shift it back to park. Again, unsure if that was a previous condition.
Any suggestions on the engine issue when putting it into reverse?
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post #4 of 9 Old 05-10-2016, 05:29 PM
tjwalker
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1. What is the history of routine tuneup maintenance? If you don't have believable records, would be a good idea to replace spark plugs, plug wires, distributor cap, rotor, check and replace air filter if necessary.

2. Clean throttle body and idle air control as they get carboned up over time and miles. This is something that often gets ignored and is pretty important on the 4.0 engine.

2. Any check engine light ever seen? If so, retrieve codes for guidance and post the exact code here

3. Check fuel pressure. For a 99, you should have 49 psi, plus or minus 5 psi. Must be done with a fuel pressure gauge; anything less is guesswork.

Good luck and keep us updated.

99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!
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post #5 of 9 Old 05-24-2016, 08:00 PM Thread Starter
Droff
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I haven't had a lot of time to get this squared away but have checked over a few things, still have a problem.

I don't know the mx records, but the plugs and wires are not original, air filter looks good, unsure on cap and rotor.

I cleaned the IAC as well as the throttle body, both have a good appearance now. No CEL has popped up. I cleaned up the grounds and the battery terminals, had the battery tested and it was 'bad', so I now have a new battery in it.

The Jeep starts and idles as usual, even stays running in drive, but reverse still kills it. It idles the same with/without the IAC plugged in.

I tested the TPS and per the instructions I should have 5 VDC input with the key on.
Connector inputs were 5.17 VDC on one pin and 4.76 VDC on another pin. 0 VDC on the third.

I don't know if I have a computer issue or something else going on.
Any suggestions going forward?
Thanks
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post #6 of 9 Old 05-24-2016, 08:18 PM
jordan96xj
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With the vehicle running and a helper at the controls, test the system voltage across the battery terminals. See that it is close or just over the 14v that it should be, then keep observing it when the vehicle is put into reverse, see if there is any abrupt change in voltage when the shift is made. Also, check to see that when put into reverse the reverse lights actually come on (brake lights will probably be on as well, look for any weirdness in the lights - like lights going off that should be on and the like). I'm wondering if there isn't some type of low voltage and/or short going on when the vehicle is put into reverse and the reverse lights get engaged. (i'm leaning this way also because of your mention of the weak starts and initial bad battery).

Things I keep around that help fix Jeeps:
AeroKroil and Fluid Film
BAFX Products 34t5 Bluetooth OBDII Scan Tool and Torque Pro OBD2 App for Android
Etekcity MSR-P600 Digital Multimeter
Bernzomatic TS4000 Trigger Start Torch + MAP Gas
1/2 inch sockets, Breaker, Cheater Pipe, and BFH
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post #7 of 9 Old 05-24-2016, 08:30 PM
jordan96xj
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Another cheap quick test would be to have a fuel pressure gauge and spark detector in place when shifting into reverse. Because unless it is something like a loose transmission housing (unlikely, I hope). Something is probably causing a problem electrically, which will probably present itself as a disruption of spark or fuel pressure when shifted into reverse. Which probably take the problem back to bad grounds/connections (which coincidentally is the fix action for about 80% of the posts on xj forums, regardless of how obscure the problem is - kind of joking, but not really).

Things I keep around that help fix Jeeps:
AeroKroil and Fluid Film
BAFX Products 34t5 Bluetooth OBDII Scan Tool and Torque Pro OBD2 App for Android
Etekcity MSR-P600 Digital Multimeter
Bernzomatic TS4000 Trigger Start Torch + MAP Gas
1/2 inch sockets, Breaker, Cheater Pipe, and BFH
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post #8 of 9 Old 05-25-2016, 06:17 PM Thread Starter
Droff
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With the battery connected I'm only reading 12.7V, not sure that's a good reading. Brand new battery too. It started right up, voltage went to around 13.5V, still a bit on the low side I think.
Today, it idled for maybe 3-4 minutes after start and then it just flat died, like it was choked out somehow. Wouldn't start up again either.
So, I got that going for me.....
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post #9 of 9 Old 05-28-2016, 07:11 PM Thread Starter
Droff
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Started troubleshooting again today, re-checked the IAC and then the TPS and the MAP, all read like they were working, but maybe not giving a full 4-5Vdc. Still had the almost 5v on the plug that should not have been there. The Jeep started again, ran rough, then cleared up and idled okay. We were on about the third start after eyeballing the ECU a little when my oldest son was fiddling with the CPS and where it was laying up on the manifold. He moved it around a little, touching a couple other things and the Jeep immediately died. No sputter, cough or anything, just stopped.
After discussing "What the hell did you do?", we started it up again and jiggled the wire loom from the IAC and also the large one that runs along the firewall over to the ECU. When we moved the larger one, it sits right on/above the fuel rail at the back, we had instant cut off again. We actually had a relay cycling when we moved the wire loom with the key on.
Turns out, something was causing a short or some other issue with the wiring. We took off the wire loom and looked at the wires but there was no cut, chaffed or rough looking wires. We re-taped, re-routed to cut down on a sharp angle and then zip tied in place.
It's running fine right now, drive and reverse. Idling better too.
We were "this close" to going with a new IAC and TPS.
Thanks for the help.
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