1996 Cherokee - Strange running issue - JeepForum.com
 
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post #1 of 9 Old 08-18-2017, 09:55 AM Thread Starter
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1996 Cherokee - Strange running issue

Hi guys,

I have a new to me 1996 Cherokee 2-door that I'm trying to diagnose a running issue with. It's a 4.0 with the AX-15 manual transmission, all stock.

The Jeep idles and revs up in neutral fine, although with an occasional stab of hard throttle, it will stumble for a second and recover (probably accentuated by bad engine/trans mounts). The weird issue starts when driving... everything is fine under light throttle, below 2-2.5k rpm's. When I try to apply more throttle and bring revs above 2.5k, in any gear, the Jeep bucks violently and refuses to rev up more. I can occasionally avoid this by gently goosing the revs above to 3k. No warning codes or CEL.

My attempts so far at diagnosing:
  1. Check fuel pressure. Dead on 49-50 psi idle, no drop in pressure below 35 psi when off for 5 minutes.
  2. New distributor cap/rotor, plugs (Champion Copper's at 0.035"), leads, and ignition coil (MSD Blaster)
  3. Clutch feels strong and not really suspected. I tested by putting in 4th gear at 25 MPH, no noticeable slip. Also tried pulling off in third gear with the parking brake set. It actually started to inch forward! So, maybe my parking brake sucks.
  4. TPS replaced.

Where should I check next? I'm beginning to suspect a vacuum leak. The throttle body is quite dirty, so I'm going to clean that and the MAP/IAC sensors as well. The Jeep also has an exhaust manifold leak, but I don't think that would cause the issue that I'm having.

I'd really appreciate any help that can be offered!!


- James
'97 5.2 Limited, just rolled over 80,000 miles!
2" BB, 245/75/16 Cooper AT3's, Kolak 3" Exhaust
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post #2 of 9 Old 08-18-2017, 10:21 AM
bluejunior
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Vacuum leak is possible, 02 sensors can cause occasional loss of power and then recovery but the relationship between revs and your symptoms really sounds like a TPS to me. Where did you get your replacement? Did you have identical symptoms before and after that replacement?

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post #3 of 9 Old 08-18-2017, 10:33 AM Thread Starter
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Quote:
Originally Posted by bluejunior View Post
Vacuum leak is possible, 02 sensors can cause occasional loss of power and then recovery but the relationship between revs and your symptoms really sounds like a TPS to me. Where did you get your replacement? Did you have identical symptoms before and after that replacement?
Thanks for the response. I thought the same, and that's why it was the first thing I replaced. I didn't test the old one though, and symptoms are exactly the same. The replacement is a BWD unit from Advance Auto. I've heard that OEM Mopar sensors are best, BUT I've also heard that BWD is an OE unit identical to the Mopar unit.

- James
'97 5.2 Limited, just rolled over 80,000 miles!
2" BB, 245/75/16 Cooper AT3's, Kolak 3" Exhaust
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post #4 of 9 Old 08-18-2017, 10:50 AM
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Quote:
Originally Posted by BackRoadSeeker View Post
Thanks for the response. I thought the same, and that's why it was the first thing I replaced. I didn't test the old one though, and symptoms are exactly the same. The replacement is a BWD unit from Advance Auto. I've heard that OEM Mopar sensors are best, BUT I've also heard that BWD is an OE unit identical to the Mopar unit.
Well, no change seems fairly conclusive to me. I'm back to a bad vacuum leak (should be pretty loud to cause all that), bat sensor ground or maybe bad 02 sensors or one operating near a cracked weld in the pipe causing it to read badly.

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post #5 of 9 Old 08-18-2017, 12:25 PM
CJ7-Tim
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IMO no currently made engine sensors are equal to Jeep/Mopar parts. I would suspect the TPS, the O2 sensors, and the Coolant Temperature Sensor in that order.


Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.

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post #6 of 9 Old 08-18-2017, 12:43 PM Thread Starter
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Quote:
Originally Posted by CJ7-Tim View Post
IMO no currently made engine sensors are equal to Jeep/Mopar parts. I would suspect the TPS, the O2 sensors, and the Coolant Temperature Sensor in that order.


Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

Cheap parts are cheap for a reason.
I know that many times the aftermarket sensors are crap, but thought in this case the BWD one was pretty good. As I search more, I'm finding some reports of the BWD sensors having issues as you say. I guess I'll try and test the BWD unit properly before dropping the money on an OEM sensor. The temptation of being able to go pick up a non-OEM part same day at an auto parts store is strong at all times...

Oxygen sensor (upstream) was replaced by the previous owner; have the receipt for that one.

- James
'97 5.2 Limited, just rolled over 80,000 miles!
2" BB, 245/75/16 Cooper AT3's, Kolak 3" Exhaust
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post #7 of 9 Old 08-18-2017, 02:25 PM
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I must admit to some bad experiences with BWd, though that was all int he motorcraft reproduction business rather than mopar. Still, even a DOA TPS should have CHANGED the behavior slightly even if the average result wasn't improved. That's why i said to think vacuum or O2 next.

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post #8 of 9 Old 08-18-2017, 03:42 PM
CJ7-Tim
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IMO BWD and even NAPA premium are slowly sliding downhill in quality to keep up with the cheap Chinese crap. Maybe after one or two returns you get a good one, I would rather buy one genuine Jeep sensor and know it will last as long as the original one did.


Quote:
Originally Posted by BackRoadSeeker View Post
Oxygen sensor (upstream) was replaced by the previous owner; have the receipt for that one.

Bosch or NTK ? Jeep 4.0L and Bosch O2 do not play well together, only buy NTK O2's.

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post #9 of 9 Old 09-05-2017, 07:36 AM Thread Starter
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Just to follow up on this, the DOWNSTREAM O2 sensor was replaced by the PO, not the upstream. Upstream looks ancient. I will probably just replace that along with the exhaust manifold and see what that does for me. NTK O2 sensor is only like 40 bucks on Rockauto.

Appreciate all the help though, guys! This week, the Jeep is off at a buddy's shop getting some floor rust repaired...

- James
'97 5.2 Limited, just rolled over 80,000 miles!
2" BB, 245/75/16 Cooper AT3's, Kolak 3" Exhaust
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