1999 Cherokee 4.0 still runs rough
11-21-2017, 04:13 PM
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Model: Cherokee
1999 Cherokee 4.0 still runs rough
1999 Cherokee Classic 4.0, 191k miles. Sat for a few months before I bought it.
Runs very rough. Replaced plugs, wires, cap, button and coil. Cleaned throttle body. Have run 2 tanks of fresh gas with Sea Foam. Runs better but still chugs and sputters. The plugs fouled up and blows black smoke again. No gas mileage either.
Runs very rough. Replaced plugs, wires, cap, button and coil. Cleaned throttle body. Have run 2 tanks of fresh gas with Sea Foam. Runs better but still chugs and sputters. The plugs fouled up and blows black smoke again. No gas mileage either.
11-22-2017, 07:18 PM
#2
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Have u checked the cylinder pressures? You can rent a tester. Easy to use. If it's not the problem you'll still always have the info.
11-22-2017, 10:48 PM
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Year: 1997
Model: Cherokee
Engine: 4.0L
Sounds like its running excessively rich belching black smoke. Could be the upstream O2 sensor gone bad, a vacuum leak, leaking fuel injectors, or even a faulty MAP sensor. Codes should always be #1 on the list. Dont replace anything else until you do.
11-23-2017, 05:13 AM
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Year: 1999
Model: Cherokee
Engine: 4.0
1. Check for codes, even if you don't have a check engine light currently on (could have pending codes). You'll need a scan tool or a code reader to do this. If there are any codes, post the EXACT codes here for comment, not just a description.
2. For any "new to you" vehicle, running a compression test on all cylinders is never a bad idea. Good snapshot in time of the internal condition of the engine. For the 4.0, the spec. is 120-150 with no more than a 30 psi variation between cylinders.
3. Another must test for you is fuel pressure. For a 99, the pressure spec is 49 psi, plus or minus 5 psi. Fuel pressure is super easy to check out and is one of the first things any tech will do for a symptomatic vehicle.
4. If all of the above tests out in spec and you don't have any codes to follow, I would next test the map sensor, which is involved with fuel/air ratio. Testing this sensor can be done with a manual and a meter, of which you should have both if you own an XJ!
Good luck and keep us updated!
2. For any "new to you" vehicle, running a compression test on all cylinders is never a bad idea. Good snapshot in time of the internal condition of the engine. For the 4.0, the spec. is 120-150 with no more than a 30 psi variation between cylinders.
3. Another must test for you is fuel pressure. For a 99, the pressure spec is 49 psi, plus or minus 5 psi. Fuel pressure is super easy to check out and is one of the first things any tech will do for a symptomatic vehicle.
4. If all of the above tests out in spec and you don't have any codes to follow, I would next test the map sensor, which is involved with fuel/air ratio. Testing this sensor can be done with a manual and a meter, of which you should have both if you own an XJ!
Good luck and keep us updated!