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1993 Jeep XJ 4.0L HO - 290K miles
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Discussion Starter · #1 ·
I am going to go through everything I have tried related to this. Sorry if this makes this long, yet I think it is better than having to go back and forth with “have you tried…”

- 1993 Cherokee XJ Sport - 4.0L / Manual / with 293K miles.

- Driving a trail in Las Vegas that had about a 4 mile downslope, so mostly idling in 2H. Reach the bottom and the Jeep won’t accelerate normally. Have to rev it up to get going in first. Once it hits 3K I let off gas a bit and it accelerates great. Shift into 2nd and it sputters at 1500-2000 rpm. While waiting for help on roadside, I let it sit at idle and it is consistent but the air intake sounds like a jet engine.

I replaced the TPS and limped 30 miles closer to home before towed in city (could not get moving out of stop signs and signals)

over last week I have:
  • Replaced TPS
  • Replaced IAC sensor
  • Replaced MAP sensor
  • Cleaned Throttle Mount assembly
  • Replaced Spark Plugs
  • Replaced fuel injectors
  • Replaced O2 sensor
  • Replaced Crankshaft Position Sensor
  • Used Sea Foam upper intake spray
  • Checked compression of all 6 cylinders (130 to 140)
  • Checked timing position (in case chain jumped) - okay
  • Reset the ECM multiple times

within last three months the Distributor Cap, Rotor, plugs and wires were all replaced (in proper firing order).

Only things I can think to do next would be:
  • Full distributor replacement
  • Fuel Pump
  • Fuel Pressure Sensor
  • ECM module
  • Keep hunting for vacuum leak

Any suggestions would be welcomed.
 

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How good is your oil pressure? These engines have hydraulic lifters and have been known the get holes worn through them. The compression is good, so, rings, valves and head gasket are ok. What brand of sensors did you get? Sometimes the cheap parts store brand can be bad right out of the box. We recommend OEM to avoid this issue.
 

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1993 Jeep XJ 4.0L HO - 290K miles
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Discussion Starter · #3 ·
Thanks for reply. Oil level was and is good. While I know I have a front and rear seal leak when running, it never leaks when off and sitting. Pressure is around 45-50 psi when running.

For the TPS, I tried to locate a MOPAR part after reading about reliability of others. I could not source one locally since they are discontinued other than resellers online. Is there a reliable OEM source to buy from?

Thanks again.
 

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Discussion Starter · #5 ·
Ordered it. I will post a follow up later in week if this made the difference
 

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1993 Jeep XJ 4.0L HO - 290K miles
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Discussion Starter · #6 ·
One more quick question: on resetting the ECM after replacing the TPS I have read two different instructions
1. Remove both battery terminals - hold them together for 30-seconds. Reattach and then turn ignition to on, and turn on then off headlights.

2. Remove negative terminal for 10+ minutes and then before reattaching turn ignition to on and turn on / off headlights.

Could you provide the the proper steps?
 

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I just remove the cables & touch them together for 30 seconds. you can turn the headlights on and off if you want. What you are doing is discharging the capacitors in the ECM and essentially resetting the ECM back to factory specs. It will then "relearn" all the sensors and adapt the fuel/air mixture to optimum efficiency based on the inputs from all those sensors. This make take upwards of a tank of fuel to reach this.
 

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Discussion Starter · #8 ·
Thank again. So, if it still performs awful it is either ECM not reset, or TPS is bad.

Seems to reason that resetting ECM to factory reset, I should get proper performance in short-term, even if TPS is bad. Wouldn’t it?

what are your thoughts on New distributor assembly and coil?
 

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If the TPS is truly bad, it still won't rev unless you sneak up on it slowly
 
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You've already thrown a lot of parts at it. But an ECM reset will let in run "normally". Check all your grounds, clean the post and mounting surfaces. Check the harness that goes around the valve cover by the firewall. The wires can rub against the valve cover bolts and short out. There is an induction pickup under the distributor. it's the cam sensor and used for fuel timing. Do you have a multimeter? It can help you test sensors instead of just replacing them.
 

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1993 Jeep XJ 4.0L HO - 290K miles
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Discussion Starter · #11 ·
You've already thrown a lot of parts at it. But an ECM reset will let in run "normally". Check all your grounds, clean the post and mounting surfaces. Check the harness that goes around the valve cover by the firewall. The wires can rub against the valve cover bolts and short out. There is an induction pickup under the distributor. it's the cam sensor and used for fuel timing. Do you have a multimeter? It can help you test sensors instead of just replacing them.
Thanks again. I have a multimeter and can test the sensors.

With the successful compression testing, I am looking at this as both the immediate fix and the 300K update. As a bit more information, below is an image of Bosch Double Iridium plugs put in Aug 7 with about 400 miles on them. I also tried to clean them, so these look better than when they came out.
Auto part Metal Electronics accessory Font Art

Clearly there is a lack of firing causing more issues. I have read recommendation for Champion plugs. Thoughts? will shift focus to grounding points and wires. If I find something, I would move to Champion going forward.
 

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Don't waste your money on bosch plugs. Stick with the plain Jane champion coppers.
 

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I am going to go through everything I have tried related to this. Sorry if this makes this long, yet I think it is better than having to go back and forth with “have you tried…”

- 1993 Cherokee XJ Sport - 4.0L / Manual / with 293K miles.

- Driving a trail in Las Vegas that had about a 4 mile downslope, so mostly idling in 2H. Reach the bottom and the Jeep won’t accelerate normally. Have to rev it up to get going in first. Once it hits 3K I let off gas a bit and it accelerates great. Shift into 2nd and it sputters at 1500-2000 rpm. While waiting for help on roadside, I let it sit at idle and it is consistent but the air intake sounds like a jet engine.

I replaced the TPS and limped 30 miles closer to home before towed in city (could not get moving out of stop signs and signals)

over last week I have:
  • Replaced TPS
  • Replaced IAC sensor
  • Replaced MAP sensor
  • Cleaned Throttle Mount assembly
  • Replaced Spark Plugs
  • Replaced fuel injectors
  • Replaced O2 sensor
  • Replaced Crankshaft Position Sensor
  • Used Sea Foam upper intake spray
  • Checked compression of all 6 cylinders (130 to 140)
  • Checked timing position (in case chain jumped) - okay
  • Reset the ECM multiple times

within last three months the Distributor Cap, Rotor, plugs and wires were all replaced (in proper firing order).

Only things I can think to do next would be:
  • Full distributor replacement
  • Fuel Pump
  • Fuel Pressure Sensor
  • ECM module
  • Keep hunting for vacuum leak

Any suggestions would be welcomed.
Have you checked the fuel pressure?
Chang the fuel filter!
 

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1993 Jeep XJ 4.0L HO - 290K miles
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Discussion Starter · #15 ·
Have you checked the fuel pressure?
Chang the fuel filter!
Thank you for post and suggestion. Fuel filter was replaced in May, yet I am replacing the Fuel Pressure Regulator today. I did find a vacuum elbow on FPR that was cracked, so also replacing this.

I will have an update later today after the rest of my work on this today (TPS, Clean ground points, vacuum elbow, and Fuel Pressure Regulator).
 

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1993 Jeep XJ 4.0L HO - 290K miles
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Discussion Starter · #16 ·
To close the loop and thank everyone for their advice, here is what I finally did to fix the XJ. After verifying that the electrical was good, and all fuel injectors were firing, I switched focus to the fuel tank and fuel pump.

I could have gone cheaper, but I consider this to be my 300K update. I replaced the fuel tank, evap valves, fuel pump, and fuel filter today. The old fuel pump had a hose on it that was rotted out and causing the fuel to not draw up until reaching 3000 rpm.

After installing everything and refilling the tank, it started up and ran great.
Thanks again to everyone who supported me during this repair.
 
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