I've been chasing this small, but extremely irritating problem for the last few months now. I wasn't daily driving my XJ until last week, so I just kinda let it go, but now I'm at the point where I need to fix it.
1989 Cherokee Limited, Renix 4.0, 4WD, Automatic, 156K miles.
Symptoms:
*Engine sputters when light throttle is applied starting from a stop. If you let off of the throttle, it tries to stall (and often succeeds). Applying more throttle when leaving from a stop is the only way to avoid the sputtering, but it's almost impossible to do that in any kind of traffic, and I look like I'm trying to race everyone. I can apply light throttle after the truck is already moving, and the sputtering does not occur. The sputtering/stalling is worse when reversing. It's embarassing to stall the truck(an automatic!!) pulling into a parking space.
*Low power below 3000rpm when accelerating. The truck feels like it's mis-firing or the timing is retarded too far when accelerating, until it hits 3000rpm, then it clears up. Sometimes it feels like it's going to fall on its face and backfire when downshifting to pass on the highway. As of yet, it's only threatened, but has never stalled.
*Slightly high idle when warm. The truck idles at ~950rpm in Drive or Reverse, and ~1000-1300rpm in Park or Neutral. I don't know where these things are supposed to idle, because this one has never idled properly, but I recall reading 650rpm somewhere. Is that the correct idle speed?
*Poor fuel economy. I am getting 10-13mpg mixed city/highway. I have a heavy foot(70-80mpg cruising on the highway), and combined with the first problem I listed, I'm sure that's contributing. The truck also has 30" tires and a 2" budget boost, but I'm pretty sure that all of these factors together don't add up to 10mpg.
Here's what I've done so far;
*Replaced/adjusted TPS. Re-checked adjustment probably 40 times, and it's spot on.
*Cleaned and added grounds. I added two large ground cables, one running from the battery to the firewall, and one running from the firewall to the passenger's side of the engine. Battery ground cable is brand new OEM. Battery terminals have been cleaned and checked.
*Cleaned and dielectric greased sensor connectors. TPS, IAT, o2, IAC, CTS, and other connectors have all been cleaned and greased. The knock sensor is brand new.
*Cleaned and greased relay connections on the passenger's side of the engine bay. Replaced LATCH relay and o2 heater relay.
*Cleaned, checked, and lubed IAC valve. Replaced with 3 others I had laying around, no changes.
*Cleaned IAT sensor, also swapped out with numerous spares, no changes.
*Checked plugs, wires, cap, and rotor - all are in near-new condition.
*Replaced ignition control unit(under the coil) for an un-related(at least I assume) problem.
*Cleaned and lubed EGR valve.
From my testing(found testing procedures and specs at http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm), I have put together the following:
IAT sensor is within operating specs.
Coolant temp sensor is within operating specs.
MAP sensor is within operating specs.
TPS sensor ground is in perfect shape. I get 0 ohms of resistance between it and the negative battery terminal.
Crank position sensor is relatively new and within operating specs.
The only sensor that appears to be out of spec is the o2. The resistance between terminals A and B was almost nothing, and the voltage did not fluctuate at all(it was steady at 5.07v). So, it appears I have a bad o2 sensor(which I'll be replaceing on Monday). I'm pretty sure it's going to help the fuel economy issue and maybe the hesitation below 3000rpm problem, but I'm not convinced that the new o2 is going to cure my hesitation issues. I've read a ton of threads onthis site in search of an answer to my problems, but I haven't found anything concrete.
Any input is welcome and appreciated. :thumbup:
1989 Cherokee Limited, Renix 4.0, 4WD, Automatic, 156K miles.
Symptoms:
*Engine sputters when light throttle is applied starting from a stop. If you let off of the throttle, it tries to stall (and often succeeds). Applying more throttle when leaving from a stop is the only way to avoid the sputtering, but it's almost impossible to do that in any kind of traffic, and I look like I'm trying to race everyone. I can apply light throttle after the truck is already moving, and the sputtering does not occur. The sputtering/stalling is worse when reversing. It's embarassing to stall the truck(an automatic!!) pulling into a parking space.
*Low power below 3000rpm when accelerating. The truck feels like it's mis-firing or the timing is retarded too far when accelerating, until it hits 3000rpm, then it clears up. Sometimes it feels like it's going to fall on its face and backfire when downshifting to pass on the highway. As of yet, it's only threatened, but has never stalled.
*Slightly high idle when warm. The truck idles at ~950rpm in Drive or Reverse, and ~1000-1300rpm in Park or Neutral. I don't know where these things are supposed to idle, because this one has never idled properly, but I recall reading 650rpm somewhere. Is that the correct idle speed?
*Poor fuel economy. I am getting 10-13mpg mixed city/highway. I have a heavy foot(70-80mpg cruising on the highway), and combined with the first problem I listed, I'm sure that's contributing. The truck also has 30" tires and a 2" budget boost, but I'm pretty sure that all of these factors together don't add up to 10mpg.
Here's what I've done so far;
*Replaced/adjusted TPS. Re-checked adjustment probably 40 times, and it's spot on.
*Cleaned and added grounds. I added two large ground cables, one running from the battery to the firewall, and one running from the firewall to the passenger's side of the engine. Battery ground cable is brand new OEM. Battery terminals have been cleaned and checked.
*Cleaned and dielectric greased sensor connectors. TPS, IAT, o2, IAC, CTS, and other connectors have all been cleaned and greased. The knock sensor is brand new.
*Cleaned and greased relay connections on the passenger's side of the engine bay. Replaced LATCH relay and o2 heater relay.
*Cleaned, checked, and lubed IAC valve. Replaced with 3 others I had laying around, no changes.
*Cleaned IAT sensor, also swapped out with numerous spares, no changes.
*Checked plugs, wires, cap, and rotor - all are in near-new condition.
*Replaced ignition control unit(under the coil) for an un-related(at least I assume) problem.
*Cleaned and lubed EGR valve.
From my testing(found testing procedures and specs at http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm), I have put together the following:
IAT sensor is within operating specs.
Coolant temp sensor is within operating specs.
MAP sensor is within operating specs.
TPS sensor ground is in perfect shape. I get 0 ohms of resistance between it and the negative battery terminal.
Crank position sensor is relatively new and within operating specs.
The only sensor that appears to be out of spec is the o2. The resistance between terminals A and B was almost nothing, and the voltage did not fluctuate at all(it was steady at 5.07v). So, it appears I have a bad o2 sensor(which I'll be replaceing on Monday). I'm pretty sure it's going to help the fuel economy issue and maybe the hesitation below 3000rpm problem, but I'm not convinced that the new o2 is going to cure my hesitation issues. I've read a ton of threads onthis site in search of an answer to my problems, but I haven't found anything concrete.
Any input is welcome and appreciated. :thumbup:
