OK, so I put up a post a month ago stating that I had a trans shudder. It didn't feel like a miss to me, but then again I'm from SBC land, and a miss in a V8 is not like a miss in a I6. My thread went cold so I'm starting a new thread.
History: bought a 2000 XJ with 123k four weeks ago, got it home, then it started running rough. Felt like a trans shudder. Got codes P0300, P0303, P0304. So, I checked & changed the plugs. All plugs looked good and exactly the same. Also changed B1S2 O2 sensor per recommendation of the previous owner.
2 days later it wouldn't start, so I cleaned all grounds, pulled the neg. battery cable, reattached it, and it started right up. Stalled & wouldn't restart the next day, so I changed CKP guessing that was the most likely candidate. Now it starts every time, but in the cold it starts hard (I have to put it down to about half-throttle or so to get it to start, have to keep the revs up for a minute or so to keep it running, then it runs OK, but rough). The RPM's fluctuate between 600-750, or so at idle all the time, and it feels a little rough, but it's really noticable between 1100 - 1800 RPM, whether under load or in the driveway in park. Since I changed the CKP it doesn't throw any codes, but the miss or 'shudder' is noticeable. Engine temp doesn't seem to matter. It's a '00 with 0331 head, and I checked all the obvious signs of a cracked head (except for compression test/leakdown test).
It seems related to RPM; as soon as I get to 1800 (in any gear, or in park) it goes away. When I changed the plugs, it didn't feel like the coil rail 'snapped' on to the plugs, but haven't had an '00 before (I'm more familiar with the Renix XJ's) so I don't know if that's normal. I also cleaned the TB, which was exceptionally filthy. Running the scanner while I drive it doesn't reveal anything obvious and doesn't show any codes.
But, it's missing bad between 1100 and 1800 all the time. Any suggestions?
The coil rail doesn't exactly snap onto the plugs, but you can also have a plug boot bunch up, and not seat correctly. The 4.0L seems to have specific preferences for spark plugs. 1999 and older do best with everyday Champion plugs and the 00-01 seem to like AutoLite APP-985's.
Originally Posted by pedal
I have to put it down to about half-throttle or so to get it to start, have to keep the revs up for a minute or so to keep it running, then it runs OK, but rough.
It needs some routine maintenance and maybe a battery or alternator.
For 1996+ Jeeps, the OBD-II engine computer (ECU/PCM) re-boots, and the idle settings are deleted, when you: (1) let the battery run down by leaving the lights or radio on, (2) disconnect the battery for an extended period of time, (3) when the battery goes bad and needs replacing, (4) when the alternator is not properly charging the battery, (5) or when poor battery connections result in a voltage drop at the PCM or poor battery charging. Loose, corroded, or damaged battery cables or ground wires may also cause or contribute to the problem.
Your symptoms are: (1) having difficulties starting the engine without depressing the gas pedal, and (2) the engine will have a low idle and probably stall unless you keep your foot on the gas pedal. (3) The ECU will relearn the idle settings after a short period of driving and the engine will start and idle normally.
Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables and replace them as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body.
If the symptoms reoccur, you need to have your battery and/or the alternator load tested at a repair shop or auto parts store. This is usually a free service they offer to bring in potential customers. Even with low battery voltage, the engine will start, but the ECU can re-boot multiple times and a new battery may be required.
Cleaning the Idle Air Controller (IAC), regular tune-ups, and using fuel injector cleaner should be part of your routine preventative maintenance.
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Thanks. I replaced plugs with Autolite 985's when I changed them. I checked, removed, cleaned, and replaced star washers on all ground connections. Checked and cleaned other battery/starter/alternator connections. Battery terminals were a little corroded, but cleaned them up and no difference.
When I turn the key it starts strong, so i wouldn't think it's the battery, but I've seen stranger things so I'll have it load tested...I was actually wondering if it might be related to the alternator/voltage regulator as my problem seems to be directly related to engine RPM - so I'll test them too.
Will also check the IAC -thanks for the heads-up.
I'm pretty good about routine maintenance, but as I mentioned, I just bought it so I don't know anything about the car's history...Thanks for the response.
I replaced that when my cherk kept stalling if I stopped to quick. It also felt like it was missing at around 65 mph. Its expensive, so try and clean it first! Good call on the 331, Ive seen/ heard of many going at almost exactly 120k.
OK, so battery tested good and alternator is good at 14.4 volts. Re-checked the grounds. Cleaned IAC (I think - that's the one closest to the valve cover, right?). It starts OK now, don't need to hold down pedal, but it still feels like it has a slight miss at idle (and the tach fluctuates a bit, too). Still have the miss in the low-midrange RPMs (from 1100 - 1800 RPM). But like clockwork, once I'm above 1800 RPM it feels smooth and runs like every other 4.0 I've had. Mash the pedal and it goes great, but under part throttle I still have the miss. And still, no DTC's.
Plugs changed, CKP replaced with Mopar CKP. Wiring connections seem to be OK, but it seems odd that my problems are limited to a defined RPM range. It doesn't stall. Maybe CMP? PCM? TPS? WTF? Aarrrghhh - Gremlins!