cklame

Took my wifes 01 Cherokee to the dealer for a recommended tuneup to combat PO300 , PO301 and PO304 codes, mechanic said with 115k on her a tune up would solve things. Today (2 days later) the drive ability issues are back. Low idle was corrected but misfire condition not solved. Jeep is also tossing a PO432 (catalytic converter code) any advise on correcting this is appreciated!

cklame

Also forgot to mention that the idle dropped a bit at stop lights or when parked. Just read that a brake booster leak could cause that? Any thoughts? Thx!

freegdr

id go right back to the dealer you paid for the problem to be fixed and it was not fixed plain and simple

SteelBlue99

X2! They messed it up, they need to fix it!

tjwalker

1. Your random/multiple misfires have one COMMON cause. I'd start with verifying fuel pressure. You should have 49 psi, plus or minus 5 psi. Marginal fuel pressure can absolutely create the misfire condition you are seeing.

2. The P0432 can be either the cat itself, or the oxygen sensor AFTER the cat.

3. Taking it back is not a bad idea, but as they didn't handle things well out of the gate, they might not do well the second time around.

4. How is your coolant level? Unexplained coolant loss can be caused by a cracked 0331 cylinder head (this head has a known defect). So keep an eye on your coolant level like a HAWK.

cklame

Thanks guys for the info! I took the jeep to my mechanic to have him clean the throttle body (which took care of this issue last year) and he suggested I have him tune it up for $300... lol.. its winter in upstate ny and way to cold and snowy to DIY in the driveway, so I called a dealer to have unrelated recall work done, asked how much a tune up was and found that $141 bucks sounded much better than my long time mechanic wanted. I told jeep about the issues and figured the tuneup would cure them, I dnt specifically ask them to fix the codes so I'm not sure what theyll do for me. Was wondering about the brake booster as when the brake is applied at stop lights the idle drops.

tjwalker

As there is no distributor on an 00-01, a "tuneup" is really just spark plugs. Man, that $141 buffers in a nice profit margin for 15 minutes of work and 6 plugs!

Be sure that you aren't using Bosch plugs; numerous threads about "mysterious misfires" with this brand of plug on certain (not all) 4.0 engines. NGK is a good choice. In fact, it is the OEM plug for the 00-01.

Always chase the specific codes. OBD is subject to some interpretation, but it is really, really good at leading you in the right direction!

cklame

Thanks tj... I was able to keep an eye on the tech and noticed that the plugs was about all he did. I figured a tune up included a throttle body cleaning and a coil test or things lime that. Saddly it wasn't the case. I. Gave the jeep a few squirt of throttle body cleaner but dint run the engine while I did it. I'm told in hind sight that I should have ran the engine to properly clean it. Also heard of a carbon build up issue that can trigger those codes.. guess jeep has a TSB on it.