Brother's CEL came on - what are these issues?

My brother has a '00 XJ w/ 185k miles on it and the other day I was doing SeaFoam on my Z28 and he decided he wanted to do it on his XJ too. I've done this on my '91 XJ w/out issue, but for some reason his CEL is now on. He went to AutoZone and had them pull the code. He's only 17 and not too familiar w/ engines, so I'm just relaying what he told me from what he could remember. The guy told him both were very minor, but he's obviously concerned as am I b/c this is his daily driver.

He said one was PO456 - some sort of emmission vapor or something like that?!? The other code (couldn't remember #) was cylinder 4 undetected - guy told him it was probably a bad plug or loose wire which would make me think the code was misfire detected and not cylinder undetected, but like I said, I'm just relaying info. What sensors could this be and what exactly is wrong? I'll obviously check the plug, but can SeaFoam foul that? Also, what would be an emmission vapor - a leak? Some sort of hose/valve? I just disconnected the brake booster hose, but it is tight and I even had him double check when he got the code pulled. He said it runs fine, but it did take longer to start at one time today than usual - he said it spuddered and sounded like it was gonna die, but didn't. TIA

that code usually means a bad gas cap...or some other leak in the fuel system chain...maybe a vac line disconnected.

as for the other code...not sure. if AZ didn't clear the codes, I'd check the gas cap and the vac lines on the intake manifold, then disconnect the neg battery cable for about 15 minutes to clear them out. Reconnect, take it for a drive and see if they come back. if you sucked in the seafoam through one of the vac lines, then that could have triggered the P0456 code

I have heard of seafoam, when run through the intake, fouling out a plug or two, as well as screwin with the o2 sensors.....although most have zero problems with running it through the intake.

I will have to agree with the previous posts. First check your gas cap. Make sure it clicks at least twice when you tighten it. Then disconnect your battery for a few minutes to clear the codes. You may want to check your plugs. I ran seafoam through my 99 on new plugs. I pulled the plugs afterwards and there was alot of crap on them.

Well, I pulled the #4 plug - wasn't expecting the coilpack rail thing. I have a '91, so I have a good 'ole distibutor & wires - definitely like that better from a "working on the vehicle" standpoint. Anyway, the plug was gapped .076 - far cry from the .035 it's suppose to be. I don't know if a piece broke off or what, but we're now going to do all the plugs this weekend.

I disconnected the battery and CEL went away. I haven't talked to him today to see if it came back. I told him to make sure and tighten the gas cap good b/c I couldn't find any loose/disconnected vac lines under the hood.

Thanks for the help.

i would highly recommend you don't get used to unplugging your battery everytime something is wrong on your brothers jeep. if you do that close to emissions time, they'll know that you unplugged the battery and fail you instantly. make sure you go to the parts store and ask them to clear the codes after you have completed repairs.

scorpio_vette said:

i would highly recommend you don't get used to unplugging your battery everytime something is wrong on your brothers jeep. if you do that close to emissions time, they'll know that you unplugged the battery and fail you instantly. make sure you go to the parts store and ask them to clear the codes after you have completed repairs.

Click to expand...

I appreciate the advise, but FL is emissions free!!! :laugh3:

I started a new thread though b/c I have a new, more serious issue...