Hey guys I just bought a 98' last week, I've been looking around on the forum and have asked a few questions already but I've got a few more. The jeep has 198,000 miles on it..Manual trans everything basic, is perfect exactly what I wanted! The guy at the tire shop said it looked like a government model.. Runs strong other than a few cosmetic things and worn suspension bushings it's seems to be a solid runner. It was throwing a P0302 code and I figured no problem because I was planning on doing a tune up anyway. So here's what I've done so far.

1. Seafoamed Crank Case, Full fuel tank, and did the Seafoam spray in the throttle body. (I plan on changing all the fluids this week) (cleared P0302 code) Drove to the tire shop and back - No Code/Check engine Light
2. Installed an Accel Tune up Kit (runs great)
3. Installed New Air Filter.

I drove it about 35 miles and pulled onto my road and the Check Engine light came on again .. it's now throwing a P0420 code. Is this something I should worry about.?.. I know the 420 code has something to do with the Catyletic converter but.. I also know with these new "smart" engines can throw up codes for the slightest variance in readings. It runs fine and I'm not very worried about it but...I don't like looking at the "check engine light either"...

Also what's your opinion on the Neon injector swap? Should I do this on my 198K mile engine.. I noticed there's a guy selling them pretty cheap. If it makes that big a difference I figure why not? Will I see any decline in mileage by doing the swap? Is there a video or step by step instruction thread on here for how to do the swap? Do I need any specialty tools for the swap?

Any other suggestions of what I should do engine maintenance wise?

Just wanted to say thanks in advance...The support and information on this forum is one of the main reasons why I decided to go with a Cherokee! Not to mention all the cool aftermarket stuff!

 

After sea foaming it's common for a p0420. Clear it and see if comes back on.

 

https://www.cherokeeforum.com/f51/in...ap-4-0l-92149/

This is a good write up for the injector swap. It is a very good idea. You won't see a decrease in mileage, if anything, you'll see a slight increase. I'm assuming the original injectors are on it? If so, they're probably dirty and getting old (and if you're buying neons, make sure the seller cleans them beforehand) You'll definitely see an improved throttle response, this is because the neons have 4 holes as opposed to a single hole that oem injectors have. Hence a different, more efficient spray pattern. You won't need any special tools to do it either. So get em and do it if the price is right! The job should only take about an hour to complete

 

I hadn't even thought about that! Thank you!

Will do thanks for the help!

 

No problem. Could also be a good idea to change out all fluids: differential, t case, coolant. Something you always wanna do when you get a new used car, unless you were given records of when they were last done

 

Ok.. been running the XJ put a full tank of Seam Foam treated fuel through it. Seafoamed the crank case ran it and then changed the Oil yesterday. Cleared the codes and yesterday the P0420 code came back up. I've got a set of new 703 injectors coming... After an injector swap I will clear the code again... If it comes back up what else should I be looking for?

 

Did the injector swap. Runs noticeably smoother better throttle response everything many posters have said.. However the P0420 code has come back again. I noticed it only comes up when I'm at a stop light or while the engine is just at idle, specifically after the the engine is fully warmed up. And it does idle a little rougher at this point. Could it be that the performance of the converter is changing after it reaches a certain temp? and it's triggering the sensor? What should I look for next? Sensor or change the converter??

 

Bump. Any help would be greatly appreciated! Thanks.

 

how bad were the plugs you took out it could have messed up the cat, who knows how long the guy before you drove it like that

 

Maybe an o2 sensor? I'm not sure, I don't have experience with codes. But if it has to do with the cat, those are a good possibility. You should have one in the cat and one in the downpipe in between the headers and cat. I'm thinking that may do it for you. They're a little pricey too but if anything and that doesn't clear the code, you could see a small increase in mileage with fresh ones

 

The plugs had less than 200 miles on them and were new the previous owner had the plugs changed, and a half assed tune up done before she SMOG'd it.. (required to do in California before selling)

Yeah I'm thinking that's the next thing I'll do before spending $180+ on a new cat. I've been reading post on here and they say use the "NTK" O2 brand sensors which are only $40ea on the Rock Auto web site.

 

ok then ya its most likely not the cat. if its a p0420 then start with the rear o2 thats the one that tells the pcm the cat condition. the mopar one is like 50 bucks but that was my cost im not sure how much it is normally

 

Will do. Thanks!

 

Yeah I've heard good things about NTK as well. Those are the ones I'm gunna use when I get around to replacing em. I say go for it

 

Mine comes on at idle too and I get the same 420 code.

Did you ever get it figured out?