EHarris

Hey everyone. I am going to attempt this repair myself but I just want to make sure I am doing things correctly and I am sure that many of you will have some useful information to make this much easier.

First off P0303 is Cylinder 3 Misfire. I have a super chips and have the 87 octane tune installed right now. Please let me know if I should return it back to stock tune for any reason.

What type of wires should I purchase? Is this an item I should get at a local parts store or OEM from the dealer? Should I replace the coil pack at this time also? I currently have 94k on it and I did the plugs at 55k (Champion Double Platinum Power Part # - 7440 RE14PLP5).

My plan is as follows, get either new coil pack, wires or both. I will trace #3 from the coil to the engine block which appears to be passenger side closest to the firewall. I will only replace the #3 wire. Drive the vehicle and see if I still get the code. If code goes away then I will know it was the wire. Then replace all of the other wires accordingly. If I still throw a code then its the coil pack that needs to be replaced. So in that case, all wires will get replaced (which needs to be done at 102k anyway) and then do the coil pack. If I still get the code after replacing both then I may be outta my league and have to take it to someone.

If you do new wires should you just do a new coil pack also? Not sure what the set standard is here.

Thanks again in advance for all of your help. I really do enjoy learning how to work on my JK and this forum has helped me greatly since 08 when I joined. Part numbers, manufacturer name ect... would be helpful for wires, coil or both depending on what the recommendations are.

EHarris

Another question, would anyone recommend doing plugs also at this time? I have 94k on it and I did the plugs at 55k. See post above. Also, to make sure it is in fact the wires causing the problem, could I swap the #3 with another wire and see if the code follows the cylinder? Thanks again.

EHarris

Update! I did it myself tonight!!! So stoked and it wasn't really even that hard!!! A few quick questions....

Why is the # 3 plug colored gray attaching to the coil pack and the rest are black. This happens to be the trouble code # I am getting.

Does the plastic sheathing go behind the engine block where it is difficult to get your hands? It's split into two places and when I took them off they were closest to the coil block and close to the engine block. I'm assuming they should be trying to protecting the wires from melting so they should be placed wherever the wires could touch hot places?

I broke the drivers side plastic tray that holds the wires. I can order a new one from the dealer for $7. Should I bother?

I am still getting P0303 engine code. I will replace coil pack tomorrow which seems easy. Hopefully that makes the problem go away. If not I guess I am looking at replacing the plugs?

Big step for me on the self wrenching. Now that she has 94k I'm not so worried about messing things up and I'm ready to get my hands dirty. Funny how hard it was for me to work on it years ago. 25 years old and my first new car purchase. Almost vomited when I signed the paperwork. Lol

DJ1

I'm no master mechanic but I would have pulled the plug first to see if there was any fouling.

If so, then you'd have to change the plug out and most likely the coil as well. Since you're changing the coil, you're not looking at much more $ to change out a single wire on top of that but I'm not sure you can buy the wires individually.

DJ1

...and this is just one route. You might actually have oil leaking past the spark plug seal. Other routes are checking the fuel injector to see if it's actually squirting fuel. Then checking compression to see if you're losing air. Loss in compression would probably set you back the most $.

I'm sure the more seasoned engine mechanics will chime in....

EHarris

Yea I really didn't want to have to pull the plugs. #3 is kinda tough to get to along with I think #1. If I have to change one plug I would have to change them all. I didn't mind doing the wires since owners manual recommend getting them changed at 102k and I'm at 94k with a big trip coming this summer from so cal to cabo San Lucas.

EHarris

We will know tomorrow with the changing of the coil pack. I have lifetime powertrain warranty so of that doesn't do it I will take it to the deal and let them pull the plugs and deal with it I guess. Hope it's not that.

EHarris

Can anyone please tell me if a new set of factory ignition wires should have one that is colored gray? Look at the picture. I only ask because I changed them last night and I'm still throwing a cylinder 3 misfire. This happens to be #3 with the weird color.

Kerberos

Can't believe I've never noticed it before on Wranglers, but the #3 wire on my '08 3.8 is gray also...

Strange.

Can you feel the misfire?

You're on the right track...

Best DIY diagnosis for misfire is swapping components...

Swap the plug first (after inspecting for any obvious problems) then swap the plug wire...

If the misfire moves to the cylinder you moved the plug/wire to then obviously replace that component.

Plugs and wires are due at 102k miles per the maintenance schedule (as you said)... so since you're nearing that you might want to start with a new set of both before doing too much head scratching.

And yes, it can be a bit of a pain, but you really need to inspect the plugs visually before going much further.

Also, before dropping a benjamin on a new coil pack ($102 for OEM) you should buy a spark plug tester at your local parts store...

Generally less than $10 and super easy to use.

Good luck!

EHarris

Ok glad to know it's the same on other peoples vehicle.

I did buy the coil pack already but I figured might as well replace it since I plan on driving the JK to 200k with the lifetime powertrain warranty.

Do others have experience with bad coil packs or is this definitely a waste of $$ and I should go return it.