Mary Jane (2003 R53) is sick...... again. She has 90K on her and just recently replaced the harmonic balancer, tensioner arm assembly, tensioner stop and belt. Boy when those balancers come apart they are not kind.

Anyways she has been misfiring for the last 6 months here and there and just now she finally put up a code, misfire cylinder one. I replaced the plugs and the problem seems to have gotten worse.

I've read on here of the horror stories of this particular code and I got concerned.

My question is before I spend the money for new wires and coil should I take her to a shop and get the compression checked? As far as I can tell the coil and wires are stock.

 

Did you notice anything different about the old #1 plug (sooty or extremely white)? Have you checked and cleaned all the coil terminals? Have you made sure that all plug and coil terminals are fully seated? Are the spark plug wires and coil the originals? If so, they don't owe you anything and I'd get new ones. After that, I'd go to Harbor Freight and buy a Compression Gauge or borrow one. If you can change plugs, you can do a compression test.

 

Everything is seated well and the coil is very clean. I'm not sure if they are the original wires and coil or not but was thinking I would replace them tonight anyways.

When I changed the plugs 1 & 3 were looser than 2 & 4, finger tight loose. There was black on the upper white part of the plugs (1&3) above where they are threaded.

 

Yup, carbon on the white plug insulator will definitely give you a misfire. The carbon is a perfect conductor for the high voltage to shoot to ground. Replace all the plugs and plug wires. Don't even try to clean them, not worth the trouble and you probably can't get them clean enough. And, torque the plugs if you have a torque wrench. If you don't, buy one.

 

Happen to know the torque specs for plugs off the top of your head?

 

18-22 lb.-ft. But be careful...Aluminum head! Did you not state in your first post that you've already replaced the plugs...and it got worse? While replacing the plug wires, suggest you back off and re-torque. Do not exceed the 22 lb.ft.

 

Yes before you spend money on parts do a compression and leak down test. This will tell you how the engine is before you put a bunch of parts on it to find out you have low compression.

 

As other have said a compression test would be a good thing to do.
I would suspect spark plugs, spark plug wires, or coil. I know you stated the coil connections were clean but did you look up into the spark plug boot to make sure it was not corroded. Some people clean the corrosion off the coil contacts but forget or cannot reach to clean the metal contact in the boot. It is surprising to me that the coil contacts were clean with 90k miles, most I have seen have corrosion on at least one contact by 90k. That is why I suspect they have been previously cleaned.

 

Bently manual says 20 ft/lbs.
IMO you need the parts anyway. At a bare minimum replace the plugs and use alcohol or something to clean the boots. Good luck. You just can't get all the carbon off. Someone played a trick on me years ago. They took off the plug wires and used a pencil to draw a line down the insulator. Car ran like crap and I couldn't figure it out, new motor, plugs and all. One night I opened the hood just to think and listen. 4 blue arcs were running from the plug boots right to the block!

 

Thank you all for your replies. I replaced the wires and coil tonight and I am happy to say the patient is running like she should again. It looks like I dodged a bullet and don't have a head problem.........yet.

Bruce on post #4 gave me the idea that at least the wires needed replacing. Carbon is a MF on electronics and I have had problems with it in the past in the kind of work I do.

Thanks again everyone.

 

Glad it worked out!