Original owner 11/19/01
~225,000 miles
Mobil 1 Synthetic since day one

I dealt with random misfire codes for about the last year. At first I replaced all the coil packs and spark plugs and would still get the codes. Then I took it to a shop and he did a fuel injection cleaning. He also showed me the top of the pistons with his fancy Snap-On color camera. You could see where that fuel injector cleaner was hitting the top of the piston and cleaned it off, but I still had carbon around that. He wanted to do it again and run a second cleaning through it, it was $150 so I said no. Time goes by then I took the top cover off the intake and cleaned out all the carbon, that lasted for awhile but eventually got codes again. I then did multiple cans of seafoam through throttle body, gas, and oil. Again that lasted for a while but then it would eventually throw the misfires codes again. You could hear and feel the misfire at idle and when coming to a stop at a stop sign. Since it was time for my timing belt/water pump maintenance I decided to really go at it. I was contemplating taking the heads off so that I could get the carbon build up off the top of the pistons, but I didn't take it that far. Anyway, I took off the entire manifold/throttle body and cleaned it completely. Changed the timing belt, water pump, idlers, tensioner, accessory belts, radiator hoses, and EGR. I also took the valve covers off and adjusted the valves. I replaced everything will all new gaskets, o-rings, and seals. The car runs MUCH better now. It has not thrown a code. The only thing else I can think of is that carbon build up on the top of the pistons. Compression check was within tolerance with all six cylinders.

 

My guess is you had a valve too tight causing the misfire code. Carbon buildup on the piston woldnt cause it. (unless it was measurably thick, wich at that point you would have other issues)

 

What issues do you get when you have a lot of carbon on top of piston. THis would be good to know. There was a thickness of build up. When I had the injector cleaning it made it nice and clean on a certain area of the piston. When I looked at it through the camera it reminded me of taking a water hose and spraying mud off of cement, how it leaves a shelf.......

 

I agree with fsttyms1 that carbon build up is not the cause of misfires. Carbon will cause pinging and maybe some engine de-tuning when the ECM is trying to stop the pinging, but a slightly open valve will cause a misfire at idle. You are lucky to catch it before burning a valve.

 

That would be my first guess as well.

 

any carbon on the pistons after multiple seafoam thru gas tank, and thru MASTER vac port at TB -wont be enought to worry about (you did the oil method too?)
If its actually building layers upon layers of carbon- the compression would rise and the danger of contact with a too tight exhaust valve increases (it opens at the wrong time and farther than spec)

I think it was finally cleaning the egr system thru the manifold did a lot for you
and valve adjust always helps--
yet some people will argue they dont need adjustment at 105!

 

seafoam says noobs should repeat in a month/1500-2000 miles to finish off residue
then good for a year/15kmiles

Not surprising your guy wanted to do another cleaning,,we can do same for 10 bucks!

the shine on pistons goes away quickly from combustion byproducts- stuff left behind from additives in gas,,thank E10 for more of that than the old days~
clean intake valve stems and seals are important--see pic on bg44 ad when it pops up-half clean half dirty valve