High compression in #4 cylinder

Hey all. New member here. Been a lurker for years though and learned a lot.

I'm having an issue I'm hoping y'all can help me with.
Rough idle, lack of power and a CEL.
I put a code reader on it and got a p0304 misfire code.
I changed the plugs, all looked good except #4(was black and sooty) and tried swapping the coil packs, no change.
I then did a compression test and found that #4 cylinder read 215ish psi while the other 5 cylinders read 175-180psi.
Any idea what would cause the misfiring cylinder to have a higher compression than the others?

 

Maybe carbon buildup due to running too cool in that cylinder while not getting good spark.

 

Bingo.... 1/2” of crap on top of piston...

 

Thank you both. Is there any easy remedy?

 

Old school cure is to trickle water into throttle body while reving engine.

 

Short of removing the head, your options are limited. Could also try a piston soak with sea foam or similar. Be careful not to do too much too fast, or you risk hydrolock. https://en.wikipedia.org/wiki/Hydrolock

 

Seafoam through a vacuum line. You can buy it in an aresol can now which makes it so much easier. Follow the directions, works the cats ass BUT you MUST change the oil asap afterwards

 

Thanks everybody. Just checked my valve lashing and everything is good there. Currently waiting on new seals and gaskets. After I get it all back together I will try out the seafoam treatment.

 

Hy there guys I'm new to this forum and ide like some help it be much appreciated it all started with my 1995 toyota t100 300,000+
Miles one day it heading out to work it wouldn't start fuel pump fused burned replaced it then got engine light on after then gave me 2 codes p0170 and p0303 miss fire so I did all 6 spark plugs replaced including all 6 cables replaced coil#3 did oil change got codes removed ran it for 200 miles and light didn't come back on until another 145 miles and noticed every time check engine came on my truck looses power then another 60 miles came back off so then stop to put gas and came back on there for I decided to take it for a compression test #3 came out 185 and the bottom one same the top one came 225 and the mechanic said #3 was to low how ever any other suggestions of what might be the truck is very well maintained interior and exterior I'm just now wondering if the fuel pump or gas filter has anything to do with it oh I also cleaned up mass air sensor i can really take some advice thank you All so much

 

Welcome to Tacoma world. T100 isn't a tacoma, but you may nevertheless get some help here. I suggest you start your own thread, so we don't clutter this one up. In the meantime, try a new fuel filter, and please use some punctuation...your post was kind of hard to decipher.

 

No punctuation? Swipe left