Spark Knock, Code p0300, Compression difference of 100psi, HELP!!!

What's up guys. I'll get to the point. 02 tacoma TRD S/C 216,xxx. About a month ago i noticed i had a "dead spot" when i was on the highway going up hills, around 70mph. The issue kept getting a more noticeable. The "dead spot" was now really noticeable when accelerating in 2nd and 3rd etc. It felt like a lack of fuel when under load. Changed fuel filter and pump, which were both original parts. No better, no worse. Check engine light comes on one day for o2 sensor and knock sensor. Changed both o2 sensors. Gas mileage got better still had what i will now call a miss/ misfire feeling when under load. Pretty noticeable now when i get in the throttle but after say 4k RPM i don't have an issue and the truck runs good. Decided it would be a good idea to change the plugs/ wires/ coil packs, all parts taken off were original. Start the truck and its starts fine like always and idles good like always, purrs like a kitten. I drive it and it feels good until i put it under load but now which the new plugs, wires, and packs the "dead spot, jerky, misfiring thing" is still there but the noise is SIGNIFICANTLY louder, I'm guessing due to the plugs and such. I am in the process of changing the knocks sensors and wiring harness. I did a compression test earlier out of curiosity: #1 cyl 197 #2 200 #3 140 #4 120 #5 195 #6 155 Looking for guidance on what these numbers mean before i go any further. I'M NO MECHANIC so any help would be appreciated.

 

I'm no Mechanic either...but
Book Says.

178 PSI or more
Minimum 127 PSI
14 PSI or less, Difference between Cylinders.

If your readings are accurate you have a problem.
Cracked head or leaking head gasket, Worn rings maybe.
Are you seeing any white smoke out of the tailpipe. Any unusual consumption
of coolant?

 

Piston rings or worn valve seats. Worn rings would cause high carbon build on the plugs. If the plugs look to be to ok.......it MAY be the worn valve seats.

 

don't forget the well known crack in the #3 cylinder area. still hold 175 compression but did a leak down test, air came out of the tail pipe.

 

squirt some oil in one cylinder and see if you get higher compression readings, if its just a little higher its the valves, if its a lot higher its the rings. do each cylinder one at a time. if you put oil in all of them the oil may get on the valves by the time you get to the next cylinder.

when you see three out of 6 off like that and one being on the opposite head, its more common its a valve sealing issue going on.

if you are lucky they just need adjusting but I think you might need to have the heads pulled and the valves redone. not all that bad really.

 

Pretty sure worn rings wouldn't be the issue but there again you seem to have quite a discrepancy in your numbers, did you take out all plugs before doing test ?? I'd run another test with a diff. comp. gauge just to be sure its not a bad read from defective tester..can't hurt & doesn't cost a dime

 

That dead spot could be part of a bad tune if you have the 7th injector kit. If you retard the timing too much it will cut acceleration. If you don't have the 7th, you may have pinged hard and melted a crater in the pistons. It happens.

 

You did pull all of the plugs to do the compression test right? You said you are no mechanic so im just checking the basics first.

 

If the compression is off that much you have a problem and a knock sensor ain't going to fix it. The sensor is probably doing it's job is has a code because it's still knocking despite the timing retard. The low numbers are on different sides so likely as not it's no head gasket. Bottom line it need to come apart. By the way the knock sensor is under the intake manifold.

 

It's a pain in the ass to get to the knock sensors. I need to replace my sensor harness sometime.

 

Original pump....was the pump ever upgraded for more fuel since it's s/c?

 

Do a wet test. If the numbers don't change much, for instance if they stay within 20 psi of each other then it isn't the rings. If that's the case, move on to do a cylinder leak test. That way you can pinpoint to a certain degree where the leak is. It will be in any of three areas.. Intake; exhaust or the actual cylinder head (gaskets). You'll here or feel the air coming out.