so the car has been acting wierd lately. it runs perfectly fine and normal with normal cruising or DD'ing it, and when going through the gears everything seems to run fine 10.8 around diping down to 10.6 or 11.2 occasionally (i was tuned a year ago in feb) the thing is when i do a pull in only 4th gear i would run extremely rich at 10.0 as the wideband says. also have been having backfire (poping noise with fluctuating afr (17.8 to the normal ---)) if i was to be in higher rpms (5-7k) and let off the gas

so i did a compression test twice in 2 days and wanted to share my results because something isnt right i believe with them
cyl. 1- 156
cyl 2 - 116
cyl 3 - 165
cyl 4 - 150

i did it again with a half a cap of oil to see if it was the piston seals and it came out as.
cyl. 1 170
cyl. 2 120
cyl 3 170
cyl 4 156

my main concern was cyl 1 and 2 as they were the cyl that were most off. i wanted to know that when you do but oil into the spark plug hole, is any increase in compression bad, or is there a limit

these 2 test were with 100% throttle with cam sensor unplugged and a warm motor, i did do the test the day before on a cold motor as well as no throttle and the power for the fuel pump removed and got 155/135/170/155

oh i forgot to mention that i did do a boost leak test and found no leaks as well as checked the sparks and they look normal
not sure if i just have a weak cyl, bad piston ring or maybe like a valve seal or something. any help would be appriciated because a few others and i are stumped

 

Hey man-

Found this online:

"If compression is low in one or more cylinders, you can isolate the problem to the valves or rings by squirting a little 30 weight motor oil into the cylinder through the spark plug hole and repeating the compression test. The oil temporarily seals the rings.

If the compression readings are higher the second time around, it means the rings and/or cylinder is worn. No change in the compression readings would tell you the cylinder has a bad valve."

http://www.aa1car.com/library/compression.htm


-Bink

 

Great Info! Thanks man!

 

Welcome, dude!




-Bink

 

yeah i read that before, so im assuming that since the psi did rise even within 14psi then i would be thinking about blaming it on the bottom end? btw i didnt have a leak down tester as that would be my next planned assault on finding out the problem

 

Before pulling anything apart - definitely do a leak down test. Then go from there.


-Bink

 

second that!