So I decided to do a compression test both wet and dry to see what kind of condition the bottom end is in. Now I busted 1 plug so I have to order it so minus #9 cylinder I have the rest. I would have finished the test but that plug is a REAL beast to get to, so I will only do it when i have the plug. Now the first tests I didn't use quite enough oil, so they are a little low 10, and 8, and maybe 3, but you get the idea. Tell me what you think? Engine was mainly cold. No leak down test was performed.

............Dry...........Wet

#1.......115..........176
#2.......115..........161
#3.......114..........143
#4.......112..........161
#5.......116..........157
#6.......112..........160
#7.......117..........154
#8.......114..........132

#10.....110..........128


Now remember that the OEM compression ratio was like 8.6:1 or 8.4:1????

 

I keep reading that a cold test shows nothing. I would try again at operating temperature.

 

but if you get good numbers when it is cold then the engine is most likely not bad.

those numbers are not great but they are above 100psi and within 10 psi of each other. it might be a good idea to try a few while it is warmer. could maybe use some new rings.

 

+1 cold test results mean very little. The motor needs to be at opt temp. Also don't forget to set the throttle to WFO or WOT for this test.

Edit: Specs from the 1996 FSM Section 9-156 8.0 liter

 

Yea I forgot to open the TB to WOT......LOL


The motor runs great, I was just doing it for a test as I was replacing the plugs anyway.

Compression Pressure 1069-1172 kPa 155-170 psi is for the 8.3L Viper motor which has a Compression Ratio of 9.6:1. I think there is a mix up or something. I don't think 8.4:1 should be that high.

But yea, I'll have to redo the test. Problem is it is a huge PITA to do that truck! But then again, I don't need to do a wet test.