Engine compression read out

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soaringcowman

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Hey guys i just did a compression check on my 318 today, did it while it was cold. main reason i did it was because the motor would make a slight noise through the exhaust, people kept asking if it was cammed, but from my knowledge it is bone stock. but here is what i got on compression....

tranny
135 143
34 142
160 142
130 145
fan
... whats your guys thoughts on this.
thanks
adam
 
is that cylinder really 34 or is it 134 ? Thats a problem if its 34.

You need to warm the motor up, pull all the plugs and wire the throttle wide open before taking the readings.
 
Like Adam says.. You never perform diagnostics cold. Because that's not how things are in the running engine. Those readings are all over the place, and the "34" doesnt fit. The right way to do it is got it to operating temp, T stat open and coolat flowing. Then shut it down, pull all 8 plugs, and block the throttle wide open. Then to the test again, writing down the results. Also FYI... on mopars, cylinder #1 is the driver's side front, #2 is pass side front, and they just go 1357 and 2468 respectively.
 
Yeah it was 34, and i got the same numbers after i put some oil in the cylinder. i was kinda stunned myself. but i'll do a warm test tonight, can't i just hold the gas down all the way while i'm cranking it over? how long do you guys suggest to crank it?
 
this is what you do...

do the regular test first

then do it again but put a lil oil in the spark plug hole and if the number goes up alot you have a ring sleaing problem if it doesnt go up alot then your good
 
well alrighty, i drove the car around the block a few times and got it pretty warmed up. it odviously cooled down a bit by the time i got all the spark plugs out. but the number came back the same. And i also had seen on a previous thread how you can do the dollar bill test. were you can hold a dollar bill up to the exhaust and if it wants to suck it up then it's a burnt valve. all i did was just make the dollar bill flop around, not really suck up or anything, because i gave it some slack and never wanted to be sucked away. but a buddy had mentioned it could possilbe be a flattened cam??? and another buddy said try some seafoam to see if there might be some built up carbon on that vavle?? whats your opinion? thanks everybody
 
Pull the valve cover and start engine and see if offending lifter operation looks similiar to ones around it. Caution, you will have to make a cardboard type splash guard when running engine with valve cover off or oil will splash onto exhaust manifold. My opinion from what you've stated is what I originally thought. Bad valve or seat. How many miles on engine? JMO, Mike
 
Make sure valves are closed on that cyl. and put air to the plug hole. Hear any air comeing out of the carb or exhaust? Valve problem, out of the block/oil fill tube hole-rings bad.:toothy10:
 
i'll see if i can borrow a leak down tester. is there any special way to do a leak down test with tester?? just incase it don't have instructions lol. so how about the flattened cam idea my buddy mentioned??
 
You'll need an air compressor to use the leak down tester. Rotate the engine to TDC on the compression stroke on the bad cylinder. The tester will have two gauges. Regulate the air pressure on the first gauge to 100 psi. The readout on the second gauge is the amount of leakdown. For example, if the second gauge shows 60 psi, you have 40% leakdown, if the second gauge shows 85 psi, you have 15% leakdown.

Listen at the tailpipe, carb and valve cover breather. Where there is noise, there is leakdown. I'm betting that you'll hear air whooshing through the tailpipe.
 
do you have to take all the spark plugs out to do it? or can i just take the on out on the 34 cylinder??
 
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