quick question on doing compression test
#1
quick question on doing compression test
Never done a cylinder compression test before, but I'll be replacing my valve covers soon and figure it would be a good time to do it (having some power issues, roughness, etc.). Did a search here and also checked the FSM, but didn't see a mention of using an extension (OHC extension) with the compression gauge. Is it trivial to thread the end of the hose into the cylinders AND tighten it enough to do the compression test, or is it suggested to use an extension due to the length of the spark plug tubes? I'd hate to tear everything apart only to find that I don't have all the necessary/recommended tools. While at the same time, I don't want to buy more crap I don't need . Thanks.
#2
Yeah....it needs to be tight. I'd use the extension. First, of it just runs a little rough and misses some, try some solid copper "cheaper" plugs gapped down to .030. With the inherant problem of these crappy coilpacks the NGK's takes the load off. Don't be nervous about yanking the intake, its easy. No new gasket is required. Try the plugs first.
Also, pinch the PCV line off with your fingers while it is idleing. Make sure you can hear it "click" to make sure its working and your not driving around with a vacuum leak.
Also, pinch the PCV line off with your fingers while it is idleing. Make sure you can hear it "click" to make sure its working and your not driving around with a vacuum leak.
Last edited by NmexMAX; 03-04-2013 at 11:53 AM.
#3
Yeah....it needs to be tight. I'd use the extension. First, of it just runs a little rough and misses some, try some solid copper "cheaper" plugs gapped down to .030. With the inherant problem of these crappy coilpacks the NGK's takes the load off. Don't be nervous about yanking the intake, its easy. No new gasket is required. Try the plugs first.
#4
I've never heard of gaping the copper spark plug other than OEM specs to fix a rough idle... So I would like to know where you got that idea lol.
As for the compression test. It's unnecessary to use an extension to get it tight. Hand tight should be just fine as long as the O ring is seated right. Make sure the engines hot because by the time you get everything off it could cool down and not give accurate results so try to work fast! So before you change the valve cover check compression asap.
I ran a dry compression test on my max and got cylinder # 2,3,5 at 155- 157psi, #4 at 147, and #1 at 175, #6 165. Wet compression got me an average of 220psi all around. Still runs like a champ.
Make sure you run a dry compression test first then a wet test. Drip like 2tsp of oil into each cylinder and then re test. Don't add oil to every cylinder at the same time because when you crank it most of the oil will spit out the spark plug tubes.
Brodie
As for the compression test. It's unnecessary to use an extension to get it tight. Hand tight should be just fine as long as the O ring is seated right. Make sure the engines hot because by the time you get everything off it could cool down and not give accurate results so try to work fast! So before you change the valve cover check compression asap.
I ran a dry compression test on my max and got cylinder # 2,3,5 at 155- 157psi, #4 at 147, and #1 at 175, #6 165. Wet compression got me an average of 220psi all around. Still runs like a champ.
Make sure you run a dry compression test first then a wet test. Drip like 2tsp of oil into each cylinder and then re test. Don't add oil to every cylinder at the same time because when you crank it most of the oil will spit out the spark plug tubes.
Brodie
#5
Of course gapping the plug tighter helps the coils. I got that from years of Turbo, procharger vette builds, which is what I do...... I am here to help, I will post good tech advice from experience if you would like some help. Don't add any oil to your test. It gives false readings. It doesn't run with oil in the chamber, so don't test with it. Also, a low cylinder wont show as a miss, just low power. Power surging is usually a vac. leak through a PCV valve if fuel pressure is good. Check plug gaps, then vac. leak. If you compression test it, prop throttle blade open, and spin every cylinder roughly the same amount of times.
A copper plug with no coating and a smaller gap is easier to fire. That's why we don't run coated plugs on nitrous, boost applications. Frankly, other than lasting longer, they suck.
A copper plug with no coating and a smaller gap is easier to fire. That's why we don't run coated plugs on nitrous, boost applications. Frankly, other than lasting longer, they suck.
Last edited by NmexMAX; 03-04-2013 at 10:17 AM.
#6
Of course gapping the plug tighter helps the coils. I got that from years of Turbo, procharger vette builds, which is what I do...... I am here to help, I will post good tech advice from experience if you would like some help. Don't add any oil to your test. It gives false readings. It doesn't run with oil in the chamber, so don't test with it. Also, a low cylinder wont show as a miss, just low power. Power surging is usually a vac. leak through a PCV valve if fuel pressure is good. Check plug gaps, then vac. leak. If you compression test it, prop throttle blade open, and spin every cylinder roughly the same amount of times.
And obviously the engine doesnt run with teaspoons of oil in it but that's why they call it a dry and a wet compression test. If you get good readings with a wet compression test and poor dry test it means your rings are probably worn and you will be able to see if your valves are sealing good.
And funny how hes going to prop the throttle open with the entire manifold off.. Yeah you may claim to be tech savvy but I actually go to school for this. 6 hours a day. 5 days a week.
#7
Lol....dude. Forgot on Max's the intake is off. Either way, you are full of bad information. I will bounce from this site soon if nobody wants help. You guys can get back to your lips and rims and Newb bashing. You don't even understand spark plugs...quit giving advice....and looking to UP somebody. My 14yr old son just finished his first Ls1 nitrous engine. You probably will never achieve that. Listen and learn.
#8
Lol....dude. Forgot on Max's the intake is off. Either way, you are full of bad information. I will bounce from this site soon if nobody wants help. You guys can get back to your lips and rims and Newb bashing. You don't even understand spark plugs...quit giving advice....and looking to UP somebody. My 14yr old son just finished his first Ls1 nitrous engine. You probably will never achieve that. Listen and learn.
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