Attn: Advice for doing Compression Check.
Thread Starter
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Attn: Advice for doing Compression Check.
I am getting ready to do a compression check on each cylinder in my motor. Here is what I know, remove each spark plug, hook up gage and crank the motor over 5-6 times and then record the compression for each cylinder. Do I have to ground out any of the spark plug wires when I do this? I am wondering if I need to do anything with the spark plug wires..on old cars (w/distributors) if you did not do this when doing a compression check you could fry a diode. Advice is appreciated.
Melting Slicks
Joined: May 2001
Posts: 2,596
Likes: 120
From: East Tennessee
Re: Attn: Advice for doing Compression Check. (Shinobi'sZ)
unplug the coil packs or the car will start if you leave some plugs in, probably woulnt bw a bad idea to unplug all the injectors or unplug the fuel pump relay if you are going to do a lot of cranking
Race Director
Joined: Apr 2001
Posts: 19,329
Likes: 15
From: Saint Augustine, FL
Mid-TN Events Coordinator
St. Jude Donor '03-'04-'05-'06-'07-'08-'09-'10-'11-'12-'13-'14-'15-'16
Re: Attn: Advice for doing Compression Check. (kp)
unplug the coil packs or the car will start if you leave some plugs in, probably woulnt bw a bad idea to unplug all the injectors or unplug the fuel pump relay if you are going to do a lot of cranking
I would definitely remove the FP fuse also. Also, it sounds like you already knew this, but make sure you remove all the plugs.
Melting Slicks
Joined: May 2001
Posts: 2,596
Likes: 120
From: East Tennessee
Re: Attn: Advice for doing Compression Check. (jreed99)
thats true, all the plugs should be remove to keep things even - not to mention your battery will last longer. Been a lot of years since i did a compression test, been using a leakdown tester for the last 20 years :)
Thread Starter
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Re: Attn: Advice for doing Compression Check. (kp)
I was going to do a leak down test,,,but I was worried that it would not isolate...or be specific to each cylinder. Doesn't it indicate everything valves, rings, etc...wouldn't a compression check be very specific just to the cylinder..plus I could see the specific compression for each cylinder. I don't know..which one should I use?????
Melting Slicks
Joined: May 2001
Posts: 2,596
Likes: 120
From: East Tennessee
Re: Attn: Advice for doing Compression Check. (Shinobi'sZ)
using a leakdown tester is easier to isolate if a cylinder is leaking though the rings/valves/head gasket, you can compare the readings on each cylinder but it takes a little more time to do a leakdown. A compression test is much quicker to see if there is major difference in one or two cylinders, thats all you are looking for now.
If you find a low cylinder or two you can then leak those down and see where its leaking from.
[Modified by kp, 10:31 AM 11/4/2002]
If you find a low cylinder or two you can then leak those down and see where its leaking from.
[Modified by kp, 10:31 AM 11/4/2002]
Thread Starter
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Re: Attn: Advice for doing Compression Check. (kp)
Gotcha...either the poopie is right or it isn't. If there is a big difference in one of the cylinders...I know it is not valves..so it will have to be a cracked/hole in the piston...or rings..and if thats the case..I will pull the motor and put some forged pistons in it and forget about it...I mean I planned on this someday anyway...maybe I will put some recessed pistons in it and drop the CR. If all the cylinders are close to the same...I am just going to run it..and do the PCV stuff.
Thanks
Thanks
Melting Slicks
Joined: May 2001
Posts: 2,596
Likes: 120
From: East Tennessee
Re: Attn: Advice for doing Compression Check. (Shinobi'sZ)
Thats pretty much it :)
Problem is when you pull the motor 'just' to put forged low compression pistons in you will start seeing a lot of other 'weak' stuff in there to replace, and so it goes on and on..
Hopefully there is nothing wrong, like I stated before a quick check is taking off the oil cap when idling. I would also take the breather line off the coupler on the blower inlet and use a small breather/puke tank at the front. If nothing is wrong consider yourself lucky, 10psi on a stock LSx short block is a ticking time bomb even you really keep on top of tuning.
Problem is when you pull the motor 'just' to put forged low compression pistons in you will start seeing a lot of other 'weak' stuff in there to replace, and so it goes on and on..
Hopefully there is nothing wrong, like I stated before a quick check is taking off the oil cap when idling. I would also take the breather line off the coupler on the blower inlet and use a small breather/puke tank at the front. If nothing is wrong consider yourself lucky, 10psi on a stock LSx short block is a ticking time bomb even you really keep on top of tuning.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
Burning Brakes
Joined: Apr 1999
Posts: 1,150
Likes: 0
From: Saratoga CA
Re: Attn: Advice for doing Compression Check. (Shinobi'sZ)
Hey Shinobi. What happened, why do you want to do a compression check? Hope everything is cool with your car. Having done it before, I think everyone has covered what you need to do. Try to make sure you get a gauge that has a stainless steel braided hose because otherwise it's tough to really twist it in to the #8 cylinder. And keep a note of where the pressure goes to on the first crank and each successive crank, and just stop cranking when the compression starts to top out. It's best to have a friend so he can crank it while you watch the gauge. Good luck.