2.4L compression test - TerrainForum.net: GMC Terrain Forum
 4Likes
Reply
 
LinkBack Thread Tools
post #1 of 13 (permalink) Old 01-17-2020, 07:55 PM Thread Starter
Newbie
 
Join Date: Jan 2020
Posts: 2
2.4L compression test

So I jumped on a deal for a 2013 nox with 97k miles before doing any research on potential issues. Being a little paranoid of high blow by, I bought a compression tester and got around 240 - 250 psi on each cylinder. Does that seem high to anyone?

There are no obvious issues with the vehicle other than being a little rough in reverse. Also I think the internal PCV orifice is plugged which will make for a fun manifold removal job (I'm no mechanic by any means).

Thanks for any insight.
mknuns is offline  
Sponsored Links
Advertisement
 
post #2 of 13 (permalink) Old 01-18-2020, 12:47 PM
Theta Freak
 
rednox301's Avatar
 
Join Date: Nov 2014
Posts: 1,903
Quote:
Originally Posted by mknuns View Post
So I jumped on a deal for a 2013 nox with 97k miles before doing any research on potential issues. Being a little paranoid of high blow by, I bought a compression tester and got around 240 - 250 psi on each cylinder. Does that seem high to anyone?

There are no obvious issues with the vehicle other than being a little rough in reverse. Also I think the internal PCV orifice is plugged which will make for a fun manifold removal job (I'm no mechanic by any means).

Thanks for any insight.
Many variables can give you different compression readings.
What you are looking for is an even reading between cylinders.
Keeping in mind the 2.4 has a 11:1 compression ratio I don't think 250 PSI is too high.

Some things to look for is when doing a compression reading:

Crank the engine 4 complete cycles for every cylinder and use that reading.
If the reading on the first cycle is low and slowly builds on the other 3, you could be looking at a ring problem.
An engine that uses oil will give you a "wet test" reading that is not as accurate.

A good rule of thumb is if 3 cylinders have a reading of 150 and the 4th is 125 or below, you have a problem.

2014 Equinox LTZ FWD 3.6L. V-6 (LFX)
GM6T70 Transmission-Gen II(M7W)
Crystal Red Tintcoat-Brownstone Leather-(FE2) Suspension-18" Wheels
Build Date: Nov. 04, 2013-Delivery Date: Nov. 25, 2013

Last edited by rednox301; 01-18-2020 at 12:53 PM.
rednox301 is offline  
post #3 of 13 (permalink) Old 01-20-2020, 08:39 AM
Sr. Member
 
repairman54's Avatar
 
Join Date: Sep 2017
Location: Montague, NJ
Posts: 392
Garage
Within 10% variable across all cylinders is the usual OK for stock engines.

Some suffer from insanity, I choose to enjoy it
'16 nox 3.6 AWD LTZ
'11 Tahoe LTZ
'15 Malibu 2.5 LT
'17 Continental 2.7 Twin Turbo
'01 FLHR
Ski Doo's
Malibu forum contributor
repairman54 is offline  
Sponsored Links
Advertisement
 
post #4 of 13 (permalink) Old 01-20-2020, 05:14 PM
Theta GOD!
 
Join Date: Jan 2010
Posts: 9,782
Quote:
Originally Posted by rednox301 View Post
Many variables can give you different compression readings.
What you are looking for is an even reading between cylinders.
Keeping in mind the 2.4 has a 11:1 compression ratio I don't think 250 PSI is too high.

I agree with the 10% rule, but I thought that the "highest" compression reading that you could get with an 11:1 compression ratio would be 14.7x11, or about 160 PSI. I suppose his gauge could be reading about 50% too high.
c&wsinbad likes this.

2018 Equinox LT1 1.5 L 4 cyl, AWD, S/R Cajun Red Tintcoat/Black

2010 Equinox LTZ 2.4 L 4 cyl, FWD, S/R Cardinal Red/Black
RIT333 is offline  
post #5 of 13 (permalink) Old 01-20-2020, 06:16 PM
Theta Freak
 
rednox301's Avatar
 
Join Date: Nov 2014
Posts: 1,903
Quote:
Originally Posted by RIT333 View Post
I agree with the 10% rule, but I thought that the "highest" compression reading that you could get with an 11:1 compression ratio would be 14.7x11, or about 160 PSI. I suppose his gauge could be reading about 50% too high.
Google how to compute a compression ratio, it's more involved than your formula.
I think your formula is for volume of the combustion chamber.

Other things must be considered like the crown of the piston.

Summit Racing has a good compression calculator, just plug in the numbers.

2014 Equinox LTZ FWD 3.6L. V-6 (LFX)
GM6T70 Transmission-Gen II(M7W)
Crystal Red Tintcoat-Brownstone Leather-(FE2) Suspension-18" Wheels
Build Date: Nov. 04, 2013-Delivery Date: Nov. 25, 2013

Last edited by rednox301; 01-20-2020 at 06:43 PM.
rednox301 is offline  
post #6 of 13 (permalink) Old 01-20-2020, 06:58 PM
Theta Freak
 
rednox301's Avatar
 
Join Date: Nov 2014
Posts: 1,903
Quote:
Originally Posted by repairman54 View Post
Within 10% variable across all cylinders is the usual OK for stock engines.
10% is good to use, all depends on the situation, is it yours, is it for a customer, under warranty??
My rule of thumb numbers comes out to 16%.

2014 Equinox LTZ FWD 3.6L. V-6 (LFX)
GM6T70 Transmission-Gen II(M7W)
Crystal Red Tintcoat-Brownstone Leather-(FE2) Suspension-18" Wheels
Build Date: Nov. 04, 2013-Delivery Date: Nov. 25, 2013
rednox301 is offline  
post #7 of 13 (permalink) Old 01-20-2020, 07:03 PM
Jr. Member
 
Join Date: Nov 2016
Posts: 58
Quote:
Originally Posted by RIT333 View Post
I agree with the 10% rule, but I thought that the "highest" compression reading that you could get with an 11:1 compression ratio would be 14.7x11, or about 160 PSI. I suppose his gauge could be reading about 50% too high.


Quote:
Originally Posted by rednox301 View Post
Google how to compute a compression ratio, it's more involved than your formula.
I think your formula is for volume of the combustion chamber.

Other things must be considered like the crown of the piston.

Summit Racing has a good compression calculator, just plug in the numbers.
But he's not calculating the compression ratio, he's using GM's given compression ratio of 11.4:1. In theory you'd take absolute pressure of the atmosphere, and multiply by the static compression ratio. So at sea level that'd be about 14.5 psi x 11.4 = 168 psi.

In reality there is a dynamic to it all. Cam timing during cranking, harmonics of the intake and exhaust, plus overlap events, etc will all change the psi read out. Plus the obvious, blowby, valve leakage, etc.

That said, 200+ psi seems much too high. Inaccurate gauge?
RIT333 and c&wsinbad like this.
adam728 is online now  
post #8 of 13 (permalink) Old 01-21-2020, 10:42 AM
Sr. Member
 
repairman54's Avatar
 
Join Date: Sep 2017
Location: Montague, NJ
Posts: 392
Garage
Plus there is the wet or dry test to determine if valves or rings are leaking. 200 is very high IMO. Throttle should be wide open when cranking / testing also.

Some suffer from insanity, I choose to enjoy it
'16 nox 3.6 AWD LTZ
'11 Tahoe LTZ
'15 Malibu 2.5 LT
'17 Continental 2.7 Twin Turbo
'01 FLHR
Ski Doo's
Malibu forum contributor
repairman54 is offline  
post #9 of 13 (permalink) Old 01-21-2020, 12:15 PM
Jr. Member
 
Join Date: Nov 2016
Posts: 58
Quote:
Originally Posted by repairman54 View Post
Throttle should be wide open when cranking / testing also.
Is that possible with throttle by wire? I've never tried while looking at data. Typically on cold starts it shows the throttle body throttle position between 30-35% TPS. Not sure if it reacts to pedal input at cranking.
adam728 is online now  
post #10 of 13 (permalink) Old 01-22-2020, 08:28 AM
Sr. Member
 
repairman54's Avatar
 
Join Date: Sep 2017
Location: Montague, NJ
Posts: 392
Garage
Quote:
Originally Posted by adam728 View Post
Is that possible with throttle by wire? I've never tried while looking at data. Typically on cold starts it shows the throttle body throttle position between 30-35% TPS. Not sure if it reacts to pedal input at cranking.
Yes you manually open it but have it disconnected as not to damage it. It probably will set a code but if your doing advanced diagnostics you have code reset capabilities.
bigb12359 likes this.

Some suffer from insanity, I choose to enjoy it
'16 nox 3.6 AWD LTZ
'11 Tahoe LTZ
'15 Malibu 2.5 LT
'17 Continental 2.7 Twin Turbo
'01 FLHR
Ski Doo's
Malibu forum contributor
repairman54 is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the TerrainForum.net: GMC Terrain Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome