Performed compression test today

gmcman

Original poster
Member
Dec 12, 2011
4,656
I put together a short video of the test but didn't go into great lengths on setting anything up. Basically pull the fuel pump relay and spark plugs, one at a time or all of them doesn't really matter, then screw the tester in the plug hole and snug against the O-ring.

Crank the engine for about 5-6 compression strokes and observe the reading, should build fairly quickly and will settle down as shown in the video.

I'm not sure exactly what the specs are for the 4.2 but honestly I thought they may be slightly higher than normal. Nonetheless, there's only about 8 PSI difference from the lowest to the highest so that's a good sign. I'm not consuming any large amounts of oil so I'm fairly certain the cylinder walls have the normal film of oil on them.

Engine was cold, sat outside for 18 hours, throttle closed and nothing added to the cylinders. The angle of the camera wasn't straight on most of the time so the readings were as follows:

206, 205, 210, 205, 204, 202 PSI .... Cyl 1-6


[video=youtube;Zv_fPrIwwHQ]http://www.youtube.com/watch?v=Zv_fPrIwwHQ&feature=youtu.be[/video]
 

seanpooh

Member
Jan 24, 2012
461
I just checked the 4.2L Engine Repair manual we get here and it states that a normal pressure reading from a cylinder is 215psi so you're in a good range with the amount of mileage.

I just watched Eric the Car Guy on youtube (who is very good I think) and seen his compression test and a leak down test. When he did the compression test, he did it dry and wet. But you aren't loosing that much pressure so I don't see a problem... it's pretty good numbers. I should do mine, where'd you purchase the compression test or was it borrowed?
 

Dillyo82

Member
Aug 17, 2012
80
You know the thread size by chance? I'd like to get a tester that I could use on my Pontiac Sunfire as well as the TB.
 

mrphoenix80

Member
Jan 1, 2013
251
I want to say it is 14mm x 1.5, but don't quote me on that. I got mine from harbor freight and it has all the common ones in it. The Sunfire is the same thread so you will be ok.
The only one I have not been able to do is the F150 triton, AND WHO WANTS TO WORK ON THOSE!
 

CaptainXL

Member
Dec 4, 2011
2,445
gmcman said:
I'm not sure exactly what the specs are for the 4.2 but honestly I thought they may be slightly higher than normal.

215 psi is the spec for a new engine. Those readings are kind of unbelievable for 180K miles. It almost seems as if you have a newer engine in there or there are a lot of carbon deposits.
 

gmcman

Original poster
Member
Dec 12, 2011
4,656
CaptainXL said:
215 psi is the spec for a new engine. Those readings are kind of unbelievable for 180K miles. It almost seems as if you have a newer engine in there or there are a lot of carbon deposits.

My readings are 5-12 psi below spec for a new motor and I take good care of it. I have run Mobil 1 for most of its life and run alot of 44K through it. I let it idle for a few min 99% of the time before i drive it away to let the rings build up heat as well as the cylinders.

Fuel mileage is still good and I dont think there is much carbon in there with as many high-load take-offs as I do....:biggrin:
 

CaptainXL

Member
Dec 4, 2011
2,445
gmcman said:
My readings are 5-12 psi below spec for a new motor and I take good care of it. I have run Mobil 1 for most of its life and run alot of 44K through it. I let it idle for a few min 99% of the time before i drive it away to let the rings build up heat as well as the cylinders.

Fuel mileage is still good and I dont think there is much carbon in there with as many high-load take-offs as I do....:biggrin:

What overall long term benefits have you seen from using the 44k?
 

gmcman

Original poster
Member
Dec 12, 2011
4,656
CaptainXL said:
What overall long term benefits have you seen from using the 44k?

Sorry for the late reply....I suppose not having hardly any driveability issues....rough idle mainly. I did slack off last year and went almost 2 years and I did notice a hard idle where it would seem like it was misfiring or just a stumble and the 44K quickly cleared that up.
 

Forum Statistics

Threads
23,229
Posts
637,063
Members
18,390
Latest member
jgriff

Members Online