Hey guys,
So i did a compression test yesterday because I am going to replace the timing chain. I wanted to see if I should have the head gone through while im right there or any other issues. I performed the test and got
Cyl 1 - 175
Cyl 2 - 175
Cyl 3 - 175
Cyl 4 - 175

Then tonight after I had allready taken a bunch of crap off the truck I realized that I forgot to tell my buddy who was cranking the engine to hold the throttle wide open. I have a few questions -
Should I interpret the numbers differently?
If the throttle was wide open would the numbers be lower but still the same comparatively like every cylinder would be 20 lower.
If I had a valve or piston ring issue the cylinder still would have been lower than the others correct?
Should I put the necessary pieces back on to do the compression test correctly?
IF i need to do any engine work I want to know right now while It is easy to get too. Thank you for the help guys.

 

Main thing you look for in a compression test is evenness. When turning an EFI motor over, having the throttle closed makes no discernible difference that I have found in 8 years testing 1000+ engines.

The engine is not sucking in enough air to make a difference when simply doing a compression test, so the air bypass lets plenty of air by.

 

^^^ What he said... ^^^

 

Thanks alot for the quick response. I had the same feeling that if they were all even it would be okay. I just got the truck its a 1990 with 200,000 and it seemed too good to be true when I got all 175 so I was worried. thanks for the info