I have a slight miss that i was trying to troubleshoot. I was in the process of changing wires and plugs so I figured I'd do a comp test. I've done the following, as posted in another thread I've found (except I have a large screwdriver in the tb since its a DBW). I did this on 3 cylinders already and dont get anything over 30psi then drop to 0. I doubt all three are bad since I've been driving the truck daily and it hasnt been giving me problems. I rented a tool from Auto Zone.

 

Is there an o-ring at the end of the tool's threads, so it will seal? Also, is the shrader valve still in the end of the tool?

Just wondering if the tool is missing parts or damaged since it's a rental/loaner.

 

Also, you need to hold the throttle wide open while you're cranking. Can't "compress" the air if you're not letting any in. Cracked open with a screwdriver is not good enough.

Just hold the pedal to the floor.

 

Added video. The valve is still on the end of the hose as well as the o-ring. I have the tb wide open. I may just take back the tool and pick up another.

 

See if the tool's air bleed valve is open. Should be up near the gauge.

 

I tried 2 different gauges and both seem to be closed.

Also the video above is the 4th cylinder to be checked

 

I can see that the cylinder is building pressure. But the gauge is leaking or bleeding it off somewhere. It's either not set up properly, or it's junk.

 

Thanks for the help. Went to an other auto zone and rented another tester. everything worked fine, everything except the results.

 

i was getting about the same results on my truck after doing a full engine rebuild... turned out there wasnt enough oil on the rings and it was getting blow by since i had cranked it for so long without it firin (ground wire to computer wasnt connected) but after getting it to start i tested it again and there was 175+.. try starting it and letting it run for a bit then try the compression test again.. you could have dumped to much fuel into the cylinders and effectivly cleaned the oil from the rings

 

Thanks for the advice. Unfortunately, the readings were the same. Will be doing a leak down test here soon.