Compression test prob.

[TSi90Awd]

I just did a compression test on my 90 Talon. Al cylinders read fine except for the 2nd one in from the driver's side. I couldn't get a reading on it. I put in a little oil, as the vfaq tells you to do, and still no luck. Does this mean the ring is bad or what? I'm going to do a leak-down test this week to see if the head gasket is bad. Could a blown head gasket effect this? Any feedback is greatly appreciated. Thanks.

 

[sechen77]

sometimes it's the valve seals, guides that can lead to low compression numbers, leak down would be able to tell you what's the problem...

 

[GTM]

Originally posted by TSi90Awd
I just did a compression test on my 90 Talon. Al cylinders read fine except for the 2nd one in from the driver's side. I couldn't get a reading on it. I put in a little oil, as the vfaq tells you to do, and still no luck.

My guess is you have a burned or bent valve when you have "0" compression. You need to set that piston to TDC on the ignition stroke. To do this you will first establish TDC ignition on #1, rotate the crank 1 and 1/2 revolutions for firing order is 1,3,4,2 and you are checking #2. You need an air source so if you don't have a large compressor you can use a vacuum cleaner exhaust and then force air through the sparkplug hole. Check the rear exhaust for air leaking by either feeling or use a burning cig. smoke. The intake can be checked by removing the T/B intake hose and opening the throttle plate. Again the same process as with the exhaust; however; if the vacuum is too noisy you may need a listening hose inserted past the throttle plate.

Cheers,
GTM

 

[Defiant]

Originally posted by sechen77
sometimes it's the valve seals, guides that can lead to low compression numbers, leak down would be able to tell you what's the problem...

Not the seals, the seats.