Ok, So my check engine light came on and Cylinder one was misfiring. I changed the plugs, wires, and the coil pack and it still was missing. I did a compression test and Cylinder 1 was 170 psi while the others were all around 125-130 psi. What causes High Compression? Also My truck has 218,000 Miles on it.

 

That is an odd one.

My guess would be valve train issue, pull valve cover on #1 side and check intake and exhaust valve rockers and rotate engine thru all 4 strokes to see if both are opening fully.

I would think compression on all cylinders should be around 160-180psi.


Cold engine
all spark plugs removed
throttle propped open at least 1/2 way, put something on gas pedal or press it down when cranking

test each cylinder with at least 4 compression "hits"

Many recommend warm engine compression test but over the years I have found as a diagnostic tool the results of cold vs warm tests provide the same diagnostic information, and cold engine is just easier to work with.