Dear Marr,
Sounds like you have a problem with number 4 intake or exhaust value. The fact that the compression for #4 cylinder is lower than the rest of the readings is leading me to believe this. Also the backfiring suggest that the intake (back firing through the throttle body) or exhaust value(through the exhaust) is leaking. I think you should do the compression test again on the #4 cylinder, except this time do a wet test. Add 2 to 3 tablespoons of motor oil through the spark plug hole before doing the compression test. If the rings are bad the compression will go up considerable. If not (this is what I think will happened) the value or values for that cylinder is bad. FYI a 4 cylinder engine may not start with one cylinder not working properly. Hope this helps Backyardmechanic :)

Answered by backyardmechanic
3 questions asked