Engine runs awful

mazda
millenia

#1

what could be wrong with it? timing belt ok timing ok compression ok spark ok fuel pressure ok cylinder 6 spits sir out of intake when doing compression test, but has 150 lbs compression and no cylinder leakage with cylinder leak tester


#2

You may be entirely on the wrong track to diagnosing this problem. Many issues with the way an engine runs are much more likely to be electronic or sensor related than mechanical in nature. Some mechanical problems that can influence sensors should also be explored, such as vacuum leaks. Have you checked for trouble codes or had the vehicle scanned to watch the behavior of sensors and other components? Lastly, could you be a little more descriptive about what the problem is other than that the engine “runs awful”?


#3

It stumbles and backfires and idles rough. it was running really really well and as it was warming up, it suddenly started to run terrible, as if the “run terrible” switch had been turned on. i have a scanner, and many many codes were found. i wrote them all down, cleared them, and got one code for engine misfire cylinder 6. then additional codes started to appear. i summized the misfire was causing other error codes. i checked spark and vacuum and the spark was hot and the vacuum was at 18 in merc. since this last email i have found the problem…


#4

…and the problem is/was?? It is useful and helpful to all to know the outcomes.


#5

the problem was a broken exhaust cam. the air spitting out was actually the exhaust not being able to exit through the exhaust port, and due to the slight overlap of intake and exhaust valve timing, the exhaust would actually exit the intake just as the intake valve opened. the higher compression on that cylinder was a result of a “double compression stroke”, since instead of exhausting, it actually compressed the exhaust. the cam was broken right in the center of the adjascent cylinder, and that cylinder only had one exhaust valve functioning. picked up a used cam today for 18 dollars and will keep ya posted…