99 Mazda Premacy automatic with rough idle. The car developed this problem shortly after having the radiator and head gasket replaced. Now idles extremely rough at a max of 500/600rpm but runs perfectly...
Sorry to say I would tend to agree with the mechanic at this point. Too bad all of that didn't get sorted out before spending big bucks on the head gasket repair. The cylinder with 90 psi is probably the reason for the rough running-makes me wonder if the mechanic used due diligence. Was the head checked for straightness of the head to block mating surface? It doesn't take heat very long to warp an aluminum head, and subsequent head gasket failure. Or it could be an exhaust valve not seating well, or a worn cam exhaust lobe on that cylinder. The bottom end has not "now failed", probably pretty worn piston rings; it is just questionable that the low cylinder is from the bottom end or the top end. A leakdown test of that cylinder would pinpoint the problem-I think I would suggest you get that test done-it is more precise than a compression test. It may help you decide-the leakdown test definitely will find the reason for the low compression in that cylinder.
Even so, if you got that one cylinder back to snuff, you would still have an engine with 130 psi as top compression-that is a bit on the low end, probably below the minimum compression that Mazda would recommend. It would still run good, but you might notice a loss of power, compared to an engine with 150 psi or more.
If it runs that well at higher revs, you could just drive it as is-what harm could it do? If the engine craps out, it was just meant to be! It's your call to have this engine rebuilt (again), swap in a better engine, or just run it into the ground till the engine finally gives up. But I would do the leak down test just to know what is up in that cylinder.
Good luck, Vern. Post back with what happens.
Put a vacuum gauge on a manifold vacuum tap and check the vacuum reading; from the hard brakes, it probably has low vacuum, but whether from a loose vacuum line or the engine can't make good vacuum with that low cylinder, I don't know.
Sep 07, 2013 |
Mazda Premacy Cars & Trucks