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Chevrolet Repair/Pontiac montana misfire


Just bought a 2006 pontiac montana sv6 90k lmiles.  It has a "misfire " while at steady speeds, doesn't matter if cruise control is on or not. Changed plugs and wires and used fuel,treatment - didn't help.  I thought it was tranny , bit when the tranny shop  scanned it all that came up was engine misfire, but when I took to a shop they couldn't get a code at all. This "misfire" only causes  rpms  to fluctuate about 200-300.  Thank you

Crank engine over with fuel pump fuse out. indicated on cover of fuses.While cranking, do you hear a steady sound pattern of the starters work turning the engine over [a continuous pulse/beat ie.[..........]with no gaps,or does it have a missing pulse/beat ie.[... ..... ..] or similar.[A quickie, ballpark,compression test.] If you determine the latter to be evident, your problem is a dead cylinder[low compression]. Most likely then if this is the case, the offending part would be a burnt exhaust valve. It could be something else, odds are it isn't,that is,if indeed the compression is low. I am assuming it has this miss fire across the spectrum, idle too. If comp. is good, I would take a look at the fuel system, the injectors in particular. Run a good cleaner through system.  SeaFoam is a good one.If you get no improvement, give it time,patience matters here . I once treated a Grand Am to the SeaFoam diet, and 22 days later, after continuous treatment, when I was at the cusp of other options, as to cause,  B A M,  car cured. So let her "soak". Best of luck!  

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Daniel Ostrowski


Any questions pertaining to Alignment, brakes, emissions systems, major engine repair foreign and domestic, performance and the not so common questions such as the chemistry related to emissions, What scavenging is, piston offset, purpose of harmonic balancer etc.


troubleshooting mechanicle failures. Differential repair, electrical systems, disc and drum brakes {all}.Major repair all aspects of a vehicle except paint and upholstery.

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