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Misfiring problem, heavy on 1 and 4, some on 2 and 5, none on 3 and 6

G

genki

New member
Car seems to run ok and sounded OK but I got check engine light that came one, and it would be flashing if I was over 30 MPH. I had someone plug in the shop's $4,000 computer and it reported very large number of misfire at P0301 and P0304, and some misfire at P0302 and P0305. None at 3 and 6.

Coil, cable, and spark plugs were shifted around, the problem did not follow. Replaced the ignition module, problem did not go away. Checked vacuum and compression, it was all within spec (and out some money for labor since I don't have equipment for vacuum or compression checking). I noticed when mass air flow sensor was unplugged, the misfire stopped.

So how can I check if something's clogged between engine and sensor or if the sensor itself is the problem?
 


I would do a compression test to really find out if its something serious. Autozone loans the tool with a deposit.
 
He said when the MAF is unplugged the misfires stop.

So I take you have tried to drive the car a little bit with it unplugged to make sure that its not missing then??
 


Personally ide change my fuel filter if it hasnt been changed. Check fuel pressure while idle and while driving. Ide smoke the vac lines and exhaust to make sure there are no leaks and then if all else fails ide revert to the o2 sensor or maf.
 
what engine you got, year and miles?

last known tune up was???

flashing cel usually leads to needing a tune up bad, or the cat is clogged.
 


2005 Grand Prix, 3.8L, 132k miles, no idea when it was last tuned up (just got the car last week). Not sure what brand plugs or wires are but moving them around didn't change the problem so it's not likely them.

Yes, it was driven with mas unplugged. Since the engine still sound the same before and after it was unplugged, either the mas was bad or something else.

Catalytic looks new and probably less than 5,000 miles ago (compared to somewhat brown muffler) so unless it was defective it shouldn't be an issue. I'd have the mechanic install a temporary bypass to rule out clogged converter. Also I'll ask to check the fuel pressure and replace filter.
 
i dont think a cam sensor is out of the question either but make sure fuel is on par and your cat is in good standing
 
id do a tune up, (new plugs and wires) if you just got the car with those miles is very possible that its never had one before.

i didnt see where you moved the plugs around, so they could be the problem. low fuel wont cause a misfire either. but bad plugs sure will lol
 
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