low rpm stumble/misfire
09-09-2008, 10:15 AM
#1
low rpm stumble/misfire car is a 99 ws6 m6 77k miles. all stock powertrain except for lid and flowmaster muffler.
1 month ago: changed plugs/wires & added mac ory, broke manifold studs in the process - drilled them out under the car and temp. repaired with bolts/nuts. car ran perfect like always except for a VERY small exhaust leak.
3 days ago: added 01 exhaust manifolds, removed air/egr, had the mac ory modified to work. car is still on stock tune. wot is great. normal driving above 2k is great. at idle/low rpm the car stumbles and randomly misfires, but not enough to set off a code. only codes are for rear o2s, air/egr.
car runs great except for low rpm. any ideas? i've been over the plugs/wires twice. the car has always been SMOOTH AS SILK accelerating, lugging, whatever...it always ran perfect. i typically drive the car very easy unless i have a purpose. the car has never given me one second's worth of trouble and always ran perfect. the smoothest ls1 m6 i've ever driven, probably because it was still stock haha.
1 month ago: changed plugs/wires & added mac ory, broke manifold studs in the process - drilled them out under the car and temp. repaired with bolts/nuts. car ran perfect like always except for a VERY small exhaust leak.
3 days ago: added 01 exhaust manifolds, removed air/egr, had the mac ory modified to work. car is still on stock tune. wot is great. normal driving above 2k is great. at idle/low rpm the car stumbles and randomly misfires, but not enough to set off a code. only codes are for rear o2s, air/egr.
car runs great except for low rpm. any ideas? i've been over the plugs/wires twice. the car has always been SMOOTH AS SILK accelerating, lugging, whatever...it always ran perfect. i typically drive the car very easy unless i have a purpose. the car has never given me one second's worth of trouble and always ran perfect. the smoothest ls1 m6 i've ever driven, probably because it was still stock haha.
09-11-2008, 10:34 AM
#2
update:
after driving the car more, the misfire almost completely goes away and becomes very intermittent. sometimes it stops completely. until i shut the car off and start it up again, that is...then it does it for about 5 minutes and almost goes away completely..whiskey tango foxtrot?
after driving the car more, the misfire almost completely goes away and becomes very intermittent. sometimes it stops completely. until i shut the car off and start it up again, that is...then it does it for about 5 minutes and almost goes away completely..whiskey tango foxtrot?
09-11-2008, 01:55 PM
#3
Launching!
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Not to stray off from the original question, but why go through the work of changing your stock cast manifolds for other stock manifolds? Im not saying its wrong, just curious as to why. 
09-11-2008, 06:43 PM
#4
because when i added the ory i broke 5 of the 6 studs on the factory manifolds. then i proceeded to drill them out while on the car. i couldn't get straight on one of the driver's side bolts so i just bolted it back together and decided if i had to pull the manifolds i would just replace them with something else. i got a set of 01s for free so i threw them on.
10-08-2008, 08:23 PM
#5
ok, so i replaced the o2 sensors and still have a problem. cold start the car is fine for ~30 seconds, then it begins misfiring badly. driving it the problem persists and seems to get worse. there is no consistency. i can mash it in 4th gear and it will stumble and misfire for 10 seconds, then pull cleanly from 3-5k, then start breaking up again? it's so random wtf.
i have another maf to try next. i opened the hood at night and closely inspected the engine while the car was running, i could not see any arc. took a bottle of water and sprayed it around the plug wires, etc...still nothing. wtf? i want to sell this car asap and this is the only thing prohibiting me.
i have another maf to try next. i opened the hood at night and closely inspected the engine while the car was running, i could not see any arc. took a bottle of water and sprayed it around the plug wires, etc...still nothing. wtf? i want to sell this car asap and this is the only thing prohibiting me.
