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Old 03-03-2008, 01:03 AM   #1
Plays_With_toys
Scooby Specialist
 
Member#: 82556
Join Date: Mar 2005
Location: Parker, Colorado
Vehicle:
1996 Legacy L wagon

Default Compression brake down a hill ----> Misfire?

I've had a cylinder 3 misfire every now and again. It happened once like 4 months ago, and while I never got the code, it had the same kind of stumbling idle a few months before that.

I went on a canyon drive with a friend and at the end (30-40 miles of driving, and mind you not even hard driving as there were other motorists/bicyclists) I was coming down a rather long hill, second gear, about 35-40mph engine braking. Out my exhaust I could hear it humming and then a quick pop and then back to humming for another 4 seconds and then again a pop. It did this about 5 times, threw a flashing CEL, at which point it idled fine and stopped popping. Usually the motor pops a bit when I rev-match downshift coming to a stop, and it was doing this with less intensity with the CEL. I got it checked out and it was a cylinder 3 misfire again.

Mods on the car are:
Dodge Neon coil pack
NGK BKR5E plugs (1 step hotter)
91 Octane
open element short ram intake
lightened crank pulley
wrx midpipe/axle back with different muffler welded on

The misfires occurred before I had done the neon coil pack and the hotter plugs. After going to hotter plugs I make sure to only fill up on premium, and often put in e85 as well. My gas mileage has been better now that I fixed a timing issue, and I thought I'd try a pure 91 octane batch of gas, and the gas mileage has dropped quite a bit this tank, and now this misfire. I've been reading on here trying to find some ideas. Alot of them talk about arcing, but my wires are nice and snug. The plugs when I pulled them are the best I've ever seen them color wise (before it looked like the engine was running lean, but these are a nice dark caramel)

Edit: plug wires are about a year old, fuel filter is less than a year old, I put seafoam in the tank every 6 months
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Last edited by Plays_With_toys; 03-03-2008 at 01:09 AM.
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Old 03-03-2008, 11:39 AM   #2
06OutbackSport
Scooby Newbie
 
Member#: 160318
Join Date: Sep 2007
Location: Scotia, NY
Vehicle:
2006 Outback Sport

Default

I'm not sure why something like this would happen other than timing or a bad plug. The rich caramel color is obviously from the engine running rich. Ideally there shouldn't be much on the plugs.

I can't imagine why you'd put e85 in your engine unless you've changed some of the seals in the fuel pump. It won't be a problem now, but down the road it'll end up hurting you. But even then, I doubt it has anything to do with your misfire.

What was the timing issue you were having before this?

A real giveaway of timing being the issue is if you're pressing firmly on the gas in 2nd (at 30 or 40) then you drop your foot off the gas and the car misfires.
Other than that, I'd guess it happens periodically anyway (with this particular example being a bad hiccup) and it's less noticeable at other times due to a foot on the throttle. If the issue is common, I'd say to swap back in the old parts if you've still got them, and see if it happens then. If not, you know it's a conflict with the plugs or coil you installed.

(I'm just going to assume it's not the intake, pulley, or exhaust)
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