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B5 S4 misfire, can't figure it out!

B5 S4 misfire, can't figure it out!

Old 02-10-2017, 12:23 PM
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Default B5 S4 misfire, can't figure it out!

First i'll start off with all of my mods that may relate.
Copper plugs (can't remember gap but i think i set to .032"
APR stage 2+ tune 16psi on Ko3's (Yes I have Ko4's but want to figure this out before I install)
Catless DP's

Other then that i have a few non-engine mods

A while back, my car threw codes for both upstream o2 sensors. Down-streams are removed and coded out with tune. Both upstream codes occurred at once and completely randomly. I swapped both sensors with Bosch universals, making sure that they would work for my car.

There was no misfire present at the time of both o2 sensors going out, but I thought it should be included just in case. No other check engine lights have appeared, not even to this day.

One day, suddenly my car started to misfire when the engine was under load. 1st and second gears would pull just fine but 3rd and above would misfire and lose basically all power when WOT. This has been getting worse and now its to the point that I never go WOT with worry that it will only worsen the situation i am in. Unfortunately I do not have a second means of transportation until the whether picks up so I must daily the S4.

Any input would be appreciated.
RedManS4 is offline  
Old 02-13-2017, 08:38 AM
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Are the misfires throwing codes? Do you have a CEL or flashing CEL when you lose power?

Common things to try when getting misfires (depending on the code):

1. Swap coilpacks from misfiring cylinder(s) to another to see if the misfire moves
2. If a whole bank of cylinders is misfiring swap ICMs to see if the misfire moves to the other bank

Those are the most common I've seen. There are many random and esoteric reasons for misfires, but best to rule those out first.
auditna is offline  
Old 03-24-2017, 12:57 PM
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If you haven't found the problem yet and juggling the spark coils didn't work, I would suspect a vacuum/boost leak. I have experienced your symptoms and usually it's a vacuum or boost leak. Though most recent was a bad spark coil on #5 cylinder.
johnkk is offline  
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