Cylinder Misfire

[SmokerX]

Hi, I have a 1998 Subaru legacy outback that's showing a Check engine code for no spark on cylinder 4. I changed the wires, plugs and Coil pack already and it persists.

 

The misfire comes and goes. When I visually observe the spark by disconnecting the wire at the Pack while Running in park, 4 seems to have weak spark and an intermittent miss. When I switch to Drive and check, it has no spark. This is exactly how it feels when driven except I think weak spark returns after no spark when accelerated.

 

I'm not familiar with anything involving spark beyond the Coil pack on Distributor less engines. I was hoping the coil pack would fix this. The connections to the coil pack look fine. Is this an ECU issue? or a loose harmonic balancer? O2 sensor?

Edited May 2, 2012 by SmokerX
add info.

[Fairtax4me]

The coil pack is made up of two coils, each hump in the pack is a separate coil, with a terminal at each end. Both terminals are fired at the same time, so both plugs attached to that coil spark at the same time. Weak or no spark will affect both plugs that are fired by that coil. With one cylinder misfiring, it's spark plug, wire , fuel injector, or something internal in that cylinder.

 

How many miles? Have you ever had the valve lash adjusted? An all too common problem with these is the exhaust valve face wears and the lash clearance becomes too tight, eventually leading to the valve burning. With the 2.5 DOHC engine, cylinder number 4 seems to be the lucky cylinder for burned valves.

 

Assuming you have quality spark plugs and wires, meaning NGK spark plugs and NGK or Subaru OE plug wires, a consistent misfire on cylinder 4 could be due to no compression. A compression test or leakdown test will confirm a burned valve.

[SmokerX]

Hi Fairtax, thanks for the response. Would a burnt valve or injector retard the timing to make 4 not fire? I think it would just notice a change in torquing of your drive shaft and throw the misfire code without a real misfire.

 

When I visually inspect mine I can tell 4 is not getting spark so it's definitely a spark issue not a compression issue causing an idiot light unless there's something I dunno about as far as compression causing no spark. I'll recheck all 4 sparks to make sure only 4 is not firing since I only checked 4 and w/e plug is on that side to compare it to.

[SmokerX]

I found this in another thread.

 

someone thru some crap autostore plug wires on it, and there were a couple ends that wouldn't "snap/click" onto the end of the plug right. In fact, when i went to look at the car, the owner before me said it had a miss. I looked, saw the new "junk" plug wires on it, and snapped the one end on the plug, it cleared the miss up. Then a few days later, same thing happened under my ownership, plug wirecomes off the spark plug.

 

I'll recheck the plug to boot connection and visually check for spark again.

[SmokerX]

I think I figured it out. While changing the spark plugs the electronic connector for the fuel injector came loose. I touched it and it slid right off. It must have been jumping the small gap with electric since the misfire was intermittent. I must have accidentally diagnosed a coil in the charge pack going out or the injector contacts being loose causes a true misfire and not just an idiot light; since now visually checking the spark it looks fine even with injector contacts loose.

 

This is the 2nd time and 2nd assistant that has jiggled something loose we where not working on that caused days of head ache since it is out of mind and overlooked. The first was a main wire on a distributor while working on a starter. Both times I was underneath the car while they where on top.

Edited May 2, 2012 by SmokerX

[ivans imports]

adjust valves to tight on exhaust