2004 Limited 4.6 V8, code P0308

[pet575]

"Service Engine Soon" light came on yesterday so I took it to O'Reilly and had them read the codes. Got P0308 Cylinder 8 misfire.

Understanding is that several things could cause this, varying from a bad plug to a bad coil, bad wire, clogged/bad injector, bad cat converter.

My plan is to first swap the coil on Cylinder 8 (driver's side, closest to firewall) with the coil on Cylinder 7 and see if the code then moves to Cylinder 7. If it does, I know it is the coil. If it doesn't, I know the problem is either the plug, the wire, or the injector. No rotten egg smell or anything to indicate exhaust issue.

Additional thoughts or does that pretty well cover things? I'm at 197K so I guess I'm due to change all the plugs regardless.

 

[94Eddie]

The first thing I suggest is to pull off the plug wire and check for corrosion at both ends. My nephew had this type of code on his 4.6L T-Bird and it was caused by corrosion between the spark plug and wire. A good cleanup made the misfire and code go away.

 

[Bruce Thompson]

swapping out plugs and coils is not a bad idea. Just like 94Eddie suggested - a good clean on the connectors maybe all you need. Just remember to disconnect the negative battery terminal to clear out the code.

 

[NJExplorerFan]

I just had this exact issue issue on my '03 V8 only I had code P0304 (cylinder #4 misfire - passenger side closest to firewall). I have extra Ford 4.6L coils so I simply replaced it yesterday and so far the problem is gone and no more "service engine soon" light after clearing the codes and completed drive cycle (except for EVAP - that takes forever to set). If you don't have extra coils laying around, definitely try cleaning it first.

 

[pet575]

Got it solved over the weekend. Swapped the #7 and #8 coils and got a "Misfire" code for EACH of them (???!!!) so I cleaned up the ends of the coils and replaced both plugs. The plug wells were INCREDIBLY dirty and full of watery crap so I think this contributed to it. The cleanup/plug change didn't fix the #8 misfire it so I replaced coil #8. After that it was all good. Just to see what happened, I purposefully didn't clear the code after replacing the #8 coil. The code cleared itself, though, which I thought was kind of interesting.

 

[rewind1]

"Service Engine Soon" light came on yesterday so I took it to O'Reilly and had them read the codes. Got P0308 Cylinder 8 misfire.

Understanding is that several things could cause this, varying from a bad plug to a bad coil, bad wire, clogged/bad injector, bad cat converter.

My plan is to first swap the coil on Cylinder 8 (driver's side, closest to firewall) with the coil on Cylinder 7 and see if the code then moves to Cylinder 7. If it does, I know it is the coil. If it doesn't, I know the problem is either the plug, the wire, or the injector. No rotten egg smell or anything to indicate exhaust issue.

Additional thoughts or does that pretty well cover things? I'm at 197K so I guess I'm due to change all the plugs regardless.

Im getting P0307 (Cyl 7 misfire). Is cyl 7 the drivers side also? im assuming right before cyl 8 when standing in front of the vehicle?

 

[pet575]

That is correct.

 

[JoshMcMadMac]

Got it solved over the weekend. Swapped the #7 and #8 coils and got a "Misfire" code for EACH of them (???!!!) so I cleaned up the ends of the coils and replaced both plugs. The plug wells were INCREDIBLY dirty and full of watery crap so I think this contributed to it. The cleanup/plug change didn't fix the #8 misfire it so I replaced coil #8. After that it was all good. Just to see what happened, I purposefully didn't clear the code after replacing the #8 coil. The code cleared itself, though, which I thought was kind of interesting.

Being "full of water crap" is most likely a coolant leak of the manifold. The issue will probably manifest again, and the solution is to replace the intake manifold.

 

[pet575]

I found the source of the water. The gasket around the thermostat housing was leaking and the coolant was running back from cylinders 5 (closest to the thermostat), 6, 7, and 8 (closest to the firewall).

Didn't mention here that I replaced it because I didn't want sidetrack this thread. I've also been told at one dealer and a few different parts stores that they see lots of Cylinder 8 misfires because the design of these vehicles allows water to get into that spot on top of the valve cover near the firewall. I'm not sure I buy that entirely, but I did have a guy at the dealer and a guy at O'Reilly Auto Parts tell me to seal the top of the coil with silicone when I installed the new one.

Still debating about whether to do that or not. I'm at 198K miles and this is the first problem I've ever had. Granted, the problem DID start immediately after it sat outside during a weekend when we had really strong thunderstorms.

:scratch:

 

[JoshMcMadMac]

I found the source of the water. The gasket around the thermostat housing was leaking and the coolant was running back from cylinders 5 (closest to the thermostat), 6, 7, and 8 (closest to the firewall).

Didn't mention here that I replaced it because I didn't want sidetrack this thread. I've also been told at one dealer and a few different parts stores that they see lots of Cylinder 8 misfires because the design of these vehicles allows water to get into that spot on top of the valve cover near the firewall. I'm not sure I buy that entirely, but I did have a guy at the dealer and a guy at O'Reilly Auto Parts tell me to seal the top of the coil with silicone when I installed the new one.

Still debating about whether to do that or not. I'm at 198K miles and this is the first problem I've ever had. Granted, the problem DID start immediately after it sat outside during a weekend when we had really strong thunderstorms.

:scratch:

That is great. I did not want you to only address the problem at hand and not get to the source of the issue.

 

[pet575]

Thanks buddy, I appreciate that!