08 4.6 misses under slight (OD) load. no codes.

[BigBlockRanger]

Pulled the coil packs and they looked like this:

Squirted them full of dielectric grease and reinstalled. Fixed. Thanks for the tip!

 

[pjw73nh]

Glad it worked out for you. As an aside, while I had my coils off, I used a cotton rag and some brake cleaner to remove any dirt or contaminants from the OUTSIDE of the coil as well. I cleaned all the rubber.

-P.../NH

 

[kam327]

When you guys say it's missing, does that show itself as a slight increase in RPM every few seconds?

I have a slight increase in RPM, maybe every 2-3 seconds, while maintaining speed in the 40 and above range. The increase is just enough to clearly see the needle move, maybe 50 rpm? At one point this weekend (after refueling with the family in the car) the transmission also started clunking with each RPM increase. Maybe it was worse because the tranny was in lock up mode, I don't know, but I wasn't driving any differently than the rest of the time it happens.

This symptom started after the dealer had the engine apart for head gasket replacement in March. I had them replace all plugs and boots at that time, but not the coils. Based on the previous posts here I suspect they didn't clean and/or put enough grease on the coils and boots when they reassembled them.

57,000 miles on an '06 V8.

 

[Flatwatr]

Would you read my post and compare it to your issue? Yours is the closest I've found to mine. Thanks
Sounds and feels like rumble strips

 

[Flatwatr]

When you guys say it's missing, does that show itself as a slight increase in RPM every few seconds?

I have a slight increase in RPM, maybe every 2-3 seconds, while maintaining speed in the 40 and above range. The increase is just enough to clearly see the needle move, maybe 50 rpm? At one point this weekend (after refueling with the family in the car) the transmission also started clunking with each RPM increase. Maybe it was worse because the tranny was in lock up mode, I don't know, but I wasn't driving any differently than the rest of the time it happens.

This symptom started after the dealer had the engine apart for head gasket replacement in March. I had them replace all plugs and boots at that time, but not the coils. Based on the previous posts here I suspect they didn't clean and/or put enough grease on the coils and boots when they reassembled them.

57,000 miles on an '06 V8.

Sounds and feels like rumble strips
So the dealership has an entire rear shaft on back order, now 4 weeks. They tell me the analyzer showed no engine issues, but the center bearing support is shot and it has to be replaced as one part, with the shaft. I can buy the shaft replacement now; I've been under the truck myself, but this issues has occurred three times in the past and this is the first shaft replacement. Because of the tach oscillation, I want to think there is more to the root cause.

 

[thebrakeman]

I really hope they looked for Pending Codes. Be absolutely sure you aren't getting a misfire CEL (current or pending), because this sure sounds like the same issue to me.