I'm working on an 04 SSS that has a misfire on cylinders 4&6 according to my scan tool. I've changed plugs and wires, swapped coils from my personal ride that i know work, I've put a noid light on the injector wires and confirmed that they are getting signal, I've swapped number 4&6 injectors with number 2&8 hoping the miss would follow but no luck, I pulled the valve cover and made sure the valves were opening and closing, and I've done a compression test on all four cylinders on the RH bank. Numbers 2&8 were both 125 psi, and numbers 4&6 were 175 and 150 respectively. I'm about ran out of ideas. Any thoughts?

 

I would ask what the fuel trims are but they are going to be all whack with the misfires.

Possible bad intake gasket leak is something to look into, I'd smoke the intake and look for leaks.

 

Ok, I didn't smoke it but i sprayed brake cleaner all around it and it didn't change anything. Would there still be some benefit in smoking it?

 

Yes, the smoke can get into the places that the " carb cleaner test " cannot. And it is a sure fire way to test for intake leaks

 

Any updates with this issue?

 

Kinda. I was working on it for an acquaintance of mine in the evenings and he got in a tight spot as far as transportation so he ended up taking it to a shop. I don't know exactly what the issue ended up being but they told him the engine was shot. Something about cylinder 8 being dead and 6 being weak. I'm assuming he was meaning compression. I guess he's going with a Jasper long block. I wish I could have dug into it a bit deeper myself but I had too many other things going to spend a lot of time with it.

 

Dead cylinder usually happens when the rings arent seating against the wall properly, allowing to much blowby and in essence wiping the cylinder... Odd that the mis was showing on 4&6 vs 2&8 with the lower compression... Unless the pcm was seeing the crank speed variance more with the good cylinders than the weak ones...

 

After reviewing this a bit more, you did a comp. test on the right bank of cylinders, all numbers are relatively close within 50-/+ not bad not great, and the truck went to a shop and they said that #8 cyl. Was dead followed by #6....... Sounds A bit fishy to me that you checked the compression and received "ok" results and then a "shop" does the same thing and states a bad motor... Sounds like someone is trying to pull a fast one, unless a piston fell apart between the time you did the compression test to the time it went to the shop.

 

Yeah, check those cylinders again. Could be that the engine is shot but I would trust no shop as they are the ones getting money out of it.

 

Compression test done wet or dry? If injectors are firing it will affect compression readings