I have a 2001 Dodge Dakota with the 4.7L that's throwing the p0308 misfire on cylinder 8 code. I have a scan tool and have cleared the code a couple times while diagnosing.and it comes back p0308 each time.

- I had spark plugs so I went ahead and put those in. No difference. The 8 plug was black and smelled like fuel.
- I swapped the coils between 6 and 8. Still thowing code on 8.
- I put a test light on the 2 wires going into the 8 coil and it had power and control.
- I checked compression on 8 and 6. 8 was around 150, 6 was 180.
- I did a wet compression test on 8 and it jumps up above 180.

So I think this points to a problem with rings or cylinder. I'm just trying to piece together and follow information I've found on the internet. Do you agree with my assessment? Anything wrong with my methods? Anything else to look for?

Thanks!!

 

You can't vary more than 15% difference across cylinder compression numbers. If we assume that 180 was your highest compression reading, then you're already out of spec because you have a greater than 15% difference between the 2 (153 would be your lowest in this case). If you saw higher compression in other cylinders, the variance can only grow. What are the numbers for all the other six? How is it running?

 

Watch what fuel pressure does over time. (engine not running.) Wonder if you have one stuck open. Might try swapping injectors on six and eight, see if anything changes.

 

I had only checked those 2 cylinders. I went to repeat the test and check compression on others, but my compression gauge must have gone belly up because I wasn't reading any compression on anything. It's running a little rough. Sputters and hesitates when giving it gas. Has a bit of a sewing machine sound to it, but that's hard to tell as the engine has always been a bit on the noisy/tappy side.

I can look into swapping the injectors. I forgot to mention we did dump some Lucas injector cleaner into it.

Thanks!

 

Meant to say if you saw LOWER compression in other cylinders the variance can only grow. Again, it's already out of spec but barely so with the numbers you have. See if you can rent a gauge. You may be right on your initial hunch.

 

I swapped the 6 and 8 injectors and it still throws the p0308 code, so I think it's likely in the rings/cylinder... unfortunately.

 

Might have had bad oil maintenance. How long you had it?

 

 

I did ok on maintenance. My car which we put more milage on has the oil change indicator and I would just change both when the car was due. It did have 67,000 miles on it when I got it in 2005, and I don't know how it was treated before then. I figured rings more than valves just because the compression came up when dumping a bit of oil in the cylinder.