2000 Dodge Dakota, Crew Cab, 4.7 Magnum, 4x4.

cylinder number 6 misfire, I’ve replaced the ignition coil with a new one, and tried one from a working cylinder, spark plugs are fine, did the same and tried one from a working cylinder. We did a Compression check on the “bad” cylinder, and checked the other cylinders. All came back within 10 of each other, so we have compression. We have good fuel pressure. We checked the injector plug, and ignition coil plug with a light tester.. I forget the name, I apologize. All is good, everything is working, and yet still a misfire. The truck runs rough, and sounds bad through the rear, especially at 2-3 grand. It’s got about 153k on the engine, so yeah, it’s old. The only thing I can possibly think of is that maybe a lobe on the cam is ****ed? Or a burnt valve? The truck is stock. We’re completely baffled by this, and we cannot figure it out. I don’t think it’s worth getting rid of the truck over, but if it’s an expensive fix we might have to. The body is really good on it, so it would be a shame. Thanks for your help.

 

Remove the valve cover and take a look. You may have a valve issue, or an ejected rocker.

 

thanks, that’s likely what happened, or something similar. Could be an ECU issue, but I’m not too sure

 

95% chance ejected intake rocker

 

ECU issues don't usually target specific cylinders. If you have an ejected rocker, then it's time to change the lifters. Were you getting cold start clatter?

 

yeah, the lifters are quite loud. I hear it at low RPMs and at idle.

 

Usually they start out clattering at cold start because they lose prime sitting overnight, but after a minute or two they should fill with oil and go silent. Of course, that clattering means the lifter is wearing and being damaged incrementally. It's one of the reasons I tell people to run full synthetic 0W20 for the 4.7, because it has the fastest flow to the upper reaches. If yours were clattering all the time, that should heighten your urgency.... Eventually the lifter fails (like mine did) and spits out the rocker. It sometimes comes to rest in a place that does no harm, or it can be picked up by moving parts and completely destroy the head with all kinds of carnage. Mine failed at over 300K mi, so I wasn't bowled over with surprise. I actually drove it home from work, misfiring for 30 miles, like an idiot. I actually had the parts already when the failure occurred but was dragging my feet. I replaced lifters, springs and valve stem seals. The latter really makes the job more difficult (due to the greater degree of spring compression required, dealing with valve keepers, etc) but so worth it. Over 330K now and burns zero oil.

 

If that was the case though, wouldn’t I not have compression? We have consistent compression in all the cylinders so I’m not sure if it would be the rocker.

 

If the rocker ejects the valve will remain closed under spring tension assuming the spring didn't also get damaged. If its the exhaust valve you would still have compression. Maybe even greater compression than normal.

 

I’ll still check it out, but like I had mentioned the compression is within 5 of each other on all cylinders, so compression is extremely close