Well, still missing after installing the copper plugs, gapped them at .40. By reading the plugs I pulled, they all looked the same. But all had a slight gas scent. Not strong, but you could smell it. Also they all have a black ring around where the threads start. What could that mean?

Could the black be from running a lot of injector cleaner?

 

Can you post a picture of one?

 

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I have an 02 dakota 4.7 was doing the same thing no codes backfire through
the intake. Found my problem it was the valve seat fell out. I would do a leak test and compression test. Pull your valve covers check the rockers and lifters.

 

This is a tricky one for sure. Mine does not backfire but I do have a tap on the top end of the motor that goes away after less than a minute on a cold start only. Which would be valve lash adjusters?

 

This is a tricky one for sure. Mine does not backfire but I do have a tap on the top end of the motor that goes away after less than a minute on a cold start only. Which would be valve lash adjusters?

 

Sometimes a tap when cold is an exhaust manifold. But, with the miles/time it's not unusual for the lash adjuster to take a little time to fill either.

On the plugs, is the length correct?

 

I'm going to rent or buy a vacuum gauge and see what that looks like. Was reading the haynes manual and a vacuum reading can tell you quite a bit about an engine so its worth a shot. I bought a can of seafoam so I'll try that tmrw and see what that does. I've tried it on another car I owned and it didnt do anything but that engine might not have had carbon..so we'll see

As far as plug length goes..I did compare the old Bosch's to the champions i originally pulled and they were identical.

 

Compression test will tell you plenty. Pull all the spark plugs and fuel pump relay and crank 3 or 4 times each cylinder and record what psi each one has.

 

Got myself a vacuum gauge, and it's a steady 21" Hg. Drops when I rev it, rises up to 25" after I let go, and settles back down to 21.

So I'm thinking my problem could be ignition. Coils and injectors at this point I suppose. Funny thing is tonight on a warm start, as the idle was coming down, I definitely heard it skipping..not just felt it. No CEL. Steadied right out after a few seconds.

Also had 1 felt miss down the road in OD at 50.