OK, mechanic buddies. Step into my garage, and help me with these plugs.

Finally got off my butt and decided to take advantage of the weather, and find and fix that miss I have had.

Going to clean the threads on my rockers and loctite them down, while I am at it.

Since I don't have any car buddies living anywhere near me (mechanical ones, anyway), I ask you guys to chime in.

Take a look at these pics, and let me know what you think. I am getting acceptable burn on all but #7, which is grimy and dark. The cleanest part is where I touched it with my finger and some of the grime wiped off.

Up front:

1) This is not a WOT run-then-check spark plug inspection. This is just pulling the plugs after regular driving for several months.

2) I am not checking the plugs to tune for optimal burn or a/f mix, but just checking which cylinder I might be getting my miss on.

3) These plugs are all currently gapped near .070 and I will be closing them up to .045. I "thought" they were gapped at .044 when I assembled the engine, so that may be part of my problem???

4) Pics are big and coming from my Della picture-hosting page, so you can zoom in and take a closer look. Arrow at right side points to front of vehicle. So I apologize for slow load times and obnoxiously large photos!



Driver side only:




And passenger side only:



Thanks in advance for any comments, constructive or otherwise :Handshake

 

Whats up with #7?

 

That is my question. Why would #7 be the "odd man out", and most likely, my source of miss.

Isn't there a long-standing issue with the firing order causing the #7 wire to short over with one of the other wires that is next in the firing order? Maybe I need to insulate the wire better?

I am going to search around for that issue, if I am not thinking of something off-base.

EDIT--no, I just looked at the firing order 1-3-7-2-6-5-4-8 and if that was happening, I would expect it to happen at 5 and 6.

 

Found it! I wasn't dreaming it up, just thinking of the 302 firing order, not the 5.0. So that is NOT my problem.

 

Your wires should be self-insulating... if a wire is shorting to another... then both wires are just plain bad.

If you suspect #7, then simply investigate it. If you change the gap, then you cannot change something else. Clean the plugs, gap and drive. Then pull the plugs again in a week. See if it has changed.

 

Is it wet? or does it just look that way?

 

Yes, it was wet when I pulled it out. When I put my finger on that edge, that grime just wiped off.

But now that it has been sitting out for 45 minutes, it is dry, so likely wet with fuel, not oil.

Now that it is dry, that grime will only come off if I scrape it with my fingernail or something harder.

 

Check the plug itself, the the wire then the cap. Somethings funky with that cylinder, must not be firing.

 

I am surprised any of them were firing with .070 gap!

Just goes to show how powerful the MSD Blaster and 6A setup is!

 

Who told you to set them that big?? The internets?

 

No, I thought I set them at .044. Wondering if they are worn...they don't have maybe 500 miles on them.

 

You've got a problem with the #7 cylinder. Time to take a compression reading of all 8. You've either got broken rings there or a leaky valve guide seal. (low compression would be a ring problem, if it's within the range of the others, then look at the valve guides or seals)The wide gaps didn't help either, but they will fire with a hot ignition. It will also cause the wire to leak due to the higher resistance. And what's with the racing plugs ? All you need is the plane jane Autolite copper plugs, anything more expensive is a waste on a carbed engine.

 

I was thinking about going back to regular plugs. These are harder to gap accurately. That might be how they got gapped to .070 rather than .045.

But since I already have these plugs, and they seem to be in good shape, I just regapped them to .045, and stuck them back in.

I put #7 plug up on #1 cylinder. I will check them out after a bit and see if #7 still stays dark or if it moves to #1.

Or maybe it won't miss at all, now. Cleaned up the plugs, regapped them, re-torqued all the rocker arms with hi-temp loctite, and cleaned off the distributor rotor and contacts, which were in the shape I would expect them to be in after 500-1000 miles of use.

Loctite says 24 hours to cure, so I won't try to run it til tomorrow.

 

those gaps are too large and won't allow the timing to be as accurate regardless of the ignition used. Well.. a mag or ultra-high output coil(not what you have there unless it's a 7 or 8 series box).. would allow it.. but that's about it.

The burn won't be as clean/complete either.

Also.. did you backcut/file those ground straps?.. or are they rounded off a bit like they look in the pic's?

Personally.. I'd do as baddad mentioned and install fresh cheapy coppers jst to get a better baseline to read them from. Troubleshooting with pre-used plugs is tough to do accurately.

 

I didn't mess with the plugs. They have a really short 1/3 ground strap, so you basically have to gap them from the top corner of the tip to the inside corner of the strap. So any wear on either would make a drastic change in the gap.

I will grab new plugs next time I hit the store. Need a new air filter too, to get rid of the old paper and go with K&N or other cloth filter.