Spark plug help

[davekp]

My #1 spark plug (on the left) is very different than the other 7 (like on the right). Is this a classic symptom of something?
'91 302, Mustang EFI, new 24 lb injectors, AFR heads, 70mm throttle body, Trick flow intake. Pro-M MAF, NOID light test seems OK, header temp similar to the other cylinders.
I'm not experienced with reading plugs.

Any ideas greatly appreciated.

[rich grsc]

You say AFR heads? Those don't look like the correct plugs for AFR. I have 185 AFR, and my plugs have a gasket on them, those look like a taper fit? The all white plug looks lean?

[davekp]

You say AFR heads? Those don't look like the correct plugs for AFR. I have 185 AFR, and my plugs have a gasket on them, those look like a taper fit? The all white plug looks lean?

I think you are right- I have the wrong plugs according to AFR's instructions. Will get the right ones tomorrow. Autolite 3924. What should the gap be? I'm reading recommendation of .054 but that looks excessive.

[NAZ]

If the plug on the right is representative of the others and has been in for any length of time I'd tend to be happy with that absent any other symptoms. It looks within a normal range of what you might expect. A picture is much harder to read than the real thing but the base circle will tell the story on mixture and the one on the left appears dry sooty with some carbon build up that looks a bit like grit on the base circle indicating a rich mixture. If this carbon build up was wet or shiny looking that would indicate oil fouling but from the photo it appears dry.

So ask yourself what would cause the number one cylinder to run rich.

[davekp]

If the plug on the right is representative of the others and has been in for any length of time I'd tend to be happy with that absent any other symptoms. It looks within a normal range of what you might expect. A picture is much harder to read than the real thing but the base circle will tell the story on mixture and the one on the left appears dry sooty with some carbon build up that looks a bit like grit on the base circle indicating a rich mixture. If this carbon build up was wet or shiny looking that would indicate oil fouling but from the photo it appears dry.

So ask yourself what would cause the number one cylinder to run rich.

You're right, the build-up appears dry. I don't know why this cylinder only is rich. The injectors are new, but the same issue was present with the old injectors so I think they are not the issue.
I'm stumped.
Would a bad ignition wire do this? Like maybe failing to fire every time?
The plug seemed to have a little soot on the outside, also.
And, these are the wrong plugs, also.

[rich grsc]

I run .035 gap. I think anything around .035 and .045 would be fine. .054 too much

[davekp]

Thinking about this further-
Could a not fully seated plug result in that cylinder running lean?
Seems like part of the charge could be pushed out of the cylinder during compression resulting in a lean charge remaining to be fired.
Also would explain the sooting on the outside of the plug.

[bobl]

Running the wrong style plug can cause all kinds of evil things to happen. I would disregard anything you see now, put the correct plugs in and see what they look like after some miles. Aside from possible leaking the heat transfer will be all messed up and the plug probably is not positioned in the cylinder correctly.

[NAZ]

The mixture entering the cylinder is homogeneous -- any small amount that would escape would not lean the mixture, it would be more like if the cylinder were filled less to begin with but with the same ratio of fuel to air. But even if a lean condition would occur you would not have excess carbon build up. Black sooty dry build up on the plug base circle indicates rich not lean.

You should do a web search of rich and lean conditions look like. Note that you will get a variety of ideas about how to interpret plugs. I've been reading plugs and trying to interpret what they are telling me for five decades and during that time I have seen a large variety of ways people interpret plugs so you will not find a lot of agreement. However, you will find a consensuses about color of rich and lean. But some will tell you to look at the porcelain not the base circle. I've found the porcelain not very reliable for indicating anything but very rich or very oil fouled.

BTW, if you post photos of plugs again, it's important to look at the ground strap coloration too. A lot can be gleaned from the ground strap.

Reading plugs that have run for several hours under varying conditions, i.e. idling, slow speed, mid-range cruise, and short spurts of WOT with some goosing the throttle waiting at the stop light will quickly lead you to incorrect conclusions on jetting and plug heat range. When I check plugs on the race car they are new and the engine is shut down immediately after the finish line then towed back to the pit area. Even idling in the staging lanes will color new plugs. So looking at plugs in a street car that have many miles on them is not to most accurate way to read plugs so you have to take that into consideration before making any conclusions. And reading plugs is only one part of all the other data you use when tuning or troubleshooting.

[davekp]

The mixture entering the cylinder is homogeneous -- any small amount that would escape would not lean the mixture, it would be more like if the cylinder were filled less to begin with but with the same ratio of fuel to air. But even if a lean condition would occur you would not have excess carbon build up. Black sooty dry build up on the plug base circle indicates rich not lean.

You should do a web search of rich and lean conditions look like. Note that you will get a variety of ideas about how to interpret plugs. I've been reading plugs and trying to interpret what they are telling me for five decades and during that time I have seen a large variety of ways people interpret plugs so you will not find a lot of agreement. However, you will find a consensuses about color of rich and lean. But some will tell you to look at the porcelain not the base circle. I've found the porcelain not very reliable for indicating anything but very rich or very oil fouled.

BTW, if you post photos of plugs again, it's important to look at the ground strap coloration too. A lot can be gleaned from the ground strap.

Reading plugs that have run for several hours under varying conditions, i.e. idling, slow speed, mid-range cruise, and short spurts of WOT with some goosing the throttle waiting at the stop light will quickly lead you to incorrect conclusions on jetting and plug heat range. When I check plugs on the race car they are new and the engine is shut down immediately after the finish line then towed back to the pit area. Even idling in the staging lanes will color new plugs. So looking at plugs in a street car that have many miles on them is not to most accurate way to read plugs so you have to take that into consideration before making any conclusions. And reading plugs is only one part of all the other data you use when tuning or troubleshooting.

Thanks!
I'll get the correct plugs in today and re-evaluate. My concern is the issue is on only 1 cylinder, and the injectors are all new.

[CraigS]

Running the wrong style plug can cause all kinds of evil things to happen. I would disregard anything you see now, put the correct plugs in and see what they look like after some miles. Aside from possible leaking the heat transfer will be all messed up and the plug probably is not positioned in the cylinder correctly.

I agree. Naz has also given a ton of great info but that is for the next set of plugs. The 3924s (just buy plain Autolite brand) have a crush washer to seal them. So spin them into the head until they get to the washer. Then it will take additional torque to crush the washer. You have about 1/3 turn to get the feel for how much. As soon as it stops turning w/ that same amount of effort stop. You have crushed the washer and don't want to go any tighter.