Big Blue's Transformation

[ArdWrknTrk]

I'm going to put my DVOM on the wires and see if there is anything obvious. And check the cap. Then after I get new plugs and install them I'll use my ignition scope and see if the problem is still there and which cylinder it is.

If it is still there and I know which cylinder I'll swap a plug wire with used ones I have. But I got these from Scotty and don't remember what brand they are.

Oh, I didn't realize that they came with the longblock but it makes sense. 💡

I'm lazy and wouldn't be bothered to ohm out each wire.

It's too easy to point the dot and tell which cylinder is cold.

[Gary Lewis]

Oh, I didn't realize that they came with the longblock but it makes sense. 💡

I'm lazy and wouldn't be bothered to ohm out each wire.

It's too easy to point the dot and tell which cylinder is cold.

They are all showing 74F right now. And I'm too lazy to put these used plugs back to test. Lots easier to ohm out the wires.

Btw, is it ok to spray the inside of the plug boots with silicone spray? Some of them were a bear to get off.

[ArdWrknTrk]

They are all showing 74F right now. And I'm too lazy to put these used plugs back to test. Lots easier to ohm out the wires.

Btw, is it ok to spray the inside of the plug boots with silicone spray? Some of them were a bear to get off.

Well, suppose I would have checked before I pulled all the plugs out.

I've always used dielectric grease and rarely have to resort to my spark plug boot pliers. 🤷‍♂️

I don't think silicone oil could hurt anything but I have some doubt it will help much given how hot those insulators get.

Just don't make them all slippery on the outside.

[Rusty_S85]

Thanks, Jim.

Seems to me that the temp is about right. These are 24's and the stock one would be a 25. This Autolite site says:

Autolite indicates the heat range with the last digit of the part number. For example, 3923 has a heat range of 3. The higher the number, the hotter the plug. The lower the number, the colder the plug.

For instance, starting with part # 24 (heat range 4), if you want a colder plug you would use part # 23 (heat range 3), for a hotter plug you would use part # 25 (heat range 5).

So I have one notch colder plug. Stock NGKs would be NGK 6630 (UR4), but this NGK site says hotter is a smaller number. So now I'm trying to figure out which of the numbers needs to be bigger. I'm guessing the "4" in UR4 needs to be 5. Anyone know?

Same plugs that AFR recommended to start off with on my AFR 165 Renegade heads, I have a set of Autlite 3924`s installed till I do break in and I check the plugs to see if I need to go up or down on the plugs or leave them be. AFR seems to think the 3924`s are most likely the right ones to run with their heads.

[Gary Lewis]

Thanks, Jim.

Seems to me that the temp is about right. These are 24's and the stock one would be a 25. This Autolite site says:

Autolite indicates the heat range with the last digit of the part number. For example, 3923 has a heat range of 3. The higher the number, the hotter the plug. The lower the number, the colder the plug.

For instance, starting with part # 24 (heat range 4), if you want a colder plug you would use part # 23 (heat range 3), for a hotter plug you would use part # 25 (heat range 5).

So I have one notch colder plug. Stock NGKs would be NGK 6630 (UR4), but this NGK site says hotter is a smaller number. So now I'm trying to figure out which of the numbers needs to be bigger. I'm guessing the "4" in UR4 needs to be 5. Anyone know?

Same plugs that AFR recommended to start off with on my AFR 165 Renegade heads, I have a set of Autlite 3924`s installed till I do break in and I check the plugs to see if I need to go up or down on the plugs or leave them be. AFR seems to think the 3924`s are most likely the right ones to run with their heads.

Jim - I do have some dielectric grease so I'll use that. Thanks.

As for testing on the exhaust, I'm not sure that it'll show up there since it appears to be running, just not the same as the other cylinders. But I'll check it that way if it still shows one cylinder is acting strange when I get the plugs in.

Rusty - I'm moving to the NGK's, assuming I can find them quickly, but these Autolite 24's sure do look nice and clean. However, I'm hoping that one of them is flakey as I can't find the problem elsewhere.

I checked the plug wires and they measured as follows in K ohms, from #1 to #8: 7.3; 7.7; 9.7; 12.6; 10.6K; 8.1; 12.1; & 11.1. I twisted and pulled and couldn't get any of them to open up. But #6 @ 8.1K seems suspicious since it is essentially the same length as the #5 wire.

I also checked the distributor cap. Looks essentially new.

So I'm confused. If the plugs all look excellent, the plug wires seem to check out, and the distributor cap doesn't show any problems then what can be causing one cylinder to act that way?

[Rusty_S85]

Jim - I do have some dielectric grease so I'll use that. Thanks.

As for testing on the exhaust, I'm not sure that it'll show up there since it appears to be running, just not the same as the other cylinders. But I'll check it that way if it still shows one cylinder is acting strange when I get the plugs in.

Rusty - I'm moving to the NGK's, assuming I can find them quickly, but these Autolite 24's sure do look nice and clean. However, I'm hoping that one of them is flakey as I can't find the problem elsewhere.

I checked the plug wires and they measured as follows in K ohms, from #1 to #8: 7.3; 7.7; 9.7; 12.6; 10.6K; 8.1; 12.1; & 11.1. I twisted and pulled and couldn't get any of them to open up. But #6 @ 8.1K seems suspicious since it is essentially the same length as the #5 wire.

I also checked the distributor cap. Looks essentially new.

So I'm confused. If the plugs all look excellent, the plug wires seem to check out, and the distributor cap doesn't show any problems then what can be causing one cylinder to act that way?

I had a issue on my 302 that I chased for nearly a year, every now and then going down the highway and it would only happen on the highway at 60+ mph the engine would hiccup and tach would drop towards 0 and quickly recover, it was very random and wasnt consistent. I checked everything and even loaded the engine up in gear power braking it and no miss. It got to the point it was doing it multiple times when on the highway instead of the once in a blue moon and I was forced to start looking. I suspected the DS II ignition module getting hot and it was a module that was installed back in 1992. Still did it, come to find out cylinder 8 on my truck had a fault in the spark plug wire that I still dont know what it was cause it wouldnt do it under load only on the highway and it was random. Putting a new set of Ford Racing plug wires on solved the issue and never had it again.

I wonder if you might have a plug wire thats acting up for you but is otherwise testing out fine.

On the plug wire brand, NGK is a good brand, its the platinum plug I have in my 1 cylinder retro motor bicycle I built years ago. For me how ever I much rather stick with Motorcraft but the plugs I need for the reach and thread pitch and sealing type there was no Motorcraft option only Autolite so I went with it. I dont think I would ever run anything other than copper plugs in this engine since its a daily driver.

Also I dont know if you've ever seen this one but I saved this plug reading chart as it was one of the best ones I found online over the years.

[Gary Lewis]

I had a issue on my 302 that I chased for nearly a year, every now and then going down the highway and it would only happen on the highway at 60+ mph the engine would hiccup and tach would drop towards 0 and quickly recover, it was very random and wasnt consistent. I checked everything and even loaded the engine up in gear power braking it and no miss. It got to the point it was doing it multiple times when on the highway instead of the once in a blue moon and I was forced to start looking. I suspected the DS II ignition module getting hot and it was a module that was installed back in 1992. Still did it, come to find out cylinder 8 on my truck had a fault in the spark plug wire that I still dont know what it was cause it wouldnt do it under load only on the highway and it was random. Putting a new set of Ford Racing plug wires on solved the issue and never had it again.

I wonder if you might have a plug wire thats acting up for you but is otherwise testing out fine.

On the plug wire brand, NGK is a good brand, its the platinum plug I have in my 1 cylinder retro motor bicycle I built years ago. For me how ever I much rather stick with Motorcraft but the plugs I need for the reach and thread pitch and sealing type there was no Motorcraft option only Autolite so I went with it. I dont think I would ever run anything other than copper plugs in this engine since its a daily driver.

Also I dont know if you've ever seen this one but I saved this plug reading chart as it was one of the best ones I found online over the years.

You have a point, Rusty. My test with the DVOM didn't test the insulation, so it is possible that one of the wires is breaking down and shorting to ground under certain conditions. Once I get it back together I'll put the ignition scope on it to see if the problem is still there. If so the scope will show me which cylinder it is and I can do more troubleshooting, including swapping out the plug wire.

As for the plug chart, I'd say my plugs are all in the Good range.

[grumpin]

You have a point, Rusty. My test with the DVOM didn't test the insulation, so it is possible that one of the wires is breaking down and shorting to ground under certain conditions. Once I get it back together I'll put the ignition scope on it to see if the problem is still there. If so the scope will show me which cylinder it is and I can do more troubleshooting, including swapping out the plug wire.

As for the plug chart, I'd say my plugs are all in the Good range.

I agree, heat or cold could be affecting the plug wires also.

Could be the plug is not bad enough to show, but cause what you saw on the scope.

As Rusty said, and we’ve all experienced, strange things can happen.

[Gary Lewis]

I agree, heat or cold could be affecting the plug wires also.

Could be the plug is not bad enough to show, but cause what you saw on the scope.

As Rusty said, and we’ve all experienced, strange things can happen.

Thanks, Dane. I'm hoping it is one of the plugs since I'm going to change them anyway. Would sure be an easy solution. Those pics were taken after we drove the truck home 30 miles at highway speeds with very little idling. So it is possible that it only acts up at idle, although I'm not sure what would cause that.

[85lebaront2]

Thanks, Dane. I'm hoping it is one of the plugs since I'm going to change them anyway. Would sure be an easy solution. Those pics were taken after we drove the truck home 30 miles at highway speeds with very little idling. So it is possible that it only acts up at idle, although I'm not sure what would cause that.

Ok, after taking several looks at the plugs and the resistance readings on the wires I have the following thoughts.

Plugs, several of them look borderline too hot or lean (blued electrodes). Since the EFI system is adjusting the mixture on each bank, they shouldn't be too lean. I would say one step colder plugs than what you are running.

Plug wires, the old rule of thumb on resistance wires was 1000 ohms to the inch is the nominal resistance. This means for a 20" wire length, 20K. Less than that is not a problem, more indicates a wire breaking down internally. For your Mopar #7 wire 84K. I would do an after dark check, a slight "halo" around the wires is normal, arcs to valve covers, fuel rails etc are an issue, also Ford recommended that # 7 & 8 not be run side by side, if you remember on the carbureted engine plug wire routing on the left side was 5768 for the 460, the older small Windsors were 7568 on their routing. This is done to prevent cross firing.