I have a 1985 F-150 4wd with an AOD transmission and an EFI 302. Can anyone tell me why after only 84,000 miles I have just one cylinder that fouls spark plugs? It is the #8 cylinder, driver's side nearest the firewall.

 

I have saw that several time on 302 and 351's. The last 351 had a scar on the cylinder wall and a 302 with broken oil ring and (I think 302) with stuck rings and it is the #8 cyl.

 

I'm just wondering out loud, but I wonder why usually it's #8. I was speaking with another Ford truck owner, and he has the the same problem.

 

Whats it being fouled by, oil or gas?
Steve G.

 

I dont know for sure, but it could be the design of the intake manifold. #8 cylinder could be getting less fuel than the other cylinders. And because its running lean, its causing higher than normal combustion temperatures in that one cylinder. Just a guess.

 

It looks like oil.

 

Sounds like that cylinder is burning oil.

I had an 88 Ranger / 2.9L V-6 that did the same thing.

Fouled plugs aren't usually caused by running lean. Plug fouling is usually indicated by large deposits that close the plug gap (carbon build-up)

Lean running would cause thin white build-up on the plug a something similar. Also leads to cracked insulators and other discoloring.
A reddish buildup is caused by fuel additives. (Not necessarily harmful)

 

The reason i said that cylinder might be running lean was because the previous poster's were saying they had trouble with 351's and 302's with broken piston rings and scared cylynder walls in the #8 cylinder. Possibly from running lean over time it will cause detonation in that cylinder and cause damage to the rings and cause low compression or oil fouling.

 

Number eight on a ford is the last cylinder to get coolant. If you check with an infared thermo you will always see that area of the engine running warmer than the cylinders further forward it has been an issue with a lot of v8's. I have seen this before and on one I changed the plugs and it hasn't happened again. You also want to remember that the lions share of the oil from the rockers goes to that drain holes in the rear of the head so the valve stem seals have to be good back there also. I have rebuilt a number of 302's and when I measure the cylinders before boring number 4 and 8 (the two rear ones) have always had more wear than the forward cylinders.

 

Now this will probably seem goofy as the fellow at Disneyland but I've seen a remedy for improper cooling such as this done on a high output intercooled turbocharged Chrysler 4 cylinder. In the thermostat housing they installed a steel bung and then plumbed it with rubber hose to another bung installed in the hot spot of the heads freeze plug. I suppose if this is a real worrisome issue you could do something similar and run a line to the back of the head near the firewall. I believe 302 heads have a freeze plug in them but it has been so long since I've owned a 302 or worked with one of them.

Also might as well cover my bases as well. Does the 300 straight six have any issues with one section of the engine being hotter than the others?