#8 plug keeps fouling,why?

I`ve noticed lately when i hear my car backfiring while i`m warming her up i know # 8 plug is fouled,no oil residue or wet just carbon,the rest seem fine,what would cause this?should i run a hotter plug?any help appreciate it,this has been happening ever since i switched to the aluminum heads.

Thanks

 

Could be several thngs George.
Sticky valve which I doubt since the heads are brand new.
Could be the head gasket which I know you don't want to hear.
Or it could be a bad ring on the piston.
First thing to do is a compression check. If you get a low number for the cylinder put a spoonful of oil through the plughole and check again. If the reading goes up substantially, its most likely a ring.
Good luck bud!!

 

Did a compression check its perfect,but like i said its carbon not oily or wet.

 

oh yea and the car does not smoke at all or anything like that whether its cold start or hot.

 

have you changed the plug?
Try switching plugs from a clean cylinder.
See if its the plug or the cylinder.
Just looking for the easy stuff first.

 

Im gonna try running a hotter plug and see,cause i`m running cold plugs now.

Thanks

 

I don't think one plug would foul because of heat range.
One other thought. Do you have power brakes?
If you do, where does the booster pick up the vacuum from.
Intake of #8 on the manifold?
Check for a vac leak.

 

I`ll check it.:TU:

 

If you run your PCV off the vacuum port on the manifold, IT will lean out that cylinder. I was running my power brakes from that port, and I noticed the same problem. After drving for a while with the radio off, I noticed when I stepped on the brakes I could hear the booster hissing vacuum. I replaced the booster and I haven't had a problem yet.

 

I believe cylinder #8 is also the longest spark plug wire and would have the most resistance, so if any of the cylinders would tend to misfire that would be the one to do it!

 

I am running thr PCV in the stock location on the manifold,i will also switch wires from another cylinder and let it run and see how it works out,the wires on the car are pretty new,and i`ll switch to a hotter plug and hopefully it will be ok,i`ll keep you guys posted.

Thanks:TU:

 

Ohm meter?

George, if you have a meter, check the resistance on the wires. You may have one bad wire.

 

Yes i will check them out today and make sure they are all ok.

Thanks Skip

 

George: Whatever you do, don't do three or four things all at once. Do them one at a time. Nothing like doing batch changes to cure the problem. You still end up not knowing what was wrong. Or, you spend $$$$ replacing unnecessary stuff. Good luck.

 

The only thing that i remember that was different since i`ve changed over to the aluminum heads are the intake which before i had the SP-1 and now i have a B4B till the SP-1 gets port gasket matched,intake manifold gasket from stock bathtub type to AMP`s type,the heads ofcourse from steel to Aluminum and the jets on the carb i went from 71 to 73`s,i will switch back to 71`s and check the resistance on the wires today and run her and see how she runs.

 

george, just out of curiosity what size rods are you running.

 

Stock rods with ARP bolts.

Thanks

 

Like John said George. Excellent advice!:Smarty:

Wish I would follow that advice myself ALL THE TIME!

What carb are you running, I forgot. Holley 800 DP, right?

And which plugs exactly??

Still, I'd check the plug wire resistence first!:Smarty:

 

ok i checked the wire with OHM meter it read 125,and i checked #6 plug wire and that read the same,i was using NGK BP7ES plugs but i just switched them all to a AC Delco which cross referenced from a NGK BP4ES because they didnt have them in stock which is a hotter plug also,gapped at 45 cause of the MSD box and stuff,i switched back to the 71 jets in the front and fired her up,she ran good as usual i just have to run her alittle and see if she fouls #8 again,can timing be an issue here?

Thanks