Plug Heat Range
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Senior User
Joined: Jun 2002
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From: Red Deer Canada
Plug Heat Range
I have a 390 in my truck that has a mild cam, Carter 625, headers, and Duraspark ignition. Currently I'm using Autolite 45 plugs. I want to go to a colder plug, due to some pre-ignition issues, but can't find which plug is the next colder. One would assume it's a 44, but do they make such an animal? When I come off a hwy run and the engine is nice and warm, I get that "run-on" after shutting her down. I have already changed the jetting to richen er up, but it didn't seem to make any differance.
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Post Fiend
Joined: Dec 2003
Posts: 6,658
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From: "Islander"
To go richer all your going to do is build up carbon more and faster, plugs will not over heat at idle shut down to cause this unless you chopped power at a full throttle run. If then you would have bad preignition problems. Sounds like you have a hot sharp metal edge or glowing carbon hot spots.
FE "Freakin Expensive"
Joined: Dec 2003
Posts: 6,461
Likes: 4
From: Smith Mountain Lake, VA
Autolite 44S should be the next colder plug...I ran those in my Poncho and a 442 I had with mild street cams....
And if by chance as Carl said you have carbon Build-up and the tops of the pistons are coated real bad with carbon as are the chambers....
What I have done in the past was take the vehilcle out on the Hyw...and spend about 30 minutes with my foot to the floor board on and off....
Come back to my driveway and with the motor still running at operating temp..pull the air cleaner.. and take a cup of water...Yes I said water ! Run the motor up to about 3500 to 4000 rpm and pour in about an oz. of water at a time...Of course the motor wont run off water so it will drop in rpms..and then picks back -up again....You'll see a bunch of carbon and steam come out the A$$ end....
When ya get to the point all you see is steam....the chambers and the tops of the pistons should be fairly clean.....This will eliminate the hot spot theory..If there was one... JMO.... Good Luck and keep us posted!!
RJ
And if by chance as Carl said you have carbon Build-up and the tops of the pistons are coated real bad with carbon as are the chambers....
What I have done in the past was take the vehilcle out on the Hyw...and spend about 30 minutes with my foot to the floor board on and off....
Come back to my driveway and with the motor still running at operating temp..pull the air cleaner.. and take a cup of water...Yes I said water ! Run the motor up to about 3500 to 4000 rpm and pour in about an oz. of water at a time...Of course the motor wont run off water so it will drop in rpms..and then picks back -up again....You'll see a bunch of carbon and steam come out the A$$ end....
When ya get to the point all you see is steam....the chambers and the tops of the pistons should be fairly clean.....This will eliminate the hot spot theory..If there was one... JMO.... Good Luck and keep us posted!!
RJ
Last edited by RapidRuss; Nov 9, 2006 at 04:00 AM.
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From: Red Deer Canada
I believe the electrical system was from a '76 F150 which does call for a Autolite 45, and through some research i did last night, there is a 44, Champion equivalent is RF9YC, Bosch DR8BC, NGK R83CTS. Just for the record, this isn't a real serious problem, it's a fine tuning issue. The engine is pretty new -about 1000 mi on it so I'm pretty sure it's not a carbon problem. The plugs look more white than tan but still tanned and it only "diesels" for one or two RPM. Just enough to pi$$ me off cuz it ain't perfect ! Other than that it runs absolutely beautiful.
FE "Freakin Expensive"
Joined: Dec 2003
Posts: 6,461
Likes: 4
From: Smith Mountain Lake, VA
Well Like you said then..Its a new build and is probably still a little tight....which could make the motor run a tad warm....the plugs being on the whitesh side tells me its running lean..and needs to be richin up a little...and will aslo help the motor run cooler..
And you might double check you initial timing...as it maybe a little to far advanced? JMO.. Keep us posted...
RJ
And you might double check you initial timing...as it maybe a little to far advanced? JMO.. Keep us posted...
RJ
