One fouled plug
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Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
One fouled plug
My 66 F100 4x4, I run a 67 Flairlane 390 GT engine, engine has been in the truck sense 1979. At that time the engine was freshened up with rings and bearings and a valve grind, notting else. this last 2-3 years I have been having a problem with the #5 plug fouling out. 2 weeks ago I changed the points, condenser, the rotor, cap, plug wires and the plugs. Dist, was replaced with a rebuilt one a couple of years ago. It was still not running very good, checked firing and #5 was not firing. I changed the plug wire from #6 to #5 and check it again, #5 still not firing. I changed out the coil and #5 started firing. Lasted 1 week, yesterday no fire in #5. Switched #6 plug to #5 and #5 to #6 hole, firing just fine again, in both. Timing is set at 8 degress, carb is Elderbrock, compression is 125lbs, plugs are #45 Motocraft, and I'm getting a pinging after the truck is warmed up and driven 10-12 miles. Any ideas on what is doing this, I would love to hear.
Thanks
Thanks
Fleet Mechanic
Joined: Aug 2007
Posts: 1,806
Likes: 246
From: Piney Woods of East Texas
It almost sounds like the plug is not getting a ground or opened up internally. As far as pinging try backing off the timing a couple of deg. Engine may be getting carboned up, try some cleaner or give it a drink of water.
Cargo Master
Joined: Apr 2004
Posts: 2,574
Likes: 4
From: Golden, CO
Cheap gas???
It seems there have been a flurry of complaints this winter. I didn't bookmark the post, but I did read mention of winter-blend fuel causing detonation.
Are you using any fuel additives? After I started running a lead substitute, I noticed detergent fouling on my plugs.
It seems there have been a flurry of complaints this winter. I didn't bookmark the post, but I did read mention of winter-blend fuel causing detonation.
Are you using any fuel additives? After I started running a lead substitute, I noticed detergent fouling on my plugs.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 421
From: Long Island USA
What is the plug fouled with? Oil or gas?
If it's oil, I'm betting on an intake leak after the freshening up, sucking oil into the cylinder (in a big way). Either that, or your valve guides were knurled and one wore out very fast (knurling doesn't last long).
Also, another thing to check, key on, engine not running, check the voltage at the + side of the coil, and ground the meter to the battery (-). Report back.
And one more thing, check the cam in the distributor that makes the points open and close. Make sure it's not worn. Also, with the points both closed, and open, pull on the rotor back and forth in the direction of the points. If they open and close when you do this, you need to replace the distributor (or the top bushing). Sometimes, rebuilt distributors don't get a new bushing on top, and they do wear out with points. Or, convert to electronic if the bushing is shot, it won't matter anymore
If it's oil, I'm betting on an intake leak after the freshening up, sucking oil into the cylinder (in a big way). Either that, or your valve guides were knurled and one wore out very fast (knurling doesn't last long).
Also, another thing to check, key on, engine not running, check the voltage at the + side of the coil, and ground the meter to the battery (-). Report back.
And one more thing, check the cam in the distributor that makes the points open and close. Make sure it's not worn. Also, with the points both closed, and open, pull on the rotor back and forth in the direction of the points. If they open and close when you do this, you need to replace the distributor (or the top bushing). Sometimes, rebuilt distributors don't get a new bushing on top, and they do wear out with points. Or, convert to electronic if the bushing is shot, it won't matter anymore
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Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
The plug fouls with black carbon, dry shooty looking. I run Shell 93 octane gas, with no additives. I did change the dist. with the rebuilt one that's in my 428 Galaxie, did not seem to make any differance. I will check the coil, but it will have to wait untill this weekend, my wife is driving it to work and we both don't get home untill after dark. I'm going to try decarboning it this weekend and put in some octane boost.
Thanks for the ideas, it is a real help.
Thanks for the ideas, it is a real help.
FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 421
From: Long Island USA
Dry black carbon is gas. I wonder if you have a float leak in the carb and it's flooding out? (been a long time since I looked at an FE intake - not sure if #5 would be the first one to fill).
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Cargo Master
Joined: Apr 2004
Posts: 2,574
Likes: 4
From: Golden, CO
Hmmm, #5 sits up front, shares the plenum with #s 2, 3, & 8. You would think that fuel would run to #8 before any others. Do you park the truck with the nose pointed down-hill?
I don't know the Ebocks, but the one I have on the bench has fuel bowls on the sides. I guess it would be possible for the driver's side to leak, maybe run too rich?
Maybe I have it backwards. Could the other plenum be too lean and covering up a weak spark?
Before you blow out the carbon, pull all the plugs and look at them in terms of intake plenum grouping. Maybe one set is a tad darker than the other, with #5 being the worst.
I don't know the Ebocks, but the one I have on the bench has fuel bowls on the sides. I guess it would be possible for the driver's side to leak, maybe run too rich?
Maybe I have it backwards. Could the other plenum be too lean and covering up a weak spark?
Before you blow out the carbon, pull all the plugs and look at them in terms of intake plenum grouping. Maybe one set is a tad darker than the other, with #5 being the worst.
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Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
Originally Posted by Hypoid
Hmmm, #5 sits up front, shares the plenum with #s 2, 3, & 8. You would think that fuel would run to #8 before any others. Do you park the truck with the nose pointed down-hill?
I don't know the Ebocks, but the one I have on the bench has fuel bowls on the sides. I guess it would be possible for the driver's side to leak, maybe run too rich?
Maybe I have it backwards. Could the other plenum be too lean and covering up a weak spark?
Before you blow out the carbon, pull all the plugs and look at them in terms of intake plenum grouping. Maybe one set is a tad darker than the other, with #5 being the worst.
I don't know the Ebocks, but the one I have on the bench has fuel bowls on the sides. I guess it would be possible for the driver's side to leak, maybe run too rich?
Maybe I have it backwards. Could the other plenum be too lean and covering up a weak spark?
Before you blow out the carbon, pull all the plugs and look at them in terms of intake plenum grouping. Maybe one set is a tad darker than the other, with #5 being the worst.
Thread Starter
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Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
I ran some Seafoam in the carb yesterday, when I got done #5 was firing good. Looks like it was carbon build up. I will see how it goes as I drive it. Thanks for all the hepful post.
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