Found my miss. What caused this?

[hunter1]

Started removing plugs after I had replaced the cap and rotor without resolve and this is #4. What caused this carbon buildup after only about 50-60 miles on this engine? 351 RV cam with rebuilt GT-40-P heads and Fitech 400. Started having the issue week before last and then would clear back up and start again. Vacationed for a week and started it this morning and dead miss.

 

[Torkman66]

Yikes, not sure how tired that motor is, but if not too worn, could have just been some carbon that came loose. Bad gas, ethanol choke? How are the other plugs? If it were me, I would get some Seafoam and run it for a few tanks of gas. That stuff really works. I've cleaned out so many motors with it. Then once you've done that for a few tanks, every fill up put in some STA-BIL 360 (Marine). It is very economical and does wonders keeping the motor, fuel, and lines clear...especially given all the ethanol. I've done a ton of research on both products and I think of everything out there, a good clean with Seafoam followed by routine STA-BIL Marine is the way to go.

 

[Timmy390]

What do the other plugs look like?

Tim

 

[Remos69]

I would wonder also what the other plugs look like. I had a FiTech, was using self timing, had a lot of injector and timing issues. Ran 2 inline filters, but that didn't seem to matter much. Plugs were consistently dirty, not that bad. Timing went way off and broke a valve spring, not sure that was the cause but didn'ttrust the self timing (luckily no other damage). Switched to a sniper 2 and a normal distributorsetup new set of springs, never looked back.

 

[hunter1]

What do the other plugs look

What do the other plugs look like?

Tim

Most of them were sooty but had clean tips. I’ve got a new set today that I’ll try and see if it clears it up.

 

[hunter1]

I would wonder also what the other plugs look like. I had a FiTech, was using self timing, had a lot of injector and timing issues. Ran 2 inline filters, but that didn't seem to matter much. Plugs were consistently dirty, not that bad. Timing went way off and broke a valve spring, not sure that was the cause but didn'ttrust the self timing (luckily no other damage). Switched to a sniper 2 and a normal distributorsetup new set of springs, never looked back.

I have a feeling it’s running too rich. Had a hard time getting the Fitech dialed in.

 

[hunter1]

Yikes, not sure how tired that motor is, but if not too worn, could have just been some carbon that came loose. Bad gas, ethanol choke? How are the other plugs? If it were me, I would get some Seafoam and run it for a few tanks of gas. That stuff really works. I've cleaned out so many motors with it. Then once you've done that for a few tanks, every fill up put in some STA-BIL 360 (Marine). It is very economical and does wonders keeping the motor, fuel, and lines clear...especially given all the ethanol. I've done a ton of research on both products and I think of everything out there, a good clean with Seafoam followed by routine STA-BIL Marine is the way to go.

Motor is a rebuilt 351 by me. .030 over with the stock, but new dished pistons. Everything inside new. Ran great 2 weeks ago and no smoke at all. Engine sounds good running, no abnormal mechanical sounds. I’m trying new plugs this afternoon, if that doesn’t get it I’ll take that valve cover off and look at rocker arm movement on that cylinder. Hopefully I haven’t wiped out a lobe of the cam.

 

[Broncobowsher]

Massive carbon buildup. Carbon comes from fuel or oil, both hydrocarbons. Burn off the hydrogen and what is left is carbon. Typically a little rich on fuel will still burn the carbon with oxygen, but not complete and you get CO instead of CO2. To build that much carbon you need even more fuel to the point there isn't enough oxygen to make CO and you get free carbon that has nothing to do but make black carbon.

Did you change the intake when doing the EFI? Might be a bad gasket sucking oil from the lifter valley.

The Oxygen sensor in the exhaust could be fooled as well. If you have an exhaust leak, extra air leaks into the exhaust as much as the exhaust leaks out. The pulses and velocity play here. Even with old log manifolds it still happens. If air gets in, sensor sees lean engine and adds fuel.

A misfire pumps air into the exhaust, further causes a lean reading. Once the plug fouled, the self learn just goes into a spiral of putting more fuel into the engine.

I can't tell you exactly what caused that plug to foul from the start, but I do know that once the misfire started it only gets worse.

 

[hunter1]

Ok, changed the plugs and no more miss. As I said before, I don’t see any blue smoke at all so leaning more to either just a bad plug or running too rich, but looks like all of them would be fouling if it was too rich?

 

[Chiclassics]

If you personally rebuilt it probably there is no historical carb dislodged. Points to me either bad spark plug or point. Try this, clean up this spark plug and test the spark on it .

 

[Bronco4x4]

If you’re fouling all the plugs, check to see if your O2 sensor bung is in the correct location (temperature wise). I heard this can cause an improper fuel mix. I’m a carb guy so that’s all I can suggest.

 

[hunter1]

After changing plugs ran great for a few miles then started acting up again. Considering changing the coil and then if that doesn’t change things put the carburetor back on and try that.

 

[Timmy390]

Are the plugs fouled again? My money is on leaking intake gaskets.....You don't always see lots of blue smoke. In fact I feel modern oils burn so clean blue smoke is almost never seen.

Went through this with my 390FE. Hard to start and liked to miss till warm. Sure enough it was the intake gaskets. Starts like a dream now and no more miss till warm.

Tim

 

[.94 OR]

Any chance the plug wire or distributor post for that cylinder is askew? Might be a lack of good fire to that plug only.

 

[ba123]

I don't know anything about Fitech, but what's your fuel pressure set to?

 

[Chiclassics]

After changing plugs ran great for a few miles then started acting up again.

All spark plugs or just the #4?

 

[anoblefox]

Valve oil seal on that cylinder?

 

[hunter1]

Could be, but didn’t smile any before or even now. Think would’ve had some smoke if it was bad enough to foul it like that?

 

[Remos69]

Is the fitech self timing, or just a standard distributor setup where you set the timing?

 

[hunter1]

Standard distributor. I ended up removing the Fitech and put a carb back on it. Died after about 5 miles. Didn't have any testing tools with me when it happened. Had to let it cool off before it would start again. Bought a coil and relocated it to the front of the engine where it gets a little air flow. Haven't had a chance to drive it since.