440 runs perfect for 5 seconds, then starts missing. Every time. Help.

[TASummers]

* 440/508 with Solid cam. Quick Fuel 950 Race. FBO Ignition Module. Firecore Distributor and Wires. New Plugs. *

I drove my car to work a while ago. On the way home, it was running fine. I stopped at the light, and felt like I lost a cylinder. My air fuel ratio went from 12.5:1 down to 10:1. I thought I must’ve burned to a plug wire. Drove it home on 7. Did find a suspect wire, and changed it, along with all spark plugs. No change.

* * When I crank the engine, it runs clean for 5-10 seconds, then starts missing (like a running on 6 or 7). IT DOES THIS EVERY TIME. Turn it off, fire it up, clean for 5-10, then rough.

AFR drops from 12-13 to 10.

I’ve checked every ground, and added grounds. I can’t find any arcing wires. Distributor cap “looks good”. I called 4 Seconds Flat and they suggested I cycle the rev limiter. No change. I’ve got 14.5 volts from the alt.

The fact that I can repeat this “ clean to rough” cycle over and over is what’s bugging me.

What do y'all think?

 

[khryslerkid]

Try a different coil?

 

[Crowbar]

I’m with the coil as well RC

 

[Aron Gleason]

With a coil mounted sideways, if it's oil filled it can leak out over time.

 

[sam dupont]

choke?

 

[RemCharger]

choke?

Quick Fuel Q950. So no.

 

[furious70]

When it starts missing there's no cleaning it out? It's not flooding out and you can clear it out with a couple stabs?
Sticky float or crap in the seat maybe, and it evaporates when you let it sit and then the fuel pump overfills it again?

Or you're saying you turn off and immediately refire and it runs again briefly?

 

[Sixpactogo]

Fuel sock and or fuel filter mostly plugged?

 

[TASummers]

When it starts missing there's no cleaning it out? It's not flooding out and you can clear it out with a couple stabs?
Sticky float or crap in the seat maybe, and it evaporates when you let it sit and then the fuel pump overfills it again?

Or you're saying you turn off and immediately refire and it runs again briefly?

No, it will rev, but it does not clear. And yeah, it doesn’t matter how long I wait between fires. It will do it every 20 seconds or every day.

 

[TASummers]

Fuel sock and or fuel filter mostly plugged?

Don’t think so. The car has less than 1000 miles on new tank, Holley black filter and an inline filter. I see a solid 7lbs at the carb. If it was running out of fuel, I’d see lean. But I have an endless supply.

 

[furious70]

And it'll stay running in that rough idle in it's own without help?
Pull each wire off while running and see if one of them makes no change in idle?

 

[TASummers]

With a coil mounted sideways, if it's oil filled it can leak out over time.

Didn’t think about that. The issue definitely feels electronic. Maybe I’ll grab a new Pertronix coil from Amazon.

 

[R413]

Disable or disconnect the fuel pump and try it.

Look at your spark plug
one or all must be black with the AFR at 10

 

[AR67GTX]

I wonder if your carb is flooding out into the engine. Your AFR suggests that as a possibility. Have you checked your float levels? But a greater possibility may be a leaky needle and seat. A high fuel level in the bowl will syphon down somewhat when you kill the engine. And the as you refries it, it runs OK until the bowl overfills by the leaky needle/seat and floods the engine?

Just some wild guesses. But I seriously would have someone start the car while you watch the bowl levels (assuming your Quick Fuel carb has glass sight ports in the bowls) to see if the fuel rises over the sight glass. And also to look down the throats to watch for signs of gas running out the boosters.

 

[Nxcoupe]

* 440/508 with Solid cam. Quick Fuel 950 Race. FBO Ignition Module. Firecore Distributor and Wires. New Plugs. *

I drove my car to work a while ago. On the way home, it was running fine. I stopped at the light, and felt like I lost a cylinder. My air fuel ratio went from 12.5:1 down to 10:1. I thought I must’ve burned to a plug wire. Drove it home on 7. Did find a suspect wire, and changed it, along with all spark plugs. No change.

* * When I crank the engine, it runs clean for 5-10 seconds, then starts missing (like a running on 6 or 7). IT DOES THIS EVERY TIME. Turn it off, fire it up, clean for 5-10, then rough.

AFR drops from 12-13 to 10.

I’ve checked every ground, and added grounds. I can’t find any arcing wires. Distributor cap “looks good”. I called 4 Seconds Flat and they suggested I cycle the rev limiter. No change. I’ve got 14.5 volts from the alt.

The fact that I can repeat this “ clean to rough” cycle over and over is what’s bugging me.

What do y'all think?

View attachment 1668239

I want to help you, but first you have to understand that a misfire does not read rich, it reads lean. O2 sensors read oxygen, not hydrocarbons(fuel), so when a cylinder doesn't fire, the exhaust valve opens and let's unburned fuel and air into the exhaust, the O2 sensor ignors the fuel and sees the oxygen and interprets that as lean. I've seen as lean as 17 or 18 to 1 with a plug wire off and nothing compensating for it.
Now, what could be happening is the O2 sensor is on the opposite bank from where your misfire is occuring, and that causes a drop in vacuum which opens your power valve which would flood the engine with fuel. Hope you get it figured out. And if you knew all this already, my apologies.

Edited for me being in a hurry.

 

[TASummers]

I wonder if your carb is flooding out into the engine. Your AFR suggests that as a possibility. Have you checked your float levels? But a greater possibility may be a leaky needle and seat. A high fuel level in the bowl will syphon down somewhat when you kill the engine. And the as you refries it, it runs OK until the bowl overfills by the leaky needle/seat and floods the engine?

Just some wild guesses. But I seriously would have someone start the car while you watch the bowl levels (assuming your Quick Fuel carb has glass sight ports in the bowls) to see if the fuel rises over the sight glass. And also to look down the throats to watch for signs of gas running out the boosters.

Good idea. My carb does have sight glasses. I glanced tonight while running it, but had the air cleaner on and couldn’t see the level in the shade. I’ll check tomorrow.

 

[TASummers]

I want to help you, but first you have to understand that a misfire does not read rich, it reads lean. O2 sensors read oxygen, not hydrocarbons(fuel), so when a cylinder doesn't fire, the exhaust valve opens and let's unburned fuel and air into the exhaust, the O2 sensor ignors the fuel and sees the oxygen and interprets that as lean. I've seen as lean as 17 or 18 to 1 with a plug wire off and nothing compensating for it.
Now, what could be happening is the misfire is on the opposite bank from where your misfire is occuring, and that causes a drop in vacuum which opens your power valve which would flood the engine with fuel. Hope you get it figured out. And if you knew all this already, my apologies.

Thanks for the explanation on the Rich/lean condition with a misfire. That makes sense. Would you mind explaining the bold piece above one more time? And i did replace the power valve, but that was obviously not it.

 

[H. Lindley]

Could be a vacuum leak.

 

[Nxcoupe]

Thanks for the explanation on the Rich/lean condition with a misfire. That makes sense. Would you mind explaining the bold piece above one more time? And i did replace the power valve, but that was obviously not it.

Very sorry, I was in the middle of something and trying to rush my post so I could get back to it.

What I meant to say was the misfire is probably occurring on the opposite bank from where your O2 sensor is located. ie, misfire on driver's bank and O2 is on passenger side exhaust pipe.
Hope that clears it up. Sorry if I was confusing.
On the power valve, I didn't mean to allude that your power valve was bad, rather, when a misfire occurs the vacuum in the intake drops a good bit, which could lower the vacuum signal to the power valve enough that it would open thinking you are in 4th pulling up a hill and need the fuel.
Hope this clears it up and I apologize for not pre reading my post before I hit the 'post' button.

 

[4speed68rt]

High compression & low octane gas?