Spark miss on cylinder #6

[rmoe88]

Hey everyone.
My falcon has a small miss at idle, and i am confused by what the problem is. I warmed the car and with the idle speed @700rpm i put a timing light on each cylinder. On 1-4, they are all at a steady speed with no noticeable spark misses. On 5 and 6 though, there are obvious misses in the strobe light, and it almost seems as if they are blinking faster in between misses??? It also seems to miss more often when cold. I have tested it a few times with the same results, and i was careful not to pick up interference from other plug wires when testing.

A little info, i have a duel advance dizzy with a pertronix ignition. Stock coil. Running 12* advance at idle.

Things that i have ruled out so far...
1) plugs (have moved and replaced, no effect)
2) wires (have replaced, no effect)
3) coil (replaced a wile ago for a different reason, but it did it with the old coil aswell)
4) pertronix (put points back in and no effect)
The dizzy, cap and rotor are all new...

One more thing, when the timing light is on cylander #1, it is at a constant 12* timing, but when i put it on cylander #6 and i put it up against the timing wheel, it is at 12* timing but it jumps up for a second to like 20* when it misses.

I am stumped as to why this is happening. Does anyone have any ideas?

 

[66 E100 Pickup]

check your rotor fitment--it should be tight on the shaft. Back in the the good old days, there was a little spring clip to keep the rotor tight. Many of us do not have these anymore, so we 'make do' by wrapping some teflon around the shaft to get it tight. Also check to make sure the shaft is tight--there is always a possibility that the distributor gear and/or cam gear are getting a bit worn.

Or, if you get tired of fighting it, throw out the dizzy and coil and pop in $100 worth of Duraspark II dizzy, module, rotor, cap, 12 volt coil, and wires.

Best upgrade money can buy.

I am not exactly sure why your timing is floating. I've never tried putting a light on anything but #1.



John

 

[rmoe88]

I replaced by old Ford-o-matic with a newer one, and it uses a different style rotor. It just presses onto the dizzy shaft, which is keyed and can only go on one way. The rotor and cap are both very tight. It was also doing the same thing when i had the old dizzy in it, so i dont think it would be something wrong with the dizzy(but i could be wrong)

About a cam gear being worn out, what problems would this cause? Would it cause a miss in the idle?

If i cant get it to work i might get a duraspark like you say. It would be a wile before i can do this upgrade though.

A timing light has more that one use

Yea, the floating timing is what is really stumping me.

 

[fordconvert]

How did the plugs look that came out? Does it seem to smooth out when you get a load on or the rpms up? Maybe a compression check to make sure you dont have a burnt valve or something causing a screwed up mixture in those?

 

[Anonymous]

Had a similar problem once with a 2.3 Mustang engine. The car ran fine at highway speeds but would miss at idle and sometimes would be hard to start. Like you I put a timing light on each cylinder and discovered that on cylinders 1 and 2 the flashes were steady but on 3 on 4 they were erratic. My initial reaction was that I had an electrical problem, checked the plugs, plug wires distributor cap and rotor they all looked good but replaced them anyway - no difference. Next did a resistance measurement on the coil - within specs but replace anyway – no difference. Did a compression check and again within specs. The only thing left was the distributor itself so replaced it – no difference - miss at idle and erratic flashes on two cylinders only. Since there was nothing else I could think of to check or replace I begin to think maybe it’s not a spark problem. I look into the carburetor at idle and discovered that it had a small amount of raw fuel leaking into the engine a drop at a time. I replaced the carburetor and the problem went away. Why the leaking carburetor would flood out only some cylinder and not all I don’t understand but that’s what happen to me.

For what it’s worth