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Old 08-05-2009, 09:51 AM
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Odd "miss and hit" during acceleration

I have a light car with a Ford 428 in it. Car has been working great, but today a new problem started. During fairly hard acceleration, the engine suddenly seems to "miss and hit" for a second. Almost like opening secondaries, but quicker. It's a hiccup of an accelerating engine, not a pop out the exhaust or carbs.

Very difficult to describe, but almost like a shot rod bearing allowed the piston to hit the head for a second. So it could be a mechanical problem with just rebuilt engine, but there are no signs such as smoke or metal in the oil.

I suspect a carb issue. I have twin vacumm Holley's with the light springs installed. I checked the vacumm hose connecting the two secondaries and found it accidently bent down under the ignition wires, but it seemed "crack-free" other than that.

Not sure what symptoms to expect if a power valve failed.

Anyone got any ideas for this "hard to describe" problem

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Old 08-05-2009, 12:21 PM
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Problem gone, but new one now. Seems the vacuum secondary line may have been kinked a bit, and on this particularly hot and humid day, the vacuum may have collapsed the balance hose so the secondaries opened at different times. Anyway, my best guess.

So it seemed to work well. Went and got gas, and on the way home, it seemed to miss immediately when I tried to accelerate and with a lot of popping out exhaust. And that seems like excess fuel getting to the sidepipes due to weak igntion. And it's humid....HV leak no doubt. Will check at night for arcing......
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Old 08-05-2009, 02:14 PM
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Quote:
Originally Posted by Argess
like a shot rod bearing allowed the piston to hit the head for a second.
If you had bearings that worn or mismatched-clearances that wide- you'd be picking up the pieces w/a magnet.

There are many cases like in Stock class racing where the squench is so tight that there will be, on occasion, indications of the piston and head getting VERY close to one another- but this is a calculated thing, not from worn or incorrect parts.
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Old 08-05-2009, 02:26 PM
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Yes, I didn't really think that was happening, but it sort of described the sound. In fact, first time it happened, I thought a tire had thrown a rock up and hit the inner fender. Mind you, my brother had a 350 BB Pontiac engine that had lost a rod bearing and you could hear it hit. Subsequent disassembly showed the marks too. We built that into a 428, but that's a whole 'nother story.

Anyhow, I've been thinking some more (which can be dangerous....LOL) and all things point to the problems being ignition related. Going back over the facts, all problems started once engine was run quite a while....i.e. "hot". I notice the coil is also quite hot, although I am uncertain if it is hotter than normal. Somewhere my ignition is breaking down.

In the first case, it was happening at 1/2 way through an acceleration run (1/2 way between gear shifts), but that also could have been a point where the Hp, spark advance, rpm, etc all determined the point a weak spark would misfire. In the last case, the bogging and popping out the exhaust are almost certainly due to ignition break-down.

I am using 9mm Accel wires, new plugs, Mallory dist with Pertronix unit and an Echlin internal ballast coil. This old coil, of dubious origin, I had laying around in a box.....never used, but the box looks like it's 50 years old. NOS with a stress on the "O". It's been successful now since 1996 when I first got the car on the road. Perhaps it's time to upgrade.

Darned thing......coils hardly ever go bad. Guess I need to do some more testing this evening. Look for arcs and check the max spark travel from the coil to ground. Darned hard to nail down when it seems to be causing trouble only after it gets heated up.
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Old 08-05-2009, 02:36 PM
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Another thing you could try that is non invasive, would be to hook up a vacuum gage and run the engine through the RPM's where the problem exhibits itself.

There may be nothing to it, but I'd be suspecting that a valve spring may have let go. Usually this will take the cylinder out of play, but if you have dual springs- or even a stiff, tall damper- that can crutch things up enough that the engine will run acceptably until the RPM is reached that lets the valve well and truly float/bounce. Just a thought.
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Old 08-05-2009, 02:44 PM
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And it's a good thought. I am using Crane dual springs. When I first installed them abck in 96, I did have one outer spring break. I didn't even know it until I found it during routine maintenance (was going to re-set valve lash).

I called Crane (can't do that now, poor guys are out of business I hear) and they told me that was the first time they ever heard of that P/N'd spring breaking, and they started making them back in the 60's. I did send them the broken one, but never heard back.

Since I am finding that my problems seem to occur after the engine is well heated up, I am tending to dismiss mechanical problems at this point and am looking at #1, ignition, and #2 carbs. However, it wouldn't hurt to take the valve covers off and have a look...might save me a lot of $$$ depending on what I find now vs after a catastrophic failure.
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Old 08-05-2009, 02:55 PM
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I know pulling v-covers is not great way to spend your time, that's why the thought occurred to use a vacuum gage to see if there was a point at where the harmonics would cause the (if broken) spring to do a hula dance and if it did- this would show up as a suddenly bouncing or jiggling gage, where it had been smooth before.

Problem is, if that was also where the ignition was breaking down, the same sort of gage reading might also be seen.

This is where a Sun machine would be handy.

Anyway, g'luck.
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Old 08-05-2009, 07:56 PM
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Could be as simple as corroded coil connections. Just my two cents.
ssmonty
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Old 08-06-2009, 04:45 AM
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Well....could be. I did have the connections apart and they seem OK, but I'm still thinking the coil has an internal short that comes and goes and is worse when teh coil is hot. But I'll check those connections again. Thank-you.

Last night, in the dark, I started it up. No arcing or anything. I then hooked by spark tester (just an adjustable gap device with a sparkplug tip on one end and an alligator clip on the other). I set the gap for just over 1/2 inch and connected the HV wire form the coil to it. Cranking the engine over I had a nice blue spark. It was hard to tell, but it seemed that every so often I'd miss a spark during cranking. This seems to match up when I used a timing light and every so often it misses a flash. Previously I blamed it on the light. Now I'm not so sure.

Anyway, I took it for a drive after my testing and except for some light bogging just off idle, it seemed fine. Seems the problem gets worse when the engine is very hot and complimented by driving during very hot/humid weather.

More testing today........
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Old 08-07-2009, 03:18 PM
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Well....covered 20+ miles and problem is gone. To find out what the problem was, please send $1 in a self-addressed stamped envelope to.....

LOL. Actually, it's almost gone. Down to a few light misfires at various rpms and engine load. What is different form when the problem was really bad?

new coil
moved slightly chafed ignition wire
added alcohol to gas tank in case of water from condensation
day was not as hot and far less humid than before

So it may come back. I'm thinking my nice 9.5 mm Accel plug wires and other HV components may be the problem, or possibly, the ignition module. Best guess on the "bang" is crossfire vs misfire.....a cylinder firing at the absolute wrong time from crossfire. So it looks like a ignition component replacement for a while.

Oh.....I have had a bog for a while which didn't help diagnosis.....trying to seperate that from some of the other issues. Fixed that. Bumped timing to 20 intial and 38 total and swapped accel pump cams for a bit bigger fuel shot.
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Old 08-09-2009, 05:39 PM
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New plug wires cured all problems. I'm certainly aware of how wires can cause misfires and what that sounds like, but that "bang"? Crossfire I guess. When they say that it can cause a piston to end up in the oil pan, they arn't kidding. It's a very destructive sound.

By the way, if you ever get plug wires that need the dist end adjusted to length and boots and terminals installed, get a spray can of silicon oil. Without it, forget about sliding on the boots.

Thanks to all who offered their thoughts. I appreciate it very much.
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