Misfire mystery

[Fairlane514]

Thanks for spotting that....

I ran the engine tonight in the dark and did not see any sparks or fireworks at the plugs etc.

Anyone think the timing gear could be a tooth off and still run ok?

[Benson]

Originally Posted by GPierce

In the early part of the video in post 110 it looks like the #1 spark plug is firing between the base of the porcelain insulator and the steel spark plug base. I.E. the plug is shorted to ground. You can see the spark jumping.

I agree that there is a stray spark arcing in area of #1 plug.

Look closer while running in dark garage to track down stray spark.

I sometimes see the brass spark plug "wire" where it connects to distributor terminal, juggling around at same time as that flash near #1.


Also there are drops of water coming out tail pipe. This tells me that engine is NOT warmed up.

I will bet that plugs are fouling ... this will cause the missing.

I saw this MANY times with cars in 50s and 60. Too much idling and short trips where engine never warms up will foul plugs every time

You can clear up fouled plugs by running the car for 15 or 20 minutes at speeds of 35 or 40. A 10 mile run at 45 is even better.

Old time Mechanics in 50s called it "blowing out the carbon".

When checking plugs remember to look at the Porcelain part of plug.

Ignore the "steel ring" on plug it will be black because that area never gets as hot as the Porcelain.

Porcelain should be gray or brown or tan color.

It is normal for steel "ring " on bottom plug to be black.

I would not expect any OLD TIME engine that is idled for long periods and never warmed up to idle correctly.

This never happens with newer cars because computers control mixture.

My 1969 and 1973 Electronic Fuel Injected VW Fastback did not foul plugs.

This car has a computer that controls fuel injectors.

[Fairlane514]

Thanks Benson

I did check the engine running at night and saw no sparks escaping.

My dad has a 31 Roadster, starts up cold and goes into a very nice idle, no misfire etc. Now, his is 12 volt negative ground with a FS Ignition distributor.

I have a different distributor cap on it now, like a modern style with regular spark plug wires.

[bruceincam]

Originally Posted by Fairlane514

Thanks everyone for the responses....

I have tried two different distributors, one has the new style points/condenser, the other has the original style...no change

Could be the nature of the beast, I hate to admit defeat.....

Im going to try cleaning my plugs with a propane torch. I would be inclined to leave it alone, but it if causes my plugs to soot up regularly......hard to ignore.

Could get any video today, but plan on working on it tomorrow ....

My plugs do not soot up. They all run evenly clean even with the "puff".

[noboD]

My neighbor's antique had a slight water leak at the top hose. The water trickled down the hose and around the first spark plug. It flash rusted under the plug gasket and caused a sometimes miss because the plug was not grounded properly. He would put in a different plug and get rid of the miss and think he fixed it because it now was grounded. One time I removed the plug and cleaned the film of rust and put the same plug back in to prove to him what was happening. He never did fix the water leak. Something small is hiding from you. You are looking to hard.

[Fairlane514]

Sponsored Links (Register now to hide all advertisements)

I get what you are saying..

BTW no water leak there

[Rob Doe]

In the wee hours, I keyed in something akin to the following text. Apparently, I never hit the 'post' button...

I used the magnifier to watch the video. I set it at 350 percent and watched many times while the video wrapped.

The first thing I noticed was that there is smoke coming out the tail pipe at a steady flow. There is some debris in it. Maybe its water as stated above.

The next thing I did was practice double clicking very fast to stop the video and advance only a few frames at a time. When the camera returns to the engine, I have moved the view to the lower right corner of the images. It took a while to achieve this. What shows up is a flash that appears to be a front exhaust port leak. This is followed by flashes that light up the front right corners of the engine and the flat edges near the timing gear cover?? There are multiple flashes that light the right front edge of the engine head.

After multiple attempts, I was able to freeze on a frame that shows the flash at the plug along with a large white flash reflecting off the right front corner of the head. I have not come up with a great explanation for this. Perhaps an early owner of the car is messing with Fairlane and us!

I would like to see a new film shot from a better view of the right front corner of the engine.

[Fairlane514]

Hey Rob, thanks for the all the hard work...

I will get more video today.

If you can think of any other angles, let me know.

I do have a different distributor cap on it now, the more modern style with plug wires.

Yes, it does seem a little smoky, and I notice it as well. The condensation is the other thing....its Texas

Would the flash be possible from the two blade cooling fan reflecting light from the sun?

I also ran it last night in the dark.....I did not see any flashing or sparks.....

[Marshall V. Daut]

"Anyone think the timing gear could be a tooth off and still run ok?"

A Model A engine will run with the timing gears one tooth to the left or right of the index marks. But all is not well if that's the case. I have repaired at least three sluggish engines in the past three years in older restorations, whose fiber timing gears were ostensibly lined up properly with the steel crankshaft gear - but the crankshaft index mark had been stamped in the wrong place by one tooth! There were a ton of these inferior gears imported in the 1970's and sold almost exclusively through an unnamed Model A parts vendor in Kansas, who knowingly bought defective parts at a major discount from the national distributor who had rejected them - and then sold them at a lower price than honest vendors could. Knowing the "parsimonious" nature of many Model A owners, guess who they ordered the parts from! There are probably lots of those gears still running in Model A's, whose owners don't know what a Model A engine should run like. With mis-aligned timing gears, the engine WILL run, but it will be sluggish in performance. The index mark on the steel crankshaft gear should be located one tooth to the right of the keyway. The defective gears were marked opposite the keyway, effectively beginning the engine's life in a retarded condition that can't be overcome by advancing the distributor's cam when setting the initial ignition timing. The only fix is to move the camshaft gear one tooth counterclockwise and ignore the index mark on the steel gear. Not a lot of fun to do this, but that's the only way to overcome a defective crankshaft gear's index mark.
If Fairlane 514's engine performed satisfactorily before this misfire problem reared its ugly head, I wouldn't think mismatched timing gears are to blame.
Marshall

[Fairlane514]

I also used my thermal gun on the cylinders and exhaust manifold etc.
All appeared to be pretty even in temperature.

Used my screwdriver stethoscope and couldn't really hear anything unusual.

Marshall.....the misfire has been there since I bought the car in December.

Nothing has improved with the parts I have changed or adjusted.

Something I have not checked is the timing gear. That was my next attempt to discover the problem.

[Fairlane514]

https://www.youtube.com/watch?v=0yMT04PlDo8

Second video

I did remove the side inspection cover, and I have an aluminum timing gear, with all teeth intact and crisp, no wear etc

Removed the timing cover and the alignment "dots" are in the correct position one tooth to the right of the keyway.

[Rob Doe]

Fairlane, I don't hear the same puff, puffing that our coupe has in your second video. You are likely correct about the fan blade, but to be certain, perhaps holding a piece of cardboard between the fan and the engine with the same setups would verify the theory.

The unevenness of the flashes might be explained by a wandering of the fast idle by several rpms.

Pinch the black hose between your first two fingers and release slightly. Control this release amount with your thumb. The gauge may smooth out a bit.

[dansluck]

Good Job on a Tough Find

[Fairlane514]

I have pinched the hose, just not on video. Did not do much...

Im certain the fan and sun reflection are causing the flashing. I tried blocking as much sun as I could, but some still got through.

Verifying my cam gear is correct and installed properly eliminates mechanical timing being the issue, unless major lobe wear......cant really look at that without removing the cam and measuring. Maybe lifters as well.

When I had the head off and replaced the valves, springs and guides, I did roll the engine over and verify everything functioned as it should. I did not measure the valve lift from the seat. My lash is .013 Intake .015 exhaust

So, I'm back to ignition timing. Im suppose to get my new armor ignition cable today, so maybe I will know something in a couple days.

[Fairlane514]

I think im going back to the fundamentals of the ignition system.

Quadruple check everything again...

May even consider a Pertronix Ignitor I.......Yes, I said it.....

[noboD]

Step back away from the ledge. Things are not that bad. You would just introduce another problem by doing that.

[Fairlane514]

Latest:

Went back and thought about what effects idle besides ignition......Vacuum leak

I checked the throttle shaft and it was slightly loose, as was the other carburetor I tried.

I bought a new shaft, and it measured about .004-.006 thousandths larger diameter than the used one.

It is better and noticeable, fewer misfire and not as pronounced. Restart seems good as well.

I know several of you suggested check vacuum leaks, and I did but nothing really gave me a specific location of a leak. The shaft really didn't seem very loose, but I guess it doesn't take much. I have done quadrajets and replaced throttle shaft bushings, but they were very loose.

Maybe the 4 cylinder updraft system is more sensitive than a V8 downdraft.

Completely gone? Cant say, need to drive it some and see.