Seeking troubleshooting experience

[Tom in TN]

Y’all, I am puzzled, My little hot rod has “issues” and I need someextra knowledge and suggestions.
First, the details of what I have:

1934 Ford 5-window coupe – my dad bought it in 1958 and sold it to me in 2001 for a dollar.
Engine = 1936 Ford flathead
.060” overbore.
3 / 4 race cam
Aluminum flywheel
Eddie Meyer finned heads
Fenton open plenum aluminum intake for 2 carbs
2- Ford 94 2 barrel carbs w/#50 jets and idle mixture screws at .75 out.
Mallory Dual point crab-style distributor- 2002 - 2010
Accel Hi-Temp Super Stock radio suppression core 8mm yellow plug wires- 2003
Stock exhaust manifolds
2003 Walker radiator with Cooling Components electric fan/shroud
12v system

Current status- it idles just fine. I can drop the rpm so low that you can almost count the cylinder explosions. I took it out for its first road test since replacing all wheel cylinders and the master cylinder and converting to DOT 5 brake fluid; and replacing the gas tank.
It started down the road fine- hitting on all cylinders, but then it started to miss a hit or two, then it missed a few hits, then it would run ok for a piece, then go back to multiple-misses. Made it to the non-ethanol gas station and filled her up.
Left there and the same scenario happened again, when I pulled away from the station, it was hitting on all 8 and then the missing started again- extremely random- HIGHLY annoying.

So, I am looking for knowledge and experience to tell me: How would YOU go about finding out why it is randomly mis-firing under load?

Any and ALL suggestions would be greatly appreciated.
Tom

[JayChicago]

Try changing the condenser? Easy/cheap thing to try. Both coil and condenser will often work fine when cold, but then start failing when warm, giving weak or intermittent spark.

[oldbugger]

I have had bad luck with them yellow wires. Or could be the DOT 5 fluid, haha

[drolston]

If coil and condenser swap do not solve the problem, pull the distributor and check the points gaps. Could be that one or both point feet that rub on the cam have worn down, reducing the point gap too much.



I had similar problems which ultimately ended up being bad connections with the spiral wound RF suppresser spark plug wires. I replaced them with solid core, except for a one foot piece from the coil to the distributor, which is plenty to suppress radio interference.

[swedishsteel]

Fuel filter partially plugged; fuel pump weak; sounds like not getting enough gas.

[Tom in TN]

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JayChicago - will change out the coil/condenser tomorrow and see if anything changes.
oldbugger- may have to get different colored wires, too...

[Ggmac]

If it ran good after a fill up , maybe your gas cap isnt vented ?

[corvette8n]

The bearings in my distributor were shot causing erratic timing, CharlieNY rebuilt it all good.

[38convsedan]

Check that coil positive and negative wires are connected correctly.
Improper connection results in weak spark.

[John Gibson]

Number one culprit is the condenser!

[35fordtn]

Im just up the road from you and could throw your distributor on the sun machine and load test the condenser for you if you bring them by the shop

[Tom in TN]

7.29.2023 Update.

Ok, so I changed out the coil and the condenser. I know these units are good.

Engine starts just fine and idles good.

I drove it out onto the road and at low rpm it is nice and smooth. As engine rpm increases, the random misses showed up…much more concentrated than the other day. It was really bad…but it would smooth out some also….

So, with thanks to you folks, I have decided to go ahead and bite the bullet and pull the grille and radiator off; get new wires, new plugs, and new dist cap, a new rotor and change all of this out. I will freshen up the point contacts and reset them to .016.

The only thing that makes this an easier decision is that I have found a coolant trail down the outside front of the radiator, so she is in need of repair and I can get that done at the same time.

Thank you all for your thoughts – they are appreciated…when I get the work done, I will return with another update. I have a special event in mid-September that is a 100 mile poker run for Habitat for Humanity and I want to take the coupe on it…that’s my goal.

[Bored&Stroked]

If it was me, I'd take Michael up on his offer to run up your distributor. Since you're pulling the grill, it is easy to pull the distributor and bring it to ThirdGen. You can replace a lot of parts and still not cure the "issue" . . . save some money and know that the distributor is working as it should (or not).

A distributor machine is a wonderful tool to setup/run/test these distributors. I have one and it is almost mandatory when working on these early ignitions. (Or a lot of others for that matter!).

[BUBBAS IGNITION]

cOIL COIL COIL , WRONG COIL FOR APPLICATION or IMPROPER RESISTANCE OVERHEAT START SHUTTING DOWN WHEN HOT

[Tom in TN]

I hear you bored&stroked I have sent the fellow a PM and now I know his name and company name- thank you. I will certainly take him up on his most kind offer,,,

[cas3]

Listen to Bubba !

[Graeme / New Zealand]

I'm finding this thread interesting as my car runs real good when cold but after it warms up it will sometimes stumble on acceleration and miss a bit. I have a proper Ford coil rebuilt by Skip so can be confident about that. I will look at the condenser too. Will be interested in what Tom finds.

GB

[Tom in TN]

Sometimes there is a ray of light in the darkess and I am sitting in the beam.
I have read all of your posts (thank you!! ) and it seemed that my first order of business should be to check for proper fuel pressure(is it low hanging fruit?- not sure) so I got a nice little fuel pressure gauge and installed it after the pump and before the fuel block.
Cranked the engine up and what do you know - 3 psi on the nose...WOOHOO!!!
Now, on to pulling the grille and radiator.

[Anteek29]

I recently had the identical issue that you have described...drove me nuts! I eliminated being fuel related because the misses and bucking were sudden and intermittent. My '55
ran perfectly when cold and then would start missing during warmup and get worse when hot and under load. After a series of part subs I finally solved the problem...it was the COIL!

[Tom in TN]

Thanks Alan. Even though some swear that is my answer, I am kinda ruling it out because I have had 2 different coils on it...and the symptoms are pretty much the same.