Weak Spark
 

Hello, I am brand new to this forum as well as flatheads so please bare with me.

I have a 1946 Super Deluxe with (as near as I can tell) somewhere between a 49 and 53 flathead 8 in it. The car runs and drives but seems to me to have weak spark and lately has been hit or miss when I try to start it. I measure around 3-4 volts at the coil with the points open and in my research have come to understand that is about correct for the 46 flatty due to a condenser under the dash but only for a couple of model years. I also have a condenser that is mounted on the firewall next tot eh voltage regulator. My question is this, if my motor was originally intended for later model vehicle that would not be equipped with the under dash condenser, does the coil want to see the full 6 volts? Additionally what purpose does the firewall mounted condenser serve? Any help would be appreciated, like I say I am new to this vintage vehicle so please be gentle!

I suppose I should add that is a stock 6 volt pos ground set up.

Re: Weak Spark
 

I kinda think the condensor next to the regulator is NOT the ignition condensor....Condensor is attached to the distributor housing , these hardly ever fail ...

Re: Weak Spark
 

Do you know what its function might be?

Re: Weak Spark
 

could be for radio static ,I have seen them mounted on the generator

Re: Weak Spark
 

Most likely noise suppression for a radio. What distributor does your engine have? Front of the engine pancake style or the later distributor that looks more like a modern one? And, welcome to the Barn!

Re: Weak Spark
 

My (original when I got it) '51 Ford had radio suppression condensers on the voltage regulator, generator, and even the oil pressure sending unit.

Re: Weak Spark
 

Radio interference reception, that makes sense considering where it is. it is not the crab style disto it is the modern stile just in front of no 1 plug. thanks for the warm welcome!

Re: Weak Spark
 

If you want a reliable condenser (although it is an externally mounted unit), contact me.

Re: Weak Spark
 

Thanks for all of the advice so far, but I am still hoping to hear someone weigh in on what the proper voltage for a circa 1950 flatty should be at the coil. I am still concerned that the reduced voltage for the 46 chassis is causing a problem for the more recent motor.

Re: Weak Spark
 

It depends on the coil you are using and the only way to know is to measure the coil resistance. But, in most cases a "can" coil will not require an external resistor if it is still a 6v system.

You ideally are wanting somewhere in the 3.5 amp range in the ignition circuit. Current is calculated as Current (A) = Voltage (V) divided by the Resistance (R). As an example, if your coil measures 1.5 ohms (a common value for "can" coils in a 6v system), then A = V/R would be A = 6V/1.5 ohms or 4A. The amperage is a little high, but a common configuration.

In a real circuit there is additional resistance in the circuit in addition to the coil and the voltage can be higher than 6v, but that is the general idea. Your voltage at the coil should be around 6v.

If the car is not using a "can" coil, but one of the original Ford style coils, then the resistance of the coil will determine what ballast resistor is required. Just as an example, if a coils resistance is say 0.75 ohms then you would want around a 0.75 ohm ballast resistor.

Also keep in mind that if the car is still using positive ground and the coil is not wired with the correct polarity, it will reduce the coil output. On a positive ground system the (-) terminal connects to the ignition switch and the (+) terminal connects to the distributor.

*Second attached photo is of Bubba's Ignition Service checking a Ford coil.

Re: Weak Spark
 

A 1946 will have a resistor 'left side under the dash' to drop coil voltage. I always thought of this being a "Ford thing" of that period probably something to do with the
original type coil they used that needed a resistor. I have always questioned that?
At my age I have yet to come upon any 1949-53 Ford product with a coil resistor.
Here is the common sense when with this resistor = turn ignition on and you get maybe
1/2 of 6vts at the coil more or less, now hit the starter that sucks juice. Lucky the
coil will light a flashlight, But they did work with the 'square' coil. Now you have a I call it a beer can coil used on all 48 - 53 trucks and 49 - 53 cars. My positive proof I have a
fleet of trucks one 1950 F6 bought new one 1954 F800 bought new by my father 6volt
positive grd. 1950 F8 mighty 337 V8 no resistor on any. Do you have a volt meter and
connect to the minus side of the coil if you get less than 6 volts you have the resistor.
Connect a jumper wire from battery to coil = meter should jump to 6volts now hit the starter should start on a dime ...........oh make sure the wire going to the points and
condenser is good they do fray over time. sam J Seery said it all..

Re: Weak Spark
 

Ford eliminated the in line resistor in 1949.

Re: Weak Spark
 

Great info guys, that gives me a direction to go in. I will be sure and post results so the next guy that needs this post see the results as well!

Re: Weak Spark
 

Okay so time for an update. So I started the car and warmed it up, then I jumped negative side of the coil to the negative battery post (remember positive-ground 6 volt set up) and the car died and would not restart. It wasn’t completely without fire because it did stumble once or twice but did not catch. At this point I believe my coil is all but dead which is weird considering the negative terminal on the battery post runs into the car through the ignition switch and back out to the coil so jumping it should only have provide a full 6 volts at the terminal instead of the 3-4 I have there with resistor under the dash. Thoughts?

Re: Weak Spark
 

I already posted how I would have done this. But for starters, what coil are you using? It is going to make a difference depending on the coil you have.

Re: Weak Spark
 

MB IF YOUR COIL WAS WIRED BACK TO FRONT ,eg then you may have fried the points ,

Re: Weak Spark
 

There are no markings on the coil other than 6 volt. That is about all the info I have. I will start taking the reading you suggested but I suspect I will have to change the coil first. I appreciate the info you provided in you first post and would like have done that first but I work 3 jobs and usually only get a few minutes here and there to tinker, often in the dark. Thanks all!

Re: Weak Spark
 

It is a generic can style coil

Re: Weak Spark
 

With three jobs you are lucky to have any time at all. I have one more than full time job and it's a struggle to find time to work on cars. That said, if you have a can style coil AND a resistor, that is probably your problem. Wiser heads than mine can set you straight.

Re: Weak Spark
 

On my Model A. Had a fair spark but would not start when hot. Checked coil primary. Between pos and neg on coil. Meassured 5.3 ohm. Primary to secondary (output) was 9,000 ohms. Found my old coil. Primary was 1.6 ohms with 9000 secondary. Problem solved. 1in srark jump now. No start problems. Check coil

Re: Weak Spark
 

Are you saying that the resistor under the dash shouldn't be used with a can style coil? I plan on getting some resistance readings of my components today if all goes well.

Re: Weak Spark
 

It most likely does not need a resistor. Move the wire from the ignition switch to the resistor to the same terminal as the wire from the resistor to the coil. This will bypass the resistor. Make sure the ignition wire is connected to the (-) terminal on the coil and the (+) terminal on the coil is connected to the distributor.

Re: Weak Spark
 

Some coils have an internal resistor. If you have a resistor under the dash and one in the coil that could be your problem. Examine the coil closely as some are marked regarding the internal resistor.

Re: Weak Spark
 

The only way to really know is to measure the coil, but that said, almost all 6v coil have the required resistance because of the design of the windings. You want something around ~3.5 ohm of resistance and that is the range of most 6v coils.

Re: Weak Spark
 

Ok, update time. I picked up another coil on the way home just in case, I checked resistance on the old coil on the primary side I had 1.6 ohms and 9k ohms on the secondary. the new coil measured 1.3 ohm primary and 9k ohms secondary which made me think both coils are fine. i did opt to install the new coil and jumped the resistor under the dash and have the best spark i have ever had in this car. that is the good, the bad is no matter what i do i cannot get the car started to save my life. i have checked spark, fuel, put no 1 cylinder on TDC and made sure the rotor is pointing straight down at number one plug wire, checked firing order to make sure one of my helpers didn't do me any favors all with no success. I did find allot of sediment in the fuel bowl and cleaned it out but i am confident that i am getting fuel (as a matter of fact it seems to be flooding). What am i missing? Just as a sidebar i pulled the firing order off for the internet and i looked at a couple of sites to make sure they were correct and on all of them they showed No 1 Plug wire at the 12 o'clock position on the distributor and mine is at 6 am i reading too much into this?

Re: Weak Spark
 

Just to be sure, what are you calling the number one plug position on the engine and what firing order are you using?

Re: Weak Spark
 

this is what i am going by, this drawing matches my dsto because it is viewed from the drivers side across the engine.

Re: Weak Spark
 

i did confirm that this coil used an internal resistor before i jumped the under dash resistor.

Re: Weak Spark
 

How did you determine you are at TDC on the start of the power cycle?

Re: Weak Spark
 

I lined up the timing mark on the crank to the indicator on the block.

Re: Weak Spark
 

That will not give you the correct position. On a 4 cycle engine there are 2 times the crank will line up with the indicator, and only one of them is correct. You have to assure that the piston is coming up on the compression stroke (both valves closed). The engine will only fire properly when the engine is on the correct cycle.

Remove the number one spark plug and rotate the engine until you can fill the compression and align the timing marker on that cycle. The diagram has overhead valves, but the engine cycles are the same.

Re: Weak Spark
 

I did do that when I first got the car to get it running initially. Remember the car was running quite well with only a slight flutter on my vacuum gage tapped into the intake just 2 days ago. Then I jumped the - on the coil to the - battery post. It died and that’s the last time it ran.

Re: Weak Spark
 

I was having starting problems with my 38, running a 49-53 round coil, called Dick FLYNN, he said to bypass the resister under dash, did that a few years ago, will always start even when hot, puts 6 volts to coil, no point problems

Re: Weak Spark
 

So nothing has changed with the distributor and the timing since the last time it was running? If so and you have a spark and fuel and compression it should fire. Have you tried something like starter fluid? A small squirt should tell you if the plug is firing in the cylinder.

By the way, there is always what is considered a correct position and plug wire arrangement on a distributor. It doesn't really matter IF you understand what your doing and are sure you have the rotor aligned with the correct terminal on the cap for the #1 plug wire and the other wires installed correctly from that starting point.

Re: Weak Spark
 

Exactly, now you see my dilemma. The only thing that changed in the distributer was a slight adjustment to line up the rotor to number one (less than 1/4 inch rotation) and only after I confirmed I was getting both fuel and spark. I am getting a nice blue spark at the points and a good spark at the plug. I pulled the plugs and the were wet with gas. Dried, cleaned checked compression and replace each plug. Confirmed firing order again still only coughs and tries to catch but never does.

That was always my understanding as well when it comes to plug wires, I just wanted to make sure I wasn’t missing something.

Re: Weak Spark
 

Ignition condensers form an important part of the system. If they become weak or open, the spark will be severely diminished because the coil can't fully recharge between point cycles. We seem to be having a big problem with the quality of replacement condensers
today, almost all foreign made. If you are doing a routine tune up. and the engine is running OK, reusing the condenser is preferable to new non US made. I carry a spare condenser in my "road kit". I has clip leads on it and can be quickly installed connecting the leads between ground and the input terminal to the coil.

Re: Weak Spark
 

Just a thought,is the capacitor on the point side of coil! You said it hasn’t run after changing wires on the coil,

Re: Weak Spark
 

Problem solved! Weak ignition condenser. Thanks to all of you who are :Dwilling to share your knowledge, I am glad I found this forum!

Re: Weak Spark
 

Looks like Supereal and Don nailed it!