Weak spark

[Alpine 1789]

My car has been running well this spring; the only complain has been a tendency to periodically die at idle. Yesterday, the starter turned very slowly when starting the car. It sounded like an almost dead battery, although the battery is only a couple of years old and was on a trickle charger that showed it fully charged. Plus, I have a modern hi torque starter. I didn't think it was going to catch but the starter sped up a bit and it started. I was just moving the car to work in the garage so I drove around the block and parked it. A few hours later it wouldn't start at all, even with starting fluid and a booster on the battery. It was late so my wife and I just pushed it into the garage and I waited until I had some time to look into it further. I just checked and it still turns like the battery is almost dead, although it speeds up to normal with the booster. I put a spare spark plug on the #1 wire and grounded it to see if there was any spark. The best I got was a weak spark with the booster on the battery.

FWIW, I have a Pertronix distributor (their actual dizzy, not an Ignitor) that was given to me. It is probably about 5-10 years old. The coil, however, is also a Pertronix 0.5 ohm Flamethrower that I bought 25 years ago (or so) when I installed an Ignitor on my original distributor.

So, before I start buying and replacing parts, does this sound like the coil?

 

[sunalp]

JIm,
Check your grounds and battery connections. My tractor will do this sometimes as on cable connection
loosens up with use. Happens every spring too!

To answer your question, it doesn't sound like a coil as they tend to die out as they heat up. Try a different coil
from one of your other cars just too see.

 

[Alpine 1789]

Thanks, Steve. I was heading down that path - and also thinking it could be the starter cable - until it stopped starting up completely. But, I will give that a try, along with a ‘new’ coil, if that doesn’t do it.

 

[Joe-dick]

Please don't be insulted - I try to explain things very basically for anyone reading this in the future.

Having been in auto repair for over forty years I'm still confused at the complaint of "weak spark." I hear people say "weak thin spark" or "fat blue spark" or "little yellow spark" but none of this means anything. Either the spark jumps the given gap or it doesn't, the color or apparent 'thickness' of the spark is only due to atmospheric conditions. To test spark output first check if the spark jumps a standard plug gap as you probably have. Spark or no spark? Spark - OK. Now grab an old plug and bend the ground electrode open so instead of a .028-.030" gap you have about .120" gap (about an 1/8") and see if the spark will jump that gap. It should. Again, color means nothing, it either sparks or not. If you can get spark at .030" but not at .120" then you need to work your way backwards testing at the dist tower, coil wire, coil tower to see where you regain spark with a .120" gap. If you get all the way to the coil tower and still can't jump a .120" gap then it's time to inspect your points and condensor (if installed) and sub a known good coil for testing. The reason we need to test at .120" when the plugs are only gapped to .028" is because the spark plug in the cylinder under compression requires more voltage to cross the gap than required at atmospheric pressure laying on top of the engine.

As for your slow cranking troubles, it sounds like a weak battery. Put a (good) voltmeter across the batt terminals after sitting overnight. A fully charged '12 volt' battery will read at least 12.6 volts. Anything less means it's not fully charged. Now leave the voltmeter attached while you crank the engine. The battery voltage should stay above 10 volts. Below 10 volts while cranking is either excessive starter current draw or more likely a failing battery. If the cranking voltage is well above 10 volts but the cranking speed is noticeably slow then move the voltmeter leads to the starter battery cable and starter housing to test the voltage directly at the starter. If the cranking voltage there is more than a half volt below the cranking voltage at the battery posts then you need to test for dirty or loose connections between the batt and the starter on both the positive and negative sides.
In your case you said it cranks at normal speed with a booster so I'd bet on a poor battery, but test the voltage first. I've seen trickle chargers that wouldn't fully charge a badly discharged battery but could maintain battery voltage if the battery was fully charged with a larger charger. You might want to take the battery to a nearby friend or local shop with a full-size battery charger and battery tester to be sure.

Sorry for the long post. I try to write for clarity.
Joe

 

[belmateo]

Jim, I have had those float chargers appear like they were working but were not and let the battery die. Harbor Freight has some better ones now that actually boost your battery to the correct level, then maintain it.

 

[Alpine 1789]

Thanks, guys. I am planning on working on it tomorrow, starting with easy solutions and working my way up. I will report back in 24 hours.

 

[alpine_64]

Thanks, guys. I am planning on working on it tomorrow, starting with easy solutions and working my way up. I will report back in 24 hours.

Jim .. should we check polymarket for the odds of what it is?

 

[Alpine 1789]

Wait until I put in my bet.

 

[alpine_64]

Wait until I put in my bet.

Let me know 15mins before you announce tye results

 

[Alpine 1789]

Anyone who bet on "bad battery" may be entitled to collect on their bet, as long as "car starting" was not part of the bet. I took my battery over to Rocco/Mototron's shop today and used his load tester on the battery. It was fully charged but completely failed the load test. So, that explains the slow cranking. I was able to borrow a good battery from him, along with a spark tester and a spare coil. The car spins right up with the 'new' battery but still doesn't start. The tester shows I have a spark that jumps a pretty good gap. I can see gas squirt in the carb when I pump the accelerator. My coil tested fine but I swapped Rocco's in anyway with no change. Checked the plugs. A couple were damp with fuel, no doubt from all of the cranking. Dried them but no change. I'm not sure what my next steps are, but I'll get back to it on Thursday. Stay tuned...

 

[todd reid]

fuel + spark + compression = running engine. Of course spark needs to be delivered at the appropriate time. Might be worth doing a compression test if you own a tester, but perhaps the more likely scenario is that the spark delivery is being disturbed by something. Did you test spark at all four cylinders? Any chance that plug wires got crossed during previous testing (not hard to do - been there myself).

 

[Knightowl61]

fuel + spark + compression = running engine. Of course spark needs to be delivered at the appropriate time. Might be worth doing a compression test if you own a tester, but perhaps the more likely scenario is that the spark delivery is being disturbed by something. Did you test spark at all four cylinders? Any chance that plug wires got crossed during previous testing (not hard to do - been there myself).

Make sure the rotor is in the distributor. Don't ask why I suggested that.

 

[Alpine 1789]

I don't think I could have crossed the wires - I never removed more than one at a time. And the car was running fine up until Sunday, and I feel like I would have known if anything catastrophic was brewing with the engine. It also sounds fine when spinning with the starter.
I will check each wire next. I have also wondered if timing somehow got changed. The distributor felt firm, but I will investigate that further.
And, the rotor is there.

 

[Acollin]

I went back to the original posting here and I’m guessing you had more than one problem— “die at idle” and slow spin at starter.
The battery issue seems seems to have resolved the slow cranking, but die at idle doesn’t appear to me as electrical. I’m thinking fuel. When your car last ran well what was the rpm at idle? how was the coloring of your plugs? If you have spark at all four plugs and you haven’t messed with the timing, doesn’t fuel seem like the likely place to look for the no/ start?

 

[Joe-dick]

Remember when investigating fuel supply that too much (flooding) can cause a no start just as too little. Especially with a car that's been cranking slowly. If you find the spark plugs wet with fuel, in addition to drying the plugs (compressed air works well) it's good to spin the engine over with the plugs out to clear excess fuel from the cylinders. Be aware that in extreme cases a mist of liquid fuel can spray out of the plug ports on the head, so I usually lay a towel loosely over the top of the engine to prevent fogging the shop.
Joe

 

[Alpine 1789]

I called Pertronix today and was informed that I should have changed my 1.5 ohm coil to a 0.6 ohm coil when I switched from the converted distributor (I was still using a mechanical advance 45D4 from when I had the side draft carbs) to the Pertronix unit. The tech advisor told me that the car would run great with the coil but that it would eventually burn out the ignitor unit on the distributor. Replacing the ignitor and the coil will cost me $260! At least for now, I am going to put my old unit back in and see if that solves the problem. At least then I will know if that was truly the problem or if there is something else going on. More later today.

 

[Alpine 1789]

It appears mystery solved. I put the old distributor back in and it fired right up. Adjusted the timing and the idle and just went out for a short drive and everything seems to be fine. I do feel like the car ran a bit better with the Pert distributor, but not $260 better. I'll keep an eye on things and maybe change my mind, but with spring here it is nice to have the car back on the road. Thanks to all who provided advice!

One more thing: just to put the Pert repair costs into perspective, does anyone know what Advance Distributors currently charges to recurve a one?

 

[husky drvr]

One more thing: just to put the Pert repair costs into perspective, does anyone know what Advance Distributors currently charges to recurve a one?

Jim,

No idea on cost, but here's some info to help you.

HAGD

Advanced Distributors, LLC

Advanced Distributors is your source for automotive distributor service. We specialize in precision rebuilds and repair of distributors for most vintage and collector vehicles, including all Lucas, Bosch, Prestolite, and Delco distributors. We service many other brands, so please contact us to...

www.advanceddistributors.com

Advanced Distributors, LLC
17495 Marystown Road
Shakopee, MN 55379
(612)-804-5543

 

[spmdr]

I have an old dusty Sun 504

distributor machine.

It IS the tool for Dist set up.

Here you can see the result of point

bounce, with the arrows showing

and NOT showing.

With a correct functioning

Distributor, it will display an arrow

at every point opening spot.

It's SO easy to forget the attention

points Need.

DW

 

[belmateo]

I have an old dusty Sun 504

distributor machine.

It IS the tool for Dist set up.

Here you can see the result of point

bounce, with the arrows showing

and NOT showing.

With a correct functioning

Distributor, it will display an arrow

at every point opening spot.

It's SO easy to forget the attention

points Need.

DW

View attachment 38089

View attachment 38090

Used a distributor machine many times especially helpful with dual point dizzy. Set em, lube em, set engine timing and done!