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Mallory Ignition v.s Battery.... Electrical Mystery Solved!!!

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tahoe36c Avatar
tahoe36c Paul Hruza
Panama City, FL, USA   USA
1969 MG MGC GT "Little Red Rocket..."
1972 MG MGB GT "Tiny Dancer"
2002 Harley-Davidson Dyna
Here is one for all the electronic whiz kids... Strange but true!

A few months ago I took a friend out for a ride in the 69 C/GT. We drove approximately 5 miles and then stopped at a red light. The engine just shut down... No lumping, no funny noises, no nothing. It was as if I turned to key off. A quick check proved I had fuel pressure but ignition was barely there. When cranking the engine the #1 plug wire was just barely sparking about every 5th crankshaft rotation. Called a friend to come get us. We towed the car home and put it in the garage... I left it for about a week because I had other things to do and surely wasn't too happy since I've never been left by this fine running engine previously.

I finally began troubleshooting the ignition system which includes a Mallory Unilite Distributor (installed by one of the previous owners) and found three things:

The coil seemed fine but was a 3 Ohm and Mallory recommends 1.5
The ignition ballast was also 3 Ohm, and again, Mallory recommends 1.5

Neither of these two deficiencies seemed to affect the ignition system performance prior to this failure. The car has been running just fine since I purchased it... More to come on this however.

I performed the Mallory check on the ignition control module and found it bad (but don't you points lovers get all excited just yet!!! LOL)
The checkout for the module is to remove the distributor cap, power the system, then check for 12volts at the negative side of the coil. If that is good then you place a credit card sized object (I used a small piece of cardboard) to block the photo optics of the module. This is when the distributor fires. Voltage should drop to 2 volts or less. If so, it is good...

I was getting crazy crap like only 6 or 7 volts at the positive side of the coil and 1 or less on the negative side BEFORE blocking the optics!!! Then I'd walk away and come back to find 12 volts at the positive side and still only 1 or 2 at the negative side. It seemed to be ridiculous!!! I checked the battery connections for cleanliness but found nothing because I have always been a stickler of keeping the posts cleaned and lubed with Vaseline. Battery ground was also perfectly clean. I know because I removed and cleaned it again....

So in the end I got on eBay and ordered another module figuring it was bad... I connected the battery to the Battery Tender again as usual and just left it for two weeks waiting on the part.

In the meantime, I got to thinking about that ignition ballast and wondered why it was even there. I thought it was only required for points to help them last longer so I removed it... I was wrong about that too!

Anyway, the new module shows up, I install it and Vrooooommmm. She fires right up! Heck yea... Go to go. Then about 5 minutes into the warm up; dies again. Now I'm really confused so back to the Mallory test. I read through it and finally noticed the BOLD lettering; WARNING: this distributor requires a ballast. Not using one can shorten the life of the module. Shorten? Well yea! It lasted 5 minutes!!!! LOL $$$$

So that is when I called Mallory tech support, explained the entire situation, and was told to use the 1.5 Ohm coil and ballast. So I ordered a new coil, new ballast and another module. No warranty on the first replacement since it came from China (from a guy who actually was the Mallory supplier!!!).

Are you ready for this? All parts come in. I replace them. Turn the key and.... Nothing. Engine spins, no start. Now I am ready to pull out the C4 and really fix this car!!!! Grrrrrrrr

I do the Mallory Module test and guess what? Same crap as before. 1.5 volts at the negative side of the coil before I even block the optics... Now I'm thinking there must be an ignition switch problem. Not letting enough juice get to the coil. OK then, before I do that I decide to install my spare battery (the one for the B/GT rebuild) just for shits & grins. And now...

Engine cranks right up and runs like a charm... Really? Was the battery really the cause of all this from the beginning? Well... Yes. I reinstalled the original and first ignition module replacements (just wired in to make the check, not put into the distributor). They are both fine!!! So now I have two spare modules.

Car has been running fine ever since replacing the battery. The battery was found to be "low" when we performed a battery load check but still cranked the engine just fine.

OK, enough electrical insanity for this year. Hopefully all will remain operational for a while! LOL...

So there you go. Another electrical mystery solved. Mallory Ignition System; just fine, no problems. Battery was the culprit! Hmmmmmmmmm

Just took another ride today. Runs like a dream!!



Edited 1 time(s). Last edit at 2019-03-15 04:46 PM by tahoe36c.

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PETE W Sussex Peter H
Ansty, West Sussex, UK   GBR
When I started reading I thought ‘oh Christ, this will be meat and drink for the points boys’ ......but then I got to the bit about walking away and 12v when you came back, and started thinking battery. They can be a right PITA (as you now know!).

If you haven’t already, it might be worth checking your alternator too?

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tab a Thon Basom
central, KS, USA   USA
In reply to # 3909372 by tahoe36c
The battery was found to be "low" when we performed a battery load check but still cranked the engine just fine.


Pretty sure I don't understand this. smiling smiley

No matter how 'low' the battery is, if you've got enough amps to crank the engine 'just fine', I'd think you'd have WAY more than enough for the Mallory?

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tahoe36c Avatar
tahoe36c Paul Hruza
Panama City, FL, USA   USA
1969 MG MGC GT "Little Red Rocket..."
1972 MG MGB GT "Tiny Dancer"
2002 Harley-Davidson Dyna
Thon,

I completely agree with you! That's why all of this is such a mystery... Doesn't make any "electrical sense" whatsoever to me. But in the end, the change of battery solved the problem...

Peter,

Alternator output is perfect... Battery at 12.7 idle, 13.8 engine running. No ignition light (which is actually an alternator field excitation light)...



I'll just keep driving for now and see what happens next! smileys with beer

Let me know if anyone needs a Mallory Unilite Ignition Module. I have TWO spares... LOL

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tab a Thon Basom
central, KS, USA   USA
I know you checked connections, so I'd tend to wonder about a wonky wire.

You probably don't have it, but would be interesting to put the old battery back in now.

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Noble66 Avatar
Noble66 Gold Member Noble Bradford
Orlando, FL, USA   USA
1964 MG MGB "Black Betty"
1969 MG MGC GT
1974 MG MGB "Whitey"
In reply to # 3911431 by tahoe36c I'll just keep driving for now and see what happens next! smileys with beer

The story of life.

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