Coil problems

[blhickson]

Why does my coil go bad so fast? How long should a new one last? The PO had 2 used coils on board(as spares I guess?) but this one is only 6 months old and shows from 1.8 to 2.9 resistance. Is this an alternator prob and could it be related to fuel starvation shutdown issues? I've looked for arcing and cracks-nothing there. Any ideas? Coils are expensive!

[ndutton]

We need to know more before we can help. Can you tell us:

1. if you have electronic ignition?
2. the voltage between the small coil + post and the engine ground (NOT the other small coil post) when the engine is above 1000 RPM?
3. under what conditions you measure different resistances on the same coil?

With that information I bet we can solve this quickly.

edit: coil performance and fuel starvation are completely isolated from each other except for maybe a voltage issue supplying an electric fuel pump but that's really reaching.

[BunnyPlanet169]

The PO had 2 used coils on board(as spares I guess?)

Follow Neil on the coil troubleshooting - he's driven this topic and really sorted it out.

I keep a new spare, and my used coil is on the engine. I can't think of a good reason why I'd have spare 'used' coils, but a compulsive hoarder might keep a couple 'intermittent problem, but nearly as good as new' coils around. I'd consider them suspect at best.

[sastanley]

but a compulsive hoarder might keep a couple 'intermittent problem, but nearly as good as new' coils around. I'd consider them suspect at best.

Hey, now...don't judge..

[blhickson]

Electornic ignition here. Should the resistance change with the rpms of the engine? I may not be using the voltmeter correctly. I found a new coil on board (from Indigo) and I tested its resistance (in hand) and it was the same poor 1.5 to 2.8 as the one mounted on the engine. ??? The alternator was tested and it read about 25, so not so good there. The alternator reads "Transpro" on the back. It looks old and the PO was definitely not into the engine work. Just sayin'. The contacts on the alternator to the fuse are corroded on the inside.
I'm taking both alternator and coil to a reliable car mechanic to see what he says about a bench test for both. The engine was very hard to start today as has been the case since the carb rebuild, but once started, she sounds good if the idle stays up. The choke does not seem to affect the starting at all, just the throttle. I'm concerned that the starter itself is compromised. Is that in line with what is going on? I tried to start 4 times and wouldn't start, then there was nothing. There seemed to be a "tiring" of the sound of ignition so I stopped and checked the batteries. Both read 12 v.
I'm trying to locate a remotely held tach to check the rpms but they seem to be for pro mechanics and digitial and very expensive and I cant pull the trigger on that. I'm not going to change anyting until I suss out the alternator/coil problem. I have always believed the misfiring of the engine was an ignition problem, not a fuel problem. I cleaned everything 6 months ago.

[blhickson]

Also, the engine DID start after several (6) tries with the throttle and no choke and stayed running unti I shut her down to remove alternator.

[blhickson]

And I have a mechanical fuel pump rebuilt in the last year and still intact seems to be working ok.

[BunnyPlanet169]

Also, the engine DID start after several (6) tries with the throttle and no choke and stayed running unti I shut her down to remove alternator.

Are you sure the choke is operating (especially since rebuild/reinstall)? It might be a good idea to take the flame arrestor off and look into the carb with a flashlight while someone moves the choke cable. The A4 has an 'updraft' carb design, pulling fuel up through the carb body into the manifold. It really prefers having the airflow choked to help get gas flowing, especially when cold. A lot of throttle has a similar result, but then will usually race to uncomfortably high RPM.

[ndutton]

Now that we know you have electronic ignition it's important you read this thread:

http://www.moyermarine.com/forums/showthread.php?t=5845

It's not the only thread on the subject but is sort of a Cliff Notes version.

[JOHN COOKSON]

I keep a new spare, and my used coil is on the engine. I can't think of a good reason why I'd have spare 'used' coils, but a compulsive hoarder might keep a couple 'intermittent problem, but nearly as good as new' coils around. I'd consider them suspect at best.

+1
I'd consider them dead.
Coil heat damage is progressive. A heat damaged coil is no spare at all IMO.
Barbara is on the right track. Figure out what is causing coils to fail.

TRUE GRIT

[sastanley]

Barbara, You can get cheap photo sensor optical tachs now at places like Harbor Freight for about $40.

I think more important than a tach, would be a timing light. One symptom of timing being off a few degrees can be hard starting.

You have a lot of stuff going on at once..we really need to work on them one at a time.

I see there is another thread you started about carb work...multiple threads sometimes get confusing..that seems to be an older outdated thread now compared to this one.

I'd get the carb, fuel & choke under control first, and then move to the ignition. Jeff mentioned proper choke function. If choke position makes no difference when you try to start, it is NOT set correctly. It needs to be fully closed to start a cold A4 quickly. pull the flame arrestor and visually check.

[blhickson]

I will definately check the choke mechanism. I misunderstood the thread that says "always start with a closed choke." Normal operating is open and you close it "choke" it to start a cold engine. Now I get it. No wonder I smell gas so quickly! LOL and yes the blower is always on and I am very careful.
A guy at NAPA was kind enuf to let me borrow his digital multimeter and the present coil measures 4.2. Must have been operator error testing coil with analog voltmeter. The alternator needed a new voltage regulator. I will reinstall that tomorrow then I will visually check the choke. I'll find a timing light-out of curiosity, I moved the distributor back and forth to see what effect it would have so I'm sure the timing needs setting.
Thanks for the great advice.

[sastanley]

OK, Barbara, great. Making progress. Did you move the distributor around while the engine was running? If so, be sure to lock it down with the motor running the best, for now.

Yes, pulling the choke cable "closes" the choke, and allows less air into the motor, which helps it start when cold. I've found that about one hour or so after shut off, I can start without choke, but anymore than that, I need some choke to start, and fully closed choke when cold. Choke cable in = fully open..

4.2 Ω at the coil is good...the problem those of us around here have experienced with bad coils is when cool it is just fine and when it gets hot, we suspect one of those tiny little windings separates, and makes the ignition circuit fail..hence the discussion that once a coil fails once, it is toast...Once it cools off, the skinny wires reconnect and the process repeats. let's hope the resistance at the coil is still 4.2Ω after running for an hour or more.

Again..one thing at a time...but good data on the coil & alternator.

[JOHN COOKSON]

Must have been operator error testing coil with analog voltmeter.
.

Maybe a weak battery. Try a new battery in the meter.

TRUE GRIT

[Rbyham]

Haven't seen the other basic warning that is part of these discussions. If cranking a non starting engine be sure and close raw water intake if RWC... Look at me giving advice... Woohoo! ☺