On 2/11/2021 4:11 pm, keithr0 wrote:
> On 2/11/2021 5:56 pm, Clocky wrote:
>> On 2/11/2021 2:24 pm, keithr0 wrote:
>>> On 1/11/2021 11:05 pm, Clocky wrote:
>>>> On 1/11/2021 12:58 pm, keithr0 wrote:
>>>>> On 31/10/2021 5:57 pm, Clocky wrote:
>>>>>> On 31/10/2021 11:55 am, keithr0 wrote:
>>>>>>> On 30/10/2021 9:57 pm, Noddy wrote:
>>>>>>>>
>>>>>>>> OT: Car post
>>>>>>>>
>>>>>>>> As most of you are aware I own a 1956 Ford F-100. It's a cool
>>>>>>>> old thing and I love it to death.
>>>>>>>>
>>>>>>>> But....
>>>>>>>>
>>>>>>>> It was put together by a bloke who really had no idea what he
>>>>>>>> was doing, and I've been chasing problems with it ever since I
>>>>>>>> bought it last year.
>>>>>>>>
>>>>>>>> It's coming good, and I've got most stuff sorted on it, but one
>>>>>>>> problem thing it's had since the day I got the thing is an
>>>>>>>> intermittent ignition stumble, and because it's been *very*
>>>>>>>> random it's been terribly hard to pinpoint.
>>>>>>>>
>>>>>>>> Until yesterday :)
>>>>>>>>
>>>>>>>> The truck has it's original 272 cube Y Block V8 that was
>>>>>>>> reconditioned not long before I bought the thing, and is
>>>>>>>> standard apart from having an alloy 4 barrel manifold, an
>>>>>>>> Edelbrock 1405 carb, a nice set of ceramic coated headers and an
>>>>>>>> MSD "ready to run" distributor.
>>>>>>>>
>>>>>>>> One of these:
>>>>>>>>
>>>>>>>>> https://www.vpw.com.au/parts/MSD-8383
>>>>>>>>
>>>>>>>> These ready to run things are a quick and easy convert to
>>>>>>>> electronic ignition for older shitheaps like this, as they're
>>>>>>>> all fully self contained with a single pole reluctor trigger and
>>>>>>>> an ignition module mounted under the base plate. All they need
>>>>>>>> is a power feed from the coil and they're good to go. They also
>>>>>>>> have a couple of cool features such as a built in rev limiter
>>>>>>>> which is programmed by momentarily earthing the tach signal wire
>>>>>>>> while the engine is running, and their best feature in my
>>>>>>>> opinion is that the mechanical advance mechanism is *above* the
>>>>>>>> base plate under the rotor which makes changing the advance
>>>>>>>> curve a five minute job.
>>>>>>>>
>>>>>>>> On the downside, I found out not so long ago that MSD gear is
>>>>>>>> now made in China, and that gave me cause to be concerned as
>>>>>>>> Chinese automotive electrical components don't have a stellar
>>>>>>>> reputation.
>>>>>>>>
>>>>>>>> Anyway, that theory was confirmed yesterday morning when I was
>>>>>>>> coming back home from a trip into town when the thing suddenly
>>>>>>>> started carrying on like crazy and would refuse to run for more
>>>>>>>> than a couple of seconds. Long story short after much pushing,
>>>>>>>> swearing and short stop start driving I managed to get it home
>>>>>>>> and start my diagnosis.
>>>>>>>>
>>>>>>>> Checked everything. Coil, wiring, relays, temperature, the lot.
>>>>>>>> Nothing seemed to be out of order. Last thing left to do was
>>>>>>>> pull the distributor and have a look at it, but given that it
>>>>>>>> was fitted brand new and has only *just* clocked 2000 miles I
>>>>>>>> wasn't expecting it to be where the problem lay.
>>>>>>>>
>>>>>>>> Murphy's first law of automotive diagnosis: Assume nothing :)
>>>>>>>>
>>>>>>>> The distributor shaft needs to be removed to remove the base
>>>>>>>> plate and get to the ignition module. As I was peering under the
>>>>>>>> module when lifting it as far as the wiring harness would allow,
>>>>>>>> I saw this:
>>>>>>>>
>>>>>>>>> https://www.imagebam.com/view/ME4MPQ7
>>>>>>>>
>>>>>>>> Uh-oh :) I don't think that should be there :)
>>>>>>>>
>>>>>>>> The wiring harness sheath had melted itself together, so after
>>>>>>>> cutting if off and removing the base plate, the ignition module
>>>>>>>> looked like this:
>>>>>>>>
>>>>>>>>> https://www.imagebam.com/view/ME4MPQ9
>>>>>>>>
>>>>>>>> Fucking nasty. Massive overheat by the looks, but this thing was
>>>>>>>> wired *exactly* as MSD's instruction book said it needed to be.
>>>>>>>> The melted brown wire was actually jammed in between the
>>>>>>>> capacitor and the remaining resistor where it met up with the
>>>>>>>> other three wires and was fed out through the sheath in the
>>>>>>>> lower part of the housing.
>>>>>>>>
>>>>>>>> And on the other side, we had this:
>>>>>>>>
>>>>>>>>> https://www.imagebam.com/view/ME4MPQB
>>>>>>>>
>>>>>>>> Just fuck. Massive fail.
>>>>>>>>
>>>>>>>> As I said, this is a new distributor that the previous owner
>>>>>>>> paid over a thousand bucks for, it's done just over 2000 miles
>>>>>>>> and it has been installed *precisely* as instructed buy the
>>>>>>>> company who made it. Pretty piss fucking poor if you ask me, and
>>>>>>>> a *perfect* example of how paying high prices for "brand names"
>>>>>>>> isn't all that great an idea these days.
>>>>>>>>
>>>>>>>> The solution is to buy a new replacement ignition module which
>>>>>>>> comes as a "kit" which includes the module itself, the base
>>>>>>>> plate, the advance plate and the magnetic pick up. But given
>>>>>>>> that they're 300 bucks Australian and and are 6 weeks away in
>>>>>>>> the US, I'm not all that keen to wait that long let alone to pay
>>>>>>>> that kind of money only to have the exact same thing that fucked
>>>>>>>> up in the first place.
>>>>>>>>
>>>>>>>> So we move to plan B, which is to try using a remote ignition
>>>>>>>> module.
>>>>>>>>
>>>>>>>> Given that the triggering mechanism in the distributor is a
>>>>>>>> basic single pole reluctor it should work with *any* generic
>>>>>>>> module like a Bosch 021 or a GM HEI, and given that I have both
>>>>>>>> of those here and nothing else to lose my plan is to gut the
>>>>>>>> distributor and just leave the reluctor and pickup in place and
>>>>>>>> feed those into a 4 pin HEI module which I can mount in an
>>>>>>>> enclosure on the firewall. I can't see why it wouldn't work, and
>>>>>>>> I'll know by this time tomorrow if it does. If it does it will
>>>>>>>> be a good cheap home brew fix that will hopefully help other MSD
>>>>>>>> owners avoid a massive repair bill.
>>>>>>>>
>>>>>>>> In the mean time, if anyone's thinking of purchasing automotive
>>>>>>>> ignition products any time soon my recommendation would be to
>>>>>>>> stay the *fuck* away from anything offered by MSD.
>>>>>>>
>>>>>>> A bit of a disaster! We have a destroyed MOSFET, an exploded
>>>>>>> capacitor, a burnt wire and a resistor that has got so hot that
>>>>>>> it has melted its solder connections.
>>>>>>>
>>>>>>>
>>>>>>> The capacitor that has exploded is interesting, without a circuit
>>>>>>> I'd have to guess that it performs the same function as the
>>>>>>> condensor (an ancient name for a capacitor) in a Kettering
>>>>>>> ignition system i.e. absorbing the back EMF from the primary of
>>>>>>> the coil when the points open or in this case when the MOSFET
>>>>>>> switches off. If that were the case then the MOSFET would get the
>>>>>>> whole back EMF and self destruct. The resistor that fell out
>>>>>>> could possibly be a ballast resistor, if the MOSFET failed short
>>>>>>> circuit then 12v would be constantly across the coil primary and
>>>>>>> the resistor in series and the resistor would be dissipating
>>>>>>> rather more power than it was designed for (remember the days
>>>>>>> when it was recommended not to leave the ignition on for long
>>>>>>> periods with the engine stopped to avoid overheating the ballast
>>>>>>> resistor). The wire is only burned in on spot, probably because
>>>>>>> it was in contact with the resistor.
>>>>>>>
>>>>>>> The upshot is that my guess is that the capacitor was underrated
>>>>>>> and its demise lead to all of this.
>>>>>>>
>>>>>>
>>>>>> There are a few components that need to be checked if a repair is
>>>>>> attempted. Since he reported erratic ignition stumble prior to
>>>>>> failure I know *exactly* where I would start. The repair is
>>>>>> trivial, anyone with basic electronics knowledge and soldering
>>>>>> skill can fix it for a few dollars.
>>>>>
>>>>> Obviously the MOSFET and capacitor would need to be replaced, the
>>>>> capacitor with a higher working voltage item. R23 could probably
>>>>> just be soldered back in (after checking it) and the orange wire
>>>>> replaced.
>>>>>
>>>>> Then work from there, possibly being suspicious of the coil.
>>>>
>>>> A reasonable assumption however a Zener diode is prone to failure on
>>>> certain MSD distributors the symptom of which might be commonly
>>>> noted as an "erratic ignition stumble" prior to MOSFET failure. The
>>>> Zener diode has an important (and fairly typical, I'm sure you can
>>>> work out) role in this design and also must be replaced. The issue
>>>> is not of cheapness of components or "China" but of lousy design by
>>>> MSD.
>>>
>>> Knowing nothing about MSD distributors other than those 3 pictures,
>>> you may well be right.
>>>
>>
>> It a common fault. The Zener is used to regulate the voltage and when
>> it fails the rest follows as seen here.
>>
>> I expect Google to be pretty sluggish with the fraud busy Googling
>> what a Zener diode looks like. Maybe I should send him a few, then
>> he'll know :-)
>
> It's not what I'd expect to cause this problem, a failed zener would be
> very unlikely to cause the capacitor to explode.

You would if you understood the circuit. You don't think unregulated
supply voltage way above what is expected has consequences on a circuit
that switches a coil?

You said it yourself "Knowing nothing about MSD distributors other than
those 3 pictures, you may well be right."

I'm right and it's a typical failure.