On 2/11/2021 9:44 pm, Clocky wrote:
> 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.
>
Since a capacitor in that position would be rated to at least several
hundred volts, how is a zener failure in a 12v system going to kill it?