Ignition fault finding... help!

[db]

Can anyone tell me how to test my ignition? I can't find any info online, probably as it's an older ignition

It's a Mallory Streetfire IV (similar to MSD) with Mallory ignition retard unit.

What voltage should go to the dissy?
What voltage should go to the coil?

Looking at the dissy, I assume I should see a few ohms as it's a small coil?

Earths are all good, wiring is all good (assuming I've wired it correctly, it was running perfectly until it wasn't...)

With the retard unit connected, I get 9v to the dissy. With it disconnected, I get 0.6v. I don't know which (if either) is right!
Either way I don't get a spark

[Pete]

I take it if you disconnect the Dizzy and with all the power on if you short the wires that would go to the Dizzy you don't get a spark?

I had this recently (in the fire up lane at the Pod of all places) and it turned out to be an intermittent MSD Billet Dizzy fault, not the first place you would look....

[db]

Not tried that Pete. I'll give it a go ta

[Pete]

Stick a spark plug to ground on the coil and short the wires out - at least that is the test on an MSD, the alternative is to take the Dizzy out and spin it but that does not rule out a Dizzy fault. I am not familiar with the Mallory set up but I assume it is hall effect.

[db]

Yes Hall effect mate. Cheers

[ANTON]

DB do yourself a favor and disconnect the rev counter wire and try start the car. I have had this a lot lately on three different cars. The Rev counter has a earth fault and is earths out the coil.

[Pete]

That is a good suggestion, I would also disconnect the retard unit and do the the testing with the most basic installation. You can then "add" components one at a time until the fault re-appears.

[db]

Ooo thanks Anton, I'll check that out.

[Dave999]

Yes Hall effect mate. Cheers

your wiring diagram shows a magnetic reluctor dizzy

you can check

hall effect:- the bit that spins with the dizzy shaft has 8 magnets in it
and the pickup is a silicon/germanium ceramic sandwich coated in plastic with 2 wires

reluctor/magnetic pickup as per a chrylser eletcronic dizzy has a spikey star in the middle which is just soft iron it has no magnetic field until it is near a magnet.... the only magnet in the system is the centre of the pickup coil. not the spinning bit.


your coil will show 9 volts at the + if it is off and less if it is on
and that will depend on the position of the trigger unless you ignition has an OFF if rpm is lower than 200 rpm or some such

you don't need the retard unit to run the car.

set timing to start the car and try without the retard.


to test your pickup


Hall effect

set multimeter to measure ohms

connect for very short period to the 2 wires to the pickup
wave a magnet near it (try North south and south north orientation)

if the resistance changes dramatically

it works

but get it disconnected because a ohm meter is pushing 9 volts through your all effect pickup continuously

magnetic reluctor

there is no risk with this test. the only electricity generated is by the pickup coil itself

connect multi-meter to both wires and set to mini volts DC

spin the dizzy by hand off the car as fast as you can your meter should +_+_+_

set it to ac and you should measure a small millivolt Voltage which gets bigger the faster you turn.


if your ignition is a ballast resistor ignition
your coil should have a primary resistance of 1.5 to 3 ohms

if you have a sports coil for ballast resistor ignition it will be 1.2 to 1.3

if you have a 12 volt coil and no ballast

3 ohms standard

1.8 would be the sports coil

anything in the 0.5 to 1 ohm range is a HEI style coil or coil designed for an electronic ignition that expects to pump 4-7 amps through into the coil

not the 2-3 amps all other examples above would flow.

Give Mallory coils I have seen tend to be ballast resistor coils

i'll sugest its going to have a resistance higher than 1 ohm


if its in the 1000s of ohms range its busted

the secondary (measure between output pin and case) should be in the 5-10Kohm range. I think

dave

[db]

Thanks Dave, I've clearly misunderstood what a Hall effect unit is!
I'll check your figures out of interest, it would be good to know how the various bits should measure for future diagnosis.

I just got it fired up with the new MSD so it was definitely the Mallory box at fault. I'd love to know why it just suddenly died.

[db]

Ok, I have some of it worked out...

The coil is a Mallory Promaster. Primary 0.6 ohm, so that makes it the right type. Secondary is 180k ohm, a bit more than you thought.

Distributor is a Mopar electronic with the spikey star. 276 ohms across it and yes it flickers +-+-+- if I wiggle one blade of the star across the pickup.

[Dave999]

sounds like you are all good

I bet you can fix your Mallory if its old with discrete components

if it doesn't whine or buzz the bit that charges up the capacitor/ coil shenanigans inside isn't getting power (fuse links) or the switching trasnistors are knacked



if its new it will be surface mount components on a 2 or 3 layer board and nothing but the man who designed it is going to be fixing it

I have had success with old MSD but I can't work out what is up with the new ones, I still have one of Duncan's making me feel guilty every time I see it. I'm sure Mallory swapped from American ladies at a soldering station making them to production line in china making them like MSD have done

Mind I might be able to now as I have just purchased some reading glasses Boots finest

I had not realised how bad my close up sight had got, having been hawk eye, read the whole chart, all rows, its trademark and copyright notice all my life reach nearly 45 and it all goes down the pan

suddenly I need longer arms to read the menu in the curry house


fix technique

start at power in (with it powered off)
set meter to resistance
fuse wire should have none
resistors should have some and not look burned
capacitors should rise slowly as they charge, the bigger they are the faster the initial rise but the longer they take to stop if you get no indication swap the leads round.
diodes massive resistance one way next to nout the other
transistors is just like 2 diodes in some unholy clinch, base to collector and base to emitter works like 2 diodes 1 facing 1 way the other facing the other way.

power it UP

trace the voltage in across components

capacitors should not have burned bits or be bulging
anything with a burnt rusty patch round it needs swapping
anything that melted the glue that held it down needs swapping
anything showing damage from being hit by a big spark needs swapping and if it sparked to the case file the rough patch down

on a device that powers up but doesn't do what it should do.......

this sounds stupid but works

lick finger and put a small damp patch on the surface of the top of each chip based component
you need to get a view on how hot is too hot...does it smell funny does it hurt when I touch it

any that evaporate really quick are not necessarily busted but should be noted because something is stuffing too much into it or sucking too much out.
any that don't evaporate when their similar neighbours do are not powered up due to a fault with support components or are busted

sometimes works, sometimes doesn't, just depends how bloody minded you are and how much time you can commit when just getting a new one is often a more pleasurable experience


Maplins here we come

or indeed boots the chemists for glasses. transistor numbers are hard to read


Dave

[Dave999]

The coil is a Mallory Promaster. Primary 0.6 ohm, so that makes it the right type. Secondary is 180k ohm, a bit more than you thought.

yeah it was a guess damn you , you found me out its all lies you know..... but BIG...i.e much bigger than primary.... not enough and you get a very short spark or you arc across the leads or cross fire.

it would just go BLAT and screw something up

remember the magnetic field from you coil spreads out an infinite distance into space when charged, the lower the primary resistance the faster it does this.
The lower the secondary resistance the faster (up to a point) that magnetic field collapses. fast changing field = higher voltage and more current for shorter period

Too high and it never makes a spark before the next one is needed. too low and you take chunks out of the contacts in the dizzy cap.

gist of it is that its finely balanced for best results.

Dave

[db]

Awesome Dave. I wish you'd taught me in college, I might have grasped how a doll's eye switchboard works instead of being left sobbing in a corner waiting for the pub to open.
It's an older one so I'm definitely having it apart. It's riveted in the corners but nowt a careful drilling can't sort out.

I already have the replacement by the way - I got an MSD Streetfire and it seems to work fine.
I've only run it for a minute as the timing is about 10* out! I picked up a new timing gun today as mine was bust so I'll tackle that tomorrow.

The one thing that's defeating me is the retard. Again it's an old Mallory unit and I can't find enough info to confidently connect it up to the MSD. Especially as I'd only wired it up to the Mallory ignition box recently and I'm paranoid it may have killed it somehow. Or I may have wired it up wrong...
Do you think that could have been the cause Dave?

[Dave999]

retard boxes tend to monitor rpm like a tacho does

and when the RPM fits between 2 set points it switches in a delay usually based on a capacitor resistor network i.e 400-800 use this capacitor and resistor combo 800-1200 use the next one with a smaller capacitor

smaller capacitors charge faster hence the time it retards for is shorter


its basically a case of getting the retard box wireing diagram and having go.

it may only work with Mallory stuff


dave