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MG MGB Technical - Petronix test

Is there a way to test a pertronix ignitor, off the car, to see if it is good/functional?
M.A. Barrera

This is a question best addressed to the manufacturer, which is in California. Please post their response.

Les
Les Bengtson

Do you have the instruction sheet that came in the box? I thought there was a way of bench testing the unit that was in the instructions. You should be able to download a set of those somewhere if you don't have them.
Mark J Michalak

I went on their site and have the install instruction, no mention of bench testing, just some obvious troubleshooting tips.

On the cars first day of driving, it suddenly quit. Its a '71 B roadster.

Fueling all checks out. No spark to plugs, coil resistance is right at 3 ohms. All the ignition is new, coil, 25d dizzy, Pertronix, cap and rotor.

I will call Pertronix tomorrow and post their response.

Mike
M.A. Barrera

Have you tried another rotor, seems some people are getting bad new rotors. You should be able to do some checking of the Pertronix installed on the car with a test lamp. Connect the clip lead of the test light to the negative coil terminal and the probe to the positive coil terminal. Crank the engine with starter and ignition on, the light should blink when the primary circuit is triggered by the pick-up.

Clifton
Clifton Gordon

You should just be able to turn the engine with the ignition on and the coil lead connected to a plug laying on the block, and measure the voltage changing on the coil +ve just like it would for points. That will prove the LT side, and if that is OK the plug should be sparking. That will also eliminate any problems with the cap or rotor. This won't be the case with all electronic ignition systems as some just give a pulse to the coil at the firing time and not a steady current lweading up to it, but you should stkll be able to see the pulse on a meter.

But the easiest and first test for any non-starter should always be clipping a timing light to the coil lead and each plug lead before you disturb anything. When cranking if you don't see flashing on the coil lead there is either an LT problem (check voltages then) or it is the coil. If it flashes on the coil lead but not the plug leads the cap and/or rotor are breaking down. If it flashes on those most lilely fuel, or could be leads or plugs.
Paul Hunt 2

Clifton, I will give that a try. So, if the light cycles off and on, the Pertronix is switching and is ok, right?
I am going to get a new rotor today and have the coil tested. It reads 3 ohms.

Mike
M.A. Barrera

I've had a couple of Pertonix units stop working where I noticed small splits in the rubber insulation on the wires. The splits were always located just away from the black box so I know the rotor didn't cut them.
willieL

Mike, It should prove the module is switching the coil on and off and the trigger is sending a signal to the module. That should be all it needs to work.
I haven't tried it on a Pertronix, I don't have one, my information comes from a book, "How to Diagnose and Repair Automotive Electrical Systems, by Tracy Martin". In addition pay close attention to what Paul Hunt said, Paul trys to keep me straight, seriously I have learned a lot from his comments.

Clifton
Clifton Gordon

Try putting a set of points and condenser back in it and see if the car runs then. If yes, then it's probably the Petronix.

Gregg Hanks
http://homepage.mac.com/racerx69/Menu6.html
73 MGB SC
63 MGB
69 MGC GT
70 E-Type 2+2


g hanks

Well I did the test as described by Pertronix, essentially the same as Clifton outlined. Unit checks out. So, it must be the coil. Got a new one today to install. Wish me luck.

Mike
M.A. Barrera

Mike, What ever came of your Pertronix? What was the end result?
Jeff Schlemmer

I've a 'Troubleshooting Guide for the Ignitor' which I got with an Aldon unit which I think is the same as Petronix, if anyone wants a copy I'll e-mail it. It requires a voltmeter to carry out the tests.
Ron
R. Algie

Guys, I have found on one occasion that when someone installed the Pertronix on one of our club members B the wires were not given enough slack inside the distributor to allow for the 'advance' movements and after a little time one of the wires broke inside the rubber wire cover.
Barc Cunningham

The Pertronix also needs the ground wire inside the distributor same as points. North American electronic distributors didn't have this ground wire as the trigger operates differently, so when adding a Pertronix, Ignitor or similar one must be added, and it needs to be the special very flexible wire or it also will fracture in a short time and give intermittent ignition.
Paul Hunt 2

I've been out of the loop for awhile, but I used to see GM HEI dizzys machined to fit MGBs. Is anyone still doing that? Doesn't look stock but my experence with HEI is all positive. Parts at any parts counter is also hard to beat.
J Schiessl

I *think* the 45DM4 MGB distributor used HEI anyway. Very reliable, and used in millions of cars in various packages, still available from Transpo http://www.transpo.de/Catalog/Browse.htm select Ignition Module, Delco, and it is the DM1906. Needs the magnetic pickup, and I've never heard of one of those failing either.
Paul Hunt 2

This thread was discussed between 25/09/2007 and 04/10/2007

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