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MG TD TF 1500 - Pertronix ignition unit TD

I installed Pertonix LU-146LS in MGTD supplied by Moss Europe. The result was:

1. Vehicle running evenly, idling at 800 rpm with point setup.

2. Installed pertronix strictly as per instructions-wires connected correctly, new rotor installed, all connections tight etc.

3. Coil resistance checked,3.6 ohms

4. Engine started promptly, ran smoothly on the throttle with car stationary but noted idle speed 500 rpm. ran engine for approx. 3-4 mins.

5. switched off engine checked all connections, started engine again, adjusted idle speed and timing. Engine started immediately, idled smoothly. Car not yet tested on road. Made sure ignition turned off.

6. following day, started engine, drove car out of workshop, within 100 metres began missing, then backfiring, managed to get it back into workshop (just) before it stopped

7. unable to restart, no spark to plugs.

8. checked all connections, no faults.

9. substituted coil (resistance checked 3.4 ohms) no difference.

10.Followed the test regime as per, found no fluctuation in the voltage reading (steps #5 and #6), concluded unit had failed.

11. removed Pertronix, reinstalled points setup, engine started promptly, idles at 800 rpm, performs as expected on the road.

Contacted supplier who supplied a replacement module.

1. Installed unit - had to slightly elongate fixing hole on unit to get adequate clearance between cam lobe and unit - clearance is 18 thou, had to sand down base of rotor button to reduce diameter to get clearance between rotor button and unit, securing screw wrong thread, substituted screw.

2. Engine started immediately, adjusted timing and idle speed(both minimal)

3. Took vehicle for test run, approx 12 kms, performed faultlessly

4. Two days later took vehicle for run(no other use since test run above), engine stopped after approx 6kms, engine stopped approx 10 times to get home, distance between each shutdown got progressively less.

5. Back in the workshop, all aspects of installation checked, no problems identified. Engine ran initially for approx 10 mins then stopped. Time between each restart and shutdown became progressively less culminating in engine not starting at all. Bypassed ignition switch and then ran lead directly from battery to bypass loom with no success.

6. Reinstalled points, no problem, cars runs perfectly

Everyone that has looked at the vehicle points to the pertronix unit, but this is the second unit. No problems have been identified with the wiring, electrical settings etc with the vehicle.

Any help greatly appreciated

Graeme Smith

G J Smith


I cannot help you but your summary is impressive! Chapeau!

Hope someone chimes in who can identify the cause of the problem.

JL Nederhoed TD3966

Graeme, last fall I installed an LU-146LS in place of my LU-146 just to learn about it. Had a similar issue with the distributor mounting plate and screw. Easily fixed. Had to create a set of interference-free ignition cables. The LU-146LS worked like a charm. Only briefly zipped up over 5,000 rpm.

A couple of questions -- Are you running non-hardwire cables? Is your unit an LU-146LSP12? (That's the one required for positive ground systems.) I haven'tb seen the installation directions for the LU-146LSP12 so I don't know about the wiring instructions. The positive ground version of the LU-146 required a change in wiring. Bud
Bud Krueger

I'd stick with the points!
I hate tow trucks...

cj schmit

Many thanks for the responses.

Bud, the pertronix unit is a LU-146LSP12. The wiring is pretty simple (connect positive coil terminal to earth, connect unit to ignition wire and coil).

I've got the standard copper strand HT leads to plugs and coil.

All very frustrating given that the TD ignition system is basically straightforward.

Even tried heat sink/transfer paste between unit and baseplate to no avail.

Chuck - your suggestionth might well be the outcome!

best wishes

G J Smith

Graeme, it's the ignition wires. I've worked this with someone else before. The circuitry in the LS module is quite different from the basic Igniter. It's possible that resistor, suppression, spark plugs might solve the problem, but I have my doubts. If you look at the Pertronix catalog you'll see a number of footnotes for the LU-146LS. One of them says: 79 Not for use with solid core spark plug wires.

Our threaded distributor caps are rather unique and I know of no vendor who sells suppression cables that can be used with them. I created a set from a set of modern cables through the use of an expensive crimper. Some have had custom cables made by vendors. I plan on doing a writeup about the LS units as soon as this snow disappears and I can get back on the road. That'll be about June at the rate we're going. Bud
Bud Krueger

I use LS Pertronix with no issues whatsoever. Metallic core and silicone like isolation in spark plug cables.


Jan Emil Kristoffersen

Graeme, if you'll send me your email address I'll be happy send you some more details of others' experience. Bud
Bud Krueger


Mine broke after 100km using solid core leads, got a replacement and a set of new leads but I am reluctant to fit it as I, like Chuck, don't like tow trucks.

B Bridgens

I had trouble after fitting an electronic unit - a DizzyTech, not Pertronix - which we initially thought was due to having copper cables. The engine was misfiring at higher RPMs. We eventually found that replacing the rotor was the cure.

Your problem is not the same, but it could be worth trying a new rotor.

D A Provan

I got this lead from Peter.
magnecore makes RFI & EMI Suppressed spark plug wires and will make a set for the TD with the proper fittings. I bought a set from them recently.
Mort 50 TD

The only problem that I have with going that route is the price tag. I believe it's on the order of $100. I'd love to see what the distributor cap end of the Magnecor cable looks like. After buying a $75 crimper, I find that I can make a set for about $25. Onset of winter held me up from doing the writeup about the Pertronix LS Igniter. Bud
Bud Krueger

Bud ,
Here is a picture of the wires with the other parts.

Mort 50 TD

Thanks, Mort. I'm puzzled by the number/color of wires. I take it that you have some other ignition. An LU 146LS should only have 2 wires. Any chance of getting a closeup of the distributor end that's covered by the nuts? Bud
Bud Krueger

Graeme & Bud, my set consisted of the Magnacore cable & the fittings for both the dizzy & the plugs. Cost less than $30 AUD. My local electrician crimped them for me after I'd cut them to the desired length & fitted the cable manager, original (slightly modified) plug caps & dizzy caps onto the leads. He charged me $20 AUD. All up about $40 US. Can be done & for way less than $100 US! Check my thread in the archive for the "how to". Cheers
Peter TD 5801
P Hehir

I agree with you, Peter. The $100 figure was their charge to a fellow BBS'er for a set. I can readily make a set for $20, not counting the cost of distributor cable nuts. (I seem to have acquired a bunch of them.) Bud
Bud Krueger

The wires you see are from the distributor that I purchased from 123Ignitions.

Mort 50 TD

+1 on points.

Sorry. I don't think Lucas liked 0's and 1's.
L Rutt

Thanks, Mort. Mystery solved. Bud
Bud Krueger

You might notice that the distributor also has a vacuum port. This is going to be interesting.
Mort 50 TD

I thought that's what I saw there. What model of distributor is it? Bud
Bud Krueger

Mort I had my original dizzy reconditioned & converted to the 123 system over in Holland & there are just 2 wires, one black & one red. I too was intrigued by your wires. I intend to cover both with white heat shrink & paint on the black trace to make the wiring appear more original looking. When I'm over at the car next I'll take a pic & post it. Cheers
Peter TD 5801
P Hehir

It is basically a Lucas DKY4 that has been modified.

My set up is for a supercharged engine. That may explain the difference.

I am using the diagram on the bottom for positive earth. It may be hard to see the 4th (bottom) wire that is yellow. This is run to a switch that grounds the yellow wire on demand. This changes the distributor to a second curve and can be done on the fly. In certain conditions(racing?) this comes in handy for running under different loads.

The advance and retard are now controlled by the RPM's and the vacuum in my supercharger manifold. That's between the impeller and the intake ports.

With all this winter weather I haven't had a chance to test it yet.

I hope the weatherman understands that it's only 1 week to Spring!

Mort 50 TD

That must be it Mort. My wiring for positive earth only shows the two dizzy wires. Hope the weather clears for you soon. I've been waiting for a week of low humidity weather for the past four months here in Sydney to touch up my bulkhead & repaint the front apron, fuel tank & scuttle. It's been nothing but rain, humidity & more rain. The way things are going, autumn will soon become winter here & it'll be too cold to paint acrylic lacquer in my backyard "paint shop"! Cheers
Peter TD 5801
P Hehir

Thanks to everyone who replied to my plea for help. I had a set of leads made up (cost $60Au, $11 postage) and now the car goes like a dream. Have been using it the past week with no trouble. To me it runs more smoothly, better pickup etc with the Pertronix and more importantly renewed my enthusiasm.

There is no doubt that finding the fix was only possible by getting onto the Enthusiasts website and then getting your advice. Otherwise I cant imagine solving the problem.

So many thanks for your interest and advice- I'm very grateful

G J Smith

This thread was discussed between 27/02/2015 and 18/03/2015

MG TD TF 1500 index

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