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MG TD TF 1500 - Today's puzzler

1951 MG TD XPAG engine electronic SU fuel pump.

Yesterday while driving the car it would randomly shut off. This happened after driving the car for about an hour with no problems. Once it stalled trying to start it would prove fruitless. But If I turned the ignition off and back on the car would start and run anywhere from 1 minute to five and then shut off again. If the car was in motion when the engine shut off turning the key off and on would allow the engine to restart by disengaging the clutch. The engine temp was a steady 80 degrees. Any advice or suggestions would be very welcome.

Tim
TD12524
TD26711
Timothy Burchfield

Sounds like something amiss with the ignition switch....bad wiring connection or faulty contacts inside the switch.
L E D LaVerne

Tim, it sounds as if your power is disappearing from the white wire(s) that power your fuel pump and coil. Loss from either one could result in that effect. I recall that you've done a bunch of wiring work while going solid state in your lighting. I'd suggest keeping your test light handy. The next time this happens (while the key is ON) check for power at a white wire from terminal A3 of the fusebox. If you don't have power there then LED's idea about the ignition switch is right on. If you have it at A3 you'll need to trace it to the fuel pump and ignition.

Nothing like tracing an intermittent electrical glitch. Good luck. Bud
Bud Krueger

LaVerne I plan on replacing the ignition switch in case that is the problem. Thanks.

Bud, on one occasion when the car died I left the ignition switch on and checked the fuel pump by depressing the ticklers on the fuel bowls. When the floats were depressed the fuel pump ticked over. What I didn't have when the car died was a volt meter to check the various wiring so I couldn't check the voltage to the coil. I will check the things you mentioned. Thanks

Tim
Timothy Burchfield

Tim, ticking over meant that there was power to the fuel pump. That strikes me as saying that your issue is loss of power to the ignition circuit. Which pertronix system are you using? Bud
Bud Krueger

Bud, yeah, that's what I trying to say, that the fuel pump still had current. The Petronix system is the lobe sensing type (I don't have the number in front of me). I contacted Petronix before posting this issue here and they said the module would work or fail. It wouldn't work intermittently. I'm going to replace the coil first (that is the easier job than the ignition switch) it does get very hot. But I don't really see how turning the ignition off and on could affect the coil's performance. The problem is that I had the same issue a couple of weeks ago and I just tightened all the wires going into the fuse block. The next time I drove the car I didn't have an issue. But yesterday it happened again. Nothing more fun than intermittent problems.

Tim
Timothy Burchfield

Think it is worth trying with a wire from the battery direct to the distributer and maybe also to the pump.
YS Strom

Over the weekend I was repairing the choke cable,(thats another, soon to be posted, story. As I was finishing up, I found a large brown wire hanging down under the dash. Referencing WSM, probably #33 main, feed from the battery to ammeter.
Crawling under the dash, again, the brass set screw that secures the wire to the ammeter had taken flight.

How long has this been missing? I have noticed erratic meter movement! Car never stopped though. It would not take much movement for a connection to be made or broken. Just the engine shaking would be enough.

You might check the tightness of that feed point. It controls everything on the dash.

Jim B.
JA Benjamin

I had exactly the same symptoms in my 1949 MG Y-Tourer about three years ago. A cold beer and studying the wiring diagram led me to suspect the ammeter, so I bypassed it and fixed the problem far from home.

It turned out to be a cracked solder joint inside the ammeter that had oxidised and the bumps in the road would sometimes break the contact. Turning the ignition off would allow the joint to cool - making good contact again, and off you go to find that special bump in the road and loss of ignition again.

These cars were not designed to last 70 years, 50 maybe, but not 70 !.

Good Luck

Tony
A L SLATTERY

When I had this problem it took me nearly a year to work out what was wrong. Replaced everything, coil, points, plug leads, the lot. Turned out to be a float chamber valve intermittently sticking shut.
So my advice is, if it sounds like a fuel problem, it probably is.
David
David Wardell

YS I'll give it a try.

Jim B. I will check everything. Thanks for giving me a starting point.

Tony, the ammeter appears to be operating Ok. When the car stops running the Ign warning light comes on immediately. If the ammeter was faulty wouldn't the light fail to illuminate? I'm starting to think I wasn't made to last 70 years either :-)

David, the cars shuts off as if the ignition key was put in the off position. i would think that if it was a fuel problem I would get some sputtering before the engine stopped. But at this point I'll chek everything.

Thanks gentlemen

Tim



Timothy Burchfield

I had a similar issue with my 67 B. I found it was a loose low tension wire going from the coil to the distributor.

My recommendation would be to clean and tighten connections for the regulator, coil and distributor and see if that fixes the problem. Check that the terminals are also tight to the wire.
Bruce Cunha

Some of the Moss ignition switches were reported to be intermittent. The switch didn't come from there, did it?
Lew Palmer

Tim if you find that the switch is the issue I still have a couple of original MRN and FA's with NOS Wilmot Breeden Union keys. See pic. Cheers
Peter TD 5801


P Hehir

There are 3 things fed from the ignition switch that are not fused, generator warning light, fuel pump and ignition.

At least two continue to work, generator warning light and fuel pump.

I would be looking at wires connecting to fuse block, probably near the A3 connection.

Unless it isn’t electrical, but a dead stop of the engine says yes it is electrical.

Peter
P G Gilvarry

Tim, I think that you're going to find the culprit in the ignition circuit wiring from terminal A3 through your Pertronix. The fact that your ignition light comes on says that the ignition switch is functioning. Bud
Bud Krueger

The ignition switch is original to the car but rebuilt. I've checked the wiring for loose connections. The lat time I had the issue I tightened all the wires to the fuse block and it seemed to go away. but I don't drive the car that much so it could be something lurking just waiting for the right conditions. It could be heat related. It seemed to happen after driving for awhile and the engine compartment getting very hot (I can tell by the furnace blast from the carpet next to the gearbox tunnel).

Pertronix tells me that the module either works or doesn't but I'll put the points back in to see if that is the problem. thanks everyone. I'll keep you advised of my progress.

Regards

Tim
Timothy Burchfield

I agree with bud. How about a temporary light attached to the 12V side of the coil, the one with the white wire.

If that light is on all 3 unfused circuits are live.

Appears the other 2 are OK.

maybe a new white wire from the A3 to the coil?

Peter
P G Gilvarry

Is your distributor clamp grounded to the generator mount bolt? If you have the 'floating' clamp, it must be as the distributor shaft will not maintain the ground. See my website under engine installation.

Warmly,
Dave
Dave Braun

First, thanks everyone for the advice and suggestions. Turns out it was the Pertronix module. I happen to have another one that I installed on the 53. So I switched them out and no more shut offs. I'm not sure Pertronix would have taken my word for it unless I had been able to compare the results with two units. But they didn't hesitate to agree to ship me another. Interestingly they had me cut the wires and send them a picture of the defective module. They didn't want me to return the defective one. I guess If I hadn't been able to compare the two modules they would have wanted the defective one back for testing. Again, thanks for the assistance.

Regards

Tim
Timothy Burchfield

This thread was discussed between 25/06/2018 and 03/07/2018

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