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MG TD TF 1500 - intermittent engine stoppage

I would appreciate any thoughts or suggestions on how to deal with an intermittent curse which plagues my 1250 MG TF. Simply put, the engine ocassionally dies without warning. It doesn't choke, gasp or make any noise related to fuel starvation. It suddenly dies as though the ignition were turned off. Once dead, it will not restart for about 30 seconds. During those 30 seconds the starter will turn over the engine with fine fervor but none of the cylinders fire. After about 30 seconds it will start and run as though nothing ever happened.

This problem only began after the engine was rebuilt (the result of a failed rod bearing). Before the rebuild, I replaced the generator with an alternator and added a petronix unit to the distributor. The ignition switch was just replaced this week but that did not solve the problem.

The car runs for long test drives without problem and then craps out on a short jaunt an hour later. In every instance to date, the engine has failed while travelling at relatively slow speeds, but that may just be coincidence (or my reluctance to face failure on the freeway). Weather, rain or moisture are not factors.

Any suggestions on how to diagnose this problem?
P. Hejmanowski

check out your coil. If it runs fine and just dies but will start after sitting a while it sounds like the coil is overheating. This could be a bad coil or a wire short causing the coil to overheat. A poor wire splice could be the villian. I had same problem with the 1955 Thunderbird . Replace fuel pump, points / condensor, coil and experienced the tow home 3 times only to have the car start right up once off the trailer 45 minutes later. I than installed a petronix ignition and discovered 3 splices in the wire that goes from dist to ignition. Replaced wire and no problem after that. Just a thought as i fully understand the frustration when the car stops on the highway. Mine cut off between 15 and 20 miles from the house each time.
Russ Little

also -- the Thunderbird is a 6 volt positve ground set up. My 1952 MGTD is a 12 volt positive ground so same electrical principle.
Russ Little

I think one of the easiest things to try would be to take out that petronix thingie, and put a new set of the good old reliable points back in,,, then take it for a drive,,,
Yes, it could be the coil as stated above,,,but I would think the coil would be more apt to overheat and quit during a long drive,,, not the short jaunt,,

maybe do a search in the archives about petronix failing,,,,

Besides the good advice above, have you changed the distributor rotor? Is the one you have black, brown, or red? If not red, get one of the red "Advanced Distributors" rotors from Moss. There is an epidemic of failed rotors out there. George
George Butz

Good point George, I forget about the rotor problems,,,


I vote for a defective rotor! Sounds very much like the problem I had with a bad rotor.
Bob Jeffers

If I remember right the red rotor I got with my Petronix had to be shaved down a bit. Had to put the bottom up against the side of my grinding wheel (ala Bud).
They may have solved this problem with the new ones.
Mort Resnicoff (50 TD-Mobius)

A few thoughts. Nevada? Hot Weather? Slow speeds?
Restarts after a short rest?
Could these clues lead to vapor lock?
Insulate carbs from heat?
GF Metz

First step is to determine whether it's fuel or spark that went away. Do a planned "failure" run. Pack a timing light with you. Pick a route that will allow you to pull off the road and do some short investigative work. When it dies, pull over and pop open the bonnet. Hook up your timing light and spin the engine over with the key on by manually manipulating the starter switch under the bonnet. Point the timing light to a dark spot under the bonnet. If you don't see any flashes then your electrical system is a fault. If you do see flashes of light but get no fire then you have other issues ..most likely fuel. Once you determine which has failed it will make the diagnosis much easier.
L E D LaVerne


It's good to hear from you again!!!!!!!!!!!!!!!!!

I am going to take a wild guess:
"Older" Lucas Sports Coil?

If "yes" start there ...took John Twist all of 3 seconds to swap mine out years ago and solve the problem.

Not sure about the newer ones, but yaers ago there were some bad ones...I had 2 of them in a row!
David Sheward

I will be surprised if it is the Petronix setup, as (knock on wood), I have never had one fail....
There is no mechanical contact in the unit, and induction is always present.....
I would NOT be surprised if it is a coil failure, but most likely is either a loose connection somewhere , or a bad rotor....(as previously mentioned).
Recheck your wiring for the Petronix, as one of the connections may be making intermittent contact....(or the wire may be broken inside the insulation).
Edward Wesson 52TD

when you say 'none of the cylinders fire', have you visually verified that you do NOT have any spark, or are you just stating that it not creating a combustion event and trying to start?

Big difference.

I had roughly the same problem. I had gas, at least I thought I did, I had spark but suspected bad condensors, bad coil, etc. So after $100 of replacement parts, I put in a larger $2 fuel filter and fixed all my problems. There was enough fine sediment coming from my tank to plug the small see through filter I had but it didn't look like it. After 15 minutes or so enough gas would get through to re-fill the bowls and it would start and run for a few blocks then, 'the sould of silence again'. Bigger filter solved all my problems. That was a 6 month ordeal.

In this case, it did not follow the old addage that 90% of carb problems are electrical, it truly was a fuel problem.
L Rutt

+1 for the rotor. Put a red one in anyway for piece of mind. If it is the bad Lucas style it will fail anyway. They look good, but do not work. I have had this same problem several times. Once was a rotor, once was a condenser and once was a plugged fuel cap (creating a vacuum in the fuel tank. I'd change the rotor and if it happens again I'd pop the gas cap to see if that fixes it.
D. Sander

Mort brings up something to check also: at one point, the Petronix collar would keep the rotor from fully seating, causing it to be crammed into the center contact of the cap and basically hogging out the plastic. Check for that with your old and new rotor also. George
George Butz

I want to thank everyone who weighed in on my problem. It really is a great help and I am very appreciative. There is a new coil and rotor in my immediate future.

P. Hejmanowski

Paul, see for the story about the pertronix-related rotor problem. The symptoms were very rough running, definitely not an immediate cessation of running. Your symptoms are awfully close to those of MGB owners whose fuel tank is not vented. The next time this happens to you pop your gas gap loose and give itb a try. Bud
Bud Krueger

paul, i'm a little late to this thread, but i'm going to jump in. most of the ideas here are worth considering..but laverne is right on the mark. before you can solve your problem you have to determine what the problem is. what you have provided is a symptom..the car dies without sputtering and restarts in 30 seconds. that is the symptom of your problem, not the problem.
in all problems you need to troubleshoot and gather data..right now you have several ideas that MAY lead to a solution...but you need to start troubleshooting to give the guys here something to work with.
do you have spark? if not find the fault.
as you are back-tracing your primary and secondary ignition circuits observe the primary circuit wire from the distributor to the coil. is the tach gear box on the back of the generator contacting the post on the distributor?

i will state with a high degree of confidence that it is not vapor lock. i have never heard of these engines vapor locking while running at speed. the only time i have ever heard of, or experienced vapor lock happens when a run has been made and a quick "stop at the store" allows temps to build under the hood.

i believe there is a very low probability of a fuel issue causing your troubles as fuel would have to be cut off to all cylinders simultaneously and then restored 30 seconds later...but without more data this is based on symptoms you have described on not on troubleshooting data.
the one thing i cannot express strongly enough is troubleshoot BEFORE you start throwing parts at your car. regards, tom
tom peterson

I have some ideas where I would look but not before I knew for sure if I had spark or not.
L E D LaVerne

I like the timing light to evaluate ignition- keep one at home and one at the shop for those emergency checks.

Rig up a voltmeter and observe your voltage. Do it and eliminate some of the guesswork- make sure your generator & regulator are charging. Points may fire until the battery is virtually dead, but I've had the Pertronix quit when voltage gets down just a bit below 12V even though there was plenty of amps left for the starter.

A discharged battery recuperates when the current quits so it may restart with a brief rest. Positive and negative ions align over the oppositely charged plates when it is discharging, and an intermission allows the electrolyte to homogenize a bit at the plates for that second wind.

Check the volts and then report back!

Here's an item I've had in my toolbox for over 40 years. You can tell a lot about the ignition system by the quality of the spark, especially after you get a picture in your head of what a good one looks like. You can install it and go for a ride. That's one advantage over a clamp-on timing light. The other is being able to tell if it's a good spark, or one that's just strong enough to make it run.

I didn't feel like walking to the garage and taking a picture. HF has them for less than $6. That's the one in the picture. It's probably typical HF quality but there's not much in it so not much to get wrong.

J E Carroll

J E Carroll,
That's an interesting little device. What would happen if you put one one each spark plug?
Mort Resnicoff (50 TD-Mobius)

I have the old "analog version" that you seperate the legs on ...marked for "good & bad".

David Sheward

Looks like the Tesla version of Gummby :-)
L E D LaVerne


They make a more modern version of your "gumby" that's semi sealed and graduated in approximate voltage. Yours is better than my method of increasing the gap 'til it jumps to me. Ouch!

The new engines that have a coil for each plug have some pretty hot coils, they really bite! Must be 40-50,000 volts.


There's no reason you couldn't buy 4 of them and have a little light show display. You can see a dead cylinder right away.

A coil that gets weak when hot is fairly obvious as well.

You radio guys can dust off the oscilloscope and see a good indication of what's going on. In my very early career some of the planes I worked on had an engine analyzer (oscilloscope) built right into the FE's panel. You could tell the bad plug or wire and even tell if the compression was low. It was sure helpful with 18 cylinder engines. Although I never was involved with R4360s I'm sure it was a necessity as 28 cylinders = 56 spark plugs.

J E Carroll

I've never seen one of those spark measurment tools that you posted a pic of,,, any idea where I can get one????


While I was doing a search for Davids spark measurement tool, I came across this,,,, A four pack of J. E. Carrolls device!!!!!!!!<yp=AllFixedPriceItemTypes&var=sbar

only $17.99 !!!!!!!!

I had a similar persistent and erratic problem with my '62 Corvair which the PO had modified by installing a Pertronix ignition. The problem was solved by down-modifying to the original point ignition system.
Corey Pedersen 1951 TD #7169

Steve ,
I'll look at the back of it when I get home (Sunday) and see if there is "maker info" on it.
Think I have had "Teslagumby" since the early 70's?
David Sheward

Steve ,
That's a good deal. I already ordered 4 from HF for $6.00 each.
Mort Resnicoff (50 TD-Mobius)

Duh ...gunson's Flashtest.
Remember now ...was part of a package years ago with the ColorTune.
David Sheward

The Pertronix units do fail! Usually, they don't come back to life, but those nice silicon covered wires do fail due to the wire strands breaking and you can't detect it by feeling the wires. It becomes an intermittant problem and goes away by just touching or moving a wire.
FIRST find out if it's a spark/ignition problem as noted above. You can hookup a cheap electronic Tach which will go to zero if/when your ign. fails. I'd change one part at a time as most electronic parts are non-returnable.
cj schmit

This thread was discussed between 20/02/2013 and 25/02/2013

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