QuestionHi Howard
I have a 1972 MG Midget 1275cc. Its starts relatively easily when cold but after running for about 20 minutes it starts to splutter and cuts out. It is then very difficult to get started again but sometimes will start. If not have to leave a while before I try and start and then it will start. The ignition coil is about 7 years old but only done about 1000 miles. is that most likely cause of issue?
Thanks a lot
Padraig
AnswerHi Padraig,
An ignition coil can be bad after 30 years or after 2 minutes so how old or how many miles on it is useless info.
Also symptoms can lead you to a section of a car for a problem but they are usually also useless.
Testing is the only way to diagnose a problem. There are only three items necessary for a engine to run so when an engine don't run or quits it is because one or more of the three is missing.
Compression, Fire and Fuel with conditions on each.
Compression will not usually come and go. So you can rule it out for now.
That only leaves Fire And Fuel. Testing must be done when the car is in a failed mode. Meaning you need to know if the engine lost Fire (Spark) or Fuel at the time of failure.
It is easy to test for fuel supply to the carburetors at the time of failure by putting a "T" fitting in the fuel line just at the carburetor that receives fuel from the fuel pump. Attach a long hose to the "T" and run it out from under the hood (bonnet) to a low pressure fuel gauge and put the gauge under a wiper arm so you can see it while driving. Be sure to put clamps at all joints.
If you don't have a fuel pressure gauge you can usually get a vacuum gauge that has a small section for testing fuel pressure. (not expensive) You need to see if you have form 1.5 PSI to 3 PSI at the time of failure.
Ignition can also fail after running 20 minutes so you also need to know if you are loosing Fire (spark) at the time of failure. When I get such a complaint I have to also SEE the failure and to do that all you need to do is to connect a timing light to the coil wire (not the plug wire like setting timing) Tape the trigger down and also put the timing light under a wiper arm so you can see it from the drivers seat. On a bright sunny day you may need to tape a piece of card board over the light so you can see the flash. The flash will be so fast as to look like a steady light since you are testing the coil wire. Any misfire (your sputter) will be seen as a blinking in the steady flash of the timing light.
These two tests will pin point to either fuel supply or primary ignition problems. Further tests will be needed after you run these two. Since they both can be done at the same time it will not take long to do.
let me know and I will tell you the next test.
Howard
