Triumph Repair: 1976 Triumph Spitfire, fuel pressure gauge, intermittent failures

Question
Car starts and idles perfectly.Start driving and soon starts to sputter and tries to stall. Can keep running using clutch and 1st gear, soon roars back to life as though nothing happened and runs o.k. for short time then acts up again. Irregular can happen at any time.

Answer
Hi Tom,
Symptoms do not tell you what is wrong either in fuel or in ignition. So the only way to find out what is going wrong is to test. The testing must be done in the failed mode. Since this is not all the time you must run a couple of tests that we had to run on cars with intermittent failures like yours.

You will need a timing light and a fuel pressure gauge with a "T" fitting to put in the fuel line close to the carburetor. Put the "T" in and a long hose so you can run the line out from under the hood and place the gauge under a wiper arm so you can watch it when road testing the car. (Be sure to put clamps on all hose connections)

Drive the car until it acts up again and watch the fuel pressure at that time. You need to see from 1.5 to 3 PSI at all times until the engine is stopped. If you see a lowering of pressure just as it starts to act up, you should first check any fuel filter that has been installed then remove the fuel supply line from the fuel pump and lower it down below the level of the tank to see if you have a constant fuel flow from the tank. If you do have that and you have confirmed that the fuel filter is clear (if one is installed) and you seed below 1.5 PSI on the gauge then you need to replace the fuel pump.
If you didn't get a good flow from the tank line then you first need to check the venting of the tank and for trash in the tank or line.

If the fuel pressure is ok then you need to check the carburetor for trash and /or a float level problem.

If all that is ok put the timing light on the coil wire (not a plug wire) and tape the trigger down and place the light under a wiper so you can see the light flash while driving. Road test the car and watch for any flicker in the light as the car acts up. This only tells you that it is an ignition problem not what is wrong. If it is a ignition you would be best advised to locate a shop that has a scope to look at the whole ignition system or if you are skilled enough you can test each item in the ignition system to locate the problem.

Howard