Triumph Repair: 1979 Triumph tr7

Question
Hi Jeff,

I have a 1979 Triumph TR7 with a stalling problem.  It was always ran great since I restored her 10 years ago; zero problems other than basic maintenance!  Now, consistently - after about 5-6 minutes of idle, the car shuts down.  It does not make a difference if the car is driving or idling.  After the car cools down it will start right back up, but die again after 5-6 minutes.  I am thinking crank sensor but not sure if these motors have one? I do not suspect a fuel problem as the car just shuts right down, no sputtering or shuddering. Thanks for any input you may have!

Answer
Hi Dan,

I'm not Jeff, but I will try to answer your question. Good thoughts that it is not a fuel problem due to the symptoms. And it does point toward ignition. However diagnosis should be done in order and in a specific manner.

All engines only require 3 items to run and they are Compression, Fire and Fuel. Testing must be done in that order too.

True it is unlikely Compression as it is very rare that Compression can come and go and return. So "Fire" (Ignition) should be tested next. A simple method to test for Ignition and Fuel at the same time is to spray "Starting Fluid" into the intake while trying to restart when it dies.

You shoould attempt to resatart while it is still hot and if it does not start, quickly spray starting fluid into the intake and if it starts but dies as soon as you stop spraying fluid into the intake, then it is for sure a fuel problem and not a ignition problem. If however,  it does not try to start on starting fluid then you have an ignition problem.

Quickly at that point you should remove the coil wire from the distributor and spin the engine over with the end of the coil wire close to any metal part of the engine to see if you have any spark. If you don't have spark quickly feel the coil as an over heated coil has the symptoms of dying when hot and then recovering when cooled off. The probelm is that most electronic ignition systems also have that same symptom.

Look at the distributor to see if it has a box mounted on the side with the vacuum retard unit mounted on it. If so, that is a Opus/Lucas system which is noted for a high failure rate. However, even if you hve the box it is unlikely you have the system still in use as most died more then once while still in warranty (one year). Now look inside the distributor and see if the wires from the box have been clipped off and a different electronic pick-up has been installed. There were several different aftermarket electronic ignition systems that took the place of the orginal Opus/Lucas system by installing the new pick-up in place of the old one but did not use the wires from the box on the side of the distributor.

Most aftermarket systems used a 6v coil as did the Opus/Lucas system. To use a 6v coil it required a resistor wire to drop the voltage. There was an additional ballast resistor used on the Opus/Lucas power for the box. This all made it confusing for mechanics who tried to install a replacement ignition system. Many ended up using the wrong wire to power the coil and thus applied full 12v to the 6v coil and that caused the coil to over heat and die. Some aftermarket units also used 6v for the unit but some used full 12v for the unit but all had to have some kind of resistor for the 6v coil.

First look at the system in the distributor to see what system you have. Then look at the coil to confirm that it is still a 6v coil. Now put the (+) test lead of a volt meter on the (+) side of the coil and ground the (-) test lead. Then remove all the wires off of the (-) side of the coil and turn "On" the ignition (not start).  At that point your volt meter should read 12v. Now connect a test lead from the (-) terminal of the coil and just touch the other end of that test lead to ground and read the volt meter. It should read about 6v. If it reads high, like 11v or 12v then they have connected the wrong wires to the coil.

It is highly unlikely that you still have the Opus/Lucas system in operation as they had so many failures.

At this point you most likely have either the wrong voltage applied to your coil or you have a coil that is dying or a control unit that is dying or has the wrong voltage applied to it. This is just my guess from your symptom. Even though symptoms should never be used to diagnose a problem. Only testing should be used and always in order.

Let me know,

Howard