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Triumph Repair/no-starting issue - 75 TR6...coil?

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QUESTION: Hi Howard,

The car was running well one day and then about a week later went to start and it'll turn over, but not start. Faint attempt at firing, but not close to enough effort to start. I changed the wires, cap, condenser, points, plugs within the last few years but have done very little driving.

I tested the coil...6,500 ohms on the secondary winding, but couldn't get a consistent reading on the primary - it kept fluctuating wildly without settling on a number. I've heard it's rarely the coil, but I'm not clear what a "bad" reading would be for the primary winding.

Cheers,
-Cam

ANSWER: Hi Cam,

I learned working in dealerships that when I had a car that would not start I had to use a procedure in diagnosing the problem. My procedure was a 100% fix rate on many different brands of cars over a period of several decades.

There are only three systems that can make a car not start and run with conditions on each system. You must determine which system has failed before looking for a specific part in that system. The 3 systems are Compression, Fire and Fuel. They MUST be tested in the correct order too.

First is Compression. You can not skip this because it was ok yesterday or an hour ago or ten minutes ago. You need to see from 125 PSI to 170 PSI with little difference between cylinders.
(throttle open) If it don't pass this test it is a waste of time looking at Fire or Fuel.

Second is Fire (ignition). We could look at the whole ignition system in one glance with a scope. But most people don't have access to a scope, but there are other ways to test the ignition system. First remove all 6 plugs and place each plug on it's wire and lay each plug on a metal part of the engine.

Here is a rough preliminary test of the ignition system using no tools except the plug wrench you used to remove the plugs.

Place your thumb over #1 plug hole and have someone spin the engine over while you watch the plugs fire (not in bright sun light). As the engine spins it will blow your thumb off of the plug hole with a "Pop" sound. The spark plug will make a "Click" sound as it sparks. The spark should be thick as a pencil lead and blue in color. The "Pop" will appear to have caused the "Click". If you have a "Pop-Click" or a "Click-Pop" the timing may be off far enough not to start. If the "Pop" and the "Click" are at the same time it doesn't mean the timing is correct but does mean it is close enough to start and run.

If you have a thin hair size spark and it is orange or yellow in color it is an indication you have a weak spark and it may not run.

If you have the first two tests correct then and only then can you look at fuel.
Fuel system is very easy to test. Just spray starter fluid into the intake when trying to start the engine. If it starts and dies but will keep running if you keep spraying then you for sure have a fuel problem and further fuel tests must be run.

If you spray starter fluid into the intake and it does not start then you skipped one or both of the first two tests.

Let me know which system has failed and I will give you the next tests.

Howard





---------- FOLLOW-UP ----------

QUESTION: Thanks for the quick response, Howard. I should have mentioned that I pulled the fuel lines at the carbs and they were spurting fuel pretty well. I also pulled 3 plugs (1, 6, definitely and maybe 4). 1 and 6 had faint yellow spark and the other had no spark.

I'll pull all 6 and run the compression/spark test and report back.

Cheers,
-Cam

ANSWER: OK, let me know the results of all the tests.

Howard

---------- FOLLOW-UP ----------

QUESTION: Hi Howard - finally got to run these tests...the car's in a different city so progress is slow to say the least.

Compression: every cylinder tested between 125 and 140 psi.

Timing: the pop/click were simultaneous across all plugs/holes with one exception. One didn't have a spark (#4 I think), so I just had the pop.

Spark: the sparks were all light yellow and as mentioned, one did not spark.

I went on to fuel and sprayed some quick start. It sounded more promising, but still didn't start (that said, it's a pretty old can of quick start...not sure if that's an issue).

...based on this, I'm guessing spark is my problem?

Thanks again,
-Cam

Answer
Hi Cam,

The sequence of testing must always be the same. Compression (yours was ok) Fire (yours was not ok so it is a waste of time proceeding to fuel until "Fire" is correct.

You need to correct the faulty ignition system before even looking at Fuel.

End result you should see a thick spark (as thick as the lead in a pencil) and it must be blue in color. Orange or yellow and thin like a hair are two clear indications of a weak spark and even though you can see a weak spark out of the engine the spark will not even jump under compression. The color is an indicator of the power of a spark. It does need to be inside and or in the shade as sunlight distorts the color and it makes it more difficult to ID.

On a scope the old British cars only had from 25,000v to 35,000v from their coils. The contact points in the distributor only break the contact of the coil and then the coil's field transfers to a secondary coil inside the coil and that is the winding that is connected to the coil wire going to the distributor cap and the rotor inside turns to point to a peg in the cap that is attached to the spark plug wire. So the "not so hot" 25K v to 35K volts has no place to go except down the coil wire to the cap and then to the rotor and then it has to jump a gap to the peg and then it has to run down a plug wire to the spark plug and inside the spark plug to a another gap before it can get home to a ground (the head).

If you have a lot of resistance in the contact points (or a faulty electronic ignition unit), the coil doesn't get a good field charged up. (if the coil is good) but even if it does get charged up and there is a lot of resistance in all the travels it needs to go to get to the plug and if the plug is got carbon on it the charge is wasted by going down the carbon and very little is left to jump a gap.

The coil can be tested with an ohm meter as can the coil wire and plug wires (roughly 5k ohms per foot of wire.)(if it is resistor wire) You need to look up the specs on the coil for your car but it will be close to 3.5 ohms for a 12v coil or close to 1.5 ohm on a 6v coil. If you have a 6v coil you will have a ballast resistor at the coil and none if it is a 12v coil. This ohms reading is on the primary of the coil (across the two connectors)

After you get a good spark and only when you get a good spark you can then look at fuel.

Let me know,

Howard

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Howard M. Fitzcharles III

Expertise

Triumph TR-4 up & Spitfire, and Engine theory

Experience

Dealership line mechanic on MG, Triumph, Jaguar for 15 years, Instructor in commercial mechanics school 2 yr. Product information manager for piston and valve manufacture, Instructor & hotline answer man for import car parts importer 15 yrs.

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Associate member SAE EAA member

Publications
Import Car magazine

Education/Credentials
ASE Master Auto with L-1 certification up to 2000

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