Years ago I had an interesting intermittent problem starting a MG TD that might
be of interest.
First, some definitions:
Engine Cranks - Starter rotates the engine (crankshaft) but the engine doesn't
start and run on its own.
Engine Starts - Starter rotates the engine AND the engine starts and runs on its
own.
Anyway, the engine always cranked but didn't always start. I finally realized
that the times it DID start, it started after I had released the starter knob
but before the engine had stopped rotating.
I checked the TD workshop manual and found that the car was missing a ground
strap between the engine and the frame. I installed the strap and had no
further problems starting the engine.
I surmised that without the ground strap between the engine and the frame, the
current path between the battery and the coil had sufficient resistance to
reduce the voltage at the coil to a point that I was not getting enough (any?)
spark at the sparkplugs while the battery was powering the starter. Once the
starter was no longer drawing current, enough voltage was available to cause
the sparkplugs to spark, and the engine to start if it was still rotating.
Interestingly, I didn't notice an improvement in the speed at which the starter
rotated the engine after I installed the strap.
Even with a ground strap in place, you could have the same problem if there
isn't good metal-to-metal contact between the strap and the engine and/or frame
(and therefore, low resistance).
Ed
|