Confirm my theory for fixing a non-starter?, rocket surgery Options

[wobbletop]

I thought I'd create a new thread instead of fouling the CanAm Mosport thread...

My 914 6 conversion died just as I got to Mosport. I could feel it stumble slightly on the last few km to the track. It's about an hour and 40 minutes of highway driving to get to the track. Temp gauge got up to about 212 and stayed.

Car stalled at the gate to the track and wouldn't start again.

Car would turn over but not catch and start. I could smell fuel from the exhaust and there was fuel in the clear fuel filter. Car would turn over, although it started getting slower and slower with the amount of cranking I was doing.

I figured I wasn't getting spark but it was tough to test in the parking lot, far from home.
Someone suggested a coil so Mark kindly brought one with him to the track, but swapping it out did nothing.

It also has a MSD6AL ignition and someone also said they go bad frequently.

Anyway, I towed it back home, pushed it into the garage, put the charger on the battery and left it for the next day.

Next day, with the charger still on it, the thing fired up right away. Turned it off, took the charger off, and it still fired up right away.

Checked the age of the battery (Optima red top) and it's older than the hills. Decided to swap the battery for a new one. The battery was old... terminal lugs were weak, and I could hear the battery bubbling internally.

So... the question is... is it just the battery?

At the side of the road, I figured if it could still crank the engine over, that the battery still should be able to provide spark, so I didn't consider just getting a new battery from CAA.

I'm thinking that maybe the MSD6AL requires more voltage to produce a spark, than the starter needs to turn over the engine, and this is why it would turn over but not start.

Can anyone with more experience with the MSD chime in and confirm this?

Should I get rid of the MSD? I like having it as it provides a soft rev limit for the engine.

Thanks for you attention,
Walter

[Superhawk996]

All electronic modules have a voltage threshold below which, they will not operate.

Typically, around 10.5 volts but varies widely across the industry dependent on who's module. Within automotive industry safety critical modules are required to maintain some level of basic function down to around 9 volts but will have dramatically reduced performance.

When you are cranking a car the starter looks almost like a dead short.

A dead short across a voltage source (the battery) will tend to drop the voltage source to ground potential (0 volts) while simultaneously flowing a lot of current.

However, the starter motor isn't a complete 0 ohm short. A good battery has the ability to flow the necessary starter motor current AND keep the voltage up around 11.5 - 12 volts simultaneously.

An Optima battery is a AGM battery. If you hear bubbling, that battery is cooked.

In your case, with the weak battery it is flowing enough current to move the starter motor but most likely the voltage has dropped below the module threshold and isn't functioning. Maybe take a quick look on MSD documentation and/or call them. They should be able to tell you the minimum voltage requirement.

You could check the voltage input to the module, while cranking. My bet is the module voltage is down below 10 volts, therefore no spark.