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.

[wobbletop]

Thanks for the reply,

I looked online and MSD says it should work from 9-16V. I don't have the battery anymore (used as core when buying new battery) and I'd have to wait for it to discharge somehow to reproduce the problem.

I guess the old battery could have gone below 9V when cranking.

I'll assume that the old battery was the problem.

[Superhawk996]

Bad battery could easily go below 9V.

The other possibility is that it technically operates but with weak spark and depending on your mixture, it might not light.

One thing to be concerned with. Since it was running then started to stumble, I'd have your alternator checked out. Make sure it is putting out proper voltage and trying to keep the battery charged.

Bad battery on it's own could be a possibility (Optima's are a mixed bag for automotive in my opinion) but you need to have the vehicle charging system checked regardless - don't assume just the battery. Don't rely on the idiot light being off as a sign of alternator health.

AGM batteries can be a bit flaky. They don't like being deeply discharged, overcharged, and don't like heat. An AGM battery in a 914 engine compartment really isn't Optima(l) pun intended. I have several of them in motorcycles and my 1991 Miata used them successfully but the battery is mounted in the trunk away from engine heat and vibration. A 914 voltage regulator being what it is (an ancient electro-mechanical device), isn't ideal for controlling AGM charge current.

https://batteryuniversity.com/learn/article...t_glass_mat_agm

There are reasons why most major automotive OEM's haven't moved to AGM's in mass production and it's not just related to cost.

[914_teener]

Bad battery could easily go below 9V.

The other possibility is that it technically operates but with weak spark and depending on your mixture, it might not light.

One thing to be concerned with. Since it was running then started to stumble, I'd have your alternator checked out. Make sure it is putting out proper voltage and trying to keep the battery charged.

Bad battery on it's own could be a possibility (Optima's are a mixed bag for automotive in my opinion) but you need to have the vehicle charging system checked regardless - don't assume just the battery. Don't rely on the idiot light being off as a sign of alternator health.

AGM batteries can be a bit flaky. They don't like being deeply discharged, overcharged, and don't like heat. An AGM battery in a 914 engine compartment really isn't Optima(l) pun intended. I have several of them in motorcycles and my 1991 Miata used them successfully but the battery is mounted in the trunk away from engine heat and vibration. A 914 voltage regulator being what it is (an ancient electro-mechanical device), isn't ideal for controlling AGM charge current.

https://batteryuniversity.com/learn/article...t_glass_mat_agm

There are reasons why most major automotive OEM's haven't moved to AGM's in mass production and it's not just related to cost.

Nice post.

Yep the Cayman has an AGM and it works great. But, it is mounted in the frunk near the top where the ventilation is optima (yes also pun intended.)

I would not put an Optima in the rear engine compartment of a 914 just because of the voltage reg. and the engine heat. I'm sure the core would get up to 125 degrees, especially in parts of the Southwest. So, I kept my FLAPS acid battery there and made sure there was an acid mat below it and made sure the alternator was in good working order.

Yea so with respect to the OP, yes it is a good theory. Not sure what the conversion is 3.4?

[wobbletop]

It's a 3.0L six with carbs.

That battery owes me nothing... there were stickers on it to indicate (I think) when it was purchased and they only went up to '99. Old as dirt as I said. Also, I'm in southern Ontario, and it really doesn't get stupid hot here. I also have no rain tray.

I checked the voltage when idling with the old battery and it was 13.25V. Not the best (I thought it should be 14V at least) but adequate.

[Retroracer]

So I have a similar set up to the OP; 914/6 conversion with a red top Optima and an MSD ignition module (Streetfire). The original 914/4 relay board and regulator are used, with the battery relocated to the front trunk. Have had no issues with the setup.

As to the described symptoms: I'd check the voltage regulator operation. Overcharging (from a malfunctioning regulator) can cook/damage a battery pretty badly. A depleted or weak battery would struggle cranking the engine over - but that seemed OK?

Not sure if sustained high voltage (for example: broken voltage regulator, freeway driving) would damage the MSD enough to cause a misfire or self protect somehow?

Curious mix of symptoms, but would suggest checking charging and voltage regulation with the new battery in place.

RE: "I checked the voltage when idling with the old battery and it was 13.25V. Not the best (I thought it should be 14V at least) but adequate." So that indicates alternator is doing something - increase revs and check it does not climb beyond 14V?

- Tony

[porschetub]

So I have a similar set up to the OP; 914/6 conversion with a red top Optima and an MSD ignition module (Streetfire). The original 914/4 relay board and regulator are used, with the battery relocated to the front trunk. Have had no issues with the setup.

As to the described symptoms: I'd check the voltage regulator operation. Overcharging (from a malfunctioning regulator) can cook/damage a battery pretty badly. A depleted or weak battery would struggle cranking the engine over - but that seemed OK?

Not sure if sustained high voltage (for example: broken voltage regulator, freeway driving) would damage the MSD enough to cause a misfire or self protect somehow?

Curious mix of symptoms, but would suggest checking charging and voltage regulation with the new battery in place.

RE: "I checked the voltage when idling with the old battery and it was 13.25V. Not the best (I thought it should be 14V at least) but adequate." So that indicates alternator is doing something - increase revs and check it does not climb beyond 14V?

- Tony

AGM batteries are strange with charging,my 55amp 911 Bosch acts kind of weird with charging but is way better for my car as not started/driven as much as I would like (IMG:style_emoticons/default/sad.gif) .
I have a wet cell backup spare and it appears to charge as normal,buggered if I know.
Don't be put off buy your idle charge,it should however be above battery voltage if charging with a battery that needs it,14V is ok under rev's so your VR must be ok.
I run blue permatune box with matching $$$ transformer coil reason being its super reliable,went to go MSD and found a fairly high failure rate,heaps of used non functioning ones on ebay (IMG:style_emoticons/default/sad.gif) .
Good luck.