Odd starting on my 3.2

911hillclimber · Saturday at 10:42 PM

My 73T has had this 3.2 in it since 1994 and it is faultless. It has never been apart, maintained to death over the years.

Over all those years I've got used to the way it starts and this 'sound' has never changed unless one of the batteries fails, which has happened twice, once about 10 years ago and second time a month ago.
On one battery the starting 'churn' is labloured, but the engine would fire and run a treat.
Every time.
Hot or cold.

I replaced the dead battery of the pair (about 10 years old) with an identical Bosche silver unit, same rating as the other good one, thus one battery is old, the other new.

Charged the car with my new charger until 'full'.
This was a few days ago.

Came to start the car this morning for a longish run to a local hillclimb.
Turn the key, press the start button ( a mod made about 3 years ago) and the engine churned over with some speed, far quicker than before, but the usual few seconds passed and 4 secs later the engine started, ran perfectly.

It has never delayed to start ever. I never touch the throttle when starting.

Starting from cold again to drive back from deepest Shropshire, the same quick turn-over and the delay to fire was slightly longer, about 5 sec. Ran perfectly.

The only thing to have changed is the battery replacement and the full charge.

I can't see why a fresh battery added, a full car charge (didn't take very long) would lead to a longer than usual time to fire.

I guess the car would not have max volts in the past, but that would make the delay worse?

The engine is about 140K miles, E5 fuel, stock DME Bosch controller.
1000 rpm tick over (as always), 180F engine temp fully warm and certainly on all 6.

Any thoughts?
Will start it again tomorrow to see if it delays again

73T 911

T911UK · Sunday at 8:14 AM

Might be worth "jumping" with a standard bigger battery to see how it reacts (with the 2 smaller ones disconnected)

Maybe you have improved the contacts on the battery/ground while changing them?

911hillclimber · Sunday at 9:17 AM

Thank you for the reply.
The contacts are given a simple wipe/rub with a scotch pad to remove any surface corrosion, but nothing more.

The system had been as fresh as this and as charged-up as this before and the starting 'sound' says the same.
When one of the batteries fails the cranking speed drops to about 50% of the full charged speed but this engine always has fired after a routine delay of about 2 secs, you just get used to this over so many years.

I'll start it again tomorrow with the car now charged by the alternator so normal condition and see if that changes anything.

The only thing changed is a new like-for-like battery and a full charge using my new charger.

Just as an aside, I bought recently some Hella wipers for the car from you and used them yesterday, they are so much better than the Bosch parts, they comform to the curves of the 911 screen so much better.

Motorhead · Sunday at 10:28 AM

I can’t explain what’s causing the issue Graham, but it’s odd that the engine is cranking faster with the new battery, so presumably more current is being drawn by the starter circuit and maybe starving the ignition temporarily? Other than that, perhaps the fuel supply system [pump; carbs] is slower to catch-up with the increased volume of air being drawn in?

Just shooting in the dark really!

Jeff

911hillclimber · Sunday at 12:46 PM

Thanks for the thoughts Jeff.

The 1973 911 had 2 x 12V batteries in parallel to run the car and start it. A few years later the cars had a bigger single battery.
I put the 3.2 engine in the car way back in 1994/5 to go faster on hillclimbs, which worked!

The engine then was a bit slow to churn over, so fitted a high torque starter which is still in the car.

It did make a 'bit' of a difference in cranking speed but the engine fired just the same way.

The initial cranking is only about 5 crank turns and it fires/runs on 6 perfectly. This is very similar to my Boxster.

I like this churn as it starts a bit of oil pressure before the fire.

The last 2 starts have been different, longer (5 secs) churn and then a fire, what I call the delay here. These two starts are after fitting the new second battery a few days ago.

I'm always suspicious when a normal sound/routine suddenly changes on a car, and in an early 911 you can hear EVERYTHING.

The car now should have max volts, max current so should be great, but now this delay. Odd!