3.2 911 engine: bit odd stating?

[911hillclimber]

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

[911hillclimber]

I'm hoping this extra bit of info will stimulate some interest in this problem.


This morning, 4 days after the last run, came to start the garaged car.

Fast turn-over, NO fire. (after 5 secs).
Switched off and repeated the start, turn over the same but ticked the accelerator pedal and it fired as clean as it ever has.

Drove 35 miles to Shelsley Walsh hillclimb (to watch) and got back to the cooled down car 3 hours later to drive home.
Same result as above.

So the delay has become much worse.

Got home no probs and decided to disconnect the new battery by removing the earth strap from battery to chassis.

The other battery is 12.94V and is 2 years old.
1 hour later and started the car.

Turn over as quick and the engine fired as it has before over the last 30 years!

The battery I removed is at 10.4V after 2 weeks sitting under the bench.

So, I have no idea why getting the system to the best level does this to the firing.

Next step is to fire the engine tomorrow with the new battery disconnected and see what happens.
If that all works, then swap the older battery to the new one and see what happens.

As stated before, the two good batteries are the same spec, same manufacturer, just 2 years apart.

[PeterK]

Just idle ramblings while sitting the other side of the world Graham, but I would check that the ECU is fully powered during crank. You’ve got a separate starter switch, but is the ECU awake.

Other than that, I’d probably be looking at fuel or physical things, not just the size of my electrons now.
Is the delayed start just more noticeable now that the starter spins more quickly with the new battery
Does the 3.2 have a check valve in the fuel line ? (that might have gone bad concurrently with the battery change)
Is the (ECU) fuel pump priming - could you rig a fuel pressure gauge to check initial pressure
Is there any wiring that could be disturbed, especially fuel pump wiring, while you’re playing with the battery (not sure I can remember which one you replaced)
Peter

[911hillclimber]

Thank you for your distant thoughts Peter!
I will explore a few things today.
When I changed the duff battery (the one on the bench loosing charge slowly disconnected from anything) I added a simple charger connection across the older battery that came with the new charger. The new charger simply plugs into the battery system to charge.
However, can't see why that would change things.
Nothing else has been disturbed at all, and nothing changed for 30 years.

Others on other Porsche forums think it is the new battery, the only thing changed!

More details this evening to ponder over a beer.

ps: still have your cam tool safe and sound. John not too sure yet what he is going to do with his cam chains/guides.

[911hillclimber]

However…

got a plug out, rested against the engine and wife pressed the starter button.

No spark….

wiggled the key in the ignition switch, and it fired!

Now have the ignition switch out and stripped, but looks perfect inside. It is the original 1973 switch.

will reassemble and see if all the position contact correctly turning the key, then back in the car and see if it is reliable.

If not, then will check the starter button and wires.

I installed a starter button a few years ago as an anti thief device.

[911hillclimber]

hate wires!

switch back together and into the car.

starter button ( a momentary type) checked for continuity, but can be a bit iffy. Will replace with a decent motorsport one.

All back together, both batteries connected and it started on the button, but not every time, but much better than 24 hours ago.

Must be the ignition switch, as the button only engages the starter motor which works 100%.

New ignition switch is £100, so not too bad even if getting it out/ in the dash is a pain!

[911hillclimber]

No start this morning, engine just turns over, no fire.
So, with some difficulty, ordered a new ignition switch.
Finger's crossed.

On Impact Bumpers a member there has had a similar issue, cured with a new switch.

[jwhillracer]

Hi Graham, just a thought, do you have an FIA cut-out switch on the car from its competition days?
The ignition cut-out side can play up after a while, especially if it has been scuttle mounted and out in the weather.

JW

[911hillclimber]

Jonathan:
Yest it has from when I did the PCGB Speed Championship way way back.
With the clock out I did look at the connections which looked good, but of course not the internals.
Good call though, and worth a poke about, thank you.
I need a bit of support right now!

So far;

Not sure just where I am with this problem.

The new ignition switch arrived from Design911 24 hours after ordering it!



Put it on, car turns over as ever, no firing.

Sigh....

Checked the sparks were there at one plug.

Initially no spark...but then a spark, and then it fired.

Let it run for a few mins to clear it's throat, turned off and it is now cooling down.

Will re-start again later and see what happens.



Thus, we have a new switch (the inside of the original old one looked perfect) and at worse the starting is intermittent, at best it works.



If it is intermittent, what would be the next step?

I've disconnected and reconnected the crank sensors (to clean the contacts) and likewise the car-to-engine multipin plug.



Any suggestions please?

[jwhillracer]

Jonathan:
Yest it has from when I did the PCGB Speed Championship way way back.
With the clock out I did look at the connections which looked good, but of course not the internals.
Good call though, and worth a poke about, thank you.
I need a bit of support right now!

On the bottom of the master switch are 2 pairs of spade connectors.
One pair should be connected to a large resistor to dump the alternator output when the engine is cut, the other pair cut the supply to your ignition to ensure the engine stops. It's worth connecting those two cables, bypassing the switch just to check that you haven't a fault there.
We used to have to replace the cut-out regularly when it was mounted on the scuttle, as the contacts corroded. Since we moved it inside (mounted in the clock space on the dash) we haven't had a problem.

Hope that helps

JW

[911hillclimber]

It is my focus for this afternoon!
I have no resistor and haven't for 20+ years.
I tried the cut-out with the ignition on (red light on on the dash) and it kills the ign light every time.

What gets me is that until I replaced the one duff battery for a like spec new Bosch one everything was good, zero probs.

Since fitting the new battery this has all happened.

After the switch I'm going to put the duff battery on the car a with the 2 year old one and see what that does!

What a flippin' faff!

[jwhillracer]

It is my focus for this afternoon!
I have no resistor and haven't for 20+ years.
I tried the cut-out with the ignition on (red light on on the dash) and it kills the ign light every time.

Careful that you don't damage the alternator or regulator without the resistor in circuit.

Don't assume that the contacts are OK because the light comes on, they may be good enough to light a little bulb, but too dirty/corroded to power your ignition.

JW

[911hillclimber]

Good point.
Too fed-up with it today, will try pulling the isolator switch out or just get a new one.

Keep on going back to it was perfect before changing the one battery!

Another 'feature now is the oil pressure gauge shows MAX pressure (off the scale) at tick over or any rpm.
When you kill the engine the needle drops to Zero immediately.

However, when running and the gauge showing MAX if I pull the wire off the top of the sensor the reading stays at MAX. despite it being disconnected....

I have seen this before quite a few years ago but it sorted itself out.

Whilst running the charging volts are 13.1V on both batteries at tick over.

[hot66]

you did tighten the battery connectors when you replaced it ?

[Nine One One]

If the oil pressure is showing MAX all the time, it is self earthing somewhere..............that could be the cause of your problems if you have a dodgy earth. Have had one car, where the main earth on the inner wing was rusty as anything behind the nut. Cleaning all that away and the ring connectors back to bare metal cured a lot of issues?