Impact switch

[JohnD]

I've advocated these, especially for injector applications, and pointed out many manufacturers use the same switch, which has to speak for its reliability, and explains why so many are on sale on eBay, used.   I've also advocated the three-terminal type, that will light up a warning  on the dash if it triggers.   The problem with ebay is that the switches are often sold without a connector.

Car Buillder Solutions are marketing a kit, of a new three-terminal switch, with connector.  See: 

John

(No connection with CBS, just a useful product, I think!)

[Alfredo]

I have always wondered if this is really needed, on a crash the engine will either shut off and the ecu won't send a signal for the fuel pump to run, or after the crash the engine will keep running and consuming the fuel, so no danger... I know they are there for a reason and the manufacturer will not spend in what is not needed, but is this the case of a regulatory issue? I would really want to know your opinion. 

Cheer

Alfredo 

[JohnD]

Um, Alfredo, 

Obviously, you crash in a way that will not rupture fuel lines.   Clever boy!

John

[PeteStupps]

6 hours ago, Alfredo said:

I have always wondered if this is really needed, on a crash the engine will either shut off and the ecu won't send a signal for the fuel pump to run, or after the crash the engine will keep running and consuming the fuel, so no danger... I know they are there for a reason and the manufacturer will not spend in what is not needed, but is this the case of a regulatory issue? I would really want to know your opinion. 

Cheer

Alfredo 

Is it common to have the ECU controlling the pump? I haven't got an ECU but I have got an electric pump, and ought to put an inertia switch in. However the car is currently held firmly in its own inertia

[rogerguzzi]

47 minutes ago, PeteStupps said:

Is it common to have the ECU controlling the pump?

Hello Pete

                 Yes on my Microsquirt it runs for 3 seconds then stops if the engine is not trying start but I still have cut off switch just in case?

Roger

[Nick Jones]

13 minutes ago, rogerguzzi said:

Yes on my Microsquirt it runs for 3 seconds then stops if the engine is not trying start but I still have cut off switch just in case?

This..... and if you have the car  on it's side or roof and still running, it's really much better/safer all round if it stops.  Inertia switches are simple and cheap - so why not?

[Escadrille Ecosse]

1 hour ago, Nick Jones said:

This..... and if you have the car  on it's side or roof and still running, it's really much better/safer all round if it stops.  Inertia switches are simple and cheap - so why not?

Yep. Any electric fuel pump should have one in my opinion

I have an original TR6 one in the Spitfire has the added benefit that you can manually trip it as an extra device to slow down the light finger brigade.

[rogerguzzi]

39 minutes ago, Escadrille Ecosse said:

I have an original TR6 one in the Spitfire has the added benefit that you can manually trip it as an extra device to slow down the light finger brigade

Hello all

             When I had the Huco fitted I had a push push off switch for that reason but the biggest problem most of the time I forgot to use it!!! (and I was younger then!)

Now thinking about it I can not remember if it is still in circuit on the EFI (Now I know I am getting old !) but then again who is going to steal a Spitfire that is not Konkers? (not the lads that do donuts etc!)

Roger 

ps how they do it in India! full safety gear!

[Escadrille Ecosse]

[ahebron]

Back in the 90s my Mk1 Lancia Delta HF Turbo had a similar switch that decided to work with out crashing.
Being Italian I suppose I was lucky it didnt rust out before the switch played up.
To keep driving I bypassed the switch and plugged the fuel pump into the cigarette lighter, just had to remember to unplug it when I turned the car off. 

[John I]

1 hour ago, ahebron said:

 plugged the fuel pump into the cigarette lighter, just had to remember to unplug it when I turned the car off. 

We’re you a smoker at that time?

[ahebron]

46 minutes ago, John I said:

We’re you a smoker at that time?

Never

[MilesA]

TR3A - Electric fuel pump - So CBS-type Intertia switch installed - No Brainer (still need to install fire wall).

Miles

[PeteStupps]

6 minutes ago, ahebron said:

Never

just as well - you'd have had to choose between lighting up or keeping the fuel pump running!

[PeteStupps]

Forgive my ignorance but where do people mount these? On the dash or in the engine bay? If they can trip spuriously I guess you'd want to be able to reset from the driver's seat

[Nick Jones]

2 hours ago, ahebron said:

To keep driving I bypassed the switch and plugged the fuel pump into the cigarette lighter, just had to remember to unplug it when I turned the car off. 

 Eeek!

9 minutes ago, PeteStupps said:

Forgive my ignorance but where do people mount these?

Usually on the bulkhead/firewall somewhere accessible. Spurious trips are rare. 
 

My Vitesse one is mounted on the passenger side a pillar up under the dash, so could be reset from inside. All the others (PI, GT6 and Spitty) are on the bulkhead under the bonnet. The only spurious trip was from the OE Lucas thing on the PI which probably had other issues (like it wasn’t very conductive even when set!), so it got swapped for a modern one.

[PeteStupps]

2 minutes ago, Nick Jones said:

Usually on the bulkhead/firewall somewhere accessible. Spurious trips are rare. 

Aha OK, thanks Nick. I was thinking they might trip if you hit a pot-hole or something, then you splutter to a halt and get flattened by a delivery van... 

[Gt64fun]

Advice is to fit to a rigid panel.

The bulkhead is probably the most rigid panel on our cars.

Ian

[Bumblebee]

All of mine have an inertia as well.  All bulkhead mounted although the one in the GT6 has a bypass switch on the dash as at the time I was (and still am  possibly) thinking about trying some hillclimbs in it ,and John pointed out if I had an off and tripped it I would then be stuck, so I wired a bypass switch in. As that switch is untouched and away from normal driving area you would have to actually think about it to use it.

[John I]

3 hours ago, PeteStupps said:

just as well - you'd have had to choose between lighting up or keeping the fuel pump running!

You beat me to it, exactly what I was thinking...........would be an interesting driving technique to get one lit.

[PaulAA]

Forgive the slight (but not irrelevant) thread drift... at the risk of stating the bleedin' obvious, the question of an inertia trip would only be relevant in the carb TR6, were the mechanical fuel pump to be replaced by an electric one.

Which is a good jumping-off point to seek opinions on replacing said mechanical pump.  I understand that a pump pushing around 2psi would be adequate for twin SUs, like the Facet Posi-Flo.  Question is, does it make sense?

Paul

[Nick Jones]

If you have a perfectly good mechanical pump and no issues with fuel vaporisation in hot weather..... why fix what is not broke?

However.... if you do have fuel vaporisation problems the pump is quite a likely source of the troubles and an increasingly frequent problem with the repro mechanical pumps is excessive fuel pressure as they are sprung for 5 psi or so for far eastern carbs.....

If wanting to go electric, Huco should also be on your list.

Inertia switch on your ignition circuit would still have some purpose even without an electric pump but most manage without.

[Escadrille Ecosse]

On 4/22/2021 at 12:22 PM, Bumblebee said:

All of mine have an inertia as well.  All bulkhead mounted although the one in the GT6 has a bypass switch on the dash as at the time I was (and still am  possibly) thinking about trying some hillclimbs in it ,and John pointed out if I had an off and tripped it I would then be stuck, so I wired a bypass switch in. As that switch is untouched and away from normal driving area you would have to actually think about it to use it.

I thought I was just as likely to incinerate myself doing a hillclimb which is why I put mine inside the car where I can reset it if it's ever needed

[PaulAA]

13 minutes ago, Nick Jones said:

If you have a perfectly good mechanical pump and no issues with fuel vaporisation in hot weather..... why fix what is not broke?

However.... if you do have fuel vaporisation problems the pump is quite a likely source of the troubles and an increasingly frequent problem with the repro mechanical pumps is excessive fuel pressure as they are sprung for 5 psi or so for far eastern carbs.....

If wanting to go electric, Huco should also be on your list.

Inertia switch on your ignition circuit would still have some purpose even without an electric pump but most manage without.

Thanks, Nick.

Pretty sure mine's original. But it does do the fuel vaporisation malarkey in hot weather. Howerever, I'd assumed that this was the result of under-pressurisation, rather than too much.

[PeterC]

5 hours ago, PaulAA said:

Thanks, Nick.

Pretty sure mine's original. But it does do the fuel vaporisation malarkey in hot weather. Howerever, I'd assumed that this was the result of under-pressurisation, rather than too much.

The original TR6 PI switches are now a liability, prone to killing the engine in normal driving. After the second such exciting event, I bypassed mine,but should really fit a replacement to kill the supply to the SU. So tks JOhn.

Peter