Fuel pump inertia switch

[Tom W]

Has anyone fitted a fuel pump inertia switch to their E-type? There doesn’t seem to be much reference to them on here, but I would have thought it were essential for anyone who’s converted to EFI and worthwhile for anyone running Webers and a high volume fuel pump.

My car has a Facet fuel pump, which has a far greater flow rate than the standard SU pump. I’ve already added a relay to the fuel pump circuit, though the Facet pump only needs a 3 amp fuse so the draw isn’t great anyway. I have an inertia switch, which I’m considering adding to the low current feed to the relay, so the switch doesn’t take the full fuel pump current. I’m also considering whether the inertia switch should also cut the ignition. Without, the engine would continue running until the float chambers are emptied. This is potentially an advantage if the switch were inadvertently activated, the car would still run long enough to pull over safely. However, inadvertent actuation shouldn’t happen if the switch is properly mounted. Loads of modern cars use them, and I’ve never had one trigger accidentally.

If you have a switch, where have you mounted it? I’m currently thinking that under the bonnet on the bulkhead is the best place. There are some unused fixings where the brake reservoirs would normally mount on a RHD car. I don’t want to drill any extra holes in the car, everything should be reversible.

I’m also thinking of wiring the redundant choke warning light to operate when the inertia switch is triggered.

All input gratefully received.

[angelw]

Hello Tom,
I've just supplied a Sensata Inertia switch to a client for fitting to an S3. The important thing regarding a mounting point is that it allows full transmission of the inertial to the switch. Accordingly, it needs to be rigid. The switch from Sensata needs to be mounted vertically to give 360deg impact triggering of the device. Your switch may, or may not have that requirement, but its worth investigating.

Regards,

Bill

[Tom W]

The switch I’ve bought is genuine MG Rover. No instructions supplied with this one, but yes, I believe it needs to be mounted vertically, and to a stiff structure. So no flimsy brackets, and not screwed in the centre of a large unsupported panel. Most OEM installations seem to be in the footwell area, but that doesn’t look possible on the E-type without some permanent modification.

[johnetype]

I do believe an inertia switch is a sensible addition. For me I debated including it in the ignition circuit as well as the fuel pump and decided not to partly because I felt the easiest place to fit the switch was alongside the fuel tank and spare wheel mounted - rigidly - to the bodywork there. Having the switch mounted there makes it easy to wire it into the pump and I'm reluctant to add any wiring to the ignition circuit that potentially could add unreliability.

For those who feel the comfort of doing something the way Jaguar did, then an inertia switch could be mounted in the passenger footwell and wired up as per Series 3 XJ6's.

My switch is a simple make/break device so using the choke indicator light to show it had been activated - ie turned off - would require a relay and diode. Again, for me I'd be happy just to listen out for the pump and if I can't hear the pump and I've had a crash I've probably got lots to worry about - or nothing

[christopher storey]

The only cars of this era that I had with inertia switches were the Triumph 2.5PIs, where the switches were mounted on the LH front of the bulkhead

[Tom W]

Thanks.

The switch I have is a 3 terminal switch, so it operates as a change over switch. I can use the 3rd terminal to feed a warning light, should the switch be operated inadvertently.

Whereabouts in the boot did you mount the switch? I guess with that option, you’re running the feed for the fuel pump through the switch, and not a relay. The boot is a good option as it keeps the switch clean and dry. That’s one reservation I have with the engine bay option, though the area I’m looking at seems to stay clean. The car gets used in all weathers, and rarely cleaned, so it’s a reasonable indication of which areas of the engine bay stay clean.

[johnetype]

I mounted the switch using an existing hole in the flange that runs across the car in front and between the petrol tank and spare wheel.

I did intend to relay my SU petrol pump but given the adequate thickness of my original loom white lead to the petrol pump and the relatively low consumption of the SU pump I considered the benefit mute and haven't done it yet.

[abowie]

I believe it needs to be mounted vertically, and to a stiff structure.

The one on my XJS race car is mounted on the driver's side A pillar so can be reached by the driver and is covered when the door is shut.

I think your idea is a good one, and I think including the ignition circuit in this is also good. You could run them both from a relay behind the centre console and control the relay with the switch on the low amperage side as you suggested.

I guess your only concern with including the ignition would be making sure this doesn't affect power steering if you have it.

[MarekH]

Dear Tom,
Check out how this is handled on the XJS.

On my car, it controls 12v power to the fuel pump relay winding. The return from the fuel pump relay winding is controlled by the ECU.

http://www.jag-lovers.org/snaps/snap_vi ... 1352157009

kind regards
Marek

[Tom W]

It looks like either option is suitable. I think my switch is the sort used on a Range Rover P38, where it interrupts the live feed to the fuel pump.

It probably comes down to where it’s easiest to mount, though cutting the engine as well as the fuel pump in the event of an accident does sound beneficial.

The A-post seems to be a common location for OEM fitment.