Collision Sensor (Fuel Switch)

[bullfist]

The ECU in the super-spec (appears to) pump fuel only when the engine is running. Do I need to add a collision sensor switch in case of impact?

 

These switches started to appear in cars when they started using fuel injection (i.e. the little switch in the cabin that would pop out in case of minor impact). But modern cars don't have them (I don't think) - I assume that the ECU cuts the fuel pump if the engine becomes stationary.

 

Should I fit one?

 

Thanks,

-steve

[fry61]

Got one fitted to Florin; it came in the box of XR3i bits that were fitted to change from carb. to injection. Fitted to fire wall & inspite of the best efforts of our pot-holed roads hasn't given a false trip --- yet.

[Longboarder]

The worry is to find yourself trapped in a crash with the engine still running and an open petrol pipe squirting petrol. Fit one in the cockpit where you can reach it so you can reset if it trips accidentally. Connect to supplies to both pumps LP and HP if you have them. Obviously only appropriate to electric fuel pumps.

 

Nigel

[Al Milton]

It's probably one of the best passive safety items you can fit (and with more than a little tap it can double as an immobiliser).

Easy to reset as well with the reset switch on top, as Nigel says fit it somewhere where it is easily reached.

 

Readily available on E-Bay, just search for fuel pump inertia switch.

[Guest stevenkirk]

My Superpsec is fitted with an inertia switch from Rover - i thought these were part of the kit ?

[knights_templar]

At the risk of the displeasure from the above posters, sorry, reasons given below.

 

I would not add a weak link into the system PROVIDED the ECU switches BOTH pumps.

 

why?

 

I have spent to much time explaining to customers why their pride and joy has just cut out on a sleeping policeman and is now blocking the high street,

 

where the damn thing is fitted and, in the case of Fiat, that they will have to remove Auntie Maud from the passenger seat while they grovel arround under it for the little red button.

 

have been told, many times, that their car, unlike all the other vehicles of that type, hasn't got one, I am wrong because they can't find it, usualy with some choice wording.

 

Then when they do find it, where I said it was, being told it is a stupid idea, they could have had an accident, they were stuck hours and missed little jonny's birthday party, they wan't compensation. etc etc

 

if they had read the manual in the first place?

 

please forgive my jaundest view. and I appreciate we know a little more about our cars than the general public.

 

As you say, all the manufacturers now use the ECU, probably they got the same complaints as the dealerships.

 

As for safty, as soon as the engine loses fuel pressure, it will stop anyway, switching off the pumps, yes there will be some spillage, but so would there be with a trip system if the fuel line was cut, its just it trips out even when there isn't. what if you hit a pot hole on a blind corner, switch trips, engine stops and the 38 tonner behind you can't stop?

 

yes extream I know, but there are always two sides

 

I like Al's idea of the imobiliser, but adding an unessecary weakness does seam pointless IMO

[Longboarder]

You risk no displeasure but we can disagree. You lines on Aunt Maude's ill informed nephew/niece in his/her Fiat are not really relevant to this post although I share your love of customer service.

It's debatable that it's a weak point. It's a safety feature. It comes with good points and bad points as do many safety features. If over sensitive it will be irritating and you can construct a scenario where it could be dangerous. However you can also construct scenarios where it could be a life saver. Any crash, including a rollover, where the engine is not stopped but the fuel return is disrupted the ECU will not stop the engine. Or if the supply pipe is partially cut it may supply enough fuel to keep the engine running and produce an inflammable aerosol. Similarly in a carbed car (this post is about an injected car) the fuel pipe may be cut or partially cut and the engine will run on the fuel in the carb bowls for a while and there may be no ECU to stop the pump. In these situations an inertia switch sounds like a good thing.

My full harness is irritating every time I struggle into it in Tesco's car park and rarely someone dies wearing a seatbelt who would have survived if they were thrown clear. But the evidence is hugely in favour of wearing one.

It's up to the builder to make an assessment. Is he/she prepared to risk the occasional false cut out? I also try not to crash in the first place but sprinting or trackdays increase the risk.

 

Nigel

[bullfist]

Thanks all for your answers.

No, I didn't have a collision sensor in my super-spec kit.

Have picked one up off ebay and will fit within easy reach of the cabin, and will see how it goes.

Will add a lamp in parallel with the sensor, so if sensor triggers, lamp lights.

[sTART TECHNICAL] Will use op-amp/comparator to sense, and drive lamp so effectively appears as high impedance, otherwise lamp in series with pump might drive pump [END TECHNICAL].

Did the same with LEDs in parallel with fuses - LED lit means blown fuse - very useful. But LEDs aren't very bright in daylight.

-Steve

[fry61]

There is also the clutch pedal "safety device" engine dies-- drop the clutch & look for a safe hidey-hole. Lots of "what ifs" but I feel sure most of us drive with "next move will be" when a "what if" should cross the path of our high powered eggshells.