using oil pressure switch to shut down engine, shuts power off to fuel pump Options

[Tom]

A recent thread got me to thinking. I understand having the power removed to the fuel pump would cause the engine to turn off on a fuel injected engine, but carbs, I think, would be a different matter. On the fuel injection engine when the fuel pump shuts down, the fuel pressure goes to zero very fast as there is no reservoir to keep pressure steady. With carbs, the engine would continue to run until the fuel level in the float bowl gets too low. Wondering how long that would be and would that be long enough for engine damage to occur?
Don't newer cars have several reasons for the fuel pump to shut off for safety reasons? Crash, low oil pressure, over temp???
Tom

[sportlicherFahrer]

If you're going for engine safety, instead of wiring it to the fuel pump on a carbed motor you could wire it to the ignition to cut spark. Wouldn't have to worry about running the engine till the float bowls are dry in that case... (IMG:style_emoticons/default/idea.gif)

[Mike Bellis]

I run an inertia switch, also known as an impact switch on my fuel pump.

With carbs, you would have to cut spark. Could be a PIA if you have low pressure at idle.

[02loftsmoor]

They've been doing that for years on class 5,6,7,8 trucks some drivers don't under stand "0" on the oil gauge and the Big red oil light is trying to tell you something.
what you have to watch for when taking off the oil pressure can drop, be sure your pressure switch is higher trip pressure than the lowest oil pressure drop. you can stall on take off Wes

[McMark]

I think it's dangerous to have an engine that shuts itself off unexpectedly. Your reasoning is sound, but this just isn't a good idea. Use the safety switch between your ears to make sure your engine stays safe. Add a loud buzzer to the light if you want, but don't cut power to the engine unexpectedly.

[02loftsmoor]

Been done for years, ford has a fuel cutoff most cars do, brake a fuel line in wreck, fuell will keep pumping, trucks have had it for over 30 years

I think it's dangerous to have an engine that shuts itself off unexpectedly. Your reasoning is sound, but this just isn't a good idea. Use the safety switch between your ears to make sure your engine stays safe. Add a loud buzzer to the light if you want, but don't cut power to the engine unexpectedly.

[McMark]

Been done for years, ford has a fuel cutoff most cars do, brake a fuel line in wreck, fuell will keep pumping, trucks have had it for over 30 years

I think it's dangerous to have an engine that shuts itself off unexpectedly. Your reasoning is sound, but this just isn't a good idea. Use the safety switch between your ears to make sure your engine stays safe. Add a loud buzzer to the light if you want, but don't cut power to the engine unexpectedly.

That's an inertia switch like Mike mentioned above. It's a COMPLETELY different setup. We're talking oil pressure and I've seen enough cars with the oil light coming on at various points during driving to know that you will cut power when you shouldn't. Do it. Prove me wrong. It's your car and I've shared my opinion.

[Mike Bellis]

In impact switch like this http://www.ebay.com/itm/1995-2001-Ford-Exp...r#ht_500wt_1047 is cheap ($25) insurance for dumping all your fuel in the event of an accident. With a carbureted car, with the fuel pump running all the time the ignition is turned on, this is a good investment. All modern EFI cars have this feature.

Shutting off the engine with low pressure is a double edge sword. on a T4 the pressure can be really low at warm idle. This may shut off the engine when not warranted. If you have 15psi at idle all the time, then a shut off at 4psi may be OK.

[02loftsmoor]

Already has been proven, been the the trucking for over 30years standered now,
$30,000 engine you want to protect it

Been done for years, ford has a fuel cutoff most cars do, brake a fuel line in wreck, fuell will keep pumping, trucks have had it for over 30 years

I think it's dangerous to have an engine that shuts itself off unexpectedly. Your reasoning is sound, but this just isn't a good idea. Use the safety switch between your ears to make sure your engine stays safe. Add a loud buzzer to the light if you want, but don't cut power to the engine unexpectedly.

That's an inertia switch like Mike mentioned above. It's a COMPLETELY different setup. We're talking oil pressure and I've seen enough cars with the oil light coming on at various points during driving to know that you will cut power when you shouldn't. Do it. Prove me wrong. It's your car and I've shared my opinion.

[02loftsmoor]

is the whole thing the sensor and switch?? or is there a remote impact sensor? it would be clean set up

[Mike Bellis]

Already has been proven, been the the trucking for over 30years standered now,
$30,000 engine you want to protect it

On a Diesel engine the internal pressures and forces are so great, a drop in oil pressure could be catastrophic. I install and maintain big diesel generators for a living. There are various switches and sensors to kill the engine. Most of the sensors kill the engine via fuel way before anything bad happens. My gensets cost $250k - $1M.

This is not a debate of weather it is a good idea or not. Only the application is in question. On a T4 engine the idle oil pressure is not high enough to be a reliable trigger for use with affordable pressure switches. You could buy a $300+ switch that would be sensitive enough but it's not practical. An oil pressure gauge and an aware driver is a better bet. Just turn the key. Oil pressure switches are great if your engine can maintain greater oil pressure at idle; Like a diesel. An Inertia switch is a better fuel cut off solution for an emergency situation.

[McMark]

Thanks for writing that more effectively than me, Mike. (IMG:style_emoticons/default/smiley_notworthy.gif) Exactly what I was trying to say.

[Tom]

I was not thinking of doing it to mine. The other thread just got me to thinking, if one would be doing this to protect the engine upon loss of oil pressure, running carbs would seem to be detrimental. Your answers seem to agree with my thoughts.
And I totally agree, loosing engine power at the wrong time could be very bad!
Thanks for the answers,
Tom

[02loftsmoor]

any way here is a link, the system does work, works in rollowver and so on. this is a old school system, why would it cut the power at the wrong time, or am i missing some thing

http://www.mechanicshub.com/index.php?opti...=15&lang=en

[ape914]

look at a VW water cooled vanagon my 1986 vanagon has an oil pressure warning system. it uses 2 pressure switches, (they trigger at different pressures something like 6 psi and 10 psi or so) the lower pressure switch will illuminate an idiot light anytime the pressure drops lower than the switch (like the system on the 914 does) here's the trick, the second switch will trigger and if and ONLY if the tach shows more than about 2000 rpm or so (ie.. your driving not sitting at idle) the light will illuminate AND a LOUD alarm will sound. that is a signal to turn off the motor ASAP.

becuase the second switch is wired with the tach speed sensor there is no danger of false alarms do to low engine rpm. Yes rather than sounding a loud alarm (or your horn) you could configure it to shut off your pump or kill the ignition, but the loud alarm should suffice to warn you to shut it down manually.


the circuitry for the low oil pressure warnign system is contained in the vanagons dash instrutment cluster, you might be able to pul one out of a vanagon at a wrecker and use it in the 914.

[ClayPerrine]

In the late 80s, Pontiac had a oil pressure triggered fuel cutoff on a lot of their cars. It was just a switch that screwed into the oil pressure galley and opened the fuel pump circuit when the pressure got too low. I remember replacing a lot of leaking switches for Fieros that came in on wreckers because they wouldn't run.

I just googled it, and the first entry was this: "87 fiero 2.8 oil pressure sender/fuel cutoff switch"

Personally, I wouldn't have one. I am smart enough to turn the engine off if the oil pressure goes away.

[edwin]

Not long ago I was out on a spirited drive and during a pretty fast corner the oil light flashed momentarily. I would hate to think of what would have happened there if the engine switched off mid corner