Alternator triggered electric fuel pump saftey measure failed; drama, dogs, troubleshooting

[Marktt]

I wired my electric fuel pump to operate on the alternator idiot light scheme assuring that unless my fan belt and alternator and idiot light sys are operating correctly no fuel would be made available to avoid burning up the motor and saftey recommendations.

My circuit included the primer option for start up.

Low and behold it came into play following a fan belt break likely caused by the combination of applying belt dressing just hours earlier and a momentarily stuck gas peddle (carpet mat caused) sending the motor to destruction if not for key off reaction. The combo of belt treatment and 6-7k maybe higher, engine winding for a mere moment fatigued belt, minutes later belts gone, my fuel pump relying therefrom did in fact stop working.

For entertainment and general FYI involving events, I'll add: Loosing power unexpectedly and the environment and reaction taken can result in terribly consequences; fortunately avoided but barely. The loss of fan belt, engine, was not bad. Traffic and momentum and lights operating allowed freeway exit but just moments earlier when traffic was heavy, I'm in fast lane and it's dark and remaining lane to right is ending forcing lane traffic to my lane, Logan, my lab/pit mix bumped his ass on my newly installed battery disconnect lever. No nothing, lights, emergency flashers, engine, all gone; uphill, no momentum to exit lane, stuck and waiting to be rear end creamed at any second. Dam lucky to have noticed t handle facing wrong direction, engaged and got the hell out of the situation.

Back to fuel pump disabled upon fan belt break. Unknown source of engine quit, I attempted restart and low and behold it started, fuel pump had reengaged. Got off the hwy shoulder, noticed alt idiot light on, pulled over and confirmed no fan belt.

The obvious questions arise; is my primmer circuit feature missing a diode, maybe 2, or wired incorrectly. Here's the schematic in use. Any suggestions appreciated.

P.S. For visual re: dog and batt disconnect lever: dune buggy, no passenger seat, caged for containment, lever at base of rear passenger bottom firewall. Logan's 110 lbs and a spaz.

[Dale M.]

Alternator and oil pressure scheme are pretty troublesome for most of us... Personally I would not use them...

What I see is there should be isolation diode in relay coil circuit from alternator... IF you are just bypassing contacts in relay to prime don't think you really need diode...

Real Solution... IF you had used this controller, you would not have lost pump power therefor no stall in traffic... And ALT light would still have come on with thrown belt... BUT it can not do much for dog butt interference...

http://revolutionelectronics.com/Fuel_Pump.html

Dale

[Marc]

Wired per Speedy Jim's diagram there should be no need for a diode, and I've never had a single failure of the safety circuit to work as intended.
I use the same setup on my trike (with a spring-return toggle switch rather than a pushbutton, just because that works better for me ergonomically). When it's been sitting a while and the fuel's evaporated from the carb I have to hold the bypass switch until started and warmed up enough to blip the throttle for the alternator to kick in.

If I allow the fuel tank to run dry and the engine quits, by leaving it in gear with the key on the relay stays closed, so the pump continues to run while waiting for fuel after I've switched to Reserve. If I declutch or go to Neutral so the engine stops, so does the pump until I use the bypass switch.

The scenario you report is somewhat muddled by the interjection of the dog/disconnect switch tale, but disregarding that all I can say is that if the pump quit when the belt broke, leading to you running out of gas, the circuit is working as intended and there's no way you should've been able to restart without using the bypass switch unless your relay takes an abnormally low voltage to close. The addition of a diode would have no effect other than the added (very slight) forward resistance. What type of relay are you using?

The fuel pump relay from a K-Jetronic car (say, an old FI Rabbit) works the same as the $63 aftermarket one that Dale provided a link to (needs a pulsing signal from the "tach"side of the coil before it'll stay closed for more than a second or two). You don't even have to use the bypass switch, although you can fill the carb up a lot faster that way than by turning the key on and off repeatedly. Easy to identify at the boneyard, they have an integral fuseholder on the end. They aren't exactly known as paragons of reliability, though (in my experience the Siemens brand is the worst) so if you rewire to use one of those I'd recommend carrying a spare, or at least a jumper wire for emergencies. https://images.duckduckgo.com/iu/?u=htt ... 33.jpg&f=1

[Marktt]

[The scenario you report is somewhat muddled by the interjection of the dog/disconnect switch tale, but disregarding that all I can say is that if the pump quit when the belt broke, leading to you running out of gas, the circuit is working as intended and there's no way you should've been able to restart without using the bypass switch unless your relay takes an abnormally low voltage to close. The addition of a diode would have no effect other than the added (very slight) forward resistance. What type of relay are you using?]

As expected pump shut down when belt broke. Barely off the highway/ sholder i turned it over and no go, my primer button is next to starter button and though why not, so pressing both, started up.

The relay is a run the mill 4 wire. All the wiring has been redone w/ all relays directly powered off power block, not sure that would affect disabled alternator charging/fuel pump engage. Could it possibly be an incorrect wattage bulb?