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55 Tony
03-09-2018, 06:29 AM
When wiring an electric fuel pump I've seen how some wire a bypass from the safety oil pressure switch to the starter wire so it pumps as it cranks. And I've seen many put a push button switch to prime it before starting it if it's been sitting a while. What seems more common and makes more sense to you?

chasracer
03-09-2018, 07:19 AM
A little more detail would help. Will the electric pump be the only pump in the system or will it be backing up an engine mounted pump? Beyond that, I think it depends on HOW you want to wire it up. Just operating off the normal ignition key or a separate switch for it? If the ignition switch, then yes picking up 12v from the Start connection on the solenoid would allow the pump to run whenever you are cranking, then shutting off when you release the switch. And until the engine lites and provides oil pressure to the safety switch, the pump would not run. If you are running it via separate switch then there's really no need for the momentary contact switch you mentioned. Simply flip it on, prime and turn it off if that's what you want to do with it. When the engine lites, you could then turn the pump back on. And a couple more tips. You didn't say which electric pump you were using but most electric pumps hate to be dead-headed. They will work and for a long time, but it puts more stress on them than having a return type system in place. So don't put an electric pump in dead-headed and expect it to last forever. The other thing is using a relay to power the pump. Whether it is operating off of the ignition switch or a toggle switch, a relay will help reduce the amperage load pulled across the switch contacts, this in turn will lengthen the life of the switch itself plus the pump will get full voltage and amperage allowing it to operate more efficiently.

55 Rescue Dog
03-09-2018, 07:58 AM
The oil pressure switch will close as soon as you start cranking it anyway, and turn on the pump relay. Assuming your mechanical pump is ok with the right stroke from the pump pushrod, and no other issues, how will the electric pump lower the boiling point of your fuel I'm wondering? The chrome carter style mechanical pump I used from summit said it didn't need a regulator, and it was putting out 9.5 psi, so I added a regulator to dial it back to 6 psi and it holds it steady at all RPM, no matter how hot the engine or ambient temp is. Plus it is pulling it through a filter ahead of the pump using 3/8 line from the tank.

55 Tony
03-09-2018, 01:32 PM
The electric pump will not change the boiling point of the fuel. It will vastly lower the temperature of the fuel as compared to the hot engine mounted pump. It will be mounted back at the tank where it is cool. I'll put a regulator somewhere BEFORE the hot engine bay and once in the engine bay, a line as short as possible to the carb so the fuel doesn't have time to get so hot. If I need to use a bypass I will use it, I already have it run. Although some pumps run easier when dead headed. Don't even ask about that one.

55 Rescue Dog
03-09-2018, 02:37 PM
Maybe at idle fuel could get hot enough to cause a problem, but at full power it is moving too fast to pick up much heat. An electric pump will get pretty hot too, which is why every car made now has them inconveniently mounted in the tank.

TrifiveRichard
03-09-2018, 02:44 PM
In my experience, wiring the electric fuel pump thru an oil pressure switch is done to shut off the pump in case of an accident where the ignition switch is still on but the engine is not running. An electric pump isn’t usually wired to the acc ignition switch terminal, but the on terminal, thus the pump is powered during cranking anyway.

55 Rescue Dog
03-09-2018, 03:36 PM
In my experience, wiring the electric fuel pump thru an oil pressure switch is done to shut off the pump in case of an accident where the ignition switch is still on but the engine is not running. An electric pump isn’t usually wired to the acc ignition switch terminal, but the on terminal, thus the pump is powered during cranking anyway.
In addition to that, some cars have a crash switch to shut down the whole electric system in a crash. I think Ron Francis Wiring sells a setup for that, and that's not a bad idea either.

55 Tony
03-09-2018, 04:18 PM
In my experience, wiring the electric fuel pump thru an oil pressure switch is done to shut off the pump in case of an accident where the ignition switch is still on but the engine is not running. An electric pump isn’t usually wired to the acc ignition switch terminal, but the on terminal, thus the pump is powered during cranking anyway.

That is exactly what I was talking about, maybe I worded it poorly? And I think TriR is saying the same thing. The accident kill switch sounds like a good idea, who knows if the engine would continue to run and have fuel pressure and keep pumping. The reason I asked about a primer switch/button is because if my car sits a week or two I can pump the throttle twice and it starts but then stalls right away. Then usually the next pump and crank it will keep running.

55 Rescue Dog
03-09-2018, 04:36 PM
That is exactly what I was talking about, maybe I worded it poorly? And I think TriR is saying the same thing. The accident kill switch sounds like a good idea, who knows if the engine would continue to run and have fuel pressure and keep pumping. The reason I asked about a primer switch/button is because if my car sits a week or two I can pump the throttle twice and it starts but then stalls right away. Then usually the next pump and crank it will keep running.
Anytime I don't drive any car daily for days, or months at a time, I just plan on a couple of false starts, which is the least of my worries. It just mean I need to drive it more. I just fired up a 1950 Chevy truck with a 235ci six in it that hasn't run for several years, and it started in 3 seconds!

Rick_L
03-09-2018, 04:55 PM
I'm not sure what's meant by "don't run an electric pump deadheaded". If the pump is making the desired pressure when the engine is running, it has the same load on it that it would if "deadheaded". Doesn't matter what the engine's fuel demand is. You need a pressure regulator and it will always regulate the pressure to what it's set at. Pumps also have a relief valve built in to protect against true deadheading. As an example, the trusty old Holley "blue" pump is used with a pressure regulator (actually it's a pressure reducing valve with no bypass). But the blue pump has a pressure relief valve built in it.

As for the safety switch, there's another setup you can consider. It's called a "rollover switch", if the car rolls it cuts power to the fuel pump. Some, maybe all, Fox body Mustangs had them. I'm sure many others too, but that's the one I know of.

If it was my car, I'd wire the fuel pump with a relay. The relay would be activated with the ignition switch in cranking and run positions. Using a relay minimizes the electrical load on the switch, and lets you run a 12-14 gauge wire for the pump from the battery to the relay and from the relay to the pump.

I would not run a "hybrid" system with both an electrical and a mechanical pump. Choose one, either a mechanical pump or an electric pump. Do the electric pump installation correctly, with gravity feed. Don't use the stock pickup for an electric pump, as electric pumps don't make much suction. An in tank pump would be the best way to do this for a street driven car, because most of the other solutions have plumbing hanging below the tank which is not good for the street, as it could get damaged (safety again). Don't use the drain fitting in a stock tank as it's only 1/8" pipe, not big enough for a BBC, or a healthy SBC.

On the other hand, there is nothing wrong with a properly operating mechanical pump which uses the stock type pickup. But Tony won't admit there's something wrong with his because he can't/won't find the problem and fix it.

Rick_L
03-09-2018, 04:56 PM
I'm not sure what's meant by "don't run an electric pump deadheaded". If the pump is making the desired pressure when the engine is running, it has the same load on it that it would if "deadheaded". Doesn't matter what the engine's fuel demand is. You need a pressure regulator and it will always regulate the pressure to what it's set at. Pumps also have a relief valve built in to protect against true deadheading. As an example, the trusty old Holley "blue" pump is used with a pressure regulator (actually it's a pressure reducing valve with no bypass). But the blue pump has a pressure relief valve built in it.

As for the safety switch, there's another setup you can consider. It's called a "rollover switch", if the car rolls it cuts power to the fuel pump. Some, maybe all, Fox body Mustangs had them. I'm sure many others too, but that's the one I know of.

If it was my car, I'd wire the fuel pump with a relay. The relay would be activated with the ignition switch in cranking and run positions. Using a relay minimizes the electrical load on the switch, and lets you run a 12-14 gauge wire for the pump from the battery to the relay and from the relay to the pump.

I would not run a "hybrid" system with both an electrical and a mechanical pump. Choose one, either a mechanical pump or an electric pump. Do the electric pump installation correctly, with gravity feed. Don't use the stock pickup for an electric pump, as electric pumps don't make much suction. An in tank pump would be the best way to do this for a street driven car, because most of the other solutions have plumbing hanging below the tank which is not good for the street, as it could get damaged (safety again). Don't use the drain fitting in a stock tank as it's only 1/8" pipe, not big enough for a BBC, or a healthy SBC.

On the other hand, there is nothing wrong with a properly operating mechanical pump which uses the stock type pickup. But Tony won't admit there's something wrong with his because he can't/won't find the problem and fix it.

chasracer
03-09-2018, 08:36 PM
It's actually rather simple and I believe one of the reasons that car manufacturers do not run their electric pumps "dead-headed". This does not have anything to do with whether the pressure is high, low or in-between. If we have a pressure port fuel regulator in the system, that regulator is constantly opening and closing as the engine uses fuel. During those closed periods, the pump is pushing fuel against the regulator that is basically going no where. This puts additional heat into the fuel pump and in turn there is some additional wear on the pump mechanism itself. Again, I have run pumps dead-headed in the past, they last a few years but that same pump put into a return system where there is less heat and work for the pump will last a hell of a lot longer. It can also reduce some load on the electrical system although that may be very marginal. We have used Holley, Barry Grant, Aeromotive and Magnafuel - they all eventually fail in a dead head situation. My preference is simply to provide a fuel "loop" from tank back to the tank, then using a bypass type regulator, pull off the fuel from this loop that my engine combination requires. I currently have an Aeromotive pump that is on it's 12th year in a loop system. Oh and one other minor detail, the fuel itself will also be just a bit cooler in the whole process.

55 Tony
03-10-2018, 04:46 AM
But Tony won't admit there's something wrong with his because he can't/won't find the problem and fix it.

Rick, you gave me a good LOL! :) Don't forget, there must have been something wrong with the previous pump also, it did the same thing.

Are you up to the $1000 challenge? Come on, I could use the money.

Rick_L
03-10-2018, 05:50 AM
No I want to be the judge, and I'll sell the tickets to the show too.

55 Tony
03-11-2018, 12:31 PM
No takers and I already took out the mechanical pump so forget selling tickets. I get the feeling that if this works no one will believe it. :(

chevynut
03-11-2018, 01:46 PM
Tony, after watching that video I posted I believe you ;). I never realized that gas could boil at such low temps. I still think it would have been interesting to see if the problem went away with the electric pump pushing gas to the mechanical pump....but in the video they say that won't solve the problem.

markm
03-12-2018, 07:02 AM
Hey Cnut did you see the part about avoiding corn gas.

55 Tony
03-12-2018, 07:18 AM
Hey Cnut did you see the part about avoiding corn gas.

I did. And I'll tell you that the butane in the gas has a far far greater impact on the boiling point then ethanol. But since I don't own a speed shop, you probably won't believe me.

chevynut
03-12-2018, 07:43 AM
Hey Cnut did you see the part about avoiding corn gas.

Only if you're still running a POS carburetor and a low pressure fuel pump. It works great with EFI that most cars use these days.

55 Rescue Dog
03-12-2018, 03:01 PM
My 2013 Tahoe police pursuit hauls ass on E-85. It's a good way to go on a high compression engine, when building a whole new fuel system setup on a hot rod. If I could do it all over on my Camaro LT-1, I would for sure go with a FI carb, and all the hardware setup to run on E-85. Just can't justify a couple grand to re-do all old school stuff that runs awesome on race gas blends, which is much cheaper in comparison.

55 Tony
03-29-2018, 06:02 AM
On the other hand, there is nothing wrong with a properly operating mechanical pump which uses the stock type pickup. But Tony won't admit there's something wrong with his because he can't/won't find the problem and fix it.

Hey Rick, I've been waiting for you to admit you were wrong and I was right. Or are you one of those who can't admit to their own mistakes? Do you also think the speed shop video that Cnut posted was staged too? Or can't you admit it again that you were wrong? It's a shame, you are an intelligent guy who knows a lot, but you are indeed wrong sometimes yet you can't admit it. And that goes for all the others who are in the same boat as Rick. Just say you were wrong. Trust me, it's enlightening. Who is man enough to admit it?