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Electric Fuel Pump


Blackpack
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Hello, I am a first time Buick owner and new to this forum. I recently purchased a 1948 Buick Super and the previous owner installed a toggle switch under the dash, which powers an electric fuel pump. The mechanical fuel pump also seems to be hooked up. I have never owned a car with an alternate fuel pump and I'm not quite sure how to use it. I turn the electric pump on just prior to cranking the engine and it starts right up. The dealer I bought the car from told me once the car is running, to flip the toggle to off, but when I do that, the engine sputters and dies after a minute or so. Are cars equipped with electric fuel pumps supposed to run with the switch on at all times? If I leave the switch on, the car stays running, but I'm not sure if I'm pumping too much gas into the system by leaving it on. Any advice would be appreciated. Jay W

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Hello Jay,

I too am new to this game of electric plus mechanical fuel pump. I recently purchased a 53 ford with both mech and elect fuel pumps however, the elect fuel pump has a bypass around it for the mech fuel pump to pull gas through (after use of the elect fuel pump to "prime" the mech fuel pump). As it has been explained to me, on my flathead engine the mech fuel pump is located high on the engine and after prolonged no-use of the vehicle, the fuel settles to the level in the tank. This causes the mech fuel pump to loose prime so ONLY on start up I use the elect fuel pump to prime the fuel line and mech fuel pump, then after the engine starts I shut down the elect fuel pump and the mech fuel pump takes over (pulling fuel around the elect fuel pump through the "bypass"). If I were you, I would investigate to see if you have a bypass around your elect fuel pump and if so, it sounds like it may not be working properly. Most, if not all, bypasses have a check valve in the bypass line to allow the fuel to flow only toward the mech fuel pump from the tank. Yours may not be working properly. Hope this helps, good luck. Willie in Phoenix

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People generally fit electric pumps because the mechanical pump is at fault, in your case it seems the mechanical pump is not working at all (or has been un plumbed) based on the fact that the engine dies shortly after you turn the elec pump off.

Whilst the elec pump is obviously doing its job there are a couple of things to consider; whenever its powered on it will be pumping, unlike the mechanical pump which stops when the engine stops, so if you were to be unfortunate enough to have a smash and the engine stalled, and you had a ruptured fuel pipe the elec pump will still be pumping, not a pleasant thought. Electric pumps, unless they have a regulator fitted, will often be designed to pump at a higher pressure/flow rate than the mechanical pump and usually this results in carb flooding as the float/needle seat mechanism is unable to combat the higher pressure.

So ideally you might like to see if the mechanical pump can be resurrected and save yourself a lot of problems, failing that you might want to consider an impact/inertia switch to wire into the elec pump circuitry as well as ensuring you can somehow regulate the pump output.

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I have had electric pumps used for priming the carb before starting for 50 years (Buicks). It works well. There is no need for a bypass, a properly working mechanical pump will suck gas through the electric priming pump when the engine is running with no problem.

To me, it sounds like there is probably crud caught in one of the valves in the mechanical pump and they are not seating and thus the pump isn't pumping. The diaphragm is OK otherwise if it were bad, you'd have gas leaking out of the pump.

If it were me, I remove the mechanical fuel pump, take it apart and have a look at the check valves and see if they are OK. Clean if necessary. If you like, rebuild parts are available from Bobs Automobilia.

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Fuel pumps come in different operation styles. There are solenoid, carotor( gear driven), and rotary vane. I will assume the 48 Buick still has a 6 volt electrical system. So that eliminates the gear driven carator, since I am not aware of any manufacturer of any 6volt model. What type do you have ? The solenoid type look like a small fuel filter in brass. Carter, AC, and Airtex are the most popular makers. Then there is the trusty Rotary Vane usually by Carter. Go to the Carter electric fuel pump website. The RV has on intake port and an outtake port . Many owners put a bypass in line. Reason: mechanical pumps(original) flatly can not pull gas through Carotor pump... the electric pump must be running all the time. The rotary vane is way better, but like a Wankel engine the electric pump motor can stop in a blocked position and interrupt the suction of the Mech pump. Solenoid pumps are Free Flow and therefore the best for priming or delaying fuel starvation( pre vapor lock). Many reasons for the mech pump to require a "booster" : Worn parts in the pump , check valves or a worn cam lobe, are just a few. Gas cap must be a vented style. Pressure and suction tests will help locate the problem. I would temporarily remove the electric pump and see why the mech pump does not run the engine.

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Thanks to everyone for the great advice. I finally figured out that I need to leave the switch to the electric fuel pump on. It's really hard, if not impossible to start the car again after it's been shut off for a short time though. I Think I may take the mechanical pump off and replace or rebuild it. It would be nice to have a back up system

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Backpack, get the mechanical fuel pump repaired. If the pump is defective you may be pumping gas into the crankcase with the electric pump. Then once repaired, use the mechanical as the primary pump and the electric for priming the system for starting and to over come vapor locking.

(o{}o)

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I was in the same situation with my 1933 Graham, my Grandfather drove her for 20 years on the mechanical pump, so that is how she runs now. The only problem I had was getting the correct kit to rebuild the fuel pump, they need to be safe for the new fuels. The alcohol fuel eats the diaphragm if the material is not correct. Most of the old AC fuel pumps have a vent opening to the engine, if your diaphragm is leaking it will normally stop pumping gas, but with the electric fuel pump it will pump gas into your crank case, this will burn up your engine in no time. Good Luck!

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Well, the dealership that sold me the car just emailed the service history and if looks like they bypassed the mechanical pump with an electric pump with regulator. I still need to take the car to a mechanic tomorrow due to a severe shaking at take off and oil leaking from the transmission. Grrr

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