Potential problematic mechanical fuel pump

[manoa matt]

For the last 7 years I've had a mechanical fuel pump on my daily driver with no problems. IIRC its a BCD brand pump, however I can't recall where I purchased it. The pump is constructed of three main housing components, a base, intermediate section, and a top cap. The top cap is held down with a single bolt with a 10mm Philips/hex head. On one occasion in the past I experienced fuel pump issues as the pump was not pulling gas from the tank. I looked and it was wet around the top section. further investigation revealed the top hold down bolt was loose. If its loose, it breaks the vacumn, the pump sucks air and not gasoline.

I also have an electric fuel pump in the trunk wired to a switch in the foot well to prime the system after sitting for a while. It also helps in the hot climate during short stops to prevent/help vapor lock. Additionally it can come in handy if the mechanical pump were ever to fail, or I need to drain the tank.

This morning I went to drive the car to work after it had been sitting about a week. I flipped the switch to prime the carb and after the electric fuel pump quieted down I heard a dripping noise near the engine bay. Sure enough that screw worked loose and fuel was pouring out of the mechanical pump at the top cap. I quickly flipped off the switch and tried to start the car. It started with the tiny amount of fuel that was in the carb float bowl but sputtered out soon after. With it still loose it could not create a good seal and the car would not start. I tightened down the bolt, checked that it was not leaking and was on my way.

If anyone has this particular style of mechanical fuel pump, you should check the tightness of the top bolt periodically, or if you experience fuel starvation.

Here is a picture of the pump in place: http://www.flickr.com/photos/71782262@N ... hotostream

[Europa]

Matt, I applaud you for posting with such detail. I have a FI Spider, but I appreciate this post alerting other Spider owners with mechanical pumps.

[sptcoupe]

Just a quick thought. It seems you have it backwards. Just use the electrical pump as your primary and you will never have to prime the carbs again, for the same reason you use the electrical to prime the carb now. No need for extra switches, etc.

Use the mechanical as your back up. Leave it on the car with the hose attached at both inlet and outlet. If your electrical fails, it takes seconds to attach the hose on your mechanical to the carb inlet and you are on the way. I did this for years when electrical pumps were not as relaible as they are nowadays. Saved my bacon twice. But I haven't had an electrical pump failure in years, but nowadays I just run with the elecrical for more consistent fuel delivery and never have to think about priming the carb. Just get a decent electrical pump with an inexpensive in-line regulator and go with that.

[manoa matt]

I find the mechanical pumps more reliable than the electrical pumps, at least the solenoid/diaphragm "cube" style which have a high rate of failure.

One of my original intentions was to have an electric fuel pump. Wiring it how I wanted it to operate is another issue. You either wire it so runs constantly with the key on which is very dangerous in the event of a crash. Or you wire it like the factory did to the 76 model years. Grounded via the oil pressure light switch with a relay in the circuit. If the fuel pump is grounded via the oil pressure light switch it will not prime the carb(s) as you will need to crank the engine several times to build pressure before the pump activates.

I had an idea of wiring in the pump to the seat belt delay switch. In that instance, when you turn the key to the on position, the pump would run for a few seconds and shut off if the car was not started. I let the smoke out of the wires a few times trying to wire it up like that and decided to quit while I was ahead before the wiring harness was toast.

When I do install a 2L with dual carbs I'll likely switch to a Carter brand rotary vane type electric pump with a Filter king fuel filter/pressure regulator and wired the way I'd like it to be. Until then I'm happy with my current setup.

Actually, the mechanical pump in question would not be potentially dangerous without the addition of the electric fuel pump as I have added. With only a mechanical pump, if the top cap is loose, gas will not spill out.

[vandor]

Hi,

Have you tried using Locktite on the fuel pump bolt?

>...the electrical pumps, at least the solenoid/diaphragm "cube" style which have a high rate of failure.

Let me add that the CHEAP electric pumps have a high failure rate. I went through 3 of them on two years.
But I switched to a Facet (made in USA) pump ~5 years ago and have not had an issue since.

[manoa matt]

I agree with your comments Csaba. I applaud you and Ramzi for sourcing the OEM Savara brand mechanical fuel pumps. Those are the best mechanical pumps for our cars. I know of an original one still going strong on a friends car after 30+ years of use.

I don't see my setup being in use much longer as I've recently freed up some time to start building a 2L street motor.