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MG MGB GT V8 Factory Originals Technical - Bosch Fuel Pump does not pump.
I am converting my V8 from Holley carb to Standard AFM fuel injection. My Bosch high pressure pump makes a whirring noise continuously but no fuel is being pumped. Currently i am just testing all the components before final assembly. The fuel pump is not yet connected to the computer. What should I look for. Thanks in advance.
The Bosch HP pump won’t suck and needs to be primed. Try to have the pump as low as possible and as near to the bottom of the tank as you can get it but it will still need to be primed. Easy with a UK tank without a breather, we can just blow into the fuel filler.
|Thanks Geoff. I will try that next, and yes the fuel tank is at least half full.|
This turned out a bit long, skip to the last parragraph if you don't want to know the whys and wherefores
Geoff is right, these high pressure pumps are a rotating "roller vane". They deliver pressure well but have very poor suction (they "suck at sucking" ho ho) This is made a whole lot worse because you need a filter which further impedes the flow. If the tiniest bit of debris gets drawn into these pumps they seize up and can't be fixed, so you must must have a filter, which also impedes the flow. I actually tried not having a filter and lasted long enough (half an hour)to need to join the RACV in a hurry. Need less to say there is no room anywhere around the fuel tank to locate anything let alone pumps plus filter (Springs, handbrake cable, exhaust all get in the way). All of this is made even more difficult by the fact that unlike water petrol has an extreamly high vapour pressure. About 90 odd KPa at 37.8 degrees C. In other words petrol is much more difficult to siphon than water so running your fuel line up and over the axle will not work particularly well. It does work, sort of, but in hot weather your pump will cavitate noisily. Also it is important that the pump have a continous supply of petrol because if it experiences momentary starvation (petrol slopping around the tank) your motor will conc out.
Weld anti surge baffels/subtank into the bottom of a new petrol tank and place the pump in the bottom of the tank with a filter on it. You will also need to have some sort of acess hatch, wireing in and out etc. This is a good solution and adopted by many modern cars, but expensive and difficult to do to an MGB and means you have a problem if you need to replace your tank in a hurry, as I did once (jack slipped!).
The better option for me was to- buy an additional supply/feeder pump. This pump can move large volumes quickly and more importantly has a reasonable suction. The feeder pump is made by Pierburg in germany and is called an Auto-suction vane cell pump. stock no. 12001. it can deliver 0.5 bar (and keep up with the main pump) when used as a primary pump. Pierburge stuff can be got at most fuel pump places. It cost $95 Australian (apply exchange rate to get an idea what it might cost localy).
Set it up as follows. To a standard tank (what you've probably already got), replace your Fuel guage level sender with a very late model MGB fuel level sender ($50). These have a fuel uptake line in it, This gives you an addittional petrol line from/to the tank. With fuel line, connect this to a large "soupcan size" cheap filter (Kmart $18) , which inturn connects to the Peirburge feeder roller vane pump, which in-turn connects to the bosh high pressure rollervane pump. This sends high pressure fuel off to the fuel rail on the engine and thence back to the old pick up point on the tank. The advantage to this is you can use a standard tank and the only addittional cost is the feeder pump, no welding new tank etc. Also this may be set up very quickly because it's all "off the shelf" parts. The feeder pump can suction petrol through the filter (which acts as the antisurge tank) up to half a meter above the fuel tank. I tried it. In other words you can put your two pumps plus filter in the boot, if you want. Eventualy I moved mine into a small box in that empty space behind the RHS wheel, under the RHS corner of the boot, Just to be tidy.
|Forgot to mention. Because of the high fuel vapour pressure you can't have any closed loops in the system. The fuel needs to return through the petrol tank to allow any vapour build up to exit the system. Via the existing petrol tank vent/charcol canister etc. Otherwise pressure builds up and will cause your pump to cavitate noisily, and the motor to run unevenly/stall. I know cause I foolishly tried variations on this until I caught on.|
This thread was discussed between 30/04/2006 and 01/05/2006
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