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Discussion Starter · #1 ·
I am trying to convert from fuel injection to carb. Will the current Bosch fuel pump handle the carb? Since I won't be using the return fuel line anymore, should I cap the line or leave it open for venting?
 

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70's Opeler, back 4 more!
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My understanding of the FI system is the Fuel pump pressurizes the line from the pump to the Injectors. The injection systems have the return line to bleed off any excess pressure. Even with the bleeding of excess pressure, the pressure at the injectors is 35 to 40 psi.

Other, more knowledgable, members will be able to tell you more, but, if it were me and I wanted to keep the same fuel pump, I'd leave in the regulator and the return line.
 

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I have never done this, but.....I don't think you can keep the injection fuel pump. It is a high pressure unit~40#. The carb needs about 3#. I don't think you would be able to regulate it down that much without it over heating and failing.
JM2C

James
 

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My Experience

I've been running a Sportwagon for years that was converted to carburetion. The pressure regulator was removed and the pump just circulates fuel back to the tank. There is a tee in the line in the engine compartment that supplies fuel to the Weber. If you're going to do it...you MUST use the return line because the pump delivers 40 psi and will blow out the carb gaskets. When I did it...I was warned that the original pump was designed to develop 40 psi and it needed the pressure and flow to keep it properly lubricated and cooled. Having said that...the car has been running this way since 1991 and the fuel pump was taken from a junk yard car that sat for 15 years. Other things you'll need to change...the distributor is different for an injected car. It only has vacuum retard. You'll be better off with a 74 distributor if you're going to carburetion. Hope this helps. -SD
 

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I used a Mallory 3-port regulator on my friend's '75 wagon when I converted it to a Holley carb (5psi). Kept the OEM EFI pump, ran it through the regulator and just hooked up the return line to the OEM return. All works well, pump stays cool, pressure is consistant. I think the regulator was $75 or so, plus I threw a 1.5" VDO gauge ($20) on it to check pressure.

Actually the '75 distributor works pretty good for a non-EFI car. Almost a factory 'recurve', so to speak. Set the timing @ 10 degrees BTDC, it will have 35 total. Response will be nice.
 

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Discussion Starter · #6 ·
Is this fuel pump wired to come on with ignition? I'm concerned about fuel flowing after a car accident. I know our windstar has a shunt trip that needs to be reset after an accident for safety.
 

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Adding FI to a GT

Don't forget you will need to replace you fuel tank with one from a 1975 model Manta, Wagon, Ascona. These tanks have a larger metal hose conection (12 mm vs 8 mm) between the tank and pump. Also, you will need (someone correct me if I am wrong) a different fuel return to the tank. There may be more...

Paul
 

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70's Opeler, back 4 more!
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I have the stock GT tank in mine with EFI and I just reworked the connections from what they were. I did install a larger hose attachment to the tank feed.
 

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Dual Relay

To answer your question...the Opel F/I system has a dual relay for the fuel pump. It's designed to run the pump when the starter is cranking and when mass air flow meter detects that the engine is running. If the engine is not running...the fuel pump cuts off. (as in an accident)
 

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Discussion Starter · #12 ·
When I take out the fuel injection parts, I will be disabling the mass air flow sensor. Therefore, I will need to jump out the sensor and install another safety control. Right?
 

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Maf

Obviously you won't have the safety of the MAF meter to shut off your fuel pump if there's an accident. There are ways to provide an auto safety shutoff if you want to spend the money. I guess it depends on how much $ you want to spend and/or how much risk you want to take. I've seen people put in inertia switches for their fuel pumps...much like the mechanism that activate air bags. Others just put in a highly visible fuel cutoff valve like you see in race cars. Older Subaru cars had an electric pump that only ran when there was a demand for fuel. There was a built-in pressure regulator/switch so the pump would cut off if the needle valve in the carb was closed and pressure built up in the line. These are just a couple ways I've seen it done...I'm sure there are many more. -SD
 

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A lot of modern cars use an inertia switch as mentioned. Cheapest would be from a Ford, such as an Escort. About $5 at a junkyard. Alternatively you can hook a Hobb's pressure switch into your oil circuit. Oil pressure drops when the engine dies....switch shuts off the fuel pump.
 
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