converting EFI over to carborater?

i have a 78 cadillac seville with EFI system and i want to change it over to a carb. i knowq i will need a intake and carb. but what will i do about return lines to gas tank. and i know i will need a manual fuel pump also, can anybody help me else am i missing any steps any body else with suggestion im open to anything that helps thanks in advanced

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  • 9 years ago
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    There are people that work on those systems and parts are still available. Often times its a pretty simple issue like temp sensors or the connector for the fuel pump relay. Check out and post on the CadillacLasalleClub.org forum if you want to try and save the system.

    For those that dont know 1975 multiport EFI became an option for most Cadillac models which at the time had a 500 cubic inch engine. 1976 it was standard on the then new Seville which used an Oldsmobile 350 engine. System was made by Bendix. It was an analog ECU so it was not very easy to tune but the good news its not full of obsolete chips so the can usually be repaired. The system was used till 1980 when the DEFI (digital) system came out. The DEFI was what became the throttle body injection system that was used on the GM trucks till 1995.

    For converting I would consider just getting a fuel pressure regulator and keeping the electric pump(s) and the return system. I say pumps because I know the earlier systems did use 2 pumps. If you remove the pumps you just need to re connect the lines. The fuel pumps for cars with AC have a return line anyway so you can still use the return line. One question would be did they still put in the fuel pump eccentric? On the Olds motors it bolts on the front of the cam in front of the cam sprocket. Installing that would be a lot of work because technically you have to drop the oil pan to properly remove and reinstall the timing cover.

    They did have an electronic spark control system on some of the 78's. From looking at the books it looks like it may be able to operate without the ECU. Easy way to tell is to see if the distributor has the vacuum advance canister on it. If it does you are good to go because its a standard GM HEI the only mod to it was there is an extra sensor mounted down in the stalk to trigger the EFI system. Unhooking that wont hurt anything. Only reason to remove it would be to sell it to someone that wants to keep one of those systems going. Try not to damage anything removing the system so the parts can help someone else. Post them for sale on that Cadillac site or ebay. If the distributor does not have the vacuum can you may have to find another one but its a standard short deck Oldsmobile engine so anything that fits the 403 and smaller should drop right in and work fine. The only one that wont work is the OE ones for the 307's because those were computer controlled. The 307 was the 80's motor. Again how to tell is they dont have the vacuum can.

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  • 9 years ago

    better make sure there,s a place to install a manuel fuel pump. i have before plugged the place for the return line.

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  • 9 years ago

    why?

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