1978 cadillac seville efi to carburetor conversion
#1
01-01-2011, 08:23 PM
1978 cadillac seville efi to carburetor conversion
1978 CADILLAC SEVILLE EFI TO CARBURETOR CONVERSION
This is a conversion that I performed on my 1978 Cadillac Seville. I changed my two barrel intake manifold and installed a 4 barrel aluminum Oldsmobile A4 intake manifold. I used a Quadrajet carburetor. First remove the air cleaner. You need to disconnect the fuel injection wiring harness. Injectors, sensors, grounds etc. There is one wire from the harness that needs to be removed from the firewall junction stud. Remove the throttle body and disconnect the throttle linkage. Next drain the coolant in the radiator. You will need to remove the two barrel aluminum intake manifold. You will need to find an Oldsmobile A4 aluminum intake manifold. You can find this intake in the junkyard or on ebay. The A4 intake has the large intake ports to match the heads. The A5 intake has small intake ports and does not breathe like the A4. You can find the A4 intake on 81-'84 307/350 Oldsmobile engines. The casting number is 22504086. You will see a big A4 on the front right side stamped on top of the intake. I used an A5 intake and ported the intake manifold to match the heads. You will also need the Oldsmobile throttle cable bracket that comes with the intake. Your original throttle cable will work just fine with the bracket. You will need to remove the air conditioning compressor bracket to remove the intake. After you install the A4 intake manifold, you will have to make a small offset bracket to mount the air conditioner bracket on to the new intake. One top mounting hole is offset foward than the original intake manifold. Other than that, the intake will fit on the engine just fine and you will have the same hood clearance as you did with your throttle body. You can also use your original air cleaner on the Quadrajet carburetor.
You can use your low pressure fuel pump in your tank to feed the carburetor. But you will need to disable the high pressure pump on the rear frame. You can cut the light blue wire that goes to the pump. It is located under the car near the fuel filler neck outside the fuel tank. There is a plug there for it.Tape it up or shrink wrap it so there is no shorts. You can then take you fuel line coming from the fuel tank and bypass the high pressure pump. You can keep your fuel filter that is next to the high pressure pump. I used two fuel filters. The original one on the frame and the other at the carburetor. Remove the wiring harness from the engine and push it thru the firewall. You will need to remove the wiring harness and the computer. But before you do that. There is a plug with two wires that you will have to cut off the harness for the computer. It is located under the drivers side dash. The wires on the top of the plug is the Lt blue fuel pump/s wire. It turns into a Dark green wire on the harness side of the plug.The Gray wires are the same on both sides of the plug. The Lt blue/dark green wire energizes the fuel pump. The gray/gray wire is ignition power. I put an inline 10 amp fuse on the fuel pump wire and connected it to the gray ignition wire. The pump will only turn on when the key is foward and not when it is back for radio listening etc. Some guys like to connect the electric fuel pump to the oil pressure switch. But if the car sits for a few days, it will take longer to start the car. I installed my EGR valve but did not connect it. There two small wiring harnesses that goes to the distributor. One is a speed sensor for the injectors. Unplug it. The other one is the ESS (Electronic Spark Selection). Do not unplug the ESS that goes to the box on the firewall or the car will not start. You will also need to find 4 bolts to mount your Quadrajet carburetor to the intake. The rest of the job is tuning your carburetor, timing etc.
The original Seville intake manifold is aluminum not cast iron. I read that Cadillac actually designed this intake for the Oldsmobile 350 engine. It has large ports and flows very well. You can clearly see thru the intake to the other other side. It looks to me like you can use the original intake if you are going to use a 2 barrel carburetor. But you will have to seal the fuel injector holes. Or you can leave the injectors and rail mounted to the intake. This would be the easy way out. You can use a two barrel carburetor and not have to modify the top of the ac compressor bracket. I wanted my engine to look clean and wanted to rid all that wiring mess on the intake. If you are going to use a 4 barrel Quadrajet carburetor, then you want to get an Oldsmobile 307 or 350 A4 aluminum intake manifold. The A4 has the large intake ports and will match the head. I did not know that and used an A5 Olds aluminum intake. I looked for an A4 intake and could not find one in time. So, I ported an polished my A5 intake to match the A4 intake. You could use a performance intake like Edelbrock etc. But make sure you do not use a high profile intake or you could have clearance problems. I do not notice a large gain in power but I am still in the tuning stages. The fuel economy seems the same. My Seville runs and idles so smooth. I dont have to worry about computers, sensors, injectors or bad wiring connections anymore. This is the conversion that I have performed on my Cadillac Seville. I make no guarantees or responsibilities of how your car will run if you do this conversion. It has worked very well for me. I will be happy to answer any questions pertaining to this subject. My email is Flash1wax@aol.com. Good Luck.
Joe
Flash Man
Seville and Oldsmobile Intakes
Fuel pump and ignition wires/plug
4 barrel Oldsmobile Intake
Quadrajet Caburetor throttle bracket
AC compressor bracket modification
Original Air cleaner-Hood Clearance
This is a conversion that I performed on my 1978 Cadillac Seville. I changed my two barrel intake manifold and installed a 4 barrel aluminum Oldsmobile A4 intake manifold. I used a Quadrajet carburetor. First remove the air cleaner. You need to disconnect the fuel injection wiring harness. Injectors, sensors, grounds etc. There is one wire from the harness that needs to be removed from the firewall junction stud. Remove the throttle body and disconnect the throttle linkage. Next drain the coolant in the radiator. You will need to remove the two barrel aluminum intake manifold. You will need to find an Oldsmobile A4 aluminum intake manifold. You can find this intake in the junkyard or on ebay. The A4 intake has the large intake ports to match the heads. The A5 intake has small intake ports and does not breathe like the A4. You can find the A4 intake on 81-'84 307/350 Oldsmobile engines. The casting number is 22504086. You will see a big A4 on the front right side stamped on top of the intake. I used an A5 intake and ported the intake manifold to match the heads. You will also need the Oldsmobile throttle cable bracket that comes with the intake. Your original throttle cable will work just fine with the bracket. You will need to remove the air conditioning compressor bracket to remove the intake. After you install the A4 intake manifold, you will have to make a small offset bracket to mount the air conditioner bracket on to the new intake. One top mounting hole is offset foward than the original intake manifold. Other than that, the intake will fit on the engine just fine and you will have the same hood clearance as you did with your throttle body. You can also use your original air cleaner on the Quadrajet carburetor.
You can use your low pressure fuel pump in your tank to feed the carburetor. But you will need to disable the high pressure pump on the rear frame. You can cut the light blue wire that goes to the pump. It is located under the car near the fuel filler neck outside the fuel tank. There is a plug there for it.Tape it up or shrink wrap it so there is no shorts. You can then take you fuel line coming from the fuel tank and bypass the high pressure pump. You can keep your fuel filter that is next to the high pressure pump. I used two fuel filters. The original one on the frame and the other at the carburetor. Remove the wiring harness from the engine and push it thru the firewall. You will need to remove the wiring harness and the computer. But before you do that. There is a plug with two wires that you will have to cut off the harness for the computer. It is located under the drivers side dash. The wires on the top of the plug is the Lt blue fuel pump/s wire. It turns into a Dark green wire on the harness side of the plug.The Gray wires are the same on both sides of the plug. The Lt blue/dark green wire energizes the fuel pump. The gray/gray wire is ignition power. I put an inline 10 amp fuse on the fuel pump wire and connected it to the gray ignition wire. The pump will only turn on when the key is foward and not when it is back for radio listening etc. Some guys like to connect the electric fuel pump to the oil pressure switch. But if the car sits for a few days, it will take longer to start the car. I installed my EGR valve but did not connect it. There two small wiring harnesses that goes to the distributor. One is a speed sensor for the injectors. Unplug it. The other one is the ESS (Electronic Spark Selection). Do not unplug the ESS that goes to the box on the firewall or the car will not start. You will also need to find 4 bolts to mount your Quadrajet carburetor to the intake. The rest of the job is tuning your carburetor, timing etc.
The original Seville intake manifold is aluminum not cast iron. I read that Cadillac actually designed this intake for the Oldsmobile 350 engine. It has large ports and flows very well. You can clearly see thru the intake to the other other side. It looks to me like you can use the original intake if you are going to use a 2 barrel carburetor. But you will have to seal the fuel injector holes. Or you can leave the injectors and rail mounted to the intake. This would be the easy way out. You can use a two barrel carburetor and not have to modify the top of the ac compressor bracket. I wanted my engine to look clean and wanted to rid all that wiring mess on the intake. If you are going to use a 4 barrel Quadrajet carburetor, then you want to get an Oldsmobile 307 or 350 A4 aluminum intake manifold. The A4 has the large intake ports and will match the head. I did not know that and used an A5 Olds aluminum intake. I looked for an A4 intake and could not find one in time. So, I ported an polished my A5 intake to match the A4 intake. You could use a performance intake like Edelbrock etc. But make sure you do not use a high profile intake or you could have clearance problems. I do not notice a large gain in power but I am still in the tuning stages. The fuel economy seems the same. My Seville runs and idles so smooth. I dont have to worry about computers, sensors, injectors or bad wiring connections anymore. This is the conversion that I have performed on my Cadillac Seville. I make no guarantees or responsibilities of how your car will run if you do this conversion. It has worked very well for me. I will be happy to answer any questions pertaining to this subject. My email is Flash1wax@aol.com. Good Luck.
Joe
Flash Man
Seville and Oldsmobile Intakes
Fuel pump and ignition wires/plug
4 barrel Oldsmobile Intake
Quadrajet Caburetor throttle bracket
AC compressor bracket modification
Original Air cleaner-Hood Clearance
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