[RealChris]

UPDATE - GUIDE: How to Carb Swap your EFI 76 to 79 Cadillac with a 350 olds.

DISCLAIMER: Do at your own risk, I’m not a pro like the old dudes on this forum.

TORQUE SPECS -
All torque specs can be found by googling “350 Olds Torque Specs.”

ECU -
First, disconnect the ECU from the car. The ECU should be under the drivers side dash and for the 79 Eldorado it should be under the glove box on the passenger side.

EFI SYSTEM -
Once the ECU is disconnected you can begin to take apart the EFI system. Disconnect all the wires going to the injectors and sensors. The fuel rails have stands that hold them, once they’re removed the rails should come right off.

IMPORTANT - Make sure to release the pressure from the fuel rails so you don’t spray yourself in the face with gasoline.

There should be a male-female connector that holds the fuel rail to the fuel lines. Disconnect it, but leave the fuel line alone.

INTAKE MANIFOLD -
The intake manifold on the EFI Cadillacs have holes in them for the injectors. They can be plugged with pipe plugs and a 2BBL Carb can be installed on it. You can forge or buy EGR block off plates. Don't leave them open otherwise you'll have a massive vacuum leak.

If you want a 4BBL Carb you need a new intake manifold. This is where you either get lucky or it gets expensive. If you’re lucky, you can head over to a junkyard and find a car with a Carbed 350 olds.
VEHICLES WITH 350 OLDS -
1968-1977 Oldsmobile Cutlass
1968–1977 Oldsmobile Vista Cruiser
1973-1977 Oldsmobile 4-4-2
1968-1980 Oldsmobile Delta 88
1977-1980 Oldsmobile 98
1979-1981 Oldsmobile Toronado
1973-1979 Oldsmobile Omega

If you can’t find a 350 Olds non-efi intake, then you can purchase a Edlebrock Performer. They go for about 400-500, but if you’re lucky you can get them used for much cheaper.

The Valley Gasket for the Intake manifold will need to be cleaned and RTV will need to be put around the Coolant holes [?] to ensure that coolant doesn't leak into the oil.

INTAKE REMOVAL AND INSTALLATION -
IMPORTANT - Drain Your Coolant
REMOVAL -
This part will be the most difficult. There are a few things that need to be removed. First the coolant spout on the front of the intake manifold, then the coolant line on the back-left of the intake (passenger side), then you need to remove the throttle body along with all the vacuum hoses and air cleaner.

Once everything is removed, there are 6 bolts on each side of the intake manifold that need to be removed. They should be a 14mm or 9/16 socket. Once they're all removed you should be able to lift the intake manifold out. If you are having a tough time removing the intake, you can remove the distributor to give yourself more room.

INSTALLATION -
There are 2 gaskets that are on the far end and near the end of the engine block. DON'T Touch them. If they happen to break or move, you need to re-RTV them to hold them in place or replace them if they're broken.

Once you RTV the Intake Manifold Gasket, place it on the cylinder heads and allow it to dry for an hour. Put the Intake Manifold on the gasket after an hour, place the bolts back in place and hand tighten them. Wait another hour to torque the Intake Manifold Down.

DISTRIBUTOR -
The same distributor can be used but can be replaced with one from a carburated 350 Olds for better wire organization. I personally bought one for $150 for a '75 Cutlass.

The Distributor has 2 plugs, one with 3 connectors (closest to the distributor) and one positive wire that goes in the right slot of the 2 prong female connector.

FUEL PUMP -
This is by far the most tedious part. You need to jack up the rear end of the car. In front of the rear-drivers side tire, by the frame, there should be an inline fuel pump and a fuel filter. Make sure you have something to catch gasoline, then disconnect the hose running from the tank to the inline fuel pump. Let the fuel in the lines drain. Unscrew and unbolt the fuel pump, then disconnect it from the line holding it to the fuel filter. Unplug the wires from the pump.

IMPORTANT - The Intank Fuel Pump is suitable for the operation of the carburetor, there's no need to replace it unless it's faulty.

You need to install a fuel line from the metal tank fuel line to the fuel filter. I recommend using a 1/2 inch fuel hose. Clamp them down and you're done.

FUEL LINES -
The Metal fuel line that is left has a male connector on it. You can buy a male connector for cheap, then run a hose off of it.

Once you get the hose on it, you need to run a filter, then regulator, then hose to the carb.

You're entire fuel system should look like this:
Fuel Pump --> Line --> Fuel Filter --> Line --> Fuel Filter --> Line --> Regulator --> Line --> Carb

WIRING -
The Fuel Pump can be wired to any 12 Volt keyed power. To check for keyed power, take a multimeter and check a wire. If the wire is hot only when the key is on, then you're good to connect the pump there. I recommend connecting a kill switch to the fuel pump just in case. I use it if I want to have the car on, but not the fuel pump. You can get around this issue by having a mechanical fuel pump (on older 350 olds).

IMPORTANT -
On the 79 Eldorado, the Fuel Pump Power wire is on the Red connector from the ECU. It is the Thick Blue Wire.

On Earlier vehicles, I think it's the Green Wire, but I'm not completely sure. [Need Reference]

 

[RealChris]

I’m currently swapping my 79 Eldorado to Carb for personal reasons. I have a intake, 4bbl carb, and have removed the inline pressure pump. I was wondering if I will need a new distributor or anything else that I’m missing. Thanks.

 

[Ranger]

Ignition and fuel delivery are two separate functions. You should not need to replace the distributor.

I can't remember much about the '79's, but some module has to tell the injectors when to pulse. Removing or disabling that may cause some problems. That's all I can think of off the top of my head. Maybe Basscat will have some input.

P.S.
If you don't mind divulging, I'm curious why you would want to go to older and less efficient technology?

 

[RealChris]

Ignition and fuel delivery are two separate functions. You should not need to replace the distributor.

I can't remember much about the '79's, but some module has to tell the injectors when to pulse. Removing or disabling that may cause some problems. That's all I can think of off the top of my head. Maybe Basscat will have some input.

P.S.
If you don't mind divulging, I'm curious why you would want to go to older and less efficient technology?

Thanks. I was just wondering if the distributor was somehow tied to the fuel injection, but now that I think of it, that sounds silly. It’s old, janky Cadillac though, so you never really know.

I’m just going for a carburetor swap because I’ve had an issue with the EFI for a few years now. Sometimes it works, other times it half works or refuses to work. The whole thing is a nightmare and I don’t have the experience or patience to fix it. Also I kinda just had everything I needed to carb swap it on hand, so I decided “why not?”

 

[basscatt]

Thanks. I was just wondering if the distributor was somehow tied to the fuel injection, but now that I think of it, that sounds silly. It’s old, janky Cadillac though, so you never really know.

I’m just going for a carburetor swap because I’ve had an issue with the EFI for a few years now. Sometimes it works, other times it half works or refuses to work. The whole thing is a nightmare and I don’t have the experience or patience to fix it. Also I kinda just had everything I needed to carb swap it on hand, so I decided “why not?”

==========================
why not - indeed?

how are you going to deliver the fuel to the carb?
at what pressure?

 

[RealChris]

==========================
why not - indeed?

how are you going to deliver the fuel to the carb?
at what pressure?

The in-tank fuel pump has enough pressure to dump fuel into the carb. Tested it prior to installing the new intake and carb. The pressure is whatever pressure is being sent through the pump. It sends a pretty hefty amount which should be enough.

 

[basscatt]

The in-tank fuel pump has enough pressure to dump fuel into the carb. Tested it prior to installing the new intake and carb. The pressure is whatever pressure is being sent through the pump. It sends a pretty hefty amount which should be enough.

========================
fuel pressure to a carb should be around 7psi -

 

[RealChris]

========================
fuel pressure to a carb should be around 7psi -

I’ve read on here from other people that have carb swapped that the intank pump has enough pressure for a quadrajet. I’m following a guide by Joe AKA “Flash Man” with his 78 Seville (same engine/efi/pump system) where he just leaves it. I just happened to have the same carb he’s using on an old truck I had lying around.

 

[1979 Eldorado]

The EFI system is really a pretty good system if understood so sorry to hear you removed it. The advance on the EFI distributor is controlled by the ESS. I've heard running the EFI with an Olds mechanical distributor is possible. I suspect running the EFI distributor can work with a carb but it would depend on what you decided to remove from the EFI system.

 

[RealChris]

The EFI system is really a pretty good system if understood so sorry to hear you removed it. The advance on the EFI distributor is controlled by the ESS. I've heard running the EFI with an Olds mechanical distributor is possible. I suspect running the EFI distributor can work with a carb but it would depend on what you decided to remove from the EFI system.

I’ve only removed the fuel rails and that’s all I plan on removing. Do you have any suggestions on what could be done to keep the distributor, or should I start searching for a new one?

 

[1979 Eldorado]

Thanks. I was just wondering if the distributor was somehow tied to the fuel injection, but now that I think of it, that sounds silly. It’s old, janky Cadillac though, so you never really know.

I’m just going for a carburetor swap because I’ve had an issue with the EFI for a few years now. Sometimes it works, other times it half works or refuses to work. The whole thing is a nightmare and I don’t have the experience or patience to fix it. Also I kinda just had everything I needed to carb swap it on hand, so I decided “why not?”

Well because your issue could be something simple and as well there's some possibility the issue may not be related to the EFI system at all. There are good fault trees for the EFI systems. They work pretty well and often times an issue is relatively simple. You need to start by defining exactly what it's doing.

The in tank pump is a low pressure pick-up pump. The power runs through the ECU for the fuel pumps. If you intend to swap to a carb but you want to use the in tank pump without touching it you will have avoided addressing 2 of the the more common EFI issues:
-One the pick-up pump has a soft line from the in tank to the sending unit. That needs to be submersible line NOT normal fuel line. Even if it is, after 50 years, they can become hard and crack or deteriorate and leak.
-Two: The fuel pumps can draw a lot of current and the relay for the pumps is inside the ECU. What can happen is one of the pins on the ECU can burn. The pump power should be routed outside of the ECU. There's a member who freely offers the electrical wiring schematic to add an external relay to avoid the issue.

In addition if the car has cold start issues there's a very good chance you simply need to replace a sensor. If it runs rich a common issue is a cracked or loose vacuum line to the ECU. Extremely easy to check and VERY cheap to fix. If the car starts but stalls because it has no fast idle the fast idle valve has failed and someone likely compensated by adjusting the main idle screw.

I chose to mention those couple of items as they are common and can be weather related; you mentioned sometimes works and sometimes does not.

 

[1979 Eldorado]

I haven't gotten deep into the ESS circuit and advance control. I would start reading through the factory service manual FSM and read more about the ESS. You may not need to do anything special. I also replied to your other thread. I would at least try to diagnose the original system first if the fuel rail is the only thing you removed. Here's a capture of the key manuals for your car. I'm also including a capture of the index from the blue/white EFI manual. That index lists all of the potential failure modes which they include fault trees for.

 

[RealChris]

Well because your issue could be something simple and as well there's some possibility the issue may not be related to the EFI system at all. There are good fault trees for the EFI systems. They work pretty well and often times an issue is relatively simple. You need to start by defining exactly what it's doing.

The in tank pump is a low pressure pick-up pump. The power runs through the ECU for the fuel pumps. If you intend to swap to a carb but you want to use the in tank pump without touching it you will have avoided addressing 2 of the the more common EFI issues:
-One the pick-up pump has a soft line from the in tank to the sending unit. That needs to be submersible line NOT normal fuel line. Even if it is, after 50 years, they can become hard and crack or deteriorate and leak.
-Two: The fuel pumps can draw a lot of current and the relay for the pumps is inside the ECU. What can happen is one of the pins on the ECU can burn. The pump power should be routed outside of the ECU. There's a member who freely offers the electrical wiring schematic to add an external relay to avoid the issue.

In addition if the car has cold start issues there's a very good chance you simply need to replace a sensor. If it runs rich a common issue is a cracked or loose vacuum line to the ECU. Extremely easy to check and VERY cheap to fix. If the car starts but stalls because it has no fast idle the fast idle valve has failed and someone likely compensated by adjusting the main idle screw.

I chose to mention those couple of items as they are common and can be weather related; you mentioned sometimes works and sometimes does not.

Thanks for this. The idle was always an issue, I’d constantly needed to adjust the screw every day or so just to get the right idle, then there was the rocker arm bridges and electrical issues. I’m just going to beef up the engine a bit so it lasts as a daily driver, while EFI would work, I’m much better at working with carbs. I’ll keep the old EFI stuff, so if I ever want to revert back I can.

 

[RealChris]

I haven't gotten deep into the ESS circuit and advance control. I would start reading through the factory service manual FSM and read more about the ESS. You may not need to do anything special. I also replied to your other thread. I would at least try to diagnose the original system first if the fuel rail is the only thing you removed. Here's a capture of the key manuals for your car. I'm also including a capture of the index from the blue/white EFI manual. That index lists all of the potential failure modes which they include fault trees for.

I’ll keep the old EFI system in the garage for later since I might want to put it back on there if I sell the car in the near future. I did find someone who did a carb swap on a 78 Seville (same car different body), who said to simply unplug the Speed Sensor for the injectors and leave the ESS plugged in. I’ll check it out and see what happens.

 

[1979 Eldorado]

These 79 Olds engines have really poor oil returns in the heads. Mine were mostly plugged. I cleaned them out and changed the valve seals and what a world of difference. It had some blue smoke and acted like it was using more oil than it actually was because the oil took so long to drain down. I used music wire and a drill to help open the returns. I also made a valve spring compressor tool specifically for my 79 Cadillac to change the valve seals. The prior time when I did Olds valve springs let's just say it's very difficult to do safely without a specifc Olds tool and after searching twice 10 years apart I couldn't find anything I felt I had to do something about it. It was a breeze to do with a tool designed for the job and it lets you do 2 valves at a time (1 complete cylinder).

One more thing you really need to do if it's never been done is change the plastic tooth timing gear set. I plan to do that sometime before spring.

Needing to adjust the idle every day is 99.9% a bad FIV; capture included. But only necessary for you if you have second thoughts and want to stay with EFI. Even though you removed the injectors that's not that bad as the seals should be a maintenance thing once in a while to avoid dry/cracked seals and fuel spraying. The graphic shows how the FIV works. When you start cold there is an added air bypass but the internal heater extends a plunger and closes the leak. The idle screw on the front is simply a fixed air leak. If you look down from the top you will see the tip of a threaded bolt. That's what you are turning. If everything is working properly it should be around 3.5 turns out from bottomed; bottomed meaning just touching (no significant torque).