wkbrdngsnw
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This is just interesting enough to need posting. I'm probably one of the few idiots that would actually put FI on a flathead 6 instead of doing a motor swap. It just wouldn't be as cool to put a 350 and an auto in it.
As always it has to start with the back story -
Now don't go having a heart attack. This was never a restoration candidate. When I got it there was just a frame and a pile of parts. Ranks right up there with the best $500 ever spent. It is a civilian cab on a winch frame with 2 different front fenders so I feel less bad about not keeping it original. I went for what the truck might have been after the war as surplus. Took 3 years to get it put mostly together. Took it wheeling with some friends and broke a wood body mount and had to limp it back. I realized it wasn't going to be my primary 4x4, thus my purchase of a CUCV but that is a different story.
It then sat for about 4 years being used mostly like a tractor. I built a snowplow and a lifting A-frame with roll bar to support it.
It never ran right since it had a carb off some sort of jeep that was missing parts and proved difficult to find a carb kit for. The first attempt was to make a 4 barrel to 1 barrel adapter but never was able to get it anywhere near right. Probably due to the lack of vacuum signal at the venturi. A 2 barrel was also tried and still wasn't that good so the truck just sat there.
Them the crazy idea of using TBI came from my conversion on the international scout. I could have used the stock GM ecu for the 4.3 but I don't like the "hacks" that you have to do to make it think it is still in the original truck. You also have to remove the EPROM to do any tuning. My choice is the Megasquirt DIY ECU. Its basically a simplified version that comes as a blank circuit board and has to be assembled. To tune it you just plug in the laptop.
To make this work I needed a new intake manifold that would accept a GM TBI. I had to machine the flanges that bolt to the block in the same way the original manifold. To get the shape they where traced, scanned, and then programmed into the CNC to cut them out.
The top flange also had to be machined to accept the throttle body. Add some mandrel bent exhaust tubing and sheet metal, weld together and there's a manifold. A block-off for the intake heat had to be made as well but that's just a plate bolted over the hole.
After all that I was lazy and just threw the tank from my S-10 project in the bed and hooked it up to get it running. Hopefully a more eloquent solution will follow.
The next problem was the throttle linkage. There was much debate about cable vs mechanical. I kind of like a good mechanical linkage so that's the way I went. The factory rod pushes up slightly and since the TBI is on there backwards the throttle plates rotate the other way. They also are on the opposite side. The solution is a shaft with a disc on either end that rotates. The trick is one is on the top and the other on the bottom so it changes the direction. Probably not the greatest solution but it seems to work.
Add a coolant and air temperature sensors plus an O2 sensor and its basically ready to go. It already was converted to 12V neg ground with an alternator.
As of right now it starts, runs, and idles. In fact the idle is actually better that the truck the TBI came off of. Now I need to dive it around and do some tuning.
As always it has to start with the back story -
Now don't go having a heart attack. This was never a restoration candidate. When I got it there was just a frame and a pile of parts. Ranks right up there with the best $500 ever spent. It is a civilian cab on a winch frame with 2 different front fenders so I feel less bad about not keeping it original. I went for what the truck might have been after the war as surplus. Took 3 years to get it put mostly together. Took it wheeling with some friends and broke a wood body mount and had to limp it back. I realized it wasn't going to be my primary 4x4, thus my purchase of a CUCV but that is a different story.
It then sat for about 4 years being used mostly like a tractor. I built a snowplow and a lifting A-frame with roll bar to support it.
It never ran right since it had a carb off some sort of jeep that was missing parts and proved difficult to find a carb kit for. The first attempt was to make a 4 barrel to 1 barrel adapter but never was able to get it anywhere near right. Probably due to the lack of vacuum signal at the venturi. A 2 barrel was also tried and still wasn't that good so the truck just sat there.
Them the crazy idea of using TBI came from my conversion on the international scout. I could have used the stock GM ecu for the 4.3 but I don't like the "hacks" that you have to do to make it think it is still in the original truck. You also have to remove the EPROM to do any tuning. My choice is the Megasquirt DIY ECU. Its basically a simplified version that comes as a blank circuit board and has to be assembled. To tune it you just plug in the laptop.
To make this work I needed a new intake manifold that would accept a GM TBI. I had to machine the flanges that bolt to the block in the same way the original manifold. To get the shape they where traced, scanned, and then programmed into the CNC to cut them out.
The top flange also had to be machined to accept the throttle body. Add some mandrel bent exhaust tubing and sheet metal, weld together and there's a manifold. A block-off for the intake heat had to be made as well but that's just a plate bolted over the hole.
After all that I was lazy and just threw the tank from my S-10 project in the bed and hooked it up to get it running. Hopefully a more eloquent solution will follow.
The next problem was the throttle linkage. There was much debate about cable vs mechanical. I kind of like a good mechanical linkage so that's the way I went. The factory rod pushes up slightly and since the TBI is on there backwards the throttle plates rotate the other way. They also are on the opposite side. The solution is a shaft with a disc on either end that rotates. The trick is one is on the top and the other on the bottom so it changes the direction. Probably not the greatest solution but it seems to work.
Add a coolant and air temperature sensors plus an O2 sensor and its basically ready to go. It already was converted to 12V neg ground with an alternator.
As of right now it starts, runs, and idles. In fact the idle is actually better that the truck the TBI came off of. Now I need to dive it around and do some tuning.
