Fuelly Forums - TBI replacing carb

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I would think you would need to replace the tank as well. I know GM used special anti slosh tanks on fuel injected vehicles. Carbs don't care because they ran off of the fuel in the bowl of the carb. If there was a momentary interruption in the fuel flow due to sloshing in the tank the engine kept running. With fuel injection the vehicle stalls. I remember my dad had an early model Chevy Lumina minivan that did not have a good anti-slosh tank in it. He said the van would start sputtering at 1/4 tank.

-Jay

I had the tank down once and didn't notice anything special about it from other tanks. The sock is mounted to the bottom of the fuel pump and sits on the bottom of the tank. So it is always picking up fuel from the bottom. On carb equipped cars, its been so long since I had one open that I can't remember where the pickup sits in the tank.

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Originally Posted by Jay2TheRescue (Post 110214)

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Originally Posted by froggy81500 (Post 110202)

Its the way the regulation is done. The regulator bleeds off extra fuel pressure thru the return line.

It works a bit differently than that. On a carbed car, the pump only pumps what is required by the engine. On an FI car, the pump is always pumping 100% of its rated flow, and the leftovers go back to the tank. So if your pump can do 100 gallons/hour, it will pump 100 gallons/hour and the regulator will maintain pressure but return 96 gallons/hour back to the tank. This is to keep the pump cool, by always letting it flow 100% of volume, these pumps are very sensitive to overheating and the fuel is what cools the pump.

-Bob C.

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Originally Posted by bobc455 (Post 110245)

Bingo.

You don't NEED to replace the tank, but it is a good idea if financially possible (a custom-made FI tank for an older car can run about $1000 - https://www.rockvalleyantiqueautoparts.com/catalog.htm). But for me that was never an option, so I use my factory tank and just make sure the car never gets below 100%.

My car has never stalled due to lack of fuel, but it has ruined several fuel pumps from overheating when fuel wasn't available to keep the pump cool (see below).

The new tanks will accommodate internal pumps (which are best for these scenarios, although I have always used external), and will have the internal baffling to minimize slosh away from the pickup.

It works a bit differently than that. On a carbed car, the pump only pumps what is required by the engine. On an FI car, the pump is always pumping 100% of its rated flow, and the leftovers go back to the tank. So if your pump can do 100 gallons/hour, it will pump 100 gallons/hour and the regulator will maintain pressure but return 96 gallons/hour back to the tank. This is to keep the pump cool, by always letting it flow 100% of volume, these pumps are very sensitive to overheating and the fuel is what cools the pump.

-Bob C.

I think the cheapest option is to find a suitable tank from a FI car and hang that underneath. For example. On my 1981 Buick Regal - the exact same car was made with TBI from 1984 - 1987. I would have to find a fuel injected GM A body car, which would not be hard. Just about any 1984 - 1987 Malibu, Monte Carlo, Regal, Grand Prix, Cutlass Supreme, or Century woud be able to donate a suitable tank. If converting a full size car then a tank from a GM full size fuel injected car up to 1991 should be almost a bolt-in replacement. If converting a 70's or 80's model GM truck get a tank from an 87 C-10. It will fit with slight modifications. 87 was the last year of that body, and came stock with fuel injection.

Otherwise as you said before, don't let the fuel tank get low.

-Jay

why not try modifying the stock fuel pick up in the tank of a non-FI car? Use an external electric pump and modify the fuel pick up.

Quote:

Originally Posted by bobc455 (Post 110245)

This is to keep the pump cool, by always letting it flow 100% of volume, these pumps are very sensitive to overheating and the fuel is what cools the pump.

So, with an external pump retrofitted, I could skip the return line for my TBI as long as the pump can maintain 15psi? That is, assuming the pump is rated for non-continuous flow (or I hack up a cooler for it)...

Maybe like Jay said I'd just get a tank from a newer model, that hadn't occured to me.

Well, with a GM TBI unit, you'd either need to run a second line from the open side of the regulator. Or cap it off and figure a different way to regulate fuel pressure and flow. I have not looked at external pumps for some time so I do not know if you can find one that self regulates. Yes, there are some hassles with trying to retrofit this but I think you would find the GM TBI about as easy to adapt as anything.

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Originally Posted by theholycow (Post 110264)

GM made cars on the same body/frame as your 1980 Buick until 1991. The easiest to find would be either a 1990 or 1991 Caprice tank should be pretty much a direct replacement.

-Jay

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Originally Posted by theholycow (Post 110264)

I'm not aware of any electric external fuel pump that can work without a return system for full flow. A mechanical pump will not produce good results with a FI system.

A non "return-style" regulator will prevent the pump from getting sufficient flow to stay cool.

"Maybe" the Holly Blue pump (a rotary vane pump, instead of an inline pump) might work, but it is really designed to work with carbs and not with FI.

-Bob C.

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Originally Posted by bobc455 (Post 110314)

I doubt a mechanical pump will work at all on FI. Mechanical pumps deliver fuel in pulses. The bowl on the carb evens this out. I think if you could even start an engine with FI and a mechanical pump it would sputter and miss horribly, and probably would not be very driveable.

-Jay