TBI replacing carb

[Jay2TheRescue]

Originally Posted by froggy81500

Take the TBI stuff off of an 88-93 Chevy or GMC truck. My 89 Chevy was TBI. I believe they ran it until 93, give or take a year. Pretty basic, and fuel pressure is not very much, like 15 tops I think. Taking everything you need off of one of those trucks from the intake manifold up. Take the wiring harness and computer also.

Since the 3.8 V6 was not used in a truck that I know of (except for an El Camino maybe), I would have to use an 84-87 Century/Regal as a parts car. I'd need the fuel tank too, as the fuel injected Regals had a special anti slosh tank underneath to deal with the electric fuel pump.

-Jay

[froggy81500]

No, I do not believe the 3.8 was ever used in a truck. You would probably be looking at mid 80's and up for a parts car to pull from. I've seen TBI on 4 cylinder motors like the 82 Chevy Citation I used to have right up to big V-8's in the trucks. My 89 was a 4.3 V-6, damn good motor.

[theholycow]

The Astro's TBI seems to be the most popular donor for TBI conversions, apparently it works great on a variety of engines.

[froggy81500]

The Astro shares the same 4.3L found in the full size pick ups and the smaller S-10/15 pickups, and some cars also. Finding full size pickups, around here anyway, to pull parts from is about as daunting as finding a fossil. There are just so many still on the road that even when you find one in the junkyard, there isn't much left to pull. Perhaps the Astros are just a little easier to come by?

[froggy81500]

Of the various forms of fuel injection, you will find the GM TBI set up pretty easy to work on and adapt to. It is a low pressure system, 15 psi tops I think. And for the most part, much of what you need is sitting right on the intake manifold. You've got your throttle body, which includes the IAC, TPS fuel pressure regulator, injector(s), the MAP is usually mounted to a bracket on the intake, the EGR and solenoid, the CTS mounted at the front of the intake. Virtually everything you need is located right on the intake manifold, with the exception of the knock sensor and O2 sensor, and of course the pcm. Even the distributor, and ignition module have to be removed to get the intake off, so take that also. And I almost forgot the ignition coil is also mounted to the intake manifold.

[theholycow]

froggy81500, what about the pressurized fuel system? Is 15psi low enough that you can just put an external electric pump between the tank and the throttle body?

[froggy81500]

Yes I believe so. There were some early forms of FI that Ford used. CFI was one that comes to mind. My parents had an 84 LTD that had two fuel pumps. One low pressure one in the tank and one high pressure one on the fuel line under the car. I kid you not. I looked this up in the repair manual way back when they still had the car. Why 2 pumps I could not tell you. I think you shouldn't have an issue with an external pump on a TBI. I will try to track down my old repair manual for my Chevy with TBI to confirm that fuel pressure but I know it is not a lot. Also, there is a way to adjust the regulator on them. They are non-adjustable but have an adjusting screw that is soldered in place. Also, the spring for the regulator are known to rot out (ask me how I know this!) There is a slot in the side of the regulator housing and you can almost see the spring in there. since it is open like it is, moisture and crap get in there and rot the spring to pieces and leaving the engine will very minimum fuel pressure. Its not a hard fix and some places used to sell adjustable regulators, but I fould you could break the solder on the replacements and still adjust them.

You will need a return line though on these. With low pressure like it is, I can't see why regular double walled (with the braid inside) fuel line can't be used. Unlike port injection that runs upwards of 50 psi, TBI is just a little bit higher than a carb.

[froggy81500]

http://www.autozone.com/shopping/rep...00c1528008f1ea

That is the repair info for the full size GM trucks, which is what I had. The fuel pressure testing procedure calls for 9-13 psi test pressure with the engine running.

V-6 and V-8's used two fuel injectors, while the 4 cylinder motors had just one.

[theholycow]

Originally Posted by froggy81500

You will need a return line though on these. With low pressure like it is, I can't see why regular double walled (with the braid inside) fuel line can't be used. Unlike port injection that runs upwards of 50 psi, TBI is just a little bit higher than a carb.

Drat, that's the other issue I forgot. How would one install a return line? I suspect you'd have to drill and weld it into the gas tank, no?

What is the return line for, anyway? Really, why does it need to go back? Why can't it just pull the amount of fuel it needs and not let any more come forward?

Like another person posted above, the plumbing is the intimidating part of the whole thing...

[froggy81500]

Its the way the regulation is done. The regulator bleeds off extra fuel pressure thru the return line. I imagine if you are working with a fuel system that has a vapor line between the tank and engine compartment, that might suffice. The gas tank on my truck had 3 lines coming off the sending unit. 1 was the pressurized fuel line, 2 was the return line, 3 was a vapor line.

On a lot of the newer fuel systems, Dodge in particular, they run just one fuel line to the motor and have the fuel pressure regulator located as part of the sending unit/fuel pump unit. That was it vents extra pressure right back into the tank instead of having to run a second line.