Stovebolt.com Forums The Shop Area The HiPo Shop Back to the Future - GM TBI

One of the oft-cited objections to aftermarket EFI systems, like the FiTech or Holly Sniper, is the lack of available repair parts/service if a guy was to break down somewhere. If I was considering such a system (I'm not), that would be my biggest fear. I've spoken with a fair number of folks who have experience with these things and its seems they either work great....or they don't. Wide range of user experiences. There does seem to be some level of fussy or finicky behavior with some installs.

As to the parts availability question...if one was determined to run a TBI system on a Stovebolt...why not adapt a factory GM TBI instead of buying the aftermarket solution? Countless zillions of these things were produced and many still on the road. Any parts store, almost anywhere, is going to stock anything that could be a failure point.

* The parts/ materials would be dirt cheap if sourced from a junkyard. You can also buy a new TBI harness, a few different aftermarket ECMs, or just about anything else to support the GM-style system.

* This GM TBI approach has fallen out of fashion with the rise of LS swaps (for good reason, they are better) and the affordability of the aftermarket throttle body systems. Just about any information I can find in terms of a a video or website articles are 10-15 years old.

* It would appear to me, that the most popular way to "upgrade" to a TBI system, when this was more popular 10-20 years ago, was to control it with a MegaSquirt ECM. That would certainly depart from the "OE" approach to this problem. But the Megasquirt solution has been around a very long time, and has a pretty positive reputation.

* Running the junkyard factory ECM would also be an option. "How to" information on this approach is a little harder to come by. Tune-ability might also be a bit more challenging.

* Intake manifold is probably the biggest barrier. To my knowledge, the Clifford 4 bbl manifold and a suitable 2 bbl TBI adapter, would be the only "off the shelf" solution. Otherwise, you're into some sort of custom fabri-cobbling.

I'm not really really interested in debating whether the "juice is worth the squeeze" here. It's definitely not, and this is the forum for considering silly ideas. Carburetors work pretty darn well. And very, very few of us are using these trucks for daily transportation or for making a living. Nothing in this hobby is practical.

But I am curious enough about it to at least learn some more. Let's just pretend someone wants TBI for the easy starting, perhaps some additional fuel economy, and self-tuning.

1) Has anyone around here has actually tried the GM TBI swap onto a non-equipped 6 cyl? If so, how well did it work? (Perhaps coilover has done this?)

2) For those more knowledgeable around a GM TBI swap onto a different engine (say an old carb'd V8)....what else needs to be considered before a guy would try it on a stovebolt?

3) For anyone around here that has experience with BOTH GM TBI swaps and the Holley/FiTech things...which is preferable overall? Neither is perfect. The Sniper little touch screen interface is something you won't even begin to replicate with the GM approach. But that "what if I break down" question....seems like a pretty real concern.

TBI was/is a hybrid of a carburetor and a fuel injection system- - - - -and it's not really a good one. That's true for both OEM and aftermarket systems. I was teaching auto mechanics at a Tennessee state trade school when the first ones from GM showed up on new cars, and lots of us instructors attended the same factory schools as the dealer mechanics did, so we could give our students entry level training on the systems and make them better candidates for employment with the dealerships. The downside to any fuel injection system is controlling the volume and frequency of the pulse to deliver the right fuel/air mixture over a wide range of operating conditions. Air temperature, coolant temp, engine RPM, throttle position, manifold vacuum, transmission gear selection, and a bunch of other variables have to be factored in before the injector can provide the right squirt under all conditions. Making all that work on an engine the TBI unit was not engineered to fit will increase the likelihood of getting less than great performance by a pretty big margin. Good luck- - - -you'll probably need it!
Jerry

I have absolutely ZERO intention of trying this. Was just hypothesizing.

I owned an early Volvo inline 6 cylinder that had a pretty primitive port injection system on it. It was made by Bosch, and had two sets of points that triggered from lobes on the distributor shaft below the breaker plate to squirt 3 injectors at a time, controlled by a series of inputs like RPM, intake vacuum, throttle position, coolant temp, etc. It also had a "cold start" injector that delivered a rich mixture during warmup, controlled by a timer. A similar system could probably be cobbled up on a stovebolt, using three injectors, one installed into a stock intake manifold, aimed at each intake port in the head. The throttle base for a carburetor without the upper pieces attached could be used for air volume control. Three crankshaft position sensor triggers could be used to fire each injector just before the intake valve opened on each pair of cylinder head intake ports.
Jerry

What if you stripped the ring and pinion?

What if you tore a brake line?

What if you snapped an axle

What if you broke your front u-bolts?

What if you broke the frame in half?

What would you do in any of those situations?

What I tell most people is, you either fix it or tow it. Doesn't matter if it's the fuel system and fuel control system, suspension, drivetrain, electrical, mechanical, etc.

Have a basic understanding of the system you installed and what you might need to fix it on the road. Maybe add a handheld pocket scanner to the tool bag so you can see what the computer is complaining about. Maybe throw a test light in there too.

I've spent my whole career visiting vehicles on the side of the road and having to make the decision to either fix it where it sits or call the hook. And I bet you 90% of my coworkers don't like having to admit defeat and have the thing towed in. But, due to a new system that we don't understand yet, or all the big tools are back at the shop, or whatever, sometimes we have to get that tow. I can guarantee, things will break! So, it's not a matter of "if" but "when!" How familiar are you with that TBI system you installed. What basic tools should you carry with you incase it does start to hiccup. What plan do you have if you can't fix it on the side of the road?

Excited people always ask me "What do you think of the new electric wizbang the company just bought???" In my head I always say, its just another piece of crap with a company logo on it I have to work on. But what comes out of my mouth is, it has 4 wheels, still uses fluids, still has wipers, but it just has a different propulsion system. Some thing new I'll have to learn about.

My latest build, the GMC 302, I hope will be a beautiful build with sequential injection and computer controlled fuel and spark. I hope I can hide most of the sensors and wire so someone looking at it won't see clutter. And, if it manages to die somewhere that I can't fix it, I'll get a ride to pick up my modern fuel injected truck, hook up my car hauler, pick it up and haul it home where I can pretend I am a mad scientist and hook all kinds of diagnostic computers and wires to it so I can get it to tell me what's wrong. And, if I'm within a 400 mile radius of home, I'll call a friend and have them watch it for me until I can pick it up. And if I'm not near a friend, I guess asome tow company will get a few of my hard earned dollars.

Since the days of Jerry looking at TBI's, systems and parts have gotten much more efficient and reliable. Almost to the point of trouble free! Knock on wood, my '96 Chevy TPI in my '51 Suburban has never given me a problem. Except for the usual Chevy leaks, etc., we've all grown to know and love.

I have often wondered about the GM factory set up as well. There has been some success I have seen, but with the ease of a sniper I went with it. Not ready to run it yet, but I am looking forward to it. If I were to go on a trip I would know what hte known failure points of it are and buy an extra before I left.

I'm just spit balling here too. Ever see anyone ever used a 4.0L & trans from a jeep in place of a stovebolt? I mean use everything in the swap, no trying to reinvent the wheel. Having owned & driven 1, they are very responsive.

I too, have absolutely ZERO intention of trying this. I'll stick to my carb thank you.

You could also buy 3 of these: https://tinyurl.com/mpn8fwda and then build simple adapters to let you mount each one right straight on the 235 cylinder head. The size looks pretty doggone close to what you'd need anyway (1.5" diameter as I recall).

Each one of those has been engineered to supply 40 cubic inches and since no two of your siamesed cylinders will be firing sequentially, you'll be good to go. Get a common motorcycle 1 into 3 cable for the choke and throttle and also hook it up to the accelerator pump. A little fiberglass to build a 3 dock fly looking air intake using a common air filter like the Chevy Blazer and you'll be ready to go.

Oh, one other thought. These were designed for simple gravity flow fuel supply so you'll need a very low psi regulated electric pump, won't you? Sure...maybe 1.5 or so psi. Or you could gain some extra room and preserve the gravity flow scheme by mounting your gas tank on top of your cab. Or wait just a doggone minute. That room between your headliner panel and the top of your cab? That wasted space will become your new fuel tank and you can simply run a fuel line down through the roof pillar and into the engine compartment. And they thought I was sleeping in those industrial arts classes.

If it's a Suburban, you're gonna have to put in some bulkheads to prevent front to rear slosh!

Could you just use some 2 x 4s?