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?

Yes. But you must wrap them in Dynamat to help with the sound.

Dynamat or Dianabol? Some guys I knew in college used to take that to bulk up. Wait...never mind. You said bulkheads. Not bulk up. We'll go with the Dynamat.

The TBI units have the same problems as carb when it comes to fuel distribution between the cylinders. Multi-port injection addresses that issue by having an injector for each cylinder.

The big advantages to TBI systems are (in nor particular order):
-You don't have to change the tuning for environmental effects such as temperature, altitude, etc because the computer manages all of that for you.
-You don't have to worry about floats, needles, etc. Fuel pressure has a much lower effect on a fuel injection system.
-The fuel system is sealed, so you can leave it sitting for months and it will still start right back up without cranking and pumping and fighting with it.
-Closed loop tuning is possible using an O2 sensor.


The GM tbi units are pretty robust. There are a decent number of free tuning tools available for them, but a prom writer is required. There is also a company (I can't think of the name at the moment, will add if I come up with it) that sells tuned chips for different engines. Parts are easy to come up and fairly cheap.

The FiTech units (in my experience, Coilover seems to like them better) tend to have a much larger issue with inconsistent fueling per cylinder. They claim that their annular ring injector head design helps with it, but their design is kind of censored poor. The pressure differential around the ring results in more fuel spraying in from the injector sides. With it coming in sideways, it does not distribute well. If you look at the promo pictures they publish, you can see the uneven fuel distribution. If your intake works with the fuel distribution of the injectors, the autotuning works quite well.

The Holley system has a much more traditional design based on the GM sysem. You can actually use the GM TBI unit with the Holley controls if you are willing to get creative with sensor installation. The tuning has more options than the FiTech units.

Both the FiTech and Holley units can both control your timing, which is a nice bonus. I know the later (late 90s) GM systems had a smart distributor that was controlled by the ECU, but last time I tinkered with on you could only use that feature with a lot of extra hassle.

I have not personally used a megasquirt, but I have looked at them several times and been unimpressed. You have to be careful to get one assembled by someone competent. There are a lot of sketchy sellers that don't use quality parts or assembly practices. They have a limited codespace and tuning options (number/size throttle tables and such). If someone is considering one, I strongly recommend doing some in depth research.

Going with an aftermarket ECU like a Haltech is not cheap, but you can use it with a great many hardware options and the tuning is extremely flexible. It has a lot of options for boost, nitrous, transmission control, etc. I am toying with getting one for my daughter's j**p project.

Might be more info than you really wanted...

Not too much at all, Fibonachu. I was hoping for someone to reply who had fiddled with both the GM and the aftermarket types.

I’ll ask a question out of ignorance. I know just enough about LS swaps to be dangerous. Those who run them with the factory ECU have to have the VATS removed. But that’s more or less all it takes to get one to run. I don’t ~think~ the VATS step would be part of the TBI system.

Let’s pretend someone went and got a GM TBI, harness, and ECU from an early 90s 4.3 V6. Mounted it on a Stovebolt with all the sensors located, wired in, and such. Perhaps with an HEI distributor to supply that input. Would it run at all? Even poorly without a tune? Would the different firing order from the V6 computer totally hose things up?

I have not tried converting a V6 to an I6, so this is speculation:

A 4.3L is ~262CI, so the overall displacement is similar. If I had to make a guess, I think it would run but pretty badly.

The injectors are batch fired, so the cylinder firing order would not matter for them. You could deal with the timing differences/firing order in the distributor (just use a traditional distributor with vacuum advance instead of the computer controlled one).

I expect the fuelling would be an issue with the lower compression and different cam profile. Given the torque/hp curve differences between a V6 and an I6, I also expect there to be enough differences in the details of how they need to he fueled to cause issues. I strongly suspect tuning would be necessary to make it run acceptably, let alone well.

Additionally, by the time you do the machine work etc to install the GM TBI on that engine you would likely have spent more money than a Sniper (Holley) unit costs and be running 30+ year older technology.

If your goal was to keep it all GM and be able to scrounge junkyard spares, that might be worth it to you. If your goal was an economy fuel injection build, that is probably not the best approach.

Howell is the place that sells the conversion kits and they have 261 kit. Reading the description, I am not sure how much customization they are actually doing.

https://howellefi.com/product/hc261-chevrolet-261-cid-tbi-conversion-kit/

I have a friend who put one of the Howell kits on his Jeep Gladiator with the 360. It worked reasonably well. That kit was based on the Chevy 350 TBI system so the original displacement was similar and they were both V8s.

I had seen the Howell stuff in my poking around. They actually sell the complete set for several inline 6’s, including the 261. Like you, I have my doubts in how much custom tuning is done on each. And it’s far from a budget approach.

Wonder if you could buy just the “custom” chip or ECU and source the rest yourself?

If you could, I suspect that it would not be much of a savings. That is the only part unique to them and the kits are a lot more expensive than the sum of the parts.

Couldn't hurt to ask though.

A very lengthy thread from several years back. It appears this bolter got his 235 running with TBI. Trail goes cold before we hear any final tuning results.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/813034/1.html

There's another thread that I started on the subject using the Holley Sniper designed for the Ford 170/200/250.

A member (D B Cooper) responded that he successfully installed it on a 235. It wasn't done for performance enhancement. It was done to end the carburetor/fuel pump problems.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1482871/1.html

The rise of the aftermarket systems (such as the Sniper) in recent years seems to have pushed the GM TBI adaptation into the realm of a nearly lost art.

My hypothesis with this thread was that the GM approach might be better than the aftermarket in a couple ways:

1) Cheaper - I think we’ve almost disproven one. All the hard parts could be sourced cheaply. The only way it might be cheaper overall, is if you’re willing to learn to do some program tuning on your own.

2) More reliable - I still think this is an argument worth considering. The GM system, although not perfect, has been battle tested over eleventy trillion miles. I think the Sniper/FiTech systems will get more and more common, and will get more reliable. But they have a long ways to go in proving that.

FiTech != Reliable. I can think of 6 people I know personally that have installed them and had significant reliability issues. I don't know anyone personally that has installed one and not had issues. That said, I believe Coilover has used them and had better success. If someone were considering one, I would recommend discussing it with him.

I put about 50k miles on my Holley Projection (precursor to the sniper) system without having to touch it. That is longer than the factory GM TBI unit I had on my S10 lasted between repairs.

I sold the projection unit to a buddy's uncle and we put it on his boat where it has been running flawlessly for almost 10 years.

Your mileage may vary (knuck knuck knuck), but if I were it do a TBI conversion I would buy a sniper.

Just bringing some personal insight to this, great discussion BTW. I have a '93 K1500 with factory TBI, it has had a few issues over the years but all in all it very relaible. This truck was designed to support fuel injection, in-tank fuel pump, fuel return lines, O2 sensors and the like. The engine in my '93 is stock. I have built several 4.3L V6's for people with great results. I built one for an S10 blazer that pushed over 400Hp on a Dyno, it tore the center out of the flex plate once it was installed in the truck. The point is to install a TBI on a non TBI vehicle all of these additional systems must be considered in the build.

I say this because having installed a Snipper EFI on a '57 3100 with an early '70's 350 V8 it became a mess very quickly. The Holley system directs all of the fuel and electrical connections out the rear of the throttle body, the area is already filled with the distributor, coil and various lines. Add to this that the fire wall is fairly close as well. The fuel lines run over the back of the engine block and down to the frame rails and are routed to the tank. The addition of a return line adds some issues it self, if the tank is in the factory location that is must be considered, if the tank is mounted to the frame (as many are) it still must accommodate the addition of a return line. The Holley system supplies all of the materials to install this EFI, the clamp on O2 bung and rubber fuel lines just made it feel cobbled together. All this can be done but it should be planned well ahead.

The discussion of the 4.3L TBI is much the same, it can be made to work, it just needs to be planned out. By "It can be made to work" that doesn't mean it will work well. As mention earlier there are some big differences in the make up of a V6 versus an L6.

I think that a Hybrid approach could be done, Jerry said the use of single port injectors with separate crank sensors could be done. Adding the fuel management ECU and being able to tune it correctly would be the hard part. Cost wise would it be worth it ? No , but it would be COOL.