4.3 TBI to 4.3 carb swap
 

I currently have a 2000 Blazer, about 210,000 miles. Engine is on its way out, so I was considering an LS swap. Turns out, the LS swap would just be a little too expensive for me at this point. So, I did some hunting and came across an engine builder who has a 4.3 from around the same year (he said 2000 to around 2003.) Got a screamin' deal on it, rebuilt with a little extra beef. The one difference is that this motor is set up to run a carb (the only part I need to buy to make it go vroom).

I'm not the most mechanically inclined person, but I'm confident that I can pull this swap off with (hopefully) a set of helping hands. To me, it seems like this should be a fairly straightforward process, unbolt/unplug old motor, yank it out, get the new power plant in place, bolt it up, plug it in and burn some rubber (definitely over simplifying).

I talked to my sister's husband (mechanic) who told me the hardest part will be setting my truck up to run a carb. Again, I'm not the most mechanically inclined person, but isn't the function of a carb to basically use mechanical (read: non-electrical) methods to dump gas into the engine? More oversimplification on my part but my sister's husband said its basically down to "gutting the fuel pump and wiring the truck up".

He and my sister are having a baby, probably this weekend, which is when I hope to start the swap, so I won't really have him around to help.

My questions are:

1) How complicated is the wiring process, and does anyone have any experience with this part?
2) What needs to be done to the fuel pump in this swap?
3) The guy who is selling me the motor said something about an "MEI" distributor, and that I would just have to "run one wire", not sure exactly what he said because I spoke to him as I was walking into class. Any ideas here? I'll be speaking to the guy again and will ask him, but I would like to hear feedback from this group as I'm sure someone can elaborate on this.
4) While I have the engine bay empty, what should I take care of? You know, kinda like if you have the trans out to change the clutch, might as well check out the slave etc...

I'm hoping that this setup is a simpler setup than the current 4.3 I have. So many wires and sensors and things to go wrong.

Any information, warnings, advice, that anyone has in this endeavor would be GREATLY appreciated!

Fuel pump to a low pressure set up and.dist. to a HEI and it may kinnda run and that's the easy part.
Most of your electronics will not work, gauges will not work, computer will not work, ECT ECT ECT
What you are trying to do is not for the novice as it's not even close to a plug and play swap.

If it's an automatic, the trans probably won't work, either, right? In addition to all the other stuff mentioned

Also, how is the engine "set up to run carb?" seems to me you could just pull the FI intake manifold off your old engine, and put it on the new, and call it good.

Mine is currently a manual, the intake manifold is what I'm having problems with along with a cylinder that keeps losing compression.

The new motor is set up to run on a carb as in it has an Edelbrock intake with a 4100 Holley four barrel flange. I want to eliminate all the computer crap, can't I just run fuel and spark and make it work? Obviously the gauges will need to be addressed, but what is the need for the computer if there is no electronic injection going on?

I recently put a TH350 into an old Jeep that is running a carb'd 350 that has such a simple set up...no computer, minimal sensors, minimal wires, and it runs like a top. Is this application really that much different?

These are genuine questions, as I said before I'm not the most mechanically inclined person. I guess I should rephrase that, since I am mechanically inclined but am not experienced with big jobs like this.

Here are some pictures for reference:
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Basically this is a bad a$$ motor that I found by total chance at the exact right moment. The guy who built it has been building race motors for about 50 years and he is now retiring and closing up shop. This was his personal motor for his rat rod, he did all the machining himself, its a complete fresh motor; new bearings, roller lifters, new pistons, fresh cylinder walls (.030" over), timing set, cam...everything internally is new, balanced, and assembled by a life long, old school gear head. I couldn't pass up the opportunity to have something like this in my Blazer. Not only is the LS swap too costly right now, everyone is doing it. I know this won't make nearly as much power as say a sweet 5.7, but this motor is something you just don't see every day. At least I haven't seen many beefed up 4.3's besides a few on youtube.

Computer controls more than just fuel injection, and spark.
And yes it's a lot different than having a 350 and adding a th350 trans in a old non computer operated jeep
However your not going to be talked out of this set up so just be for-warned nothing that has anything to do with the computer is going to work.
You will be rebuilding each system in the vehicle into a non computerized system.
If you have the time, money, and knowledge any thing can be done.
Proof of that is in my avatar

What systems are we talking here? I'm not trying to come across as a know it all dillhole, but I am just not one to give up when something is complicated.

As long as I have speedo, tach, oil pressure, temp, voltage, lights, brakes, power steering...I'm good, right? I'm sure I'm missing things, but my point is that I'm fine with basic functions.

Well the only basic functions that you will have is power steering and maybe headlights, brakes if ABS don't screw with you.

Will the existing gauges hook up similarly in the new motor? I feel stupid admitting it, but I'm not sure which are monitored electronically and which are mechanical.

None are mechanical.
I'm not trying to talk you out of the build.
But in-less you rewire thu out the whole vehicle the computer can never be totally removed and as systems are intertwined you have the risk of failure of systems.
If you remove all the unneeded systems and had the computer re-flashed to remove all unneeded programing you may end up with a trouble free vehicle.

What systems may be prone to failure? I'm just confused because if I run fuel to it I can have it running on an engine stand no problem. If its running in the vehicle, I can then run vacuum and power to whatever needs it...right?

I suppose a more direct question would be what systems rely on the computer right now in the 2000 Blazer? Manual trans, so no issue there. I'm sure ABS has some sort of electrical situation going on...power steering is mechanical...obviously headlights/blinkers/tail lights/brake lights are electrical, but do they rely on the computer? Fuel pump needs power, but I'm fairly confident that is just straight juice and does not rely on the computer control...clutch is mechanical (well, hydraulic)...manual windows, manual locks, no anti theft, no power seats, no power mirrors, no butt warmers in the seats...The only things in the cab that require power currently are the interior lights, radio, and instrument cluster lights

Temp gauge seems fairly obvious how that works; oil pressure, tach, voltage...all seem like they would be simple to wire in a new gauge...I have no problem running a new, separate gauge for each...

It truly seems like you know what you're talking about, and I didn't think you're trying to talk me out of the build, however if you could give me more direct information that would be awesome! This is my first time diving this deep into the abyss, so I know I'm overlooking a lot of (likely fundamental) issues.

I know you don't want to hear it, but Odat is giving you good advice.

I'm going to give you a couple examples. Your gauges including speedo work the following way: Sensors input into the PCM. PCM sends computerized data signal on a single wire to the instrument cluster which interprets it and runs stepper motors to move the needles. No computer... no gauges. 2000 Blazers have what is called a BCM (body control module) which handles all power window motors and a lot of the convenience features that you rely on every day including interior lights, etc.

I have heard of people retaining the computer for running the trans and gauges and other things etc when using a carb - but knowing what to connect, what not to connect, and what you need is not a simple task.

What is your carb going to do with the 100+psi pressure your fuel pump is going to put out. There are many issues.

My advice is don't do it. Simply not worth the effort and difficult to do right. If that is a late vortec motor with metric block and crank sensor, just put your cam and intake on it and you're done.

I don't have power windows, and can't I run a new standalone speedo? Along with whatever other gauges I want to run? You say "A lot of the convenience features you rely on every day", but interior lights is the only thing I can think of besides the radio...

I'm told that an inline pressure regulator will handle this.

The goal here is to step away from the complexity of the TBI system. Mine has given me nightmares and I'm not very interested in keeping the system.

I feel that maybe I should mention: I'm currently pursuing my B.S. in Electronics Engineering so the idea of running a few wires or creating a couple circuits with toggle switches is not intimidating at all.

Basically, my ultimate concern is can I stick this new motor in, get the right fuel pressure, feed vacuum and power to the required components and drive away? This is based on the fact that I have no electronic components in the cab beyond the interior lights and the radio. If I can buy a 1945 chassis and do the same thing, why can't I do the same here? Sure, I'll lose some modern features but I'm fine with that.

These are honest questions, to be completely up front I just need a reliable, easy to work on set up right now. As long as I can monitor the things that will leave me dead in the water (temp, oil pressure...), I will be a few orders of magnitude beyond the sputtering, high idling, gas guzzling crap I'm dealing with now...and the only solution is to throw money at it and hope to "hit the jackpot"...with a carb sure I won't get the greatest fuel economy, but if something goes wrong I think it will be immeasurably easier to hunt down the issue...no?

I have a degree in electronics and telecommunications, and I wouldn't want to try and figure out how to get a carb to work in a "modern" fuel injected vehicle.

I know you want simple, but imo the simplest solution would be to either get the factory fuel injection working properly, or sell the truck and buy something that came factory with a carb.

If you do go through with this swap, please make a thread and document everything you do! Even if someone isn't trying to swap on a carb, the knowledge gained from that in depth of a look into the trucks electronics would be pretty valuable to have around here

When I built my toy thanks to all the help I had my VIN numbers to the 92 Jimmy running gear that shes built with were lost / misplaced / put where the sun don't shine { you get the idea } so if my computer ever dies replacing it will joys.
I'll be prob doing the carb set up myself. The difference is mine is a 1992 not a 2000+
With the 92 the computer is not as intertwined as in the 2000, You may get by with taking out sensors like O2, map, crank sensor ECT. You will have to leave the computer in and run temp, oil sensors ect and maybe the gauges will work,
But as the computer will be missing most of the input it needs to function I wouldn't put bets on it lasting trouble free for long if at all.
You will have to change the fuel pump out for a low pressure pump and more than likely have to run a regulator as well.
Trouble free easy to diagnose vehicle NO, you will no longer have the option of plugging a reader in to read codes, But you will get good at trouble shooting the old school way before you had a computer to tell you where to maybe look....

I guess I'm just confused because if I can get the motor running on a stand, without any computer elements, what changes when I stick it onto a chassis? Shouldn't matter if it's a model T or a 2019 Lambo, as long as it gets fuel, air, spark, it should still run exactly the same right? This hypothetical is, of course, assuming the loss of complex functions...but shouldn't the motor still run just the same?

As long as you don't mind giving up all your guages, interior lights, power locks, windows, mirrors, and seats, and can figure out how to drop the fuel pressure from 100+psi down to ~5 psi (the FI has a return line, as well, which dumps back on the pump to help cool it. Not sure if you would need that or not, depending on how you decide to do the pump) and can figure out a stand alone ignition system, you should be good.

Also, how does the starter/ignition switch tie in with the computer? That might need to be completely rewired as well. Plus, if you're using the stock pump, and planning on regulating it down to carb pressure, that might go through the computer as well, and would need some different way to be powered
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Ya it should run - and may limp down the road...
But you are missing the point that even tho it may run - if nothing else works thu out the vehicle it's still pretty much useless...
It may not charge, blinkers may not work, headlights may not work ECT ECT ECT just depending on how intergrated the 2000 system is.

Gauges, as far as I have been told, can all be ran individually (as in buy new standalone gauges and wire them up)...pain in the ass but not a big deal. No power anything inside, just interior lights, which I can wire up no problem assuming I can get clean juice. The guy who built the engine told me to put a pressure regulator in the send line and use the existing return. Ignition and fuel pump I plan on doing what I call "race car style", toggle for the pump and toggle for the starter.

Have an HEI Ignition system with it...basically I am looking at doing this like an old school rat rod except inside a nice modern body. Super stripped down powertrain, all beef no fixins haha...

The guy who is telling me the info is the guy I bought it from, who has been running a business building race engines for the last 50 years.

My other option is to talk to a friend of a friend, who runs a shop in town and specializes in custom work. He builds custom wiring harnesses and apparently does top notch work. But that's $$$...

Well, I hope the best for you!

Please, start a build thread when you get started! I'm very curious to see how it turns out!
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Yeah, I forgot that the alternator voltage regulation is done by the PCM!! No computer - no charge battery! That's another big one. And the alternator can't be rewired as it has no voltage regulator.

Just noticed that OP stated TBI to Carb in Title. Actually his 2nd gen Blazer is not TBI - a 2000 is MPFI

Dont quote me on this but I believe you can swap the fuel pump from a tbi setup, which would lower you fuel pressure closer to what you need and still run the fuel pressure regulator like your friend told you input line into the reg, out put to the carb and return to return line. Since your into electronics I would get the wiring diagrams and a poster board and create a schematic, flipping through the pages of the book tracing lines can greatly increase your chances of error and removing something you need.
then determine what sensors you need and what you can do with out and see if its possible to have those sensor on engine setup.
Second option would be to find a wiring harness and ecu from a TBI setup and go that route alot of work running/building a new harness but could limit alot of your head aches down the road. This would be my approach as I could get an ecu and wiring harness from junk yard at reasonable price and splice in approriate connectors if need be. Still might have to do something like dakota digital for instrument cluster/gauges but could take out alot of the pain that will be involved. You got a lot of research infront of you to make it work right but it can be done. what its gonna cost who knows.

What cam did he install?

LOL. What an unexpected ending. Actually I am thinking of swapping the intake with CFI for a carburetor one. It's operation is pretty similar to the LPG 2nd gen supply - injectors are inhibited, while the mixture of LPG and air goes through the throttle body. That kind of an installation is widely used, and what it require is an O2 sensor signal emulators. All other things like odo, rpm, oil pressure, transmission are in tact. RPM signal comes from a camshaft, odo from VSS, oil pressure from the galley sensor. I don't actually see the reason they won't work.

Doubt the OP is coming back but this just made me laugh. :icon_crackup:

I think you may have overestimated the power of a bunch of jerks on the internet...

I'm totally just kidding!!

Everyone's criticisms were exactly why I posted here. Unfortunately, life got in the way and I had to put things on pause. Right now I am maybe a day or two of work away from firing it up. I learned a lot during this process and I plan on doing a more in-depth thread in the coming weeks. Unfortunately, I didn't get a lot of pictures or any videos.


https://cimg7.ibsrv.net/gimg/blazerf...44bf894ca5.jpg
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Nice work. Nice electrical circuitry. Let us know how it turns out.

It's running a marine cam.

Since this thread is kinda dead for now and lacks much real organization or direction, I'll share a few small details here before I start the real build thread.

In reading my posts, I think I undersold my abilities. This was clearly due to lack of experience and the natural tendency to overcomplicate things because once I reduced everything down to bolts and plugs in my mind, there was no need to ask silly questions anymore. The old system's electronics were terrifyingly intertwined and wiring diagrams shut my brain down...so...I yanked every last wire and control module from the vehicle. Everything will be controlled by my simple, effective system. I'm approaching this as a fresh, old school rat rod. Everything electrical that remains is very simple; the most complicated things are the blinkers and wiper motor. No power steering, no AC, no ABS. Will be wrestling the pumpless power steering for a bit while I decide how to convert to mechanical steering, and I'm still researching how to eliminate the vacuum booster in the brake system. This is no ordinary project, especially for 2020...dumbed down, stripped of creature comforts...blah blah blah...

Edit to add::: The gauges that I'm using for now are just a Bosch mechanical set. Oil pressure, water temp, voltage. Just the stuff I need to feel like I know what's going on.

Really looking foward to this, very intrigued