TBI to carb swap

[MechroMenace]

I'm planning on swapping my 1988 suburban from TBI to carb, I tried searching through the forums most people don't seem to be fans of going backwards but, after adding a non-computer compatible cam by accident (I didn't think an RV would be incompatible with a computer) its been running poorly gas mileage tanked from 12 to 9 around town because the computer isn't sure what is going on and is throwing fuel at it. Since I have a Camry that is good for being reliable when I need it and the suburban is more of a toy I decided a Carb would be my best solution because I don't feel like replacing the cam again and I think it would be fun. I can also get rid of the rat nest wiring under the hood and make it look nice and clean.

Anyways I have the intake for it, a Quadrajet carb and a HEI distributor I'm pretty sure all I need more is a throttle cable and decided what to do with the fuel pump, and a manual choke. Correct me if I am wrong but from what I've been reading the 3 line mechanical fuel pumps will return the extra fuel that goes through them so technically I could leave the electric fuel pump in and add a 3 line mechanical and it should maintain fuel pressure right? also I'm assuming since the block has a block off plate where a mechanical fuel pump usually is it should be machined for a mechanical pump right?

Is there anything I'm over looking?

 

[Blue85]

If you can get a chip burned for the EFI, it will be easier, cheaper and run better. Give the specs to somebody good with TBI and they should be able to tell you if it will work OK or not. There is some info in "The Injection Section".

 

[bp71k5]

Have you done a data log to see what's really happening? Gas mileage lowering might just be from the cam change. If it is, going to a carb won't change it.

If you are really into a carb change, an electric choke would make more sense than a manual.

 

[MechroMenace]

I actually have a Moates programmer that I got when I was helping my dad restore a CJ7 which we put a TBI on. After putting the cam in this truck the BLM has been pegged at 172 and I can usually smell quite a bit of gas coming from the exhaust it also has a new O2 sensor. Honestly I just want to do the carburetor for the fun of it maybe in 5 years or so I'll find a way to get one of those marine intakes that have the individual 8 injectors, and probably a few other things. But for now I'd like a carburetor so I can get it to run right with a screwdriver. I could also wire a kill switch to the distributor for more fun.

 

[dyeager535]

I don't know as I'd run both an electric and mechanical pump. Might be possible, but also might create unintended consequences.

Assuming automatic, you'll have to figure out the TV cable portion, but shouldn't be tough if the Q-jet is set up for it. Bracket, etc. I can't recall if the '88's had TCC controlled by the ECM, but I'm guessing yes. So another problem to resolve.

EVAP is going to be a bit of an issue, since you'll lose control of that.

The block is *probably* machined for a fuel pump rod, assuming it's the original block. The early EFI year blocks seemed to be fairly consistent in that regard, but not a guarantee.

If you've got a programmer, I'd really reconsider what you are thinking of doing. Still going to take some work of course, but having to change a bunch of mechanical and electrical stuff around, vs. reprogramming, is going to be a lot more costly, with worse results in the end.

Obviously you can do whatever you want, it is your truck, but the carb is never going to beat the TBI at anything except less wiring. Maybe you don't find tuning fun, but in your case it will definitely be a challenge and should be quite rewarding to have a cammed TBI rig.

If you decide to go the carbed route, don't hack the wiring up. Butchering wiring/splicing random garbage in isn't making things cleaner. Pull it out complete, and save or sell it.

 

[MechroMenace]

it actually has a 4 speed manual in it, and all the emissions stuff was cut out by the previous owner so that will make it a bit easier. Also after doing a lot of research on this I've come to find most of the people that run both a mechanical and electric pump usually use a low PSI electric for priming and preventing vapor lock, so I came up with this idea that I sketched out, I figure I can run it this way and when the electric pump dies I'll just pull the pump and put a hose in its place. As for wiring I have a bunch of those open barrel crimps that you can find on the OEM wiring harness's that GM uses that I can use to make a clean wire setup. Also I checked yesterday, I removed the block off plate and sure enough there everything for a mechanical pump there.

This is my dads CJ7 that I did the wiring in, this isn't what it looks like now mostly because the wiring harness that I dissected and rebuilt was having resistance issues so I redid it with new wires and also cleaned up the wiring for the solenoid. It runs great but I'm glad the s10's 4.3 was close enough to the 4.2 that I just copied the tune from one of those because after many hours of research I still could not figure out how to modify the BLM tables so I resorted to adjusting that fuel injector size setting until the BLM was reading 128 + - 5, and thanks to that I have no desire to figure it out on my truck. As for the suburban when I get the carburetor put in and and the engine bay cleaned up I'll post some more pictures here.

 

[cyclic]

Oh dear lord, it'll cost you more to change it over than it would just to either get it chipped or switch to DynamicEFI. Have a chip burned will work ok, but having it actually tuned or the DynamicEFI will actually make it run great. Might even get you more than the 12 mpg you started with.

 

[MechroMenace]

Eh its not really going to cost that much so far I've spent 150$ getting the intake, distributor, carburetor and rebuild kit and I'll probably spend another 150$ for intake gaskets a few extra carburetor parts, and As long as I remove all of the stuff and keep it in one piece I'm sure I could sell the setup for close to what I'm going to spend on the carburetor setup. Is EFI better yes, but I'm sure I can get a Carburetor to run just as well with some tinkering I should be able to hit 11-12MPG no problem. Plus this isn't a practical truck I just want to have fun with it, and I feel like I could have some fun with learning how to tune carburetor plus I could clean the engine bay up.