350 TBI to carb swap.

[jacobdavis1979]

Yes just like the title says i wanna get rid of the tbi on my gmc and convert to a carb with an hei. I know you guys are gonna give me alot of hate on this one but after 11 obd codes and spending about $600 on sensors and other stuff like a fuel pump, filter, new throttle body, ecm, plugs, plugwires, etc. And still running god awfull on a motor basically brand new with over 120 compression on each cylinder. Im done. I really like this truck and wanna drive it.

I was wondering if you guys could reccomend an intake and give me other tips on how to do this swap. My buddy had a 92 gmc that he did this on has drove it for years and still driving it to this day so i know it can be done so can you guys give me any tips?

And before anyone wants to run me off the forum for this being on gbody procject i just wanna say please dont. I ask you guys because this is the best forum on the web with the most helpful people out there and i really appreciate your guys help

 

[ssn696]

What I wonder about is what happens to your gauges when you bypass the whole computer.
You'll need to decide on a carb and also must change your distributor to a non-computer controlled one.
The fuel pressure from your in-tank senders will be way too high. Your motor does not have the fuel pump pad drilled for a mechanical pump. You can try to put a fuel pressure regulator on it, but I'm not sure how well that will work out.
About the only easy problem to solve is that the center intake bolts are titled at a different angle, so you'll need to find a manifold with this feature. Here is one from Summit: CMB-03-0108

Once upon a time, Edelbrock used to sell an EFI upgrade kit that would work on these motors...it was just of $1000. Nothing comes up at Summit now...

Sorry for the doom and gloom.

 

[crotchss]

I run a 406 SBC carbed engine in my 1989 K1500. All I did was pull the fuel pump fuse and run a non-computer controlled HEI distributor. I run a mechanical fuel pump, it will draw through the electric and everything else works great. For a pump you could run a regulator or frame mounted aftermarket. What year is the truck? After 1992 they switched to computer controlled trans instead of TV cable, so that could be a problem. I have a 5 speed so no problems there. Here's a link to my YouTube video of the engine in my truck. http://m.youtube.com/watch?v=MY3JsYIIfX0

 

[jacobdavis1979]

Ok cool so youv done this? Did you have any problems with gauges like the speedo and gas gauge are they tied into the ecm? What about the heater and A/C will that still work if i pull the ecm? As for the truck its an 88 gmc sierra its a beautifful truck. As far as i know its got the 700r4 so its not controlled by the computer no problems there.

 

[jacobdavis1979]

I do have some of the old parts off my malibu i plan on useing like the hei and maybe the quadrajet

 

[olds307 and 403]

Your gauges will work. As said, either the electric pump with a regulator or a mechanical pump. Get a TV cable bracket off a Qjet powered car with the 700R4 like a Camero.

 

[Clone TIE Pilot]

Usually when converting a car or truck from computer controlled to non computer controlled just opens a can of worms and doesn't really solve your problems. Alot of times the computer system is blamed for what is really a probelm somewhere else. Have you checked for vacuum leaks? Those will throw computers into fits.

 

[crotchss]

All my gauges work fine, a/c works, etc. Only thing you will have to figure out is getting the lock-up to work on the converter because you won't have the computer locking it up. Switching to my set-up I get 15 mpg, not great, but the TBI 350 that was in there before was tired and only getting 16 mpg. Plus now she'll pull about anything and runs pretty hard for what it is. I think the 5 speed is living on borrowed time though, so I "try" to take it easy on it.

 

[jacobdavis1979]

Yes vaccuum hoses are new fuel lines are all new like i said above throttlebody all the sensors are new dizzy is new with new module ecm is new if you can name it ive changed it.


Sweet im glad to hear everything works. Did you pull the ecm harness or did you just cut the wires you wernt useing?

 

[jacobdavis1979]

Clone Pilot im sorry id like to save the fuel injection but i plan on makin atleast 400hp with this truck someday so a carb swap would just be easier for me to tune anyway