TBI TO CARB CONVERSION

[JACK34]

I have a friend of mine who has I think a early model like 88 or 89 not sure. Anyway his problem is low power all kinds of things. He has taken it to professional mechanics and they can't figure it out. They have ruled out the the engine being bad. So what he has decided to do is take the TBI off and put a carb on. Have any of you had similar problems? I have a 94 and mine runs great for now. And is there a alternative solution to his problem other than putting a carb on it?

 

[PlayingWithTBI]

The Throttle Body is very dependable. IMO he'll go through the expense of swapping to a carb and still be disappointed if he doesn't find the root cause. Did the professional mechanics put it on a scanner? Did they check fuel pressure? How old is the distributor, cap, rotor, ICM module, coil, plug wires? Did anyone even do a regular tuneup?

I have a hard time with going backwards to an obsolete system because I can't figure out what's wrong in the 1st place, but that's just me.

 

[JACK34]

The Throttle Body is very dependable. IMO he'll go through the expense of swapping to a carb and still be disappointed if he doesn't find the root cause. Did the professional mechanics put it on a scanner? Did they check fuel pressure? How old is the distributor, cap, rotor, ICM module, coil, plug wires? Did anyone even do a regular tuneup?

I have a hard time with going backwards to an obsolete system because I can't figure out what's wrong in the 1st place, but that's just me.

Yes they did pretty much what you said I think not sure. Still could not figure it out. I don't know exactly what they did I will ask him and anyone who reads this that has a idea I will relay that to my friend. I'm hoping they overlooked something simple.

 

[351FUN]

It's doable, but you'll have less power/drivability than with fuel injection. If it's an automatic he'll either need to buy a trans controller or have a switch he flips to lock up the converter, and rig a way to automatically unlock when he stops. We can't really give you ideas on what to look for without symptoms. Low power is normal, but what do you mean by "all kinds of things?"

The best solution is to fix the actual issue, because it's almost certainly not the TBI, which he'll discover after he goes through all the trouble to downgrade.

 

[454cid]

Doesn't this early of a truck have a 700r4 if it's an auto?

 

[JACK34]

Yeah I understand what everyone is saying and I agree. I talked to him yesterday and he is pretty frustrated and already has started buying things for the swap. I wish I could say specifically what the problem is and what the mechanics have checked or changed but I can't. I was not aware of the transmission issue 351FUN appreciate that info I will let him know. Not sure what transmission he has. I believe he has changed the plugs, wires, cap and rotor, timed it and just basic stuff before it went to the mechanics. I think they did a compression test and changed some sensors and did more diagnostics. It would all of a sudden run great it was fixed then without doing anything it went back to running bad. Idle up and down, hesitation loss of power, sounds like it's missing. things like that. I told him I was going to ask on this forum so hopefully someone here can help. I know it's a stretch, appreciate you all.

 

[legendman]

IAC Idle Air Control maybe ?

https://carcaretotal.com/idle-air-control-valve-symptoms/

 

[thegawd]

I'm far from a expert but i read alot about these trucks. I remember reading something very similar and I recall the problem being the ICM inside or close to the distributor. Something goes wrong and it gets fried. But it gets overlooked because it was either just replaced and or your getting spark but it's not a good spark.... there is a special thermal paste that goes with these ICMs. Again I haven't worked on one of these trucks just read a lot about them.... my trucks are a bit newer.

I understand your situation, I have a friend who would also do the same thing without fully trying to fix the root cause once he gets frustrated trying... it's a PITA trying to troubleshoot someone else's vehicle.

Al

 

[JACK34]

I'm far from a expert but i read alot about these trucks. I remember reading something very similar and I recall the problem being the ICM inside or close to the distributor. Something goes wrong and it gets fried. But it gets overlooked because it was either just replaced and or your getting spark but it's not a good spark.... there is a special thermal paste that goes with these ICMs. Again I haven't worked on one of these trucks just read a lot about them.... my trucks are a bit newer.

I understand your situation, I have a friend who would also do the same thing without fully trying to fix the root cause once he gets frustrated trying... it's a PITA trying to troubleshoot someone else's vehicle.

Al

Thank you I passed that along to him. Much appreciated.

 

[Aidan Kesler]

The less power/drivability and gas mileage issues blah blah that everyone says is, as far as I've found, a myth. I have drove 2 carbureted trucks of these models, 94 and 96. I used to have an 82 C10 with a carbureted 350 (I know it's different technology and older but still same concept). I am even considering a carb swap on my 95 now but money is holding me back for now. First thing's first is to figure out if you have the 700r4 or the 4L60E, if you got a 700r4 then you will have to buy a "detent cable adapter kit for carbs" or "tv cable adapter kit for carbs" something along those lines, if you have the 4L60E then you will either have to buy a separate trans controller or do some wire splicing and modification to the trans harness to shift properly with a carb TPS kit you can buy online, but that's a whole 'nother story and thread to talk about... if you have a manual trans then you don't have to worry about the trans. Then you will have to have an inline fuel pressure regulator that has a return line system for the stock TBI fuel pump. Next is you will have to get a carb of your choice (I'd recommend 600cfm for stock motor), a carb intake (my recommendation is the edelbrock 2104 dual plane intake) this intake is made for the TBI heads and center bolt heads. Then you will have to get an HEI distributor to replace the old TBI one. You would then just put all the parts on the motor like you normally would if you were building one. Only thing to keep in mind is your fuel pressure and detent cable for auto trans. I believe carb fuel pressure if between 5-13 psi (you'd have to look up what is recommend for your motor and your carb). Also make sure the return fuel line is hooked up or you could burn up your TBI pump. The detent cable will have to be adjusted to shift properly with the carb and for your specific circumstance. I believe that's all is needed, if I forgot something and remember it I will edit and make sure it's known. Good luck!