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Discussion Starter · #1 ·
Can you all help me out with what I will need to do a TBI to Carb conversion. Its on my chevy truck. I know I need: Braided fuel line, Fuel pressure regulator, HEI distributor, and I cant think of anything else besides carb and intake. As far a a regulator I have seen alot of different ones but I dont know which one to get. Can anyone help me out with a link to one.

Thanks....SS
 

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If you check out diyautotune.com site you'll find there is a section with directions on how this guy converted his carbed 350 to tbi. He is using a megasquirt ecm, which you do not have to use, but if you read and watch the 1st and 2nd parts of the conversion, then you'll find all of the parts needed.

In terms of parts, a short list is intake and coolant temp sensors (same sensor), IAC and TPS that is on the GM TBI, and MAP or MAF sensor depending on ecm being used. Fuel pump rated for the TBI you have. If you are using a stock GM TBI, then I believe the fuel pressure regulator is built into the throttle body. Also, if using the stock TBI, then you'll need both lines (steel braided) that attach to the rear, properly rated fuel pump, and a fuel filter rated for the TBI unit (micron size). Now that I've typed all of this, are you planning on using an aftermarket setup or stock setup?

What are you planning on using for an ecm?

And also, if you are running something like Megasquirt, you don't have to swap distributor's, but is highly recommended. Otherwise you have to know exactly what is going on with your distributor in terms of vacuum and centrifugal advance at varying MAP readings. Basically you have to have your old distributor tuned - MUCH easier to bolt on the HEI unit!
 

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Can you all help me out with what I will need to do a TBI to Carb conversion. Its on my chevy truck. I know I need: Braided fuel line, Fuel pressure regulator, HEI distributor, and I cant think of anything else besides carb and intake. As far a a regulator I have seen alot of different ones but I dont know which one to get. Can anyone help me out with a link to one.

Thanks....SS
you didn't say what year truck... but I'll guess some

you'll need what you listed..
the fuel reg. can't be what they call a deadhead. you have to use one that uses a return line.
if your trans is computer controlled it will not like this at all and you'll be forced into a stand allone controller
if the tranks is a 7004r you'll need the correct t.v. cable and brackets . if factory intake you can use the factory brackets, if aftermarket you'll need to get the brackets that work with that intake.. edel/etc makes/sells them..
you'll need a hei thats not computer controlled..

your check engine light will be on. if they plug into the service port for state inspection. you'll fail..
your cruise will not work..
and your speedo might not also (not knowing the year/model)
good luck
 

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Can you all help me out with what I will need to do a TBI to Carb conversion. Its on my chevy truck. I know I need: Braided fuel line, Fuel pressure regulator, HEI distributor, and I cant think of anything else besides carb and intake. As far a a regulator I have seen alot of different ones but I dont know which one to get. Can anyone help me out with a link to one.

Thanks....SS
Depends on year and transmission. For a stick no problem, for a 700R4/4L60 analog 4 speed automatic no problem, for the 4L60E (E for electronic) digital 4 speed automatic, 1993 in some cases and 1994 up in all cases it's a PIA to keep needed sensor data flowing to the tranny.

For the manual gear box or 700R4/4L60 automatic you will need an adjustable bypassing regulator to drop the fuel pressure to 4-6 psi. I know these regulators are expensive but by the time you fiddle the existing fuel system to accept a low pressure pump you'll spend this much or more and have to do a lot of plumbing and wiring work to boot, so the expensive regulator is the easy way through the problem of fuel pressure. by p****ing regulators prevent the pump from dead heading when the enigne is idleing preventing the electric pump from overheating Other than that you'll need a 4 barrel intake that bolts to the Swirl Port heads, the difference between these and older heads is just the angle the bolts make to the head's intake mounting surface pre 1987 use a 90 degree angle 1987 up use a 72 degree angle. Open the instrument cluster and remove the bulb from the check engine light. Hardwire the fuel pump relay to the ignition switch as the computer is looking for a tach signal to keep the fuel pump running, if you change the distributor to an older HEI (and who wouldn't in this case) there is no point to keeping the computer in the distributor loop so there will be no tach signal to the computer, so the hard wire gets around all that.

Note, this is NOT LEGAL to do anywhere in the U.S. while your state may not enforce Federal Law on emissions nor have emissions laws itself; it still is a Federal Law; so be aware of that.

Bogie
 

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Discussion Starter · #8 ·
Well I am not 100% sure of what my transmission is. I thought it is the 4L60E but How do I tell. Looks like that is my only issue Im going to have to deal with. If it is a 4L60E could I Use a computer out of a truck with a manual trans and take care of it. First tho how do I tell what trans it is? It is a 94 so Im guessing it is computer controlled. If it is what year trucks had the 4L60 in them so I can get on or is the 700r4 the same length.
 

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Well I am not 100% sure of what my transmission is. I thought it is the 4L60E but How do I tell. Looks like that is my only issue Im going to have to deal with. If it is a 4L60E could I Use a computer out of a truck with a manual trans and take care of it. First tho how do I tell what trans it is? It is a 94 so Im guessing it is computer controlled. If it is what year trucks had the 4L60 in them so I can get on or is the 700r4 the same length.
The 700R4/4L60 will have a mechanical cable link coming from the TBI throttle linkage which is the modulator control; the 4L60E will not have any mechanical linkage or cable connection with the throttle linkage. Underneath the 4L60E will have a big black box on the driver's side that the shift lever connects to and a very large wire bundle that enters the case on the passenger side.

If this has the 4L60E, my advice would be to fix the TBI. Not knowing why you want to replace the TBI if it's malfunctioning or you want more performance. Either-way it's probably less expensive to repair or hot rod the TBI. The 4L60E can be operated from a standalone controller but this isn't very cheap. The other way would be to put in a 700R4/4L60. There is no cheap solution to the fully electronic vehicles that start with the 93-95 late OBD I production and it only gets worse with 96 up OBD II production. The levels of Systems Integration just keep increasing making it ever-more expensive and difficult to simple these later model vehicles.

Bogie
 

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I know my oil pressure, coolant temp, volts, fuel has nothing to do with my computer. speedo is hooked up to my trans and my tach is hooked into my distributor.
and you'd be incorrect..
the collant tepm. sender tells the ecu if it's cold out.. and richen it up..
fyi if sender is junk the ecu goes in to limp home mode (i.e. rich)
no oil psi.. no fuel pmp power.. yes it's not as involved as a 2012 truck.. but it all works together..

malc, your f body is from the 80's..
the trucks started with the ecu controlling more of the dash in the changeover in the late 80's
 

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So are you sayin the none computer trans 4L60 has two cables hooked to the throttle body.
The 700R4/4L60 will have a mechanical cable connection from the throttle bell crank that runs down to the transmission. This is the modulator that controls shift points and kick down in relation to throttle position.

The 4L60E will not have this feature connected to the throttle; it gets modulation as digital data from the computer which gets it data from the throttle position sensor mounted on the TBI body and is connected to the computer through the electrical wire harness.

If you have a 4L60E this is the program to follow for the lowest cost solution:

- The existing computer needs the Coolant Temperature Signal (CTS), Throttle Position Signal (TPS), Vehicle Speed Signal (VSS), and the RPM (tach) signal in order to operate the transmission.

- While you can fabricate brackets and a connection to the throttle shaft for your existing TPS, Holley sells a kit that makes this way simpler but it needs to be a Holley with an electric choke. >>> Holley Performance Products Throttle Position Kit for Electric Choke Carburetors 534-202 <<<

- The VSS signal comes from the tranny, there is some variation in frequency year to year so keeping your tranny and computer together for your year of truck keeps the speedo tracking with reality and the tranny shifting correctly including the TSS converter lock up.

- The Coolant Temp Signal (CTS) is not the same as what drives the engine temp gauge on the panel, you'll need to use an intake manifold that provides space for two temp sensors unless you move the gauge sender to the cylinder head fitting. This mostly controls TSS converter lock up and prevents 4th overdrive if the engine is running hot and working hard, this protects the tranny from going up in smoke and trust me it will if overloaded in TSS and or 4th gear.

- Since going to a carb would indicate perhaps a performance application then you should also use a stand alone distributor so the computer isn't running the engine on its emissions profile, so an earlier model HEI is needed. Connect its tach lead to the purple and white wire that goes into the old distributor connector of the TBI distributor.

- The tach signal is used for shift points which are modualted by the TPS, it also contributes to converter lock up TSS and 4th gear application.

- Follow what I said for an adjustable fuel pressure regulator with a return. The return is needed to keep the pump from dead heading which will cause it to overheat.

Keep in mind that none of this is legal to do.

Bogie
 

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Discussion Starter · #18 ·
Here is some pics of the throttle body

One of the cables run to the black box by my brake booster.

Also can anyone tell me what that connector plugs into? Its been unplugged since I got the truck and there IS NO WHERE for it to plug into. It only reaches about 8 inches so I can see everywhere it could go but nothing there to plug into.
 

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My Throttle body has two cables connected to it. Is this what you are talking about. Also my temp gauge runs to my cylinder head. Im gonna go take a picture of it.
Two mechanical cables to the throttle bell crank would be the foot feed cable that moves the throttle and the modulator cable to the transmission. That would indicate that the tranny is 700R4/4L60. That makes switching the TBI to carb a lot simpler.

Bogie
 

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Discussion Starter · #20 ·
Nice..... Thats what I like to here. So is it a 700r4 or 4L60, Im gettin confused.


So all I should need is intake, carb, regulator, Some fuel line, HEI Distributor.

Can I use a manual choke or do I need Electric choke? Which one is better.
 
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