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Discussion Starter · #1 ·
I have a 1987 2.5 s10 5 speed and have had an extremely difficult time with my computer and getting everything running with the computer so I was wondering what all it would take to just carb swap the 2.5 tbi?
 

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Gun Totin *******
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Discussion Starter · #12 ·
You will need advance vacuum from the carb and manifold vacuum for climate control and of course brake booster as well as pvc which normally is a port on the carb
Thank you! Do you know if a Holley r 7697 a would fit on that adapter? I found one relatively cheap that I can rebuild instead of that $400 I’m seeing everywhere else
 

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Discussion Starter · #16 ·
Thank you so much! One more thing, what wiring changes will I need to make? I plan on installing my own fuel, rpm, volt, speed, temp and oil pressure gauges so I won’t have to worry about those. How will I power my ignition and things like that?
 

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Gun Totin *******
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Not many wiring changes needed. Only one i can think of is power to the new distributor while cranking and running. Should be able to pick that up at TBI ignition coil hookups.

Food for thought: The couple other things will be a regulator on your fuel pump or a new pump as the tbi pump pressure is more than double what a carb needs. The fuel pump relay wiring would need to reworked a tiny bit so that it would work with the carb. Basically your safety would be the oil pressure switch. Don't want it running key on without motor running.

I believe all your gauges are analog so no worrier there. I am about 90% sure your speedometer is mechanical with a drive cable to the transmission. I would touch zero dash wiring until you have the carb setup working if you are so inclined. If you add an external tach you can pickup the signal on the HEI distributor.

Other thing to think about is your truck has a catalytic converter that may not play nice with your carb. You will still have a o2 sensor sending info to your computer. However by the sounds of things computer is not functional so may be a moot point.

All in all i would not generally be in favor of swapping carb for fuel injection, however in this case it may be a good choice. The other thing to consider is if you are in an emissions testing state I doubt if a carb conversion will pass.

Rambling a bit, spitballing the challenges to make the convert successful if i were doing it.
 

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Discussion Starter · #18 ·
Not many wiring changes needed. Only one i can think of is power to the new distributor while cranking and running. Should be able to pick that up at TBI ignition coil hookups.

Food for thought: The couple other things will be a regulator on your fuel pump or a new pump as the tbi pump pressure is more than double what a carb needs. The fuel pump relay wiring would need to reworked a tiny bit so that it would work with the carb. Basically your safety would be the oil pressure switch. Don't want it running key on without motor running.

I believe all your gauges are analog so no worrier there. I am about 90% sure your speedometer is mechanical with a drive cable to the transmission. I would touch zero dash wiring until you have the carb setup working if you are so inclined. If you add an external tach you can pickup the signal on the HEI distributor.

Other thing to think about is your truck has a catalytic converter that may not play nice with your carb. You will still have a o2 sensor sending info to your computer. However by the sounds of things computer is not functional so may be a moot point.

All in all i would not generally be in favor of swapping carb for fuel injection, however in this case it may be a good choice. The other thing to consider is if you are in an emissions testing state I doubt if a carb conversion will pass.

Rambling a bit, spitballing the challenges to make the convert successful if i were doing it.
Could you elaborate a little more on the fuel pump relay wiring changes? I’m not the greatest in the world with wiring but I can almost always figure it out in the end but I’m not exactly sure right now why or what would need to be changed there. I already have budgeted for a fuel pressure regulator and all of that so everything else should be good. I’m extremely appreciative of all of your help!
 

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Gun Totin *******
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Without looking at details of wiring diagram for a 87 the computer primes your pump for 3 seconds with key on then once started the oil pressure switch activates the relay once running. The ignition signal from distributor tells injectors to open / pulse. With the computer not getting signal i dont know if it would shut down the pump relay or not. perhaps the yoda of wiring diagrams @oldeerslayer can enlighten.

My way of thinking and i may be way wrong: Use the oil pressure switch to trigger the electric pump relay, which it already does, for a safe way of operation. No oil pressure no pump. With a carb you should have plenty in the bowl to get it started and build pressure for the switch to activate the relay. There is also a prime terminal under the hood for the pump if the float bowl is dry. I am not sure it works if computer for all intents and purposes is gone.

To me the saftey issue is you do not want the pump running without engine running.
 
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