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Discussion Starter · #1 ·
Hey guys! New to the forum. I ordered an L31 Carbureted engine from Summit Racing and currently have it bolted up to the tranny. I am still in the process of gathering together the parts and resources needed to finish the job. I have done motor swaps before but they were oe and newer gens.

I have an NV4500 5 speed manual transmission, so I would imagine that other than temp sensors and the oil pressure sensor, and fuel pump communication the ECM is irrelevant. Correct me if I am wrong lol. I'm new to carbs and frankly a non oem swap. Especially in this engine model. I do understand that I need to run a bypass tree from the outlet line to the heater core to the water pump and then to the intake. However, there is only one other spot that I am aware of to mount the CTS to, and the threads do not match. Would it be smart to simply add a brass fitting, or would the coolant not reach the CTS?

What sensors are necessary for the engine to run optimally? I appreciate any response regarding this. Trying to soak up as much info as possible. Don't want to wash my money down the drain. Or better yet "blow it"
 

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The TBI in tank electric fuel pump out puts pressure around 15-20 psi which is too much for a carburetor. Fortunately you have all the plumbing in place to install a by-passing external pressure regulator. You will need a fuel pressure gauge under the hood for adjustment. Keep in mind that the high pressure pump demands EFI qualified fuel hose.

Another problem you will have is the computer runs the fuel pump via a relay, since the computer is no longer needed you will have to do some rewiring to either operate that relay off the ignition switch or an independent switch. For safety sake there should by an oil pressure shut off switch, GM used them on some models they are available in parts stores.

A similar condition exists with ignition, the TBI ignition timing is all in the computer, the TBI distributor only does basic sensing that a spark is needed and sorts the high voltage to the appropriate cylinder. So you will need a conventional HEI distributor wired from the key switch or an independent switch.

The 1988 uses an electronic speedometer but it doesn’t need the computer to operate. There is a twisted wire pair from speed sensor on the transmission sensor to the speedo once you ID these wires you can pull them out of the wire bundles they run in.

You really are going to need a decent wire diagram for the truck as you can eliminate the computer and sensors and all those wire bundles but the headache is the house keeping wiring you need to keep is all tangled up in those big bundles so the biggest effort you have is sorting all those out. Most of this job is electrical.

Bogie
 

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Discussion Starter · #4 ·
The TBI in tank electric fuel pump out puts pressure around 15-20 psi which is too much for a carburetor. Fortunately you have all the plumbing in place to install a by-passing external pressure regulator. You will need a fuel pressure gauge under the hood for adjustment. Keep in mind that the high pressure pump demands EFI qualified fuel hose.

Another problem you will have is the computer runs the fuel pump via a relay, since the computer is no longer needed you will have to do some rewiring to either operate that relay off the ignition switch or an independent switch. For safety sake there should by an oil pressure shut off switch, GM used them on some models they are available in parts stores.

A similar condition exists with ignition, the TBI ignition timing is all in the computer, the TBI distributor only does basic sensing that a spark is needed and sorts the high voltage to the appropriate cylinder. So you will need a conventional HEI distributor wired from the key switch or an independent switch.

The 1988 uses an electronic speedometer but it doesn’t need the computer to operate. There is a twisted wire pair from speed sensor on the transmission sensor to the speedo once you ID these wires you can pull them out of the wire bundles they run in.

You really are going to need a decent wire diagram for the truck as you can eliminate the computer and sensors and all those wire bundles but the headache is the house keeping wiring you need to keep is all tangled up in those big bundles so the biggest effort you have is sorting all those out. Most of this job is electrical.

Bogie
Awesome! Thanks so much. I have the fuel line and connectors along with a bypass regulator for the fuel. Would the purple/white wire work for the hei distributor? Also, what would happen if I just ran a jumper wire from the Ignition to the fuel pump?
 
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