4.3 TBI to 350 carb swap/ecm?

78Delta88

Master Mechanic
Supporting Member
May 23, 2022
417
43
SW Arizona
As the others said ... Keep it simple !

The A-Body is different from G Body but all the electric hookups are pretty much the same. Concepts of operation is all the same.

On this caprice I pulled all the wires to the side, bagged and tagged like others had said, and with the old engine pulled I cleaned up the engine bay, painted inner fenders, prettied things up a bit.

I then built my own wire loom incorporating the changes needed and once it was running and driving..., then and only then did I start cutting out the old wiring no longer needed.

Exhaust work was done by local Tucson Exhaust Works Inc. They did all the mods to the cross-member changing from single to dual exhaust. Exhaust was 2 1/4 stainless, mufflers Trush 2 1/4 Rattlers.
 

78Delta88

Master Mechanic
Supporting Member
May 23, 2022
417
43
SW Arizona
This 91 Caprice is 305 TBI, under the hood very similar to your 87.

Originally I was going Holley Sniper, but if it helps you out, I'll go carb conversion. I can always Sniper it later with a 350 or bigger.

This way we can go through the steps and post the conversion to the forum.

Like the others said don't worry to much about the electrics. It's actually not that difficult, just need good set of cutters, crimpers and box of heat shrink tubing, plus a few 30 amp relays.
 

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78Delta88

Master Mechanic
Supporting Member
May 23, 2022
417
43
SW Arizona
Follow up.. On your question about lock-up, don't worry about it.

The transmission will work just fine and will not be damaged in any way if the lock-up is not hooked up.
 

78Delta88

Master Mechanic
Supporting Member
May 23, 2022
417
43
SW Arizona
Follow up.. On your question about lock-up, don't worry about it.

The transmission will work just fine and will not be damaged in any way if the lock-up is not hooked up.
It's been awhile on follow up. All the parts were ordered for the conversion, still waiting on some.

Pic below shows wires left over from removing the C3 Q-jet on the 86. None of those wires are needed and can be cut off, just hadn't done it yet.
20220709_124206_HDR.jpg
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,416
113
Galaxy far far away
You really should not cut up good harnesses.
 
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78Delta88

Master Mechanic
Supporting Member
May 23, 2022
417
43
SW Arizona
You really should not cut up good harnesses.
You are right, these were taped and zippie tied out of the way. Just example, showing OP many of the connectors not needed when converting over to a Carb non ECU system. I don't have to emission cert when I live, but if sold and the customer does..., the car has to be taken back to OEM and pass before can be plated.
 

cloudhome

Not-quite-so-new-guy
Jul 6, 2020
14
3
Glenview Illinois
Regarding the THM 350, the "350C" model has a lock up convertor, and has the "TV" cable. B&M makes a small controller that hooks to your speedo cable, allowing you select a speed at which is locks up the convertor. I bought a $10 vacuum switch, wired the power to the B&M to it, so when I tromp the gas, the convertor unlocks. Works great.
Someone said you can't use HEI w/o the computer....Accel has a HEI distributor on Ebay for $29 new, with damaged packaging. I bought 2, packaging was fine, but it's a good deal. Gets rid of the computer control and gives you a vacuum advance. Word of caution: the module in it won't tolerate a high energy coil...I put the MSD coil in and the module immediately blew out, so I replaced it with the 2nd one and it blew too. A NAPA module ($35) works, but I've now upgraded with the MSD high reliability "circle track" version ($60) .
Regarding the "check engine" light, not sure if the 4.3 is the same as the 5.0, but if it is, there's a plastic module taped to the IP harness on the right side (closest to the door) of the glovebox door. If I recall correctly, it's green plastic. There's a plug in PCB in that module that's the check engine lamp driver. Unplug it and the light goes off.
 
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78Delta88

Master Mechanic
Supporting Member
May 23, 2022
417
43
SW Arizona
View attachment 202474
Gotta get rid of that up there 👆 Glass filters are a insurance loss claim in waiting.
Haven't had any issues with them thus far. That one was in there to see pump sufficiency and see what fuel is going through as it sat for 12 years before I got it. Tank was dropped, cleaned, and replaced with new sender. Lines were blown out but still ran a couple gallons fresh at a time for a few times until fuel would run clear.
 

pagrunt

Geezer
Sep 14, 2014
8,232
113
Elderton, Pa
Haven't had any issues with them thus far. That one was in there to see pump sufficiency and see what fuel is going through as it sat for 12 years before I got it. Tank was dropped, cleaned, and replaced with new sender. Lines were blown out but still ran a couple gallons fresh at a time for a few times until fuel would run clear.
I'd still replace it. Back on Easter, the wife's nephew had his square body burn down in his driveway after returning from Easter services. Was told over five years ago to replace it but never did or even service it with new O-rings & filter & his luck ran out.
 
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