4.3 TBI to 350 TBI swap

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FrankieD61

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Hello all, I have a 1991 K1500 with a blown 4.3l. I'm going to be swapping it with a donor 350 TBI that I bought. I've taken care of all of the accessories, cooling equipment, and such. My question is do I need to do anything with the computer? Also, what other stuff will I need to take care of this?

Thanks.
 

FrankieD61

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Yep, you'll need a chip (or complete ECM) from a 5.7L truck with the same rear end gear ratio and trans. I'm guessing you're using the injectors from the 5.7L too?

Yep. The motor came with a throttle body with injectors. Now as far as the transmission, it's a 4 speed manual with OD. I have a feeling it's going to be hard to find a prom chip programmed for a 5.7 with that trans. Do you know where Icould find one? Also, what would be the consequences of me using a chip programmed for a 5.7 with a auto transmission? Thank you!
 

FrankieD61

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Yep, you'll need a chip (or complete ECM) from a 5.7L truck with the same rear end gear ratio and trans. I'm guessing you're using the injectors from the 5.7L too?

What about the gauges? Will they work without mods?

Sorry for all the questions; I'm new to this.
 

PlayingWithTBI

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Also, what would be the consequences of me using a chip programmed for a 5.7 with a auto transmission?
You'll get an SES (Service Engine Soon) light for torque converter clutch fault and you won't have a "Shift" light which is no big deal but, the SES light is a PITA.
I have a feeling it's going to be hard to find a prom chip programmed for a 5.7 with that trans. Do you know where Icould find one?
Go to your favorite bone yard and find a truck with a 5.7L and manual trans. It really doesn't matter if it's a 4 or 5 speed. You just need to get the same gear ratio so your ECM knows it's speed. Also not a big deal with a manual trans. BTW your ECM is mounted on a shelf, with spring clips) behind the glove box. To remove it you slide it to your left and unplug the 2 connectors.

What about the gauges? Will they work without mods?
Yes

Edit: an ECM from 88 - 91 will work as long as it has the same Service #, probably 1227747.
 
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FrankieD61

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You'll get an SES (Service Engine Soon) light for torque converter clutch fault and you won't have a "Shift" light which is no bug deal but, the SES light is a PITA.

Go to your favorite bone yard and find a truck with a 5.7L and manual trans. It really doesn't matter if it's a 4 or 5 speed. You just need to get the same gear ratio so your ECM knows it's speed. Also not a big deal with a manual trans. BTW your ECM is mounted on a shelf, with spring clips) behind the glove box. To remove it you slide it to your left and unplug the 2 connectors.

How do I find out what my gear ratio is? Also, in my area, there are two junk yards and both of them aren't really the best. If someone on here has what I need, I will gladly pay them. Or if you know a good web resource, point me to it.
 

FrankieD61

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The computer I have now is a service number 16144288, and a prom chip of AWDR 4764.

Should I swap out the whole computer or just buy a new PROM chip?

Also the diff code is "GT4".
 

PlayingWithTBI

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FrankieD61

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Or... You can get an EBL Flash-II and tune it yourself. It'll work with your ECM.
www.dynamicefi.com/EBL_Flash.php

Is tuning hard? I've never done it. If there is anyway to make this plug and play, I would love that. But if I have to tune, I will.

Also, is finding computers and proms for these trucks hard? Because, if I do find one that is for a 5.7 but automatic trans, should I buy it and just deal with the SES light?
 
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