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Old 03-22-2018, 07:14 PM   #1
Signuil282
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4.3 to 5.7 swapp

I have a 92 sierra 4.3 and dropped a 94 chevy 5.7. Left all the harness for the 4.3 but it runs very rough and won't even idle...any suggestions?
Should I put a carburator?
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Old 03-22-2018, 09:31 PM   #2
b454rat
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Re: 4.3 to 5.7 swapp

Put the 350 ECM in?
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Old 03-23-2018, 08:54 AM   #3
Signuil282
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Re: 4.3 to 5.7 swapp

My mechanic said the 350 rpm won't plug in he said it is different
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Old 03-23-2018, 09:33 AM   #4
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Re: 4.3 to 5.7 swapp

Since you were told the ECM won't interchange, maybe you can get a new program chip for your current ECM.
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Old 03-23-2018, 10:23 AM   #5
Signuil282
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Re: 4.3 to 5.7 swapp

I really appreciate all of the valuuable info. Now the question is how do I get a new program chip?
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Old 03-23-2018, 03:18 PM   #6
Palf70Step
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Re: 4.3 to 5.7 swapp

I am told you can order them thru AutoZone or other parts place. But normally they need the serial number so it can be programmed for the exact vehicle. Hopefully some one will speak up, there is someone that a few folks used to have their ecu reprogrammed, but I can't find the info right now.
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Old 03-29-2018, 06:20 AM   #7
lofly'a
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Re: 4.3 to 5.7 swapp

i did the 4.3 to 5.7 swap 6 years ago, all you need is the 350 chip for the operating parameters. you could swap the whole computer but not necessary. anybody tell you otherwise is stringing you along.
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Old 03-29-2018, 09:43 AM   #8
Signuil282
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Re: 4.3 to 5.7 swapp

Thanks, I have swapped the chip only and it did not run very welll...i swapped the whole computer and it does at least run down the road
Still sputter but stays running. After a little while of running I did notice it runs ok with a miss when I first start it but then wants to stall out when I give it gas. I must have a different problem other than just the computer
..
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Old 03-29-2018, 11:19 PM   #9
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Re: 4.3 to 5.7 swapp

Did the timing get set correctly with the connector disconnected?
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Old 04-04-2018, 09:54 AM   #10
lofly'a
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Re: 4.3 to 5.7 swapp

sounds like the original ECM was bad.
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Old 04-04-2018, 11:51 AM   #11
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Re: 4.3 to 5.7 swapp

Looks like the timing was off just a bit. Also, when I disconnected the egr hose from the sensor above the valve cover it ran so much better....
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