Originally Posted by
1project2many
Hi,
Sounds like you're going to have fun with this. I believe "early" 7.4L TBI units run from 87-90 while "late" ones run from 91-95.
The IAC units are swappable. I have found it's usually easier to start with an IAC that matches the calibration you're using. If you're starting with a 5.7 Chevy cal, it's probably easiest to use an IAC for a 5.7 Chevy. Or copy all IAC values from a cal that matches the IAC you want to use. Also, maybe someone else can confirm this but I believe some of the 454 IAC's are wired differently and will operate in reverse of what's expected without wiring changes.
As mentioned, throttle position sensors come in two different styles. Early sensors have a large, oval connector and are attached with two screws. They are adjustable. Later sensors have a small, round connector and are attached with three screws. They are not adjustable.
Injector pods can be swapped. Throttle linkage is different on early 454 TB's. Early 454 was mated to a THM400 or manual transmission and does not have connection point for 700R4 detent cable. If you are using a transmission that does not need a detent cable this won't be an issue. Fuel injector springs are interchangeable although they are not the same. At some point GM raised fuel pressure in the 7.4 TBI. Watch for the taller spring to tell you it's from a higher pressure system.
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