5.7 to 7.4 tbi swap

[87chevynut]

I have a 93 GM 454 in a motor home that I am considering swapping into my 87 K20 standard 4x4 pickup. I have been looking at both set ups, and was wondering... could I run the throttle body unit off the 5.7 on the 7.4 if I swapped the Prom,injectors, regulator & fuel pump. I am wondering this because the IAC & TPS on the 454 throttle body are different. If this would be possible, I wouldn't have to cut & splice the wiring to them, or would it be better to cut & splice ? Any info would be appreciated. Thanks

[Fast355]

I have a 93 GM 454 in a motor home that I am considering swapping into my 87 K20 standard 4x4 pickup. I have been looking at both set ups, and was wondering... could I run the throttle body unit off the 5.7 on the 7.4 if I swapped the Prom,injectors, regulator & fuel pump. I am wondering this because the IAC & TPS on the 454 throttle body are different. If this would be possible, I wouldn't have to cut & splice the wiring to them, or would it be better to cut & splice ? Any info would be appreciated. Thanks

The 454 throttle body is larger diameter. The stock 454s are calibrated for the larger throttle body. I would recomeend using the 454 TBI as evven a very mild 350 runs out of air with a stock throttle body on it.

[87chevynut]

Ok , Thanks Fast355, I should be able to use my existing 5.7 harness if I splice & solder the IAC & TPS wiring & swap the prom ,right ? I'm pretty sure the wires are color coded the same.

[fastacton]

As long as you match up the colors, you should be ok. You could also buy adapters so you don't have to cut and splice. The ECM is another issue. The '93 ECM is probably a '7060 (brown connectors) and you probably have a '7747 (black connectors) in your '87. It would probably be easiest to get the correct PROM for your '7747 unless you're planning on swapping the transmission (if it's a 4L80E) as well.

[1project2many]

There might be an issue with the IAC operating in reverse even though you connect the wires the same way. If this happens you only need to swap any two wires at the IAC and it will work correctly.

[Nasty-Z]

The TPS wires will match color for color , the IAC does get spliced color for color however the pinout is different. This is the proper IAC wiring for both BBC and SBC IAC valves :

BBC IAC –
Pin A - Lt blu/blk - Coil A Low
Pin B - Lt blu/wht - Coil A High
Pin C - Lt grn/wht - Coil B High
Pin D - Lt grn/blk - Coil B Low
SBC IAC-
Pin A – Lt blu/wht – Coil A High
Pin B – Lt blu/blk – Coil A Low
Pin C – Lt grn/wht – Coil B High
Pin D – Lt grn/blk – Coil B Low

93 should be the earlier 454 injectors so the pump for the 5.7 will be fine for the 7.4 , the only thing other than the IAC wiring and TPS wiring would be a PROM swap if the ECMs are the same .


TOM

[fastacton]

Nasty-Z, if you go color for color with the IAC connectors, you'll be fine. The problem is when you go pin for pin (A to A, B to B), as your chart shows that that won't work (that chart comes in handy if you're trying to splice in a distributor connector or other connector that doesn't have IAC wire colors). I've wired in quite a few 454 IAC pig tails color for color without any issues.

[Nasty-Z]

Nasty-Z, if you go color for color with the IAC connectors, you'll be fine. The problem is when you go pin for pin (A to A, B to B), as your chart shows that that won't work (that chart comes in handy if you're trying to splice in a distributor connector or other connector that doesn't have IAC wire colors). I've wired in quite a few 454 IAC pig tails color for color without any issues.

Yes , Pin to pin is the problem , this is actually why I provided the charts . Color to color is ok , brain fart .........

The problem arrises if you use a non GM pigtail , the 4 colors are usually white and most would think to match pin to pin, which does not work out very well.

Edited my first post to reflect . Thanks for catching my non awake a$$ this morning ......


TOM

[fastacton]

The colors at the ECM don't change regardless of the engine size. If you take a 454 IAC pigtail and match it up wire for wire on a 5.7 harness, it will be wired just as it would on a 454 harness. Sometimes pictures are better than words. Here's a 454 IAC connector next to a small block connector. If you'll notice, both connectors are wired as your chart shows, so all you have to do is match color for color. You're 100% correct when talking pin for pin issues, but there aren't any issues going color for color on TBI harnesses.
94839484

[Nasty-Z]

The colors at the ECM don't change regardless of the engine size. If you take a 454 IAC pigtail and match it up wire for wire on a 5.7 harness, it will be wired just as it would on a 454 harness. Sometimes pictures are better than words. Here's a 454 IAC connector next to a small block connector. If you'll notice, both connectors are wired as your chart shows, so all you have to do is match color for color. You're 100% correct when talking pin for pin issues, but there aren't any issues going color for color on TBI harnesses.
94839484

Exactly ^^^^^

As I said , I reflected the error from color to pin in my post and corrected it . Fingers typing faster than brain thinking is what I suspect happened ................

TOM

[87chevynut]

Thanks to ALL for the all the great information! I will match the wiring color to color. I am going to get the service #'s off my computers & maybe you can help me make sure I get the proper prom. I also have a 90 burb that had a LT1 & a 4L60 trans, I am contiplating putting the 5.7 from my pickup in it w/ the 4l60. I have a harness from a donor 93 pickup w/ the blue/red connectors that my understanding will work w/ the trans. I put the LT1 in another project w/ the 4l80 from the RV. Your Help is greatly appreciated ! Thanks

[87chevynut]

Do the Proms themselves have numbers to Identify them ?

[fastacton]

They have 4 letter codes on them (broadcast code or BCC) that will help you figure out what it came out of. The code is normally also on the ECM near the service number.