1989 TBI 350 swapped in place of 1989 TBI 454- IAC wiring & ESC/knock sensor question

**Mr. Bowtie** · 04-19-2015

Newbie here. Love the forums so far. However, I need some help. I removed the 454 from a 1989 k3500 and installed a 350 from a 1989 V1500 suburban. Before you ask why in the world would I give up a big block for a small block, I'm not. The truck is my friend's and the suburban is mine and getting the 454. Straight trade and paying me labor for the install. Nice huh? Couldn't pass it up.
I've read all over that the only difference in the IAC is that 2 wires are swapped. I did find the attached drawing thanks to EagleMark back in 2012 as well as the following comment:
1227747 IAC wiring to IAC for Big Block and Small Block

Here's one that drives people nuts. SB and BB IAC are wired differently.

Wiring:
SBC Connector
IAC Plug
A ~11.86 v Lt Blue/White Stripe A Hi
B ~.452 v Lt Blue/Black Stripe A Low
C ~11.86 v Green/White Stripe B Hi
D ~.453 v Green/Black Stripe B Low

BBC Connector
IAC Plug
A ~452 v Green/Black Stripe B Low
B ~11.84 v Green/White Stripe B Hi
C ~.452 v Lt Blue/Black Stripe A Low
D ~11.84 v Lt Blue/White Stripe A Hi

My readings with key on are as follows:
Lt Blue/White Stripe- .4
Lt Blue/Black Stripe- 11.2
Green?White Stripe- .4
Green/Black Stripe- 11.2

So my question is which position on the IAC do I connect the wires(square SBC plug)?
Then when I reverse the procedure and put the 454 in mine where do I put them? I might very well be making this harder than it needs to be but electrical is my weakest area.

Also, the 350 has the ESC and knock sensor but the 454 doesn't have either. What am I going to have to do on the 350 since it has the 454 harness?

I should mention that even though they both have the 1227747 ECM I swapped them.

Thank you in advance!

**damanx** · 04-19-2015

If I read that correctly, you are going to swap the "A" wires with each other at the connector, and then swap the "B" wires, on each connector.

(think of just changing polarity)

For the ESC and knock sensor, check to see if his truck's harness has the wiring for the ESC and knock sensor, and if it doesn't, you are going to need to either get a harness with them with the wiring for those, or add those wires.

**lionelhutz** · 04-19-2015

Did you take a good look at the harnesses. Both being trucks with the same ECM you could probably just pull the engine/injection harnesses and straight swap them. That would take care of the IAC and knock sensor part of the wiring.

**Mr. Bowtie** · 04-20-2015

Harnesses are different. I chalked that up to the truck being the 1st generation of the iFS ones while the suburban still retained the solid front axle. Many things on the suburban are just like the older ones.

I kinda figured that I might have to add the wires in. I guess I was hoping for somethiEaueasier. That won't be too bad though. Does anybody have pinouts for those 2 vehicles?

**Mr. Bowtie** · 05-12-2015

Originally Posted by Mr. Bowtie

Newbie here. Love the forums so far. However, I need some help. I removed the 454 from a 1989 k3500 and installed a 350 from a 1989 V1500 suburban. Before you ask why in the world would I give up a big block for a small block, I'm not. The truck is my friend's and the suburban is mine and getting the 454. Straight trade and paying me labor for the install. Nice huh? Couldn't pass it up.
I've read all over that the only difference in the IAC is that 2 wires are swapped. I did find the attached drawing thanks to EagleMark back in 2012 as well as the following comment:
1227747 IAC wiring to IAC for Big Block and Small Block

Here's one that drives people nuts. SB and BB IAC are wired differently.

Wiring:
SBC Connector
IAC Plug
A ~11.86 v Lt Blue/White Stripe A Hi
B ~.452 v Lt Blue/Black Stripe A Low
C ~11.86 v Green/White Stripe B Hi
D ~.453 v Green/Black Stripe B Low

BBC Connector
IAC Plug
A ~452 v Green/Black Stripe B Low
B ~11.84 v Green/White Stripe B Hi
C ~.452 v Lt Blue/Black Stripe A Low
D ~11.84 v Lt Blue/White Stripe A Hi

My readings with key on are as follows:
Lt Blue/White Stripe- .4
Lt Blue/Black Stripe- 11.2
Green?White Stripe- .4
Green/Black Stripe- 11.2

So my question is which position on the IAC do I connect the wires(square SBC plug)?
Then when I reverse the procedure and put the 454 in mine where do I put them? I might very well be making this harder than it needs to be but electrical is my weakest area.

Also, the 350 has the ESC and knock sensor but the 454 doesn't have either. What am I going to have to do on the 350 since it has the 454 harness?

I should mention that even though they both have the 1227747 ECM I swapped them.

Thank you in advance!

So, I finally got around to getting this together. As it turns out I was over thinking it. I simply soldered the same color coded wires together as they are labeled the same on the IAC and the ECM. Started immediately and runs fantastic. I added in the ESC module harness somewhat easily I might add as well.
However, one thing I didn't take into consideration is the transmission. I used the ECM from the 350 even though they have the same service ID # assuming the programming would match. However I now notice that when driving, it will downshift quite routinely in 3rd gear. I'm presuming that since there is not a throttle pedal mounted switch the ECM controls the shifting and downshifting based on the TPS perhaps? I guess my question now is should I reinstall the original ECM from the 454/TH400 to see if it will control it better? If so, what about the ESC circuitry? Can I run without it? I'm really weak in ECM programming and tuning.
Thanks guys.

**lionelhutz** · 05-12-2015

I think the TH400 downshift solenoid and the 700R4 converter lockup use the same PCM output.

**Mr. Bowtie** · 05-12-2015

Originally Posted by lionelhutz

I think the TH400 downshift solenoid and the 700R4 converter lockup use the same PCM output.

So I can swap ECM's? I'm not sure that they are interchangeable like that because of the engine programming.
Thanks again.

**lionelhutz** · 05-13-2015

You could do that and fix the transmissions but then the engines won't run right. Does one vehicle have a 700R4 and the other have a TH400 or not? If you answer yes, you have to either find the right chip or do some programming to fix it.

**Mr. Bowtie** · 05-13-2015

Thank you for your reply. That is exactly what my fear issio I figured that I had nothing to lose so I put the original ECM back in & ran it. Shift problem is resolved & it appears to run perfectly. I didn't run it at WOT however. Maybe I'll do that tomorrow. The big thing I was concerned about is over or under fueling. I guess I'll see tomorrow. Thank you for your input & help. I'll update as to what I find.