350SS

iTrader: (38)

It seems that much of the Gen IV electronics are more and more codependent on the BCM being used to command different functions that used to take place without it. Just about everything runs through it in the newer trucks. For a swap into an older car most of this isn't necessary so my question is... Is there any way to do a GEN IV swap without the BCM?

As far as I know the ignition switch signal and the ac request signal has to go through the bcm to the ecm.

There must be a way around this...I'm pretty sure John @ Speartech does this with his harness reworks. Hopefully someone that has done one of these swaps will chime in

V8Rumble

iTrader: (9)

First I've heard of that. I sure HOPE that's not true, since I'm nearly ready to drop my own Gen-IV engine into place...

Going to watch this one.

68shortstep

iTrader: (1)

gettung the eng/trans to function properly doesnt require the BCM. but if you wanna run the cruise, guage cluster, etc from the donor car/truck i think you will need the bcm......i too would be instrested in someone finding a way around this

alocker

iTrader: (10)

Every thing runs through the BCM for secondary features like climate control and the single touch key start (ie hit the key and let go and it cranks until the car starts). The ecm doesnt care about any of this. Just wire your key directly to your starter circuit. For ac I believe you just ground the ac circuit on the ecm for your idle bump.

350SS

iTrader: (38)

I guess I should have worded this differently. In the stock configuration, many of the newer GenIV engines' functions like the starter and a/c run through the BCM... I'd like to know if there is a way around this.

From the other post that 68shortstep made, it sounds like there's a way to start the engine w/o the bcm.

350SS

iTrader: (38)

Good to know about the starting circuit...that's obviously one of the more important things to sort out for a swap.

Maybe I'm wrong, but I believe the newer pcms send the a/c request function to the ecm via serial data from the a/c module via the bcm or straight from the a/c module to the ecm.

If that's the case I don't know how you would mimic that serial signal. Do you know a way around this?

bhop42

iTrader: (2)

I did this with an LY6 Gen4 engine in my 96 Impala. You just go right around the BCM for the ignition. I just used my stock starter and fuel relays. I haven't ran my A.C lines yet but I did wire it. I went around the BCM and the ECM by using my stock low pressure sensor and used relays to turn on the fans. I used the + A.C request signal from my factory controls in conjuction with the stock low pressure signal and a relay to control the compressor.

350SS

iTrader: (38)

So you're just activating the starter relay with the ignition switch and there isn't anything to tell the ecm that it is in "start" mode other than the engine rotating? Thanks for the reply.

1BadAction

iTrader: (10)

I don't see why everyone is so scared of the BCM, Its no real black art to install or anything. if done right you can retain the cool **** like low fuel and gauge out of range alarms so you get a ding if your alternator takes a dump or you are low on gas (or oil, or coolant, etc) and don't realize it. for example, I popped a spare wheel that fell out of the bed of a truck in front of me in my silverado going down the highway and cracked the oil pan. didnt see anything leaking after I stopped and checked so I went on my way. 15 miles or so down the road I got a low oil alarm and light. I shut it down to check and there was oil everywhere. if it wasnt for that I most likely wouldnt have noticed the drop in oil pressure before it broke.

matter of fact, if you get the right donor truck, you can have an alarm with a factory key FOB and remote start. I dunno, maybe its just me thats fascinated by a classic car that locks and unlocks with the push of a remote button

350SS

iTrader: (38)

I agree with you on keeping the BCM so everything operates as stock, and getting some cool features as well. It just seems harder to find a complete engine/trans swap setup that has the bcm and associated wiring, so I'm just seeing if there are options without it.

The remote start thing would be cool

1BadAction

iTrader: (10)

Thats true. I wouldn't have considered doing an LS swap like I described above without a donor vehicle being at my disposal, or at least all of the interior electronics. Because of code enforcement, I had to get rid of it before I could strip it completely. Pissed me off because I could have used many of the other mechanical parts on my older truck.

68shortstep

iTrader: (1)

yes you have the start/run/crank wire and ign 1 voltage wires comeing out of the PCM, thats how the PCM knows when its trying to start.....hope this helps

350SS

iTrader: (38)

That's what I'm wondering about though...the newest pcms (E38 I believe) don't have a "start/run/crank" wire... they receive this signal via the BCM on the CAN bus.

rsz288

As well as crank, cruise control and TUTD (non Corvette) & Sports/Cruise mode on A6's at least, go through the BCM and then the CAN.

As alocker and bhop42 point out, direct to starter cranking is fine.

At least with later GenIV's there is no Powertrain Interface and/or Communications Interface as well, so its only the BCM. Looking at this a little more deeply soon to try and get cruise running.