So I just acquired my new toy (99 Silverado in signature) and forward thinking I may ditch the OEM computer and just go with the Holley for engine management and use OEM for A/C controls only (this is a must for me). I’m not entirely sure I care about the OEM dash as I could get the 7” Holley display. The X Max also offers 4l80 control so that will be nice as well. The other minor detail is that this will also have a Trick TT kit installed finally in the spring so I want to have the additional functionality + features over OEM.

That being said has anyone here piggy-backed and OEM ecm and aftermarket on 99-02 model year? Things to look out for, tips, tricks, etc.

 

I've done a few different combinations of piggyback. It's a pain in the ***, particularly with OEM ECMs.

 

I was hoping since the 99-02 does not have a BCM like the 03+ that it may be a little easier or less painful.

I do fortunately have a few local guys that absolutely love lsx swaps with all the fun stuff involved so I'm hoping I can get some insight as to what's involved. Changing altering a harness while not overly thrilled is not the end of the world but needing to know what the OEM ECM needs to remain happy is something out of my league.

 

Why not just do standalone? Unless there is some other compelling reason to try an piggyback.

 

Well the main reason was for A/C control. But I just got off the phone with Holley tech and they say that I could in fact use one of the Input/Outputs for A/C control. So if I have 4 i/o
's to use I "think" that would be something like:

* E-Fans
* A/C
* Open/TBD
* Open/TBD

Boy if that is the case it will make me a happy camper!

 

How would the HVAC control in the dash tell the Holley to turn the compressor on? Also you have to modulate the damper(s?) for temperature control and which vent and defrost. Isn't everything I listed computer controlled?

 

You will also need AC pressure input and a compressor clutch control circuit, at minimum. I built a custom AC controller for a local guy and it worked great. Only problem was not being able to feed-forward control for the torque load of the compressor on the crankshaft, so there was always a slight dip in RPM when the compressor kicked on. But otherwise worked great.

 

So what about the other stuff that I mentioned? Especially defrost.

 

Great questions that I have absolutely no idea, that’s why I’m asking as I will admit ignorance. Maybe I didn’t ask the right questions it appears? I did specifically ask if the Terminator X Max would control the OEM A/C system in a 99 Silverado and he put me on hold and came back with a yes. I know the Dominator states that it has AC inputs so I would think there is some functionality in there of some nature.

 

That's my point. I think it will take a lot more than cycling the A/C compressor.