v502

iTrader: (1)

Just wondering if anyone piggybacked the stock ecu in general. Ls2 or ls3 setups.

I bought an aftermarket Pro Efi 128 setup an year back and sold it but I still got that piggyback harness laying around and am been thinking about hooking it up with Holley Efi current setup.

Any idea's of problems I could face? ProEfi have been doing it with twin turbo vette's it seems like its running fine.

soundengineer

iTrader: (16)

do a google search...its been discussed many times on here and other forums...

Not recommended, but its not impossible

ws602

iTrader: (2)

Good luck

v502

iTrader: (1)

soundengineer I did search around, halltech guys seem to be doing it. I know for fact that Pro Efi did it years ago with corvette and still offer piggyback harness for many other applications.

Could you give me some insight why it isn't recommended or why I shouldn't try it.

soundengineer

iTrader: (16)

sensors that use resistance cannot be split typically... well.. they can....but they will not read correctly due to each device causing some resistance and skewing the actual values

things like the crank sensor require special twisted and shielded cable as they are extremely susceptible to interference...

anything that splits using a 5v or 12v signal needs diodes to prevent any accidental stray voltage from backfeeding from one device or the other
not saying it will always happen....but some pieces just arent happy being split and some funny things can happen

grounds have to all go to 1 device...not both
this can cause issues(again...not always...) with the device that has no grounds from sensors
and sometimes the solution is isolation transformers...which can get costly to do it correctly




again....I'm not saying it isnt possible...
I'm just saying that there are some challenges to overcome, and it is not recommended.

soundengineer

iTrader: (16)

this guy over on yellow bullet has tried it.....
he says in this post...
you need separate sensors to make the Holley Happy....meaning you cant split them to the holley and the stock ECU.


http://www.yellowbullet.com/forum/sh...51&postcount=7

LilJayV10

iTrader: (39)

I'm getting ready to do this.

Why would you need to split the IAT, ECT sensor for the stock ECU?

If you are going to piggy back it to keep the BCM and factory gauges happy and have the Holley control fuel/spark I can't see any reason the factory PCM needs to see anything except cam/crank.

dckmn52

No real reason. On my WS6 I piggybacked my megasquirt to keep gauges, cruise control, a/c, ect. Luxuries for the most part. If its going racecar status its not really necessary to go to all the effort.

LilJayV10

iTrader: (39)

It's something that I can do "testing" on at work on my car.

I have an extra HP ECU and some wiring harness' laying around so I'm going to see how it goes.

I know the most important thing is getting the crank/cam sensors happy. I have a scope so I can play with a pot to find out the right pull down resistance to get/keep a good signal.

I've never piggy backed an aftermarket ECU to a stock ECU before, hence why I'm using my car for testing. I'm interested in seeing in what I do and don't need to keep the rest of the car working.

stevieturbo

Stock ECU might control the dash and would need ECT for the temp gauge ?

No big deal, just add another sensor for the piggyback ecu.

Piggybacking isnt difficult...just do it.

Any powered 5v sensors, rarely is there an issue splitting these to two devices.