Flex fuel sensor - LS swap

Supercharged111

Comic Book Super Hero
Oct 25, 2019
3,711
113
Colorado Springs, CO
Im trying to find the physical sensor on the donor vehicle. I'm not to the point yet of the tune. Although that will come next. Figured I'd at least plumb it in when I do fuel lines. If I don't hook it up/ enable it now, at least I don't have to cut it in later.

BTW...2012 GMC 3500 box truck, flex fuel from factory. Hoping it just a case of retaining the correct hardware and properly setting the tune for it to work.

GenIV then, that's the easier way from a tune perspective. I can't say where the sensor is myself. Stock tunes are boost ready on a GenIV, just add a MAP sensor.
 

wskirvin

Master Mechanic
May 22, 2017
297
63
Indianapolis, In
Im trying to find the physical sensor on the donor vehicle. I'm not to the point yet of the tune. Although that will come next. Figured I'd at least plumb it in when I do fuel lines. If I don't hook it up/ enable it now, at least I don't have to cut it in later.

BTW...2012 GMC 3500 box truck, flex fuel from factory. Hoping it just a case of retaining the correct hardware and properly setting the tune for it to work.
Generally, they are on the drivers side by the trans crossmember and tucked up in the crossmember in the same area as the abs module to keep road debris off of it. That's at least been then location on the tahoes and suburbans i've fixed.
 

81cutlass

Comic Book Super Hero
Feb 16, 2009
4,309
113
Western MN
I thought Gen4 LS didn't use a physical sensor, it just looks at the O2's and adds fuel until the AFR target is met.
 
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Supercharged111

Comic Book Super Hero
Oct 25, 2019
3,711
113
Colorado Springs, CO
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81cutlass

Comic Book Super Hero
Feb 16, 2009
4,309
113
Western MN
A 14 box van won't have a flex sensor. It just calculates it.

The retrofit kits usually use flex sensors off impalas or older 02-06 pickups.

1665073287716.png

 
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Supercharged111

Comic Book Super Hero
Oct 25, 2019
3,711
113
Colorado Springs, CO
A 14 box van won't have a flex sensor. It just calculates it.

The retrofit kits usually use flex sensors off impalas or older 02-06 pickups.

View attachment 208284

There must be a year split in the GenIV stuff then, because using a GenIII sensor on a GenIV PCM makes no sense to me.
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
4,309
113
Western MN
There must be a year split in the GenIV stuff then, because using a GenIII sensor on a GenIV PCM makes no sense to me.

There's an input for the ecm to read flex, and the table in the ecm, just not the sensor or wire.
 

Tomeal

G-Body Guru
Thread starter
Apr 17, 2016
777
93
Clyde,pa
There's an input for the ecm to read flex, and the table in the ecm, just not the sensor or wire.
I'm not home yet, but there was a wire from the ecm that was for the flex fuel sensor. I will check the harness again to see where the wire went to.

I checked under the donor and didn't see anything. Stopped at the dealership, let them run the vin and tell me. They said there wasn't one.

Obviously I need to double check all this, but I'm pretty sure there isn't a sensor there. I'll have my harness hopefully back out this weekend and will chase the wire to see what it went to.

A 14 box van won't have a flex sensor. It just calculates it.

The retrofit kits usually use flex sensors off impalas or older 02-06 pickups.

View attachment 208284

If you are right then that may explain why there is no sensor.
 

Tomeal

G-Body Guru
Thread starter
Apr 17, 2016
777
93
Clyde,pa
Ok, just want to re-visit this for some closure.

There is a wire coming out of the ecm. It is cut from a connector that runs elsewhere in the donor vehicle. Looked quick again for a sensor and am not still seeing one. I'm not super concerned with it right now. Just thought if it was there and free on the donor, I would add it in when I do the fuel lines.

The donor vehicle is not going anywhere anytime soon, so may re-visit this at a later point, probably won't though.
 

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