How do I add a real flex fuel sensor to an E38 Camaro and dial in E85 — what needs adjusting beyond enabling multifuel?
Mount a genuine GM flex fuel (fuel composition) sensor in the fuel feed line so all fuel headed to the rails passes through it, wire it to 12V, ground, and the E38's flex fuel input pin. Then enable Flex Fuel and Flex Fuel Sensor under Engine > Fuel > General in VCM Editor, set the flex fuel tab's min/max and fuel system volume, copy a correct Stoich AFR vs Ethanol blend table, enable the sensor DTCs, and prove the sensor is alive by logging ethanol % with pump gas and watching it rise when you add E10 before you ever pour E85. Enabling multifuel alone without a working sensor leaves you on the wrong stoich and it will run lean on E85.
Last updated
Who this applies to
- Computers: E38
- Engines: LS3, L99, LS Gen IV V8 (E38-controlled)
- Transmissions: 6L80E, 4L60E, 4L80E, T56/TR6060 (trans-agnostic)
- Years: 2006-2013
- Not for: P01/P59 (different pin and virtual-sensor behavior); E92 Gen V (different ethanol strategy)
HP Tuners VCM Editor on a 2010+ Camaro E38 (LS3/L99)
- Plumb the GM flex fuel sensor (PN 13577394) into the fuel feed line — all fuel must pass through it before reaching the rail. sensor in feed line, 3/8 in flow-through
- Wire the 3 wires: battery 12V power, engine ground, and the frequency signal to the E38. signal to E38 pin 40; 12V; ground
- In VCM Editor go to Engine > Fuel > General and enable Flex Fuel and Flex Fuel Sensor. Flex Fuel = Enabled; Flex Fuel Sensor = Installed
- In the flex fuel tab, set the sensor min/max and fuel system volume if blank, then enable the flex fuel sensor DTCs (P0178/P0179) to report on first error. min/max + volume set; DTCs MIL on first error
- Confirm the Stoich AFR vs Ethanol table blends correctly from gasoline to E85, then set the power-enrichment EQ ratio for flex fuel. stoich blend table + PE EQ ratio
- Prove the sensor is alive before E85: with E0 in the tank the logged % should sit near 0-1%; add a few gallons of E10 and watch the percent rise. If it rises, the sensor is working. 0-1% on E0, rises with E10
Careful
- Do not run E85 until the logged ethanol % responds to fuel changes and the stoich table is correct — the car will run lean and you can hurt pistons.
- E85 needs roughly 30-40% more fuel flow; confirm pump and injector headroom on a dyno or with duty-cycle logs at WOT before leaning on E85 at full throttle.
- Treat ethanol timing adders like any WOT change: add advance on the dyno with knock ears, not by feel.
More in fuel, E85 & boost, or build a checklist for your swap with the tune checklist tool.
Go deeper
Check this first
- With pump gas in the tank, log the ethanol % PID; it should read near 0-1% on E0.
- Check the sensor's signal frequency: normal range is 50-150 Hz; 180-190 Hz means contaminated fuel, a flat 50 or 0 means a dead sensor or wiring fault.
- Verify the signal wire lands on E38 pin 40 and has continuity to the sensor (a loose connection here leaves the E85R PID stuck at 0).
Try this, then this
- Fix the sensor wiring and pin 40 connection first — this is the most common failure; one loose connection leaves the E85R PID stuck at 0. — No signal = no ethanol reading, and multifuel-on with a dead sensor runs the wrong stoich. Worked if: Logged ethanol % moves when fuel changes.
- Confirm Flex Fuel AND Flex Fuel Sensor are both enabled under Engine > Fuel > General, plus the min/max and volume entries. — Multifuel on with the sensor switch off leaves the PCM on a virtual/no-sensor ethanol estimate. Worked if: Ethanol % reads real fuel content, not a fixed virtual value.
- Upsize injectors and pump for 30-40% more flow (injectors at 90% duty or less, pump with 10-20% headroom) and use E85-compatible materials. — Correct tune on an undersized fuel system goes lean at WOT regardless of sensor function. Worked if: Duty cycle stays at or under 90% at peak power on E85.
How you know it's fixed
- Logged ethanol % tracks what is in the tank (rises after adding E10, falls after adding E0).
- No P0178/P0179 sensor codes set.
- Fuel trims stay near zero when switching between pump gas and E85 — no big lean swing after a fill-up.
- Spark advance follows the flex fuel adder with ethanol content without knock.
Key numbers
| What | Value |
|---|---|
| E38 flex fuel sensor signal pin | E38 pin 40 |
| E85 fuel system flow requirement | 30-40% more flow; injectors at 90% or lower duty cycle |
| Flex fuel tab setup in VCM Editor | set min/max + fuel system volume, enable sensor DTCs |
Every option we know of
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| Maker / product | Part # | Fits | Price | Where | Status / notes |
|---|---|---|---|---|---|
| GM / Chevrolet Performance Fuel composition (flex fuel) sensor | 13577394 | E38/E67/E92, Terminator X, Dominator; 3/8 in line | Buy GM dealers, Tick Performance, Holeshot Motorsports | In production Must be plumbed in the feed line; needs 12V tolerant frequency input |
Prices are approximate as of September 2026. We list every option we know of, including small shops and used parts we can't link to. Confirm fitment with the seller.
Time and cost: Half a day: sensor plumbing and wiring (~2 hrs), tune changes and verification logs (~2-3 hrs), plus fuel system upgrades if needed.
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