HP Tuners Power Enrichment (PE) Tuning: Commanded AFR at WOT Done Right

Power Enrichment (PE) is the ECU mode that takes over fueling under high load and wide-open throttle. Outside PE, the engine runs closed-loop at stoichiometric (roughly 14.7:1 on gasoline, lambda 1.00) and trims fuel off the oxygen sensors to chase emissions and economy. Once PE conditions are met, the ECU abandons that target, ignores the narrowband O2 feedback, and commands a fixed, richer air/fuel ratio designed to make power and protect the engine from heat.

The extra fuel does two jobs. It moves you toward the mixture that produces peak torque, and — more importantly for engine longevity — it uses the latent heat of vaporization of the unburned fuel to cool the combustion chamber and exhaust. That cooling is your margin against detonation and against melting pistons or exhaust valves. A WOT pull that drifts lean isn't just slower; it's how engines die.

The critical mental model: PE does not measure your AFR and correct it. It commands an air/fuel ratio open-loop, blind. Whether the injectors and fuel system actually deliver that ratio is a separate question you have to answer with hardware. That gap between commanded and delivered is the theme of this entire page.

In HP Tuners VCM Editor, power enrichment lives under the Fuel section. On GM Gen III/IV (LS) and many Gen V tunes you'll find it as 'Power Enrichment' with sub-tables: the commanded AFR or EQ ratio table itself (typically indexed by RPM, sometimes by RPM and load), and the PE enable conditions — throttle position threshold, the minimum coolant temperature to allow PE, the TPS or load delay, and enable/disable hysteresis. Ford and Dodge platforms use different terminology (Ford works in lambda and commanded fuel; Dodge/SRT has its own WOT enrichment structure) but the concept maps one-to-one.

Know which units your platform speaks. GM PE tables are often expressed as a commanded EQ ratio (equivalence ratio), not AFR. EQ is the inverse of lambda: EQ 1.00 is stoich, and richer-than-stoich values are greater than 1.00. So an EQ of 1.18 is roughly 12.5:1 AFR on gasoline (14.68 / 1.18 ≈ 12.4). Mixing up AFR, lambda, and EQ is one of the most common ways a beginner commands a target that's far off what they intended. If you're unsure which units a table is in, that's exactly the kind of thing TuneVault flags when you upload a screenshot — it reads the table, identifies the axis units, and translates EQ/lambda/AFR so you're not guessing.

VCM Scanner is the other half. The channels you want logged are commanded AFR/EQ (PID), the PE active flag, RPM, MAP/MAF, throttle, and — non-negotiable — a wideband AFR or lambda input.

For a naturally aspirated pump-gas LS, commanded WOT targets in the 12.8–13.2:1 range (roughly lambda 0.87–0.90, EQ ~1.11–1.15) are a common, conservative starting window. That's rich enough for cooling and detonation margin without drowning the engine and killing power. Some combinations make best torque slightly leaner, but you tune toward that from the safe side, on a dyno, watching knock — you do not start lean and hope.

Forced induction changes the math entirely. Under boost, cylinder pressures and exhaust gas temperatures climb fast, and your fuel becomes your primary thermal defense. Boosted pump-gas targets typically live in the 11.0–11.8:1 range (lambda ~0.75–0.80), and they often get richer as boost and RPM climb. The exact number depends on boost level, fuel, intercooling, and compression — there is no universal 'safe boosted AFR,' which is precisely why blanket numbers off a forum are dangerous.

Two rules hold across both cases. First, pair fueling with conservative timing on pump gas — adding boost or load without pulling spark is how you find your engine's failure threshold. Second, richer is the safe direction to be wrong in. If you're going to miss your target, miss rich. TuneVault audits your PE table against your stated setup (N/A vs boosted, fuel, injector size) and flags targets that look aggressive for the combo, but it gives you ranges to verify on the car — never a horsepower promise.

A perfect AFR table does nothing if PE never turns on, or turns on late. The enable conditions decide when the ECU switches out of closed loop into your commanded target, and misconfigured conditions are a classic silent failure: the car feels fine cruising, then goes briefly lean at the top of a pull because PE engaged too slowly or dropped out.

Watch the throttle/load threshold (PE shouldn't require a full 100% pedal if you want it active in real-world WOT), the enable delay, and the coolant-temp gate. There's also a hysteresis or 'PE delay' that can keep the engine in closed-loop or transitioning longer than you'd expect. On many GM tables the transition between the closed-loop stoich target and the PE target is also rate-limited, so the AFR ramps rather than steps.

The trap to watch for here is units on the delay and timer fields. Some HP Tuners parameters are in seconds, others in milliseconds, and a value entered assuming the wrong unit can make PE engage an order of magnitude too late. Always confirm the column header units before typing a number. When TuneVault returns copy-paste changes, it specifies the field, the exact value, and the units, so a 0.1-second delay never gets entered as 100 by accident.

This is the rule that protects your engine, so it gets its own section. The PE table is a request. The narrowband O2 sensors the factory ECU uses are essentially blind above stoich — they cannot tell you whether you're at 12.5:1 or 11.0:1, only that you're 'rich.' So the ECU has no closed-loop way to confirm it hit your WOT target. If your injectors are mischaracterized, your fuel pressure sags under load, your MAF is reading off, or your injector data is wrong, commanded and delivered will diverge — and the factory sensors will never tell you.

The only way to know your true WOT AFR is a wideband oxygen sensor, logged in VCM Scanner alongside commanded AFR/EQ. Do a WOT pull, then overlay commanded vs measured. If you command 12.8 and the wideband shows 13.6, you are dangerously leaner than you think and must not add boost, timing, or load until you close that gap (injector data, fuel pressure, or MAF/VE correction). Never make a tune more aggressive based on the commanded value alone.

TuneVault's datalog verification reads your VCM Scanner export and compares commanded against wideband measured across the pull, calling out where they diverge and by how much — but it's a second set of eyes on your data, not a substitute for installing and trusting a real wideband on the car.

Because fuels differ in their stoichiometric ratio, AFR is fuel-specific. 14.7:1 is stoich for gasoline, but E85's stoich is closer to 9.8:1, and a flex blend lands in between. That makes raw AFR numbers ambiguous across fuels. Lambda solves this: lambda 1.00 is always stoich regardless of fuel, and a WOT target of lambda 0.80 means the same combustion richness whether you're on pump gas or E85. Many tuners do their thinking in lambda for exactly this reason.

EQ ratio (equivalence ratio), which GM PE tables frequently use, is simply 1/lambda. EQ 1.00 = lambda 1.00 = stoich; richer is EQ > 1.00. To convert an EQ target to a gasoline AFR, divide 14.68 by EQ. To go from a gasoline AFR back to lambda, divide by 14.68.

The practical hazard is mixing units mid-tune — reading a lambda wideband while the table is in EQ, or assuming AFR when the column is EQ. Standardize on one frame of reference per session and convert deliberately. This is exactly the kind of translation TuneVault handles automatically: upload the table, tell it your fuel, and it expresses targets in AFR, lambda, and EQ so you can sanity-check the number you're about to write against the number your wideband reports. None of this replaces a professional tuner for a complex boosted build — it makes you a more informed one.