engine load

is engine load the speed of the engine or the throttle position in relation to speed i.e. is the load more at low speed hi gear full throttle than at hi speed hi gear light throttle .

I have been doing a lot of reading on that subject over on the iATN forums. It's something that I have been including that pid I'm WOT test drives to help point out MAF problems.
I'm still wrapping my head around this a bit.
Albin Moore is an incredibly smart tech and supporting member of iATN.
This is what he had to say in a post on iATN about the subject:




Albin MooreFeb 15
Your load pid is defined by SAE J1979. Here is its definitions.

There are two types of LOAD specified in SAE J1979

One is CALCULATED LOAD VALUE and the other is ABSOLUTE LOAD VALUE.

Please take a look in this explanation.

Calculated LOAD Value (PID 04)

The OBD regulations previously defined CLV as:

(current airflow / peak airflow @sea level) * (BARO @ sea level / BARO) * 100%

Various manufacturers have implemented this calculation in a variety of ways. The following definition, although a little more restrictive,

will standardise and improve the accuracy the calculation.

LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) * (BARO/29.92) * SQRT(298/(AAT+273))]

-- Where: STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg BARO, SQRT = square root, -- WOT = wide open throttle, AAT = Ambient Air Temperature and is in °C

Characteristics of LOAD_PCT are:

-- Reaches 1.0 at WOT at any altitude, temperature or rpm for both naturally aspirated and boosted engines. -- Indicates percent of peak available torque. -- Linearly correlated with engine vacuum -- Often used to schedule power enrichment. -- Compression ignition engines (diesels) shall support this PID using fuel flow in place of airflow for the above calculations.

NOTE Both spark ignition and compression ignition engines shall support PID $04. See PID $43 for an additional definition

of engine LOAD.

05 Engine Coolant Temperature A --40 °C +215 °C 1 °C with --40 °C offset

ECT: xxx °C (xxx °F)

ECT shall display engine coolant temperature derived from an engine coolant temperature sensor or a cylinder head temperature

sensor. Many diesels do not use either sensor and may substitute Engine Oil Temperature instead.

Absolute Load Value (PID 43)

The absolute load value has some different characteristics than the LOAD_PCT defined in PID 04 This definition, although restrictive,

will standardise the calculation. LOAD_ABS is the normalised value of air mass per intake stroke displayed as a percent.

LOAD_ABS = [air mass (g / intake stroke)] / [1.184 (g / intake stroke) * cylinder displacement in litres]

Derivation:

-- air mass (g / intake stroke) = [total engine air mass (g/sec)] / [rpm (revs/min)* (1 min / 60 sec) * (1/2 # of cylinders (strokes / rev)],

-- LOAD_ABS = [air mass (g)/intake stroke] / [maximum air mass (g)/intake stroke at WOT@STP at 100% volumetric efficiency] * 100%.

Where:

-- STP = Standard Temperature and Pressure = 25 °C, 29.92 in Hg (101.3 kPa) BARO, WOT = wide open throttle.

The quantity (maximum air mass (g)/intake stroke at WOT@STP at 100% volumetric efficiency) is a constant for a given cylinder swept

volume. The constant is 1.184 (g/litre 3) * cylinder displacement (litre 3/intake stroke) based on air density

at STP.

Characteristics of LOAD_ABS are:

-- Ranges from 0 to approximately 0.95 for naturally aspirated engines, 0 -- 4 for boosted engines, -- Linearly correlated with engine indicated and brake torque, -- Often used to schedule spark and EGR rates, -- Peak value of LOAD_ABS correlates with volumetric efficiency at WOT., -- Indicates the pumping efficiency of the engine for diagnostic purposes.

Spark ignition engine are required to support PID $43. Compression ignition (diesel)

You just gave me a headache Noah

Manifold vacuum is good guide to engine load, a bit like the old days when owners fitted a vacuum gauge on the instrument panel as an "Economy Meter", by driving and using the gear to keep the manifold vacuum high they could reduce engine load and improved fuel consumption.

Dylan wrote: You just gave me a headache Noah

:lol: The SAE stuff does get a bit technical, huh?

Like Noah, I use Load for volumetric efficiency and airflow sensor diagnostics. I figure just about all gas engines should clear 85% Load during a WOT run through first gear. Most will clear 90%, some will do 99%, depends on the make/model.

This thread might have some more useful info for you:

www.scannerdanner.com/forum/diagnostic-t...s-absolute-load.html

thanks

Dylan wrote: You just gave me a headache Noah

Ha, seriously. Anyone want to translate that?

Sent from my Moto E (4) Plus using Tapatalk

I was trying to come up with a formula for idle MAF readings.
(If a 3l engine pulls 3 litres of air every 720*...) when i found that post.
I know it's kind of a cop out to just paste that in there like that, but i didn't want to try my hand at an interpritation and give out bad info.