Diesel Engines Mechanical SSSP | Fuel Systems SSSP | HP-Fuel Systems SSSP | Fuel Metering Flashcards
Metering
Process of measuring + delivering the correct quantity of fuel to each cylinder required for various speed and load conditions from the engine (less or more to, i.e., decrease or increase in-cylinder combustion pressure a measured amount at a given time, to appropriately vary vehicle speed + power)…in Gasoline Engines, throttle plates in the Air Intake Sys also help regulate engine speed + power.
Name + Describe the diesel engine component (part) that is responsible for metering fuel, including its 3 inputs.
Governor - can be electronic or mechanical; regulates quantity of diesel injected into the cylinders by responding to input data from (at minimum) the 1) vehicle’s throttle (accelerator) pedal, 2) engine speed, & 3) air intake manifold (OR boost) pressure, using software to calculate (electronic), or linkage to move (mechanical) fuel control device, adjusting the amount of fuel injected; function to maintain a minimum engine speed, limit maximum engine speed, & regulate for everything in-between.
Diesel Governors - what is compensation?
Adjustment by governor to maintain set engine idle speed when 1 or more cylinders are cut-out or improperly contributing to engine power (i.e., by increasing fuel delivery to the remaining cylinders).
Governors - what is referred to by “Hunting”?
Readjustment of the quantity of fuel metered to correct the engine’s speed when inconsistent or irregular fuel delivery (i.e., uneven metering) is detected; may be experienced as a rythmic change in engine rpm (due to alternately decreasing and increasing diesel delivery to different cylinders) at idle speed.
Metering - what is idle adaptation?
an ‘adaptive cylinder balance’ type feature in modern diesel engines (most electronically controlled engines built since the early 2000s), where the (cam and) crank position sensor can detect slight velocity changes (varying crank deceleration rates during compression events & acceleration rates during power stroke combustion events) that enable the ECM to subtract or add fuel to each cylinder based on the measured variations to crankshaft (de/)acceleration during (compression/)power events to calculate & apply a correction factor to the quantity injected into a cylinder from 1 combustion cycle to the next IOT maintain more consistent cylinder combustion pressure & smooth engine idle (most engines since 2002) or operating speed (most engines since 2010).
Identify 7 HPI Fuel SubSys variables monitored by the HD-OBD diagnostic system manager to detect conditions that could potentially lead to excessive emissions. Identify when this monitoring occurs.
1)Fuel Pressure, 2) Misfiring, 3) Firing Voltages, 4) Cylinder Imbalance, 5) Timing, 6) Injector Deterioration, & 7) Incorrect Calibration Codes. Monitoring must occur during the entire speed and load range of an engine.
What does a cylinder cut-out test check? What central value is used and how?
Detects misfiring or a cylinder with a (comparatively) low power contribution. A pulse-width number that is higher than the baseline value beside a cylinder means good (more) contribution from that cylinder while a lower number means less contribution from that cylinder because it represents how long - the length of time (energization time - reported in degrees of crankshaft rotation) the other injectors had to stay energized once that cylinder was cut-out (either shorter or longer corresponding to the level of compensation needed to maintain engine speed; zero degrees would point to a bad cylinder as far as engine power, because would mean that cylinder wasn’t contributing at all before being cut-out (aka, was completely misfiring, or missing its fire aka injection shot(s)) and thus no compensation - no added energization time of other injectors - was caused once it was).
What does a cylinder balance test check & how does it compare to a cylinder cut-out test?
Measures the crankshaft velocity changes for each cylinder compression and power stroke to identify cylinder misfiring, unbalanced power contributions, and mechanical problems with an engine (base engine discrepancy, wear, damage, failure, etc.) such as valve out of adjustment, bent connecting rod, burnt valve, etc. Similar to cut-out in that it compares cylinders to isolate a discrepant one, but differs from cut-out test in that (for one) it measures without deactivating injectors (so doesn’t isolate them as much), results can point to a wider array of engine complaint root-causes as described above.
