Diesel Engines Mechanical SSSP | Fuel Systems SSSP | Popular OEM Unit Injection Systems | Cummins Unit Injection Pumps, Systems

Question 1

What’s so special about Cummins’ old PT System, and why can it be helpful or good for a ENG tech to understand it?

Question 2

What is the source of the PT system’s ability to change fuel pressure supplied to the injectors, & what 3 mechanical inputs does that source operate off of?

Answer 2

Source is an engine-driven (i.e., crank-driven) LP gear pump.
Inputs recieved by the gear pump are:
1) Engine Speed from the Pump Drive Gear
2) Driver Position (from the driver’s throttle aka accelerator pedal)
3) Boost Pressure from a pneumatic line connecting the PT pump to the intake manifold
(so, all other factors the same, the above 3 variables collectively determine the variable pressure of diesel exiting the pump based on engine speed [crank input], driver demand [pedal input], & load conditions [boost input])

Question 3

What design style or type makes Cummins’ PT injectors unique?

Answer 3

Their open-nozzle design.

Question 4

PT System: because the PT injector plunger is driven by the engine camshaft, available time for fuel to flow under pressure into the injector body, etc. (i.e., for fuel metering) is determined by what?

Answer 4

Engine speed (lower RPMs = less time available vs higher RPMs = more time available)

Question 5

Depending on the ENG model & power output, what is a typical PT fuel system pressure at idle? Full load & torque?
What dimension of what is carefully selected to match the engine power rating?

Answer 5

Idle: may be approximately 30psi
Full Load & Torque: 130-200psi
The diameter of the metering inlet orifice.

Question 6

What was the 1st generation of (at least for Cummins) full-authority electronic engine control?

Answer 6

Cummins CELECT
(abbreviated form of Cummins ELECTronic)

Question 7

Cummins CELECT vs CELECT Plus: name 4 upgrades from former to latter.

Answer 7

CP uses:
1) additional sensors
2) a faster & more capable ECM, &
3) additional programmable engine controls
4) J-1957 network communication compatibility (via a 6-pin data link connector [DLC] located in the cab)

Question 8

What type of induction coil does the CELECT ECM contain, & what is it used for?

Answer 8

A step-up induction coil to convert 12v DC to 75v DC, which is used to energize the injectors. Hence it is referred to as the injector inductive coil.

Question 9

CELECT ECM: where are the transistor output drivers located?

Answer 9

In 4 aluminum heat sinks.