Answer 10 free questions

Cummins: 10 free questions

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1. Cummins X15 / ISX15 Heavy-Duty

   The Cummins X15 is a 14.9 L (912 cu in) engine with a 137 mm bore and 169 mm stroke. What is its cylinder configuration and firing order?

   AInline six-cylinder, firing order 1-5-3-6-2-4 BV8, firing order 1-8-4-3-6-5-7-2 CInline six-cylinder, firing order 1-2-3-4-5-6 DInline six-cylinder, firing order 1-4-2-6-3-5
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   Answer: A. Inline six-cylinder, firing order 1-5-3-6-2-4

   The X15/ISX15 is an inline six-cylinder diesel; like most Cummins inline sixes it fires 1-5-3-6-2-4.

2. Cummins ISX12 / X12

   The Cummins X12 is an inline-6 diesel with what approximate displacement?

   A8.9 L B11.8 L C14.9 L D6.7 L
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   Answer: B. 11.8 L

   The X12 displaces 11.8 L (132 mm bore x 144 mm stroke), slotting between the mid-range engines and the 14.9 L X15.

3. Cummins B6.7 & L9 Mid-Range

   The Cummins B6.7 diesel is best described as which engine configuration?

   AA 90-degree V6 with overhead camshafts BAn inline-six overhead-valve (pushrod) design CAn inline-four with a single overhead cam DA V8 with block-mounted injectors
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   Answer: B. An inline-six overhead-valve (pushrod) design

   The B6.7 is a 6.7L inline-six overhead-valve engine with a block-mounted camshaft that operates the valves through pushrods and rockers, evolved from the 5.9L B-series.

4. Cummins XPI Common-Rail Fuel

   What is the primary function of the fuel rail (accumulator) in the Cummins XPI system?

   AIt stores high-pressure fuel and dampens pressure pulses while feeding all injectors BIt creates injection pressure with its own internal pumping element CIt filters fuel one last time at each injector feed before injection DIt meters the exact fuel quantity delivered for each individual injection event
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   Answer: A. It stores high-pressure fuel and dampens pressure pulses while feeding all injectors

   The common rail is an accumulator that holds a stable high-pressure charge and absorbs pump and injection pulsations, supplying every injector from one shared volume.

5. Cummins Aftertreatment & Emissions

   What is the primary purpose of the EGR cooler on a Cummins engine?

   ALower the temperature of the recirculated exhaust gas to further reduce NOx formation BIncrease exhaust backpressure so the turbocharger spins faster at low speed CPreheat the intake air charge to improve cold starting and cut white smoke DTrap soot and ash from the recirculated gas before it reaches the intake
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   Answer: A. Lower the temperature of the recirculated exhaust gas to further reduce NOx formation

   Cooling the recirculated exhaust makes it denser and lowers peak combustion temperature, which is the main driver of thermal NOx; a cooler EGR charge cuts NOx more than hot EGR alone.

6. Cummins Electrical & Sensors

   The engine coolant temperature (ECT) sensor on Cummins electronic engines is best described as:

   AA negative temperature coefficient (NTC) thermistor whose resistance falls as temperature rises BA positive temperature coefficient thermistor whose resistance rises as temperature rises CA variable-capacitance transducer supplied with 5 volts DA magnetic pickup that generates its own AC voltage
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   Answer: A. A negative temperature coefficient (NTC) thermistor whose resistance falls as temperature rises

   Cummins temperature sensors are NTC thermistors; the ECM feeds a reference through a fixed pull-up resistor and reads the voltage drop, which rises as resistance (cold) rises.

7. Cummins INSITE & Controls

   How does the INSITE service software physically communicate with a Cummins engine ECM?

   AThrough a Cummins INLINE datalink adapter (5/6/7) connected between the vehicle diagnostic connector and the PC BThrough a generic OBD-II Bluetooth dongle in the diagnostic connector paired wirelessly to the PC CBy tapping directly into the crankshaft position sensor circuit and reading the ECM signal off that wire DThrough a PACCAR ESA programming cable connected between the vehicle diagnostic connector and the PC
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   Answer: A. Through a Cummins INLINE datalink adapter (5/6/7) connected between the vehicle diagnostic connector and the PC

   INSITE relies on a Cummins INLINE datalink adapter that bridges the vehicle's diagnostic (Deutsch/OBD) connector to the laptop and translates the J1708/J1587 and J1939 datalinks.

8. Cummins X15 / ISX15 Heavy-Duty

   On the Cummins ISX/X15, the camshaft and main timing/accessory gear train are driven from which end of the engine?

   AFront, off the crankshaft damper BRear, at the flywheel end CCenter, off the number 3 main journal DFront, through a chain and tensioner
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   Answer: B. Rear, at the flywheel end

   The ISX/X15 uses a rear gear train at the flywheel end, which lowers gear-rattle noise and keeps the timing gears in the most rigid part of the block.

9. Cummins ISX12 / X12

   What is the X12's chief advantage over the X15 for weight-sensitive vocational work?

   AIt weighs about 2,050 lb, making it the lightest heavy-duty engine in its class BIt produces more peak torque than the X15, so it pulls heavier grades CIt uses two turbochargers in series to broaden its boost range DIt runs on compressed natural gas rather than on diesel fuel
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   Answer: A. It weighs about 2,050 lb, making it the lightest heavy-duty engine in its class

   At roughly 2,050 lb the X12 has the best power-to-weight ratio in the 10-16 L class, which frees up chassis payload for vocational and regional fleets.

10. Cummins B6.7 & L9 Mid-Range

    Which high-pressure fuel system is used on the current Cummins L9?

    AAn engine-driven mechanical rotary distributor injection pump BThe Cummins XPI (Xtra-high Pressure Injection) common-rail system CA HEUI system using engine oil pressure to actuate the injectors DCummins PT (pressure-time) injection using mechanical injectors
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    Answer: B. The Cummins XPI (Xtra-high Pressure Injection) common-rail system

    The L9 uses the Cummins XPI common-rail system (co-developed with Scania), which holds accumulator pressure up to roughly 2,200 bar independent of engine speed.