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VM Motori Four-Cylinder Diesel Engines Used by Chrysler

VM Motori started supplying Chrysler in 1992, with the Chrysler Voyager’s diesel option; it was owned by Detroit Diesel at the time, spent some time being owned 50/50 by General Motors and Fiat, and is now entirely owned by Fiat.

As for 2011, VM Motori powered several European Chrysler and Jeep cars, as well as the Chevrolet Captiva, London Taxi, and other vehicles.

2.8 liter VM diesel

Two VM engines are currently used by Chrysler: the 2.8 (Wrangler, Voyager, and Cherokee) and 3.0 V6. The 2.8 liter engine is an in-line four cylinder, exactly 2776 cc in displacement.

Starting in 1992, Chrysler Voyagers and Grand Voyagers used a 2.5 liter Model ES diesel from VM Motori, which had timing gears. In 1996 or 1997, they switched to the model GS (similar to NS) with timing chains. The only visible differentiator is the injection pump — whose model ends in 975 for the chains and in 963 for the gears. (Alfa Romeo used VM diesels from 1979 to 1997.)

The NS and GS 2.5 liter four-cylinder engines had a bore of 92 mm and a stroke of 94 mm; a compression ratio of 20.95:1; 23.6 inches of vacuum at idle; pushrod-driven overhead valves; indirect fuel injection, using a precombustion chamber; a four-stroke cycle; and an electronically controlled rotary injection pump incorporating a vacuum fuel pump. The engine code on these are stamped on the forward-facing side of the block as a three-digit code with letters and numbers.

diesel engineChrysler had new diesel engines for export markets in 1999. The VM Motori 2.5 was used in minivans and Jeeps, and the 3.1 was in the Grand Cherokee; both used:

  • Common Rail Fuel Control (CR) with a high-pressure pump to achieve 1,500 bar injection pressures, for better spray atomization, maintained throughout the full engine speed range.
  • Pilot injection — a fuel spray which precedes the main spray to initiate combustion, to reduce noise.
  • Four valve direct injection brought 15% better fuel efficiency than indirect injection; the injector was centrally located.
  • Cooled EGR (optional) to cut emissions.
  • Swirl Control (optional) at the cylinder head intake matched the air motion in the combustion chamber with the needs of the engine, without sacrificing the amount of flow. One port was tangential for maximum flow, while the other was designed to induce swirl to air entering the combustion chamber, based on engine load and speed.
  • A special NOx catalyst.

The revised 2.5 litre diesel had dual balance shafts off the crank in the oil sump for reduced vibration. Gas mileage was 15% better than the older 2.5 diesel, with more power, thanks to a variable geometry turbocharger (VGT) and other new features.

R425The 3.1 liter (3125 cc) five-cylinder engine used on the 1999-2001 Grand Cherokee had an electronic injection pump, direct injection, and electronically-controlled, vacuum-actuated exhaust gas recirculation. The 3.1, created largely by adding a cylinder to the 2.5, featured variable fuel-injection timing, a quick-sensing inlet-side positioned thermostat, and coil-on-plug ignition. A hybrid-cooling system combined inline electric and engine-driven fans, allowing the engine fan to idle at a lower speed (250-300 rpm vs. a typical 650-700 rpm), decreasing noise and vibration. A secondary thermostat control cut power consumption by 12% or 4.5 kW (6 hp).

2.5 liter (R425)*

Jeep Cherokee (XJ) Jeep Grand Cherokee (WG) Dodge Dakota (R1) Jeep Cherokee (KJ) Chrysler Voyager (ES) Chrysler Voyager (GS) Chrysler Voyager
Valves 8 8 8 16 8 8 16
Injection IDI IDI


Common Rail
Max power in kW (hp) 85 kW (114) 85 kW (114) 85 kW (114) 105 kW (140) 85 kW (114) 85 kW (114) 105 kW (140)
Torque in Nm (lb-ft) 300 Nm (221) 300 Nm (221) 300 Nm (221) 340 Nm (251) 262 Nm (193) 262 Nm (193) 340 Nm (251)
Model years 1994-2001 1995-1998 1999-2000 2001-2004 1992-1995 1996-2000 2001-10

The 3.1 liter VM diesel engine was designed to operate 240,000 km (150,000 miles) under normal conditions without part replacement other than normal maintenance items. An automatic serpentine belt tensioner increased average accessory belt life to 160,000 km (100,000 mi).

vm diesel

The new turbodiesel engine boosted power and torque by 20% over the 2.5 liter unit, for up to 12.5% better acceleration, a higher top speed, and more load-carrying and towing capacity. A drive-by-wire "electronic accelerator" controlled the throttle. The intercooled diesel had a bore of 92 mm (3.62 inches) and stroke of 94 mm (3.70 inches), with a cast iron block and cylinder head with two valves per cylinder. Peak horsepower of 103 kW (138 hp) was achieved at 4,000 rpm; peak torque was 384 Nm (283 hp); and gas mileage in the Grand Cherokee was rated at 11.7 liters per 100 km.

2.8 VM diesels
used by Chrysler*

Voyager Voyager Liberty/
Liberty, Cherokee,
Nitro, Wrangler
Power, kW (hp)110 (150)120 (161)120 (163)130 (177)130 (177)149 (200)
Nm (lb-ft)
360 (265)360 (265)*400 (295)302/339
410 (302)410 (302) /
460 (339)**
Gas mileage25/3328 comb.
8.4 l/100
21/27 (2005)   
Model Years2001-072008-112001-072008-?2007-092010-?

* In some early models this was listed at 400 (295)      ** automatic / manual transmission

RA 428 diesel engine from VM MotoriThe R 428 2.8 engine generated 150 horsepower and 265 lb-ft of torque (in 2005, 160/295), with a 17.5:1 compression ratio, in the minivans and Cherokee 4x4 (where it was rated at 148/266 and hooked up to a five speed automatic). This powerplant had a belt drive, dual overhead cams driving four valves per cylinder, and a common rail fuel system pressured to 1,600 bar (23,000 psi). The engine itself was cast iron, with an aluminum cylinder head. Redline came at a generous 4,300 rpm (electronically governed); gas mileage in the 2005 Jeep Cherokee with automatic was 21 city, 27 highway.

The 2.8 is essentially an enlarged-chamber version of the R425 engine; because the R425 used wet liners, only changes to the liner, piston, and camshaft were necessary. The engine ended up with 10% more torque at lower rpm. Like the 2.5 liter R 425, it had finger followers on the camshaft. An optional VGT turbocharger increased the power output to a class-leading 177 CV in some applications. Engine blocks are cast in Portugal.

* Figures are from VM Motori. Some inconsistencies were found in their tables.

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