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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

Created in 1947, VM Motori was named after its creators, Claudio Vancini and Ugo Martelli, who built the first Italian diesel engine — direct-injected and air-cooled. The company started making water-cooled diesels in 1974, which appeared in regular production cars with the 1979 Alfa Romeo Alfetta.

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. In 1996 or 1997, they switched to the model GS (similar to NS) with timing chains rather than gears. The most visible differentiator is the injection pump — whose model ends in 975 for the chains and in 963 for the gears.

These 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 including a vacuum fuel pump. The three-digit engine code was stamped on the forward-facing side of the block.

diesel engineChrysler upgraded their diesel engines in 1999, using the VM Motori 2.5 in minivans and Jeeps, and the 3.1 in the Grand Cherokee. They had in common:

  • Common Rail Fuel Control (CR) with 1,500 bar injection pressures, for better spray atomization, maintained through the full engine speed range.
  • Pilot injection — a “pre-spray” that cut noise.
  • Four valve direct injection for better fuel efficiency than indirect injection.
  • Cooled EGR (optional) to cut emissions.
  • Swirl control (optional) at the cylinder head intake to match air motion with the needs of the engine, without sacrificing 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 NOx catalyst.

The updated 2.5 litre diesel had dual balance shafts in the oil sump to cut vibration. Gas mileage was 15% better than the older 2.5 diesel, with more power, thanks to a variable geometry turbocharger, direct injection, and other new features.

R425The 3.1 liter (3125 cc) five-cylinder engine used on the 1999-2001 Grand Cherokee had these features with electronically-controlled, vacuum-actuated exhaust gas recirculation. The 3.1, created largely by adding a cylinder to the 2.5, also used 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. An automatic serpentine belt tensioner increased average accessory belt life to 160,000 km (100,000 miles).

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.

vm diesel

The future of VM four-cylinder diesel engines

A redesign of the 2.8 is expected to push out over 200 horsepower, with a new cooled EGR system, new manifolds, and a new block and balance shafts. It should be possible to make it meet U.S. emissions, as GM makes a version that does.

With tighter emissions controls on the way and a more competitive landscape, VM is working on a new generation of diesels, the L424. It is predicted to peak at 197 horsepower and 368 lb-ft of torque (at 1600 rpm); the L424 was reportedly designed to meet US ULEV standards. More can be found in Alessandro Bettini’s dissertation.

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

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