Jumpin’ Jack Flash, it’s a…diesel? – Mercedes-Benz E320 CDI

Hey there, time traveller!
This article was published 11/03/2005 (7558 days ago), so information in it may no longer be current.

THIS changes everything.

Hear the word “diesel” and images of black smoke, classless clatter, and lackluster acceleration will no doubt come to mind. And then there’s the lovely aroma of tailpipe emissions that anybody who’s been stuck idling near a heavy-duty diesel-powered pickup in rush-hour traffic can attest to.

But the E320 CDi from Mercedes-Benz is different. And it’s a relative bargain compared to its gas-powered sibling, the E320. At $74,400, the CDi asks for just 1,400 more of your hard-earned dollars.

Consider this: while buying a diesel would normally be considered a sacrifice of performance and prestige for the sake of fuel economy, this one actually provides superior performance that’s virtually silent and odour-free. That it consumes substantially less fuel is just icing on the cake.

At the heart of the CDi is a 3.2-litre turbocharged inline-six diesel that produces 201 hp at 4,200 rpm. But diesels are about torque, not horsepower, and the CDi delivers bags of it: 369 lb-ft from 1,800 to 2,600 rpm. The gas-powered E320’s numbers measure 221 hp and 232 lb-ft.

While we can’t do the CDi technology justice in just a few paragraphs, there are a few key features of this new diesel engine that we should touch on.

“CDi” stands for “Common-rail Direct injection,” referring to the electronic fuel injection system that separates this Benz from most other oil-burners. Where traditional diesels use a mechanical injection pump to pressurize the air-fuel mixture for each cycle, the CDi system maintains a constant pressure of almost 23,000 pounds per square inch in the common-rail fuel loop. The quantity of fuel then allowed into the combustion chamber is determined by how long the electronic injectors stay open. Among the key benefits of this technology, according to Mercedes, is better engine performance at higher revs. But it also goes a long way toward eliminating the usual diesel drawbacks.

First, the noise: credit the traditional diesel clatter to a sharp spike in combustion chamber pressure when the fuel ignites. Mercedes takes advantage of the precise control afforded by the electronic injectors and ignites two small quantities of fuel in rapid succession just before the main injection to preheat the chamber and, thus, reduce the resulting temperature and pressure increases.

Combine the engine technology with the requisite abundance of Mercedes sound-deadening materials and the diesel is virtually silent in all but the heaviest acceleration situations.

Next victim: diesel smell. One of the oddest things about driving the CDi is that it just doesn’t smell like a diesel. There is a distinctive, slightly sweet aroma from the tailpipe — a far cry from the sooty odour that we’re used to. Mercedes-Benz folks informed me that it’s the smell of more complete combustion thanks to the smaller droplets of fuel injected into the combustion chamber — yet another benefit of electronic fuel injection. The end result is a smooth, quiet luxury car that will achieve 100 km/h from a standstill in a scant 6.8 seconds, half a second faster than the gas version, according to information published by the manufacturer.

As commendable as that is, it’s the manner in which the power is delivered that impresses most. In fact, I’d even say that the diesel is better suited to a luxury car than the equivalent gasoline engine, for the simple reason that it puts its power to the road in a single, seamless rush of torque that no gas-burner could approach.

Oh yeah, let’s not forget fuel economy: the gas-powered E320 consumes 11.9 L/100 km in the city and 7.8 on the highway. That’s not bad for a large luxury car, but fill up on this: CDi-powered E-Class sedans use just 8.9 litres for every 100 km of city driving, and a Honda Civic-like 5.9 L/100 km on the open road. That’s good for a bladder-bursting cruising range in excess of 1,200 km.

Dynamically, the CDi does everything just as well as the E320 on which it’s based. The electronic “brake by wire” system was unimpressive in the E320 I drove a couple of years ago, but it has been on its second iteration since last summer and the difference in braking feel is immediately evident. It no longer takes concentration just to come to a smooth stop. If they could only address the same issue with the electronic throttle. Fellow freelancer Michael Clark commented on the goofy throttle response as he handed me the keys to the Benz. I agree — in a luxury car that’s otherwise superb in every way, the response from the drive-by-wire system needs some reprogramming.

Surprisingly, there was an awkward delay between hitting the “go” pedal and getting a response from the engine. As a result, I found that I was pressing the pedal down too far, causing a lurch when the throttle finally responded. This behaviour is certainly unbecoming of a pedigreed luxury car.

Like all E-Class Benzes, the car’s interior finishes and appointments are beyond reproach. But here’s an ergonomic goof that has long been affecting Mercedes vehicles, and now it has even spread to the new full-size cars from DaimlerChrysler. That turn signal lever is just plain too low. It’s positioned like that to allow room for the cruise stalk that extends from the same side of the steering column at a higher location. I found it too easy to set the cruise control when all I wanted to do was turn right.

The question most people asked me was this: why would somebody who could afford to spend $75,000 on a car care about fuel economy? The answer is this: they don’t mind saving money on fuel costs, as long as they’re not sacrificing luxury or performance in the process.

And on that count, the E320 CDi hits its mark.

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