OPEN LOOP: Where's the Smoke?

Jan. 1, 2020
"And where'd the rattle go?" That was my reaction when the first new Dodge 6.7-liter diesel truck rolled into our dealership ...
Where’s the Smoke?

“And where’d the rattle go?”

That was my reaction when the first new Dodge 6.7-liter diesel truck rolled into our dealership. To my sheer amazement, this beast – the largest in its class – was as quiet as a gasoline HEMI and emitted almost no odor. So, where did it go?

Well, as it turns out, there’s some very interesting new technology here that you’re going to want to know about that will surely turn into great maintenance opportunities for your shop.

First, as to the new “odorless” feature, this is a result of two changes that were government mandated for 2007. One is the new ultra-low sulfur fuel (15 parts per million [ppm]) as opposed to the old low sulfur fuel (500 ppm). The theory is simple enough – less particles, less smoke … less pollution. “ With increased efficiency, comfort and economy, 
it seems 
we have almost completely run out of excuses for not buying these oil-burning beauties.”

Second, for those last 15 ppm (heaven forbid that they should escape) DaimlerChrysler designed yet another addition to our already crowed exhaust system. This lovely little device will certainly be a part of all future diesel vehicles. Its name is self-defining – “particulate trap.” This is not used instead of a catalytic converter but in addition to it.

Chrysler is using two styles. One is included in the same component with the converter on the cab-chassis application; it looks like a 35-gallon drum under there. The other is separate and downstream of the converter on the pickups.

Both serve the same function: Catch those wicked pollutants before they escape and trap them. Then, at prescribed intervals determined by the electronic control module (ECM), the system will add oxygen, light it all on fire … and incinerate the little devils. By the way, when this cycle occurs, the exhaust at the tail is some 1800°F, which easily sets a shop rag on fire, so be warned.

Now, with the exhaust cleaned up, we can turn our attention to those obnoxious noises that have always driven American motorists away from diesel engines. Finally, “Dr. Z” has solved this illusive irritation, and once again, the solution is frightfully simple. After all, the cause of that characteristic “rattle” was the violent explosion (combustion) that occurs when the pump dumps the “mother load” of fuel into a cylinder charged with hot compressed oxygen. So how did they change that?

The answer is to stretch that explosion over a longer duration by starting it earlier, thus rendering it less violent. Enter… “pilot injection.” The ECM pulses two microbursts of fuel into the cylinder just prior to top dead center (TDC), which “preconditions” the cylinder and – voila – no rattle. As an added bonus, one side effect is increased efficiency.

There you have it: a huge, powerful diesel engine with no smoke and no noise. With increased efficiency, comfort and economy, it seems we have almost completely run out of excuses for not buying these oil-burning beauties. At least that’s what Chrysler is counting on.

For those of us old-timers, all this takes a little getting used to, but you will surely be seeing lots of these coming into your shop in the days ahead and learning more about them will present numerous new service opportunities.
In case you think otherwise because of factory warranties, remember this: failed particulate traps resulting from improper fuel use won’t be covered by the manufacturer. Additionally, there are several new systems on these trucks: exhaust gas recirculation (EGR), EGR bypass, oil contamination warning light, etc.

Don’t be shy. Jump right in and harvest the gold – smoke-free!

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