New ScanGauge-D for diesels!

[Daox]

If you have an injector signal to tap into there is a way to measure fuel usage.

[UFO]

I don't know that much about common rail injection systems, maybe my CRD has that. It would be a slicker option that trying to find the factory EVIC with a mileage display.

[Diesel_Dave]

Originally Posted by Daox

If you have an injector signal to tap into there is a way to measure fuel usage.

Older, non-common rail systems wouldn't have a signal to tap into. Newer, common rail systems do, however, there's a few issues with that. First, common rail systems typically inject more than one pulse of fuel per cycle (typically 2-5 pulses). Especially with small pulses, twice the ontime does not equal twice the fueling--it's highly non-linear. Secondly, common rail systems have large variations in injection pressures, depending on the speed and load your at (3,000 psi vs 30,000 psi), so you'd have to know both ontime and rail pressure to acurately determine fuel injected.

[Daox]

Why do they vary the fuel pressure?

[Diesel_Dave]

Originally Posted by Daox

Why do they vary the fuel pressure?

It plays a key role in the combustion process. More pressure means better atomization, shorter injection duration, and shorter combustion duration. Higher pressures mean better smoke and better fuel economy, however, NOx increases. If you run too high rail pressures at high loads, the combustion can happen too quickly causing excessive cylinder pressures. Too high rail pressure at low load can overspray the fuel directly onto the piston. So you want different pressures at different speeds & loads.

[slowmover]

Originally Posted by Diesel_Dave

It plays a key role in the combustion process. More pressure means better atomization, shorter injection duration, and shorter combustion duration. Higher pressures mean better smoke and better fuel economy, however, NOx increases. If you run too high rail pressures at high loads, the combustion can happen too quickly causing excessive cylinder pressures. Too high rail pressure at low load can overspray the fuel directly onto the piston. So you want different pressures at different speeds & loads.

Very nice set of descriptions above, not just the post quoted, DD.

A set of new fuel injectors for a CTD (Cummins Turbodiesel Dodge) is right at $3000 for a set of six. Re-mans have a poor reputation and not advised by the knowledgeable (especially considering a $17,000 longblock replacement cost should problems recur.)

DD's comments about how this system works is likely the culprit faced by [ahem] "enthusiasts" who want to increase power with electronic tuners (before any mechanical changes), but see injector failure at a higher and sooner rate than those with stock trucks. Yes, . . there are exceptions, but the correlation is not to be missed. Better fuel filtration (which BOSCH spec'd, but DODGE refused) is the usual way of increasing injector life to B50 350k spec.

It is frustrating not to be able to easily read the flow rate. Today's diesel pickups have lost their way in HP wars that -- combined with stricter and terribly expensive emission requirements -- have lost the sweet ability to combine a tremendous capability for work for well more than a quarter million miles at an [unbelievably] high mpg in comparison to pickup trucks going back a half century. 1994-2006 Dodge and shorter periods for Ford & GM trucks that are well loved by their owners. A second, third or even fourth owner may well choose to rebuild and keep using the truck as designed: make money with that truck!

Measuring flow rate is at the heart of a sound business operation for an individual. For an RV'er it is in better driving in the course of a year that savings "pay" the vacation fuel bill. For me (and some others) it is in not just mpg improvement, but in trying to look at the whole of energy inputs to live life comfortably with only truck & travel trailer . . IOW, can I "afford" to travel to that other location and take that job at the contract on offer?

Predicting fuel burn in familiar surroundings is easy enough (I do it as part of making a living), but knowing some hard numbers in carefully documented circumstances (climate, terrain, etc) is another thing altogether. One can easily lose one's profit altogether with a percentage change in fuel burn. In acquiring fuel to run the trailer. High fuel prices are now a matter of course. Availability is the next domino to fall. Tools are paramount.

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[Diesel_Dave]

Hey, slowmover, do the Class 8 truck that you drive for work have J1939 ports rather than OBDII ports? I wonder whether one of these ScangaugeD's might work for those trucks well. Of course, I don't know what factory-installed instumentation are on those rigs--I know it's much more than passenger cars and light-duty trucks.

[slowmover]

I don't know. Might make the shop nervous for me to hook one up to it. I'll look at what I can find to report back.