Diesel Suburban MPG: not what I was hoping for
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I drove the Diesel Suburban to work for the past few days to find out what fuel economy it gets. I also showed it off to perhaps a dozen coworkers and received many compliments on the installation. A couple guys said it looked like it came that way from the factory, which was high praise! Another guy said the installation looked better than the factory V-8 did. The real question about the impressions at work: Am I famous for doing this conversion or notorious?! I don't really care, but it would be interesting to know...
Back to the subject of fuel economy: I topped it off on Sunday, reset the trip odometer, and topped it off again this morning. The verdict: 22 mpg.
Certainly, as my coworkers pointed out, I'm hauling around a 6,000 lb machine with the aerodynamics of a brick. I was also in stop-and-go traffic for a good chunk of it every day. 22 mpg combined really isn't a bad figure.
This is a huge improvement over the stock 1999 K1500 Suburban. Fuelly says people are only getting 14 mpg for real-world fuel economy, which matches the EPA combined rating.
This is not bad, but I know I can do better. I'll play with the direct-injection timing and check my valve clearances, but I expect that the real answer will be a better turbo and the addition of an intercooler. Driving this around I've found out why people don't like the stock turbo that came with the Isuzu 4BD1T. This is not a high-rpm engine, but the turbo doesn't spool much at low rpms -- so it's horribly mismatched. I normally see perhaps 5 psi of boost, and haven't seen it go above 12 psi. 12 psi is done at some high rpms for this engine, but I can't tell you exactly what rpms because the tach isn't set up yet.
I know there are solutions out there. People talk about turbos that can reach 15 psi across the drivable rpm range.
Why am I talking about turbos, when I'm trying to fix a fuel economy issue?
Sounds crazy, doesn't it? Because I backed out the "power" (fuel-limit) screw 1 turn to get slightly better acceleration, I now produce some visibly sooty exhaust. It isn't the extreme cloud some of the diesel (mis-)tuners produce, but I can pick it out in the right mirror when I adjust it to view the right-rear corner where the exhaust exits. This indicates unburned fuel, which can be corrected by adding more air. I'll go do my research and provide updates on what turbo/intercooler combination I use and post on the progress of installing them. There are some family projects that require some attention right now, so it will take awhile. I'll keep blogging to provide details of the work I've already done, while covering some philisophical and self-reliance topics meanwhile.
--The quest for a 30 mpg Suburban continues!