Originally Posted by automotive breath
As I posted many years ago the simple A/B test I did with my suburban was a
huge success. The reason I'm not excited about it is the benefits only show
up when I drive the truck un-loaded. When I hitch up my >7000 lb enclosed
trailer the benefits are no longer there. I can only guess as to why. The
problem is thats all I use the old truck for.
I'm disappointed in myself that I never took the time to modify a daily driver,
that may change soon.
Yea, actually I thought you had decent at least light towing numbers from it. Either way, you're fighting basic physics (hooking a big box weighing 7K lbs is going to hurt MPG no matter what you have), and second, that extra load and if I remember right you were still running the stock chip, took you from a good spot in the stock engine ECM tuning to a crappy place that doesn't play nice with the emissions devices.
I would bet that some simple replumbing (mostly he crappy egr setup on that engine) and a custom chip would change your mind there. Turning on "highway mode" in the tuning would really make a difference (GM built a leaner than stoich mode that used extra timing to compensate for the loss of power from the leaner mixture into the 80's and 90's ecm's that they were never allowed to turn on I suspect because they didn't play nice with NOx emissions. It can be sketchy and touchy with a stock engine, but I've found that a grooved setup is much more tolerant of not getting it quite right)