Taming the Beast - Making a GMC 2500HD... Less Terrible

[slowmover]

6.0 not known for mpg.

Best to focus on mechanical, first:

1) Perfect alignment. Verify as to best, not just OEM acceptable.

2) Steering slop. From steering column outwards; eliminate.

3) KONI FSD shock absorbers.

4) Upsize front antiroll bar and install one on rear if not so equipped. Grease able polyurethane bushings.

5) Rear Panhard Rod. See if Hendersons Lineup has one for yours.

6) Zero brake drag. Verify. Get it up in air to do so, and lube all moving parts.

7) Highest quality tires, such as commercial traction Bridgestone Duravis. Wear like iron with excellent performance. On a Hunter GP-9700 balancer to Lexus/Mercedes spec. Centramatic balancers all around.

8) Get it on a Cat Scale. Driver, full fuel and normal gear aboard. For second and third scale readings have port or starboard tires off of pads in order to know all wheel position weights.

9) Synthetic fluids. Donaldson or Baldwin filters. If ten years or more in age, then new hoses and belts plus fasteners. New factory battery cables. AGM battery (Sears Diehard Platinum). All new exterior lamps (Phillips Nightguide head lamps; new housings if yellowed). Bosch Icon wiper blades after two/three coats of RainX (especially on side glass and mirrors). New windshield if sandblasted.

10) Have driveshaft removed and ujoints replaced if over 100k miles or ten years. Shop must be able to spin balance shaft. Install Balancemaster.

11) All other book maintenance 10-20% ahead of book recommendations. A new owner starts a new wear pattern on the vehicle. Get ahead of curve.

Steering pays greatest benefit after align and brakes. Shocks and bars are hugely beneficial to an EM driver. Others allow more precise control without wear issues clouding records.

The 45-mph and lower mechanical issues pay better than the 60-mph aero stuff. But, not sexy, and not clear to most as to cost/benefit. As they will in fact add to longevity, their importance must not be overlooked.

Great to see block and pan heaters!! In the diesel world we look at 90-minutes warmup as being 90% of the benefit of plugging in all night.

Every so often it's important to take it out for a 100-mile run. Burn off acids and condensation in fluids, reinvigorate greases, and get tires up to stabilized temps so oils can migrate through casing. That takes 1.5-hrs at steady state to achieve equal temps inside and out of casing.

SCHAEFFERS Oil products, also. Throughout truck.

[Deezler]

Wow.

Great list! Thanks for taking the time to type that all out.

Unfortunately you just described several thousand dollars of work.

I will need new tires next year at some point, and I definitely planned on getting aligned at that time. New shocks would also be wise before I align. Have Michelin LTXs now, which I like, but 2WD traction is lacking. Was thinking Michelin LTX M/S next time.

And yes, my truck does need the steering column bearing replaced. It's a bit sloppy right now but tracks smooth on the road. Could still be wasting some fuel and tire wear there, no doubt.

The centramatic and balancemaster products look very interesting. I like the idea a lot but cost is an issue. Same for rear panhard bar kit.... $463! ouch.

I doubt my old coolant hoses and windshield are wasting fuel though, lol. There's something to be said for not messing with things that already work....

Thanks again. A great list for any HD truck owner.

[slowmover]

Staying ahead of the wear curve pays more than day to day FE as shortened work life means another vehicle. Depreciation is low on yours, now, so don't make mistake of allowing deterioration as is usually done. I would be spending $2-5k on something like yours from the day of purchase. Too much experience the past forty some odd years that always argued for staying ahead.

Truck handling is not well appreciated. The test is to stay lane-centered despite all difficulties. Mines a slot car . . how's yours? Mine will have zero corrections to your many, and what it does have will, literally, be done with thumb and forefinger. On a freeway entry cloverleaf or other where we may compare speed. Etc.

Keep thinking thru the problem. You aren't there yet. Number of steering corrections and need to bleed speed to accommodate these lunkers is what separates them. Best shocks and suspension mods only downside is upfront money. A set of tires is $1300 for me. But they last over 120k. I could easily have wasted your savings by making the tires work harder. Etc.

Handling is huge.

[Deezler]

Again I cannot disagree with you in principle, and really appreciate your comments, but perhaps you have the wrong idea about my intended vehicle use here. This is my personal daily driver for now, but is intended to be an extra, backup vehicle in the hopefully not-too-distant future. A weekend work truck and camper hauler. Even as it is right now, I'm only driving it around 100 miles per week. No commercial hauling, no plans to ever hit 250k miles on this thing. It only has 89k miles now.

It simply does not make sense for me to blow $3000 into my suspension, nor could I afford or justify doing so. The truck rides well now, steers well, tracks straight, etc. I will try to upgrade and maintain the truck as best as I can, but throwing money at parts that may not even actually need replacement is not really responsible behavior, you know what I mean? If I "get behind the wear curve" a little, I can replace parts to bring it back again. The truck is not going to collapse into a worthless pile because the shocks get soft. And while I don't really care too much about resale value or depreciation, because I hope to keep this bad boy around forever, I'm more concerned with preventing body rust, frankly. That's what actually kills trucks and takes them off the road here in Michigan.

And from a fuel economy standpoint.... with sub-$2 gasoline, my wallet doesn't really care what mpg I get. But my pride and guilt do, and my general belief that we all just have to use less of this sh!t. I can do aero-mods for almost free... no reason not to. Steering and suspension work will be as-needed, because A) I have no garage to work in myself, and B) not much spare cash at the moment. Hopefully I can fix both of those points within the next 1-1.5 years though.

[Deezler]

Anywhoo.

Increasing engine efficiency (and power ) is always another modding priority of mine.

My last two daily drivers have been turbocharged, where increasing power is about as easy as cranking up the boost and putting on some bigger intake/exhaust pipes.

But now that I'm in the land of naturally aspirated operation and stoichiometric air fuel ratios... there's not as much easy modding to do.

An air intake upgrade is one legitimate option though. I know this flies in the face of a lot of readers here who would rather sacrifice some power with a warm air intake to help reducing throttling/pumping losses, but, I would like to be able to tow 10,000 lbs with confidence. So a less restrictive intake path can still help reduce pumping losses a bit.

Based upon some independent dyno-testing results on a GM 5.3L, I opted to go the cheaper route and replace only the filter and intake pipe. The factory airbox can already flow plenty of air.

BBP Independent Intake Test Results | Chevy Truck Forum | GMC Truck Forum - GmFullsize.com
https://dl.dropboxusercontent.com/u/...%20Results.pdf

I went with an AEM dryflow filter for it's high flow and washable characteristics.



The stock intake pipe has a funky "sound tube" appendage that surely doesn't help the airflow.



Replacement pipe still had a notch to clear the mechanical fan shroud.... GRRrrr, that fan has to go!



The next mod is not something I would ordinarily pay any extra money for, but, I got suckered in by some discounts and free shipping while buying other things. The only reason I actually bought the plug wire set was an attempt to fix an occasional P0300 "random misfire" code that I have been getting (more on that later).



Fancy red color bling, but no change in performance (duh). Was still getting the P0300 code, mainly at highway speeds. This was actually a huge problem, because any reported misfires cause the ECU to unlock the torque converter. So then you are wasting fuel into transmission heat, and eventually burning up the TC. Not cool.

Internet search to the rescue! Thankfully I have access to a professional grade GM scan-tool here at work (GM Tech II). Turns out all I had to do was a "crank position variation learn" procedure. Just select the function, rev the engine, and boom, done.



The ECU "re-learns" the relationship between the crank and cam angle sensors, and re-adjusts its criteria for determining misfires. So basically I wasn't actually having any misfires, but the ECU thought I was. No more! Hopped on the highway to verify, and had full TC lockup and ~+2 mpg.

[Deezler]

Getting much more consistent TC lockup now.

12.7 mpg for last tank though. Blarg. We can do better.

[Deezler]

Ok, getting closer to my goal of a tank-avg 15 mpg in the winter time.

Got 14.0 mpg on the entirety of my last tank. Not so awful. With a few more aero-mods, and an ECU tune, I think I can make it pretty easily. Though with a possible early spring season right around the corner, I may not truly find out until next winter as I'm not quite ready for any more mods just yet.

I can hit 15+ mpg easily on individual trips. But any short trips around town really kill the mileage. Same for days like today... 5 degrees this morning. The engine heaters can only do so much while parked out in the wind.... basically a cold start still.

[aerohead]

If you were to momentarily pull in behind a semi at close quarters and reset the Scangauge,you could tell very soon what completely streamlining the truck would do.Then decide if the numbers looked good enough to go into deep aero mods.
I added 5-mpg to the Dodge with only aero.
And 9-mpg to the Toyota.
These are HWY-only numbers.

[Deezler]

^ that's a great idea, thanks! I hardly ever drive on the highway so hadn't thought of that. Will give it a go at some point.

[slowmover]

Be sure it's a box van. Moving vans have the lowest ground clearance
If the road is clear ahead of the van, likely he'll have the cruise on.

Steering corrections per 100 miles travel is cited by big truck mfrs as FE significant. Keeping perfectly lane centered is the game. On a straight piece of Interstate I can pretty well let go of my wheel for the better part of a measured mile (my one ton Dodge or my Kenworth); really, just holding it against crown with two fingers.

If you can't, it should be top of the list to correct. Getting out of wind is a good way to isolate.