1994 Diesel Suburban Build

[aardvarcus]

I did a short fill this morning to get a reading, MPG basically stayed the same at 24 MPG. That is actually good though, considering my last tank was in September when it was much warmer. Also it was raining for this trip, the new transmission isn’t past its break in period, and the alignment seems off. Honestly I thought the MPG might go down.

I need to do some maintenance to the front end (ball joints and bushings) knock out the frame adjustment slots (thanks GM) and take it in for a proper alignment. I don’t want to pay full alignment price to just have the toe set again.

[slowmover]

Forgotten if I’ve asked: Have you scaled this? CAT Scale, top off to max fuel with only driver and gear kept permanently aboard?

It’s well worth knowing the point where additional weight starts to make a difference in mild terrain.

Mine did 24-mpg the first day I owned it (I was thrilled). I’d also scaled it (first chore after purchase).

It takes roughly 1,000-lbs in truck bed before MPG is affected (I’ve since learned how to compensate).

The 6,860-lb published ship weight is these days 7,940-lbs before I add 500-lbs work gear or hitch trailer.

I had to re-work the placement of gear & tools to keep the weight on or ahead of the rear axle. And it’s now within 40-lbs all four corners.

Scale weights are the ne plus ultra in determining tire pressure values.

Upsizing the front anti-roll bar to match the change made by adding a rear one gave me much flatter cornering response. Means less brake/less throttle for curves. Less time “into” steering degree and duration. No strange oversteer.

And any claims I’ve made about mpg are ALWAYS at same travel speed/engine rpm. Constant use of cruise control. Other approaches are flawed (using one’s foot to eak out MPG fails past hour three).

It’s not the highest number, it’s the average. The planning number where additional weight up to X, and neither darkness, rain, or traffic changes it.

$3/gal diesel at 300-miles WILL NOT exceed a cost of . . . .

That’s the number to find. Fuel cost per mile. CPM. (See sig).


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[aardvarcus]

Slowmover,

Scaling it is on my list of things to do, there is a CAT scale not too far from where I work. It is just a time thing, but I will try to make it a point to do that soon. I have my tire pressures at 65PSI right now.

I do try to weigh everything I put on and take off and try to keep the vehicle lighter than it was when I got it. I have and will add weight though for certain things but I try to keep it below the published COG of the vehicle. I have moved a few heavy items lower to help with this.

I have upsized the front sway bar and I would like to add a rear one, but right now until I get a proper alignment it is just handling wonky. I am certain the toe is out from changing the steering gear, it feels twitchy so I am bleeding off extra speed in corners to compensate. Fixing that is my top priority for the vehicle right now.

10-4 on the average fuel economy, I am trying to reduce the total cost of ownership not set some faux number. I could P&G for one tank and get 30+ but that isn’t realistic for my daily commute. I don’t have time nor energy to drive extra just to a-b test fuel economy so my daily commute is my only feedback mechanism for if my changes are helping or hurting which is why I post my single tank numbers, which as you know are easily skewed by just about anything. I always use cruise control, I just haven’t had it in this vehicle until now.

[aardvarcus]

I took the Suburban to the CAT scale yesterday. As weighted with driver, tools, and junk it was 3260 front, 3300 rear, 6560 total. Since it wasn't empty, I went home and subtracted the weights of all the items inside and subtracted them from the appropriate axles. Completely empty (no driver no tools) but with a full diesel tank the net weight is 3030 front and 3210 rear for 6240lbs. Ratings for my specific model from the spec sheet are 3750 FAWR (spring limited from 4250), 6000 RAWR, 8600 GVWR, 14500 GCVWR. The full tank of diesel represents 292lbs hanging out a few feet behind the rear axle.

[slowmover]

Wow, great answer. Thanks. Even around here these things can’t be taken for granted.

Clarification: TARE weight is, again, driver plus max fuel PLUS gear kept permanently aboard (clarification from my end). While it’s interesting to know the dead minimum, it isn’t useful.

It’s the weight ABOVE the TARE to see where steady-state is affected that matters. And only steady-state.

I don’t know what feedback gauge would work for you, but nearly anything that will give an instant or average reading and that is accurate against itself shows me in 18-wheeler or personal vehicle where “the weight problem” fits in. As adverse winds exact a higher penalty directly after travel speed, being able to understand the loaded weight against the conditions at hand make it a problem in deduction.

Thus my emphasis on dead-nuts steering. That otherwise skews all other measurements.

One doesn’t automatically get worse MPG being heavier.

There is a sweet spot (with high cylinder pressure) of, “up to XXX pound Payload is free”.

With 1,200lbs extra against ship weight, I’m penalized with current TARE. (Ha! Penalized for an EcoModder contributor, that is).

To offset that was to clean up steering/handling.

I haven’t tried to correlate 15% heavier against what percent fuel burn increase.

The improvements make for easier transitions from one stage to another. As we both have high center of gravity vehicles (relatively crude suspension) the attendant decrease in ride comfort is about getting tires EXACTLY to load, and slowing even earlier (as one can now accelerate with less penalty).

The very best shock absorbers should be on your list. Better than entry-level KONI or BILSTEIN. FOX and KING worth a call once up on applicable tech terms.
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[aardvarcus]

Slowmover,

Thanks, I really appreciate all your posts, in this thread and others. I always make it a point to read them thoroughly. I won’t ever claim to be nearly as meticulous as you, but I try to be better than the average bear.

I intended to get a Tare number, but I wasn’t in the vehicle when they weighed it. I had gotten out to stand on my tippy toes to hit the button (placed at semi-truck height) to talk to an attendant and he pulled the weight with me standing on the platform. I will bring a stick with me next time. After leaving I started to realize many of the “extra” things I had forgotten to take out of the back seat and rear cargo area. Also my permanent onboard tool kit isn’t well thought out at this point, just a bunch of stuff I “might need” if something happens. I would prefer to whittle that down to mainly what I actually need with minimum duplication. I am sure I will re-weigh at some point in the future and will try to do a meaningful tare then.

I show the bare minimum weight more as a personal gauge on how I am doing on vehicle weight reduction efforts, I agree it isn’t helpful from a economy/loaded/towing perspective like a tare is. I agree on weight not being necessarily a direct MPG hit, but from a reliability, power, and hauling/towing perspective I would rather remove superfluous weight (e.g. fancy upholstered door trim) and have a lighter vehicle or reinvest it other places (e.g. heavier sway bar). Sometimes I think Chevy took “like a rock” a bit too seriously.

The feedback gauge is complicated by the fact that I don’t have a computer anymore in the vehicle. I removed it and rewired the vehicle to work without it. So there isn’t anything I can just plug in, as there is no plug. Once the new wears off of a modification I go back to weekly tanks and plot/trend over a long time period to see the changes evolve over time.

I would really like to do coil-overs in the front, eliminating torsion bars. I would definitely spring for legitimate shocks at that point. But since there isn’t a direct GMT400 kit for that that I am aware of that is a big custom project for much later in the future.

[slowmover]

Thanks. In return I’m well past being able to do what you’re doing. It’s now in my past.

I’d stick with the torsion bar. If a later version has rack & pinion steering that could be swapped, that’d be great (My one ton CTD is coil IFS w/ rack & pinion). Makes a pickup into a sports car.

A few hundred pounds of interior items removed for MPG won’t justify removal. Sound & vibration is very wearing. A gasser would be different.

CAT Scale has a phone app. Do it all with that. Each location has ID number.

You want to get old school on feedback, here’s how it was done on a big block gasser tow vehicle:

In a fabricated sheet metal gauge cluster housing:

0-5000 rpm tachometer
Vacuum gauge
Marine fuel flow meter
Airspeed Indicator

(Also present were a marine-quality compass, an altimeter/barometer and dial-face outside thermometer).

One mounted this on the dash ahead of the driver. Canted gauges so that “up” reading was the tested ideal at a given road speed (the serious guys used a calibrated MOTOROLA “Lodax” speedometer). The discussions were around figuring “Percent Engine Load”. One could modify travel speed upwards based on real-time data and retain same MPG. Or, cut road speed to heighten re-fuel travel distance (there weren’t filling stations every five miles back then).

Expensive fun for retired guys (WWI generation; started at Model T and ended at 7-liter V8s to tow the Airstream. On brand-new Interstates, no less).

Re-engineering the carbureted fuel system for reliability (HIGHLY consistent performance) was even more interesting.


The man’s way to get cross-country circa 1969. Unit-body, torsion-bar suspension, and far ahead of the competition:

L

[aardvarcus]

Got a bunch of work done on the front end of the suburban. Punched the adjuster slots out of the frame for the upper control arm. Ended up replacing bearings, rotors, lugs, CV axles, ball joints, control arm bushings. When I put it all back I raised the front end up about an inch higher than I had it for some extra ground clearance. Took it in for an actual alignment, it is handling much better now, just need to tighten the steering box up a touch and it will be perfect.

Sorry, no pictures it was a whirlwind of activity for a weekend.

[aardvarcus]

Once I got all the front end work done, it was pretty obvious my front brakes were dragging. I replaced calipers, pads, hoses, and some hard lines. Bled the system. Then I turned my attention to some fuel lines that had previously been replaced but didn't turn out as nice as I expect. I haven't been able to reinstall the front driveshaft out of worry about the proximity of some of those lines. I was able to build a new bracket and replace the other things I was worried about. I have 150 miles on all that work and it seem to be doing fine.

In other news, I was able to find a deal on some legitimate DOT approved LED headlights with proper optics. They are the redesigned JW Speaker 8900 Evolution 2 5x7 headlights. So I have those in boxes waiting for an opportunity to install.

I am looking at getting big-rig style commercial truck reflectors, led marker lights, and led tail/turn lights to integrate into a custom rear bumper. I am having a hard time finding good information to discern quality and brightness. I am currently considering the ones on superbrightleds, grote supernova, and JW speaker, leaning towards the 4" round ones.

[grabowski]

Originally Posted by aardvarcus

I would like to add a rear one, but right now until I get a proper alignment it is just handling wonky.

I Put a Helwig on my '94 K2500 and it was a very nice addition for highway speed driving and no loss of offroad driving.

Congrats on the MPGS!