How can you get a 1st gen to squeek into the low 20mpg?

[nooblet]

One thing you need to think about also... Unless you have a GPS in your truck don't trust your fuel mileage too much. When I got my truck, bone stock 1990 3.55:1 5-speed getrag the speedometer was off 10-15 mph at 70 with stock size tires on stock rims. I've driven many 1st gens and I have yet to see one that reads within 5 mph of the actual speed at 70.

Food for thought.

Chris

[mhuppertz]

One thing you need to think about also... Unless you have a GPS in your truck don't trust your fuel mileage too much.
Chris

I checked mine on the highway mile markers, and when my tired are worn half way my speedo is dead on. When my tires are new I multiply my odo miles x .6 to get actual.

Some GPS units don't take in consideration altitude changes in calculating distance. We found this out on mountain bike trips comparing GPS to actual distance recorded by tire rotation distance, and that was with a Garmin.

just additional food for thought

[PToombs]

One thing you need to think about also... Unless you have a GPS in your truck don't trust your fuel mileage too much. When I got my truck, bone stock 1990 3.55:1 5-speed getrag the speedometer was off 10-15 mph at 70 with stock size tires on stock rims. I've driven many 1st gens and I have yet to see one that reads within 5 mph of the actual speed at 70.

Food for thought.

Chris

This makes sense. I know my '92 is off 2 or 3 at about 30. But, when 2 people drive the same vehicle for a few tanks of fuel and get different mileage......... This is what Meby was asking.

[dpuckett]

My odometer is about 2-3% slower than the truck, so I am actually getting about 1/2mg better than shown. I've never had one more than 3mph off at 70mph. If it is, I change speedo gears or adaptors.

DP

[gomerpile]

One thing you need to think about also... Unless you have a GPS in your truck don't trust your fuel mileage too much.
Chris

I checked mine on the highway mile markers, and when my tired are worn half way my speedo is dead on. When my tires are new I multiply my odo miles x .6 to get actual.

Some GPS units don't take in consideration altitude changes in calculating distance. We found this out on mountain bike trips comparing GPS to actual distance recorded by tire rotation distance, and that was with a Garmin.

just additional food for thought

and i just put a garmin handheld in my truck and looked at the trail i left across the map and it was as if i was running zigzags across the road. also mine going down the road is about 15-130" within my actual location

[mhuppertz]

I am averaging 19.675 over the last three tanks. Freeway actually hurts my mileage slightly, most of this is city.

[dpuckett]

mhuppertz- How fast do you go on the freeway, and what gears do you have? I had a 91 nonIC (4.10/ 5spd) that got ~23mpg at 60; 21mpg at 68mph; 19 at 72mph. Guess how fast I drove most of the time? yup, 70+. Until this truck, I have never had more than 2mpg difference between city and hwy driving. Guess it's my Mr Magoo acceleration. I get passed by Escorts from stop light to stop light.

DP

[mhuppertz]

I have 3.56 gears, and I drive the speed limit (75 MPH) on the freeway, unloaded.
For the most part I am doing the "egg between your foot and the pedal" thing to get high 19's. I hate it, but the fuel is killing me.

[dpuckett]

Huh. I had a truck mechanically the same as yours, and I got 22-23 all the time, w/o GV, and going 70-75. have you tried it without the GV? (or putting it in direct) There is a point of diminishing return when lowering RPM, esp at that high of an engine load. Once you get below the optimal (lowest) point of the BSFC curve, you actually use MORE fuel to make the same power, even though your RPM is slower. On a stock engine, that point is 17-1800RPM, which should be about where your GV puts you. I have achieved better MPG by going 60 in 4th (2000-2100) through the hills as opposed to 5th (1750-1800); about 1-1.5mpg better.

DP

[mhuppertz]

The GV is sitting on the shop floor. I haven't been able to use it because of a burnt O/D clutch. I need to remove it from the sig for now.
Did you have POD's?

[dpuckett]

No, I had stock injectors. That could be where a lot of your MPGs are going, especially at that speed. Bigger load makes a dirty stick even dirtier.

What are you timed at? Valve lash? Cold or hot adjustment? Fuel pressure from lift pump? Your injector pump may need a refresh. I gained 4mpg one time by doing that alone. Other time, didnt get me squat, though.

DP

[mhuppertz]

I timed it until it poped when warm, then backed it off until it was perfect. I set the lash per factory spec, but I am overdue running them. I think I will go 18 and 8 this time. I haven't checked my fuel pressure from the list pump, but it's a new piston pump, and the IP is about three years old. The truck is very strong, and it's still making 35PSI at 100 MPH.
The window sticker says I have 3.56, but the original owner might have changed them to 4.10. I need to mark the wheel and driveshaft and measure it out.
Before I bombed the truck (the original owner had a set of BD sticks and a timing bump) the truck would top out at 89 MPH, and it was totally defueled at that point. So maybe I do have 4.10's!

[6LCummins]

this thread is kinda amusing for me to read to be honest. when i first bought my truck: 1988 Crew Cab 1 ton Dually long box. i put a TH400 behind the motor and with 3.54s i was gettin 15-16 MPG. now with my NV4500 i range from 18-23MPG depending on wat im driving, city or highway. and it also depends alot on how fast im goin or how i drive it. every truck is gonna be different. My pump allows for full fuel at all boost levels and RPMs so in theory i should get lower mileage than others. but my 18 gallon tank tends to go 400-450 miles depending on how low i let it get and how i drive it. typically i can make a tank of fuel last 2 weeks when i drive like i should and mainly drive to and from work.

[mhuppertz]

this thread is kinda amusing for me to read to be honest.

Why is this thread amusing?

[6LCummins]

because it seems from wat i have read that everyone is looking for constant fuel mileage. when in fact u can never get that. ive found the more i turn my engine up the better i get in mileage but then again i have a totally different monster than most of the guys here. But then yet again every truck is different. its hard to take a stereotype and fit it exactly to every truck out there. Oh and just wait, cuz winter fuel is around the corner and its time for mileage to start gettin worse again.