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Username Post: When to stop trying to improve MPG        (Topic#358500)
thx1138v2 
Contributor
Posts: 198

Reg: 05-01-14
10-18-19 04:03 PM - Post#2778203    

Is there a rule of thumb to determine when further improving MPG will be more costly than is sensible?

I have a '94 C1500, 4.3L V6 TBI engine, 4L60E transmission, 3.42 ratio differential, 230K miles

I get about 5.5 fewer MPG in city driving than highway driving.

Does it make sense to try to improve the city driving mileage? I'm getting 18.5 highway and 13 city.



 
junkman104 
Frequent Contributor
Posts: 1424
junkman104
Age: 60
Loc: Murphy N.C.
Reg: 01-25-14
10-18-19 04:49 PM - Post#2778206    
    In response to thx1138v2

Sounds about right. A 5.7 with a 3.08 is much more efficient. I had a 90 swb 2wd that got 22 hwy and 18 in town. Never understood why someone bought a full size pickup with a 4.3 (no offense) My 04 Z71 gets better millage than the neighbors 4 cyl Toyota 4wd.



 
rockfangd 
"6th Year" Gold Supporting Member
Posts: 2765
rockfangd
Age: 33
Loc: Utica ny
Reg: 04-13-10
10-18-19 05:44 PM - Post#2778209    
    In response to junkman104

I would say that is great mileage.
Right on.
I never kept track of mine as I love my v8

Old School GM fan FOREVER


 
Mel Foye 
*VIP* Founding Member
Posts: 4905
Mel Foye
Reg: 09-29-00
10-19-19 04:40 AM - Post#2778222    
    In response to thx1138v2

For city; better route planning, no weight that is not needed, match speed to lights cycle, minimize time at idle, get into od sooner, large vacuum gauge to try to keep as high a reading as you can when moving from a stop. Tire pressure.
A good tune up and ear plugs so you can't hear the horn of the guy who wants you to take off faster.



 
thx1138v2 
Contributor
Posts: 198

Reg: 05-01-14
10-19-19 05:19 AM - Post#2778227    
    In response to junkman104

  • junkman104 Said:
Sounds about right. A 5.7 with a 3.08 is much more efficient. I had a 90 swb 2wd that got 22 hwy and 18 in town. Never understood why someone bought a full size pickup with a 4.3 (no offense) My 04 Z71 gets better millage than the neighbors 4 cyl Toyota 4wd.



I bought it new from a dealer and it was a '94 fleet truck still on the lot after the 95's came out. I got a $4000 discount on it.

I'm guessing the 4.3L and the rear end ratio are because it's a fleet truck for city driving. It's been a great truck so far.




 
1983G20Van 
Super Senior Member
Posts: 3782

Loc: Bedford, Texas, USA
Reg: 11-13-02
10-20-19 06:58 AM - Post#2778303    
    In response to thx1138v2

  • thx1138v2 Said:
Is there a rule of thumb to determine when further improving MPG will be more costly than is sensible?

I have a '94 C1500, 4.3L V6 TBI engine, 4L60E transmission, 3.42 ratio differential, 230K miles

I get about 5.5 fewer MPG in city driving than highway driving.

Does it make sense to try to improve the city driving mileage? I'm getting 18.5 highway and 13 city.



I would play with the timing advance a little. Bump the timing 2* run it for a tank. Bump it 2 more and run another tank. I have had good luck between 4-8* on most stock engines. TBI also seems to like a little more fuel pressure. 12-13 psi on a stock engine. I have done alot of datalogging and running at 13 psi the fuel trims are usually good and at about 6* of timing it would not record timing retard. Also use 1" TBI spacer and make a power bowl to eliminate the factory spacer ring under the air cleaner. None of this cost much and can give you more off-idle throttle response and more torque which keeps you out of the throttle when accelerating. You are getting about the same mileage my 5.7 G20 van used to get.

As you maintain the truck, synthetic lubricants can help mileage. Use synthetic wheel bearing grease when you repack the wheel bearings, synthetic gear oil in the rear end, use synthetic lube on the caliper slides when you do the brakes. Make sure your fan clutch is working properly. I like 180°F thermostats. A new 02 sensor would probably be of benifit at 230K as well. They get lazy over time and the air/fuel ratio drifts richer as a result.


One thing I do highly suggest for anybody with one of these trucks is to change the front/rear brake hoses. They become restricted over time as they internally collapse where they are crimped in the metal bracket that bolts to the control arm. They will cause the calipers to stick and drag. If you are trying to get the truck rolling from a stop with brake drag it eats your gas mileage up in the city. Eventually the truck will even start darting left and right as you apply and release the brakes. Braided stainless brake hoses are still about the best investment I have made on my Express van. Firmed the pedal up as well. I took the old hoses to a local place that specializes in building hoses. Got back a beautiful set of stainless lines that have worked well for 5+ years now. Don't forget the rear hose either.


1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 10-20-19 07:49 AM. Reason for edit: No reason given.

 
1983G20Van 
Super Senior Member
Posts: 3782

Loc: Bedford, Texas, USA
Reg: 11-13-02
10-20-19 08:03 AM - Post#2778311    
    In response to Mel Foye

  • Mel Foye Said:
For city; better route planning, no weight that is not needed, match speed to lights cycle, minimize time at idle, get into od sooner, large vacuum gauge to try to keep as high a reading as you can when moving from a stop. Tire pressure.
A good tune up and ear plugs so you can't hear the horn of the guy who wants you to take off faster.



I do not agree with that being the best way to accelerate. Accelerating slowly just keeps the rpm in an area that slips the converter. You want to accelerate at an RPM that is above the stall speed. Most factory TBI trucks have a 1,400-1,600 rpm converter. You want to get it up on the converter and get it rolling quickly and then once the converter locks back off the throttle.

With the 4L60E and 4L80E transmissions I change the shift tables and lockup tables to bring in the converter lockup right after the 1-2 shift during acceleration. I found these changes usually net 1-2 mpg city.

I once found in an extreme case doing this picked up 4-5 mpg. My grandmother had an 03 Alero with a 3.4. The factory converter brake stalled 2,500 rpm. GM held off lockup until 48 mph in OD. Driving around in town the converter was always slipping. Even light movement of the throttle had the engine spiking up to 2,500 rpm. Just enough throttle to maintain speed had it in the 2,000 rpm range even in OD at 40 mph. Once you got to 50 mph the converter would lock and it would drop to 1,500 rpm. The car got 17-18 mpg city. I reflashed the PCM with HP Tuners. I enabled lockup as soon as 18 mph in 2nd gear and delayed the 3-4 upshift to 42 mph. You could drive it around with the tach as low as 1,200 rpm and not touch 2,000 rpm until 70 mph. Fuel mileage increased to no less than 21 mpg city with the average tank closer to 23. Trans temps dropped 40°F as well.

Basically rather than it shifting.
1 to 2 to 3 to 4 then lockup it was
1 to 2, 2 lockup, 3, 3 lockup, 4 lockup. The PCM would unlock the converter only during the upshift amd immediately relock it after.




1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 10-20-19 08:10 AM. Reason for edit: No reason given.

 
Mel Foye 
*VIP* Founding Member
Posts: 4905
Mel Foye
Reg: 09-29-00
10-20-19 10:58 AM - Post#2778329    
    In response to 1983G20Van

Good results.



 
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