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Posted: 1/5/2012 3:32:44 AM EST
I've got a 91 Chevy Suburban and it gets terrible fuel mileage at around 10 mpg no matter what I'm using it for.
I talked to my uncle yesterday who has quite a bit of experience with cars and he had a theory that it has something to do with the fuel system.
He used to have an old Suburban as well that got great fuel mileage until it got a little older and then tanked quickly.
His theory, more specifically, is that the throttle body fuel injection wears out and starts pumping too much fuel thus decreasing the engines efficiency and fuel economy.
Does anyone have some knowledge or experience to back this up?
Link Posted: 1/5/2012 3:35:07 AM EST
[Last Edit: 1/5/2012 3:36:08 AM EST by DriftPunch]
Engine? The 454s were notorious and consistent fuel guzzlers.

My '94 TBI 350 is much better, but still has 17 as an absolute max. Traffic probably puts in below 10.

I don't believe the TBI wearing thing...
Link Posted: 1/5/2012 3:36:00 AM EST
When was the last time you did a tune up on it?
Spark plugs and wires
Cap and rotor
Fuel filter
Air filter
Clean mass air flow filter
clean throttle body
pcv valve
Link Posted: 1/5/2012 3:36:52 AM EST

Originally Posted By tothemax:
When was the last time you did a tune up on it?
Spark plugs and wires
Cap and rotor
Fuel filter
Air filter
Clean mass air flow filter
clean throttle body
pcv valve

No MASS on a TBI.
Link Posted: 1/5/2012 3:51:45 AM EST
You didn't say what engine you have but I had a 95 Z71 TBI engine that got 12mpg. Complete tune up got me another 1mpg. On a whim I ordered a throttle body spacer from Jegs. It was their house brand, no fancy cuts or anything just a basic spacer. Also ordered a fuel line extension kit that was Jegs brand also.

It got me 3mpg increase. It really did. Catback flowmaster system got another 1mpg. That's 17mpg after all the bolt on stuff.

Posted Via AR15.Com Mobile
Link Posted: 1/5/2012 3:58:11 AM EST
I had a 96 3/4 ton suburban, tops was 16.9 mpg on the highway, 8 to 10 in town. There's a few things that affect MPG, including gear ratio, tranny (like a 350 turbo vs. a 700R4 with overdrive) etc. Tire size will affect gear ratio and fuel mileage too. The TBI? Probably not other than being filthy. Change out air filter, fuel filter, and run some cleaner through the tank (try that BG fuel cleaner-good stuff!) Also, if you're one of the people that has to haul around a bunch of shit all the time, well that does it too. A Suburban is one heavy assed vehicle to begin with. Good luck.
Link Posted: 1/5/2012 3:59:52 AM EST

Originally Posted By jeep450:
You didn't say what engine you have but I had a 95 Z71 TBI engine that got 12mpg. Complete tune up got me another 1mpg. On a whim I ordered a throttle body spacer from Jegs. It was their house brand, no fancy cuts or anything just a basic spacer. Also ordered a fuel line extension kit that was Jegs brand also.

It got me 3mpg increase. It really did. Catback flowmaster system got another 1mpg. That's 17mpg after all the bolt on stuff.

Posted Via AR15.Com Mobile

No offense to jeep450, but I don't believe the data in posts like this one. Manufacturers spend millions on squeezing maximum miles out of every drop of fuel. CAFE standards are a bitch, and if a simple spacer gave such huge increases, it would have been factory. There are no silver bullets.

Perhaps jeep450 corrected a long standing problem in the process of adding the spacer, as 12 on a 350 is low.

TBI V8s are simply not efficient engines, and as they grow, their thirst does too.


Link Posted: 1/5/2012 4:24:34 AM EST
[Last Edit: 1/5/2012 4:27:17 AM EST by -Apocalypto-]

It's a suburban....10-11 city is about right...Highway 15-17....I had a Avalanche and it did about the same.



Fuel Economy of 1991 GMC Suburban EPA MPG
MODEL City Comb Hwy Fuel Cost
1991 GMC R1500 Suburban 2WD 8 cyl, 5.7 L, Automatic 4-spd, Regular Gasoline
11 City 16 Highway


1991 GMC R1500 Suburban 2WD 8 cyl, 6.2 L, Automatic 4-spd, Diesel
15 City 20 Highway

1991 GMC Suburban V1500 4WD 8 cyl, 5.7 L, Automatic 4-spd, Regular Gasoline
11 City 15 Highway

http://www.fueleconomy.gov/feg/bymodel/1991_GMC_Suburban.shtml

Link Posted: 1/5/2012 4:27:53 AM EST
My '99 gets around 16 average.

165,000 miles.
Link Posted: 1/5/2012 4:57:32 AM EST
Originally Posted By dex357:
My '99 gets around 16 average.

165,000 miles.


Different fuel system.


Posted Via AR15.Com Mobile
Link Posted: 1/5/2012 7:56:02 AM EST
My Suburban has a Goodwrench Crate 350 in it with only approx 20,000 miles on it.
I get 10 mpg when driving to and from work which is 15 miles of highway.
Link Posted: 1/5/2012 8:00:01 AM EST
Originally Posted By -Apocalypto-:

It's a suburban....10-11 city is about right...Highway 15-17....I had a Avalanche and it did about the same.



Fuel Economy of 1991 GMC Suburban EPA MPG
MODEL City Comb Hwy Fuel Cost
1991 GMC R1500 Suburban 2WD 8 cyl, 5.7 L, Automatic 4-spd, Regular Gasoline
11 City 16 Highway


1991 GMC R1500 Suburban 2WD 8 cyl, 6.2 L, Automatic 4-spd, Diesel
15 City 20 Highway

1991 GMC Suburban V1500 4WD 8 cyl, 5.7 L, Automatic 4-spd, Regular Gasoline
11 City 15 Highway

http://www.fueleconomy.gov/feg/bymodel/1991_GMC_Suburban.shtml



And that was before they added ethanol to crappify our gas


Link Posted: 1/5/2012 8:10:56 AM EST
It is a 'burban, this is what they do (haul people/stuff and suck down gas).

Only thing worse is a similar vintage Land Cruiser.
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