I have a 1998 GMC Jimmy 4.3L v-6 with 140,000 on it. It drives well, but
gets horrendous gas mileage. I wanted to check to see if any codes are set
to possibly point to a component that may be defective, hence affecting my
mileage. I've replaced the plugs, wires, cap, and rotor. Didn't check the
timing since I wasn't having any driveability issues. Can the data link be
"grounded" to flash codes or do I need to have a reader? My 94 GMC P/U will
allow me to ground and flash the "check engine" light if codes are set.
Do any other Jimmy owners out there have the same problem with mileage? Is
this just inherent with this vehicle?
Any info or advice would be greatly appreciated.
Thanks in advance.
You need a code reader to get the codes. Your 1994 is OBD-I which can be
checked by grounding the ALDL, 1996+ GM trucks are OBD-II which requires a
Per way of your gas mileage, if the 02 sensors are original, replace both
pre-cat 02 sensors.
You have not stated the length of time that you have been getting
"horrendous" gas mileage. Did you buy this vehicle new, or did you buy
it used? Is it 2WD or 4WD? What is the rear axle ratio? (The code number
can be found in the glove box.)
Here are the approximate mileage results that you might expect for a
4.3L V-6 with these axle ratios:
GU4 Rear axle, 3.08 ratio (15/20)
GU6 Rear axle, 3.42 ratio (13/18)
GT4 Rear axle, 3.73 ratio (11/15)
If you are still sure that the gas mileage is not right, you can always
take the vehicle in for a smog pre-test, which will tell you whether or
not the engine is running properly.
Generally, in larger vehicles, a V-6 is a false economy. Most of the
extra purchase price of a V-8 can be recovered at trade in time. In a
Silverado, the V-6 will be working harder, and downshifting more, than
the small V-8. This can be verified by looking at the EPA figures.
According to the 2004 EPA Fuel Economy Guide, the 4.8L V-8 gets better
gas mileage than the 4.3L V-6 when both Silverado trucks are equipped
with an electronic 4-speed automatic transmission:
Model Trans. Engine MPG Average
C1500 Silverado 2WD A-4 ..... 4.3/6 ..... 15/20 17.5 ***
C1500 Silverado 2WD M-5 ..... 4.3/6 ..... 15/21 18.0
C1500 Silverado 2WD A-4 ..... 4.8/8 ..... 17/20 18.5 ***
C1500 Silverado 2WD M-5 ..... 4.8/8 ..... 15/20 17.5
Interesting site. I ran my vehicle and according to my driving pattern and
annual mileage, I should be getting, on average, about 17MPG. At best right
now, I'm getting about 10MPG. Given the fact that this is a small SUV V-6,
I should be getting better mileage than this.
Seeing as how Doc is usually right, I'm going to try replacing the 02
sensors and see what happens.
Silverado, the V-6 will be working harder, and downshifting more, than the
small V-8. This can be verified by looking at the EPA figures.
Another thing you might want to watch and maybe replace is the thermostat.
If it isn't warming up because the thermostat is stuck open, the computer
will call for more gas until it gets up to temperature . It could take
15-20 miles instead of 7 to 10 to get up to operating temp.
just a thought. 1500 v-6 5 speed 22mpg hwy 65-70 mph in summer less in
How many miles are you getting on a tank? I have a 97 S-10 2WD with a 4.3
Liter with a 3.08 rear axle ratio. It gets horrible fuel milage too. I have
talked with other people on here and they have said they get terrible fuel
milage too. I replaced my oxygen sensors last year and I noticed slight fuel
economy increase. I have a 18.5 gallon tank and I get 300 miles on a tank if
I run the needle in the orage, bad part too is that I always run premimum or
midgrade in it, the spark knock is just terrible, but only when you stomp on
it or are pulling a load. Did I mention its a 5 speed? Very fun to drive.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.