Pulling Trouble Codes

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. Andy
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Andy,
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 code reader.
Per way of your gas mileage, if the 02 sensors are original, replace both pre-cat 02 sensors.
Doc

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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.
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people see 'V-6' and think 'economy'
the 4.3 is 3/4 of a 350....................it's not 'economical'
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TranSurgeon wrote:

True, but the one in my 94 S10 Blazer purrs like a lion cub.                                     Remo
--

Drop the gun to reply


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15 on a trip.

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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
http://www.fueleconomy.gov/feg/FEG2000.htm
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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. Andy

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.

an electronic 4-speed automatic transmission:

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Andy, 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 winter
Steve

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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.

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In article

Spark knock? Poor fuel economy? On premium fuel?
No shit!
Why don't you try the correct frickin spark plugs?
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