Gas mileage dropping...

[mike15628089]

Now I've done the searches & heard all the talk about winter gas & driving style & different tire size & I'm certain none of that is the cause. I've got a '94 k1500 with a 305 & about 65K & I went from getting between about 16.2-17.4 mpg's gradually down to 11.8-12.7 since about December, & I'm just about fed up with frustration. I even got a second vehicle because of it. The truck seems to run great, & I couldn't drive more like an old lady driving if i tried. If I really drove it, who knows how bad it could get? No check engine lights have gone off. I've done most of the easy stuff, air filter, plugs, pcv valve. wires seem ok & it's getting fuel so I haven't changed the fuel filter. I am convinced that there is absolutely some specific cause which none of the previous posts dealing with gas mileage seem to address. Winter gas doesn't account for a 25% loss of economy. I barely notice it in my other vehicles.

Now I'm not going to be satisfied with "you should be happy, I only get 10 mpgs". That seems to be the way all the other mileage posts end. I'm not happy. I went from getting great gas mileage to crap in a span of 3 months. I'm about ready to put full coverage on it & drive it over a cliff. There's got to be someone that has had a similar decline & found that replacing some item fixed it. Does the computer reset work on a '94? Should I change the cat? Oxygen sensor? EGR? Is it sabotage? PLEASE HELP!!!!

Mike

[willieboy]

Back when I had the TBI 5.0l in my old caprice (don't ask, LOL), I had an oxygen sensor going south, that caused the exact same thing; poor mileage with no other real issues. Once I changed it out, my mileage went back to normal. I also had an EGR go bad, but it threw a code from the get go. I don't remember if it affected my mileage. But the O2 sensor really did.

[MAGNUM]

Also, as strange as it sounds, for some reason on efi gm pickups, a plugged fuel filter will give a little bit worse mileage. Never had any thing like that kind of drop but a new filter every 30,000 or so for me will make a 1/2 to full mpg.

[facn8me]

My guess would be o2 sensor(s) also. Very common problem. If you have access to a scanner you can find out for sure.

[mike15628089]

O.K. Could it be a bad oxygen sensor & still not trigger a light? Can I get a code off a scanner if the check engine light hasn't triggered? I'll assume "yes" & swing it by autozone. Does anyone know if it is just a single o2 sensor that year? (I'll post back with results)

[asilverblazer]

Also, as strange as it sounds, for some reason on efi gm pickups, a plugged fuel filter will give a little bit worse mileage.  Never had any thing like that kind of drop but a new filter every 30,000 or so for me will make a 1/2 to full mpg.

 

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Mine gets thirsty with an old filter.

[Bopper]

Make sure that the gas tank does not have leak... it sounds dumb but it happened to my motorcycle.

[facn8me]

O.K.  Could it be a bad oxygen sensor & still not trigger a light?  Can I get a code off a scanner if the check engine light hasn't triggered?  I'll assume "yes" & swing it by autozone.  Does anyone know if it is just a single o2 sensor that year?  (I'll post back with results)

 

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No it may not set a code. You need live reading while it's running from a scanner of some type.

[dr9672723]

O2 sensors can get lazy without throwing a code.

[facn8me]

O2 sensors can get lazy without throwing a code.

 

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Yes

[mike15628089]

i have picked up an 02 sensor, (according to the parts dealer, only 1 for this truck) & will be changing it tomorrow. I will post the results in a few days, for anyone that might be interested.

[zr sled head]

My '98 was giving me fits about a year ago when the mileage suddenly dropped well off it's norm............check'd it for tune up / changed all the filters with no change, ran a can of Sea Foam through a vac line then dumped an second can in the gas tank just before a 750 mile trip. Within a 100 or so miles it stopped pinging and the mileage came back up to normal.

No idea what it did for sure but it worked.

[Hotwire]

I would definitely check the o2 sensor, and also check the grounds on the thermostat housing on the motor. Sometimes when people replace the thermostat they screw up the wires leading to the one stud on the housing, that's the main grounds for the pcm and your dash, if you loose the reference to the ecm, it'll burn richer than hell and never throw a code. good luck.

[d-dog]

I think this was covered a while back, but I had that problem once. It started showing up while towing a car from So. Cal to Washington State. Got real bad on hills and while at elevation. I figured out it would run better if I turned it off and let something 'reset". Took it to the dealer and as soon as he saw the K&N, he knew what it was. Apparently the oil comes off and gets on the MAS sensor wire, causing an excessively rich condition. Once that was cleaned it was good again. I now clean that MAS wire, every time I clean and re-oil the filter. (97 Z71)

Hope that helps.

[BADGERMAN]

d-dog

 

What do you use to clean the mas wire?