Newf

I just bought a 1994 K1500 Sierra Z-71 X-cab 4WD. I'm getting just terrible fuel economy... over the top bad! Looking at "fueleconomy.gov" I see it's rated to get about 13 MPG (US gallons) on the hwy. Converted to "Litres per 100 kilometres" (L/100k) which is how we measure it here in Canada, that comes out to 13.8 L/100k. That's what I SHOULD be getting, but what I'm actually getting is around 30 L/100k... I'm burning more than TWICE what I should be.

The tires are properly inflated. Just put in a new air filter and a new fuel filter. Also just got 8 brand new plugs, new cap & rotor, and a new plug wire set. Had the timing checked and adjusted.

Still getting the ridiculous mileage.

The truck seems to run nice and smooth... nothing "seems" wrong but, clearly, something is off a LOT!

Just wondering if anybody has any ideas about what might be causing this. A list of "possible" culprits... that's what I'm trying to compile here.

I'd appreciate any thoughts on the matter.

Thanks...

SLJ2137694

If you are burning twice the fuel you should be I would think the oxygen sensor would read a very rich condition and turn on the check engine light. Are you sure you are not leaking the fuel? How are you calculating your fuel economy?

Newf

Thanks for the reply Steven. Impressive credentials you have there. Hopefully I'll make it to retirement myself someday. 12 - 15 years to go, if I can just make it that long!! ;-)

Easy answer 1st: Fuel Leak - I wondered the same thing myself. I haven't seen any evidence of it. The tank, itself, looks solid and fine, and no staining or anything visible to me. No puddles left under the truck when I stop. Nothing I have seen to suggest any fuel is leaking. I wonder if it's possible to be leaking ONLY while moving and somehow being concealed from view? Seems unlikely.

More lengthy answer: Oxygen Sensor - Last week, I brought the truck in and got new plugs, wire set, cap, rotor, fuel filter, timing checked. I declined to have the "EGR" valve replaced. Mechanic said he believes the diaphram has a tiny pinhole in it but couldn't say if it really would affect the valve's function. Did a bunch of research on it on the net and the EGR valve seems pretty well dedicated to emission control... nothing mentioned anywhere about fuel economy, so I doubt it's the culprit.

That said, last weekend, on a weekend camping trip, my "Service Engine Soon" (SES) light came on. I stopped, checked fluids, etc. Everything looked fine and the truck was running perfectly (not counting the lousy fuel economy, of course) so I nursed out the trip and, after stopping, the light didn't come back on until Sunday afternoon (2 days later) on the return trip.

Once home, doing some more net research, I saw a lot of references to the EGR valve and the SES light, which got me curious, so I looked under the hood, found the EGR valve and noticed a thin rubber hose coming from the EGR valve hanging loose. It looked like it was supposed to have been connected to a small plastic module nearby that had two little **** on it. The bottom tit was capped but the top tit wasn't and the little hose length fit to it perfectly, so I slipped the hose onto the tit. I expect the mechanic failed to put it on tightly and it shook/vibrated off. I suspect that little hose being off that little tit was the reason I was getting the SES light this past weekend.

I haven't gotten the SES light since re-situating the little hose, though I'll be taking the truck out for a wee bit of a drive this weekend to see if it'll come on again or not.

2 questions come to my mind....

(1) What if the oxygen sensor is malfunctioning? Could it be sending incorrect info to the computer that mixes the air/fuel, causing the problem? (I'd have thought I'd get some kind of warning code for that)

(2) Could the computer that mixes the air/fuel be screwing up? (Thought I'd get a code for that, too)

Sorry for the book, but I'm VERY interested in getting this solved and with your experience in the field, I thought I'd best take the time to explain all I can.

Anything else coming to mind at all?

Newf

Forgot to answer your last question: Calculating the fuel consumption....

I take the litres of fuel required to re-FILL the tank, divide that by the kilometres driven, then multiply the result by 100, to give me the # of litres used per 100 kilometres. I believe that is the correct way to calculate.

Besides, after about 150 kilometres, my previously FULL tank reads about half a tank left or worse. (Awful, eh?)

SLJ2137694

Take the kilometers driven and divide by the fuel used on the re-fill for the kilometers per litre, then times 100. I think your new figures may be more in the ball park. Please get back with your results!

Newf

Nope.. that doesn't look right. Here's a recent fill-up. 123 kms 44.342 Litres

Your calc: 123/44.342*100= 277.389 L / 100 k.

My calc: 44.342/123*100= 36.050 L / 100 k

Newf

Well... I figured it out, finally!

I was out this weekend and just because it was there, I checked my odometer against a roadside Odometer Check section.

Turns out my fuel economy isn't that bad at all. A little, but far from what I thought it was.

My odometer is off! For each ACTUAL kilometre I drive, the odometer only racks up .65 of a kilometre on the dial!!

Gonna have to get that fixed!!!!!

drblackmon

My 2005 Silverado just passed 80,000 miles and the warning light for emission control just came on. I had just filled the tank, so I checked the gas cap....it was fine. What could be the problem?