Hopefully the fine people of this forum can help me out, My mpg's have been dropping by the minute on my 2000 Blazer, I just filled up and the math came up to 7.107 mpg, I have no ses light on and no loss of performance, in other words nothing that indicates a problem while operating. A friend from work brought in his scanner and the only thing he found was a cleared code of P0147, I looked it up here and it says it that sensor does not affect the operation of the engine. Since I have owned this truck the ses light have not come on and passed emissions of the state already twice, and yeah it does light up before starting the truck so the bulb is good, I am waiting now on another of the mechanics at work to have some free time to check fuel pressure and if there are any leaks, hopefully by this weekend. Any suggestions of what else I can check will be greatly appreciated since I can't afford to just start throwing parts at it because of unexpected expenses, this is my daily driver and I put on average 6-7 miles a day (that's how close I'm from work. Thanks in advance.
Jorge

 

I feel your pain. Bravadiva's avg econ went from 13 to 11 over the last cold spell. Wife does 12 mi ea way and goes to lunch every day. does14-15 in summer

First.. does your engine get up to temp normally? Should be there about 2 miles from where oyu start.

Second - while you have scanner on it, always look at ECT and IAT sensors to see if they make sense.
Then look at O2 switching rate and fuel trims
The main thing it may be is a plenum gas leak.

While you're waiting, measure resistance of ECT and IAT:


Check this before you start engine in morning - best if you have good thermometer lying on engine overnight to compare with
Also measure resistance from ECT to engine block. Should be well over a M ohm.

 

Thanks for the info, I have had this truck about 3 and a half years and was getting 13-15 depending on how much idling since I don't hit any highways on my way to work, I always known how thirsty they are since this is the the 3rd vehicle I have owned with this engine.
I have been putting off getting a multimeter (bc of lack of funds) but I'll get one tomorrow.

Yes, the temp is right, I replaced the thermostat and radiator cap about 3 months ago because when it started getting cool out I noticed it would not get up to operating temp while I got to work wich is at least 2.5 miles if I go straight.

I have read post related to fpr or spider leaking and see that most say the had rough idle or problems starting, is it possible to have a leak but do not show any change operating only on the mpg?

 

Yes, especially in the winter.
{never use a sentence when a paragraph will do}
The reason is that a small fuel leak wont affect how it runs cold. Gas will just lie around waiting to vaporize. And since it takes a while longer to get to closed loop on each startup, all that time it's running very rich.
Once it gets to closed loop the PCM will alter the injector time to compensate but if that's half or less of your trip you can see how it causes problems.
On the other hand.. in warm weather that extra gas vaporizes quickly and will be rich to start with thus hard starting and sometimes even stumbling.

 

Ok, Thanks Again.

Getting the pressure tested tomorrow, hopefully we can find the problem.

 

Everything is good with the pressure, 60 psi key on 55 psi engine running we left it almost 15 minutes and it stayed at 60 psi, no leaks. Going to do a tune up again to see if it makes a difference.

 

Okay.. I waited a while to reply so as to let it stew. After your tuneup.. AC Delco, pls!!!
.. I think you need to run a drive and scan. Look at all your sensors and especially the fuel trims.
One thing I didnt mention was IAT testing. Why is that important? Because all those 20-50 dollar 'Performance Chips' work by diddling with the IAT output. What that means is that a mis-reading IAT could affect your mpg.

If you want to ohm it out.. same chart as the ECT.
Also.. if you still have the OE type poppet spider, one or more of those lines may be cracked. Unlikely though because that should cause a misfire.

* 60 psi key on 55 psi engine running* I got to do some research on that whenever I happen to have the UM apart. Question is 'What is the pressure baseline against theoretical perfect vacuum?' For some reason I thought it was 45 lb