poor gas mileage-99 alero v6

hello- i have a 99 olds alero v6, 60k miles. when new it got 26 mpg combined suburban-highway and 32 mpg highway. however, during the last year, the fuel economy has gone down to 21 combined and 26 highway.
i have replaced the oil/air/fuel/trans filters. am using mobil 1 fluids. cleaned throttle body and egr. replaced o2 sensor. no change in mpg :(
replaced tires to pilot sport A/S. upgraded brakes to EBC green stuff and brembo discs(i dont think brakes are dragging- i suppose i would notice during coasting).
put in a can of BG 44k.
there are no driveability problems: idles smoothly (vacuum gauge reads 20 in hg when parked), accelerates well, when crusing at 65 mph (nearly 2000 rpm, flat and level, daytime, no ac) my vacuum gauge reads around 13 in hg. the vacuum gauge needle doesnt vibrate, jump around, or indicate a obstructed exhaust-so engine mechanicals appear to be fine.
i dont smell any gasoline so dont think there is a leak, and put in fuel leak dye and no external evidence of a leak.
the temperature gauge reads half way up-so i dont think there is a faulty temp sensor.
any ideas on the problem?
(there are not DTC's, if i hooked up a scanner to read engine sensors-which ones should i look at first?)
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 6 Jul 2004 06:19:09 -0700, snipped-for-privacy@yahoo.com (zark) wrote:
||hello- ||i have a 99 olds alero v6, 60k miles. when new it got 26 mpg combined ||suburban-highway and 32 mpg highway. however, during the last year, ||the fuel economy has gone down to 21 combined and 26 highway. || ||the temperature gauge reads half way up-so i dont think there is a ||faulty temp sensor.
There are more than one temp sensors. One works the gauge, another tells the ECM when it's warmed up, and there are doubtless others. If you just want to change a sensor and try it, the temp sensor for the ECM directly affects fuel mixture, so it's a prime suspect. It should cost around $20. Texas Parts Guy
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

are
On this and most other recent applications, there is only one coolant temperature sensor. The PCM sends the coolant temp over the data bus to the IPC which controls the coolant temperature gauge and/or coolant temperature warning indicator. If the temperature gauge seems to read the same as it always has, then the coolant temp sensor is most likely fine.
Roger
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
There's an urban legend storey about a guy that painstakingly tracked his mileage and it was his favourite topic of conversation with his neighbors. Having had enough of that the neighbor went out at night and first started adding fuel to the tank. Of course the guy was as pleased and proud as could be with his incredible mileage and told everyone. Then the neighbours started to siphon gas out at night. While reluctant to tell anybody about his now dismal mileage, the neighbour quized him on it repeatedly about it. Could you live in such a neighborhood? Steve g.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I would get rid of the Alero, they are junk and built like junk, their not dependable like other GM cars

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
A Frazier wrote:

Dependable like other GM cars? You're kidding, right??
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Ok Some other GM cars were actually reliable. Maybe older stuff.
+

not
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I also have a '99 Alero V6, just turned up 80,000 miles. My mileage figures were just like yours, about 27 overall, up until about 10,000 miles ago, maybe 7 or 8 months ago, when they dropped to where I am getting more like 24 overall. Still not poor, but not as good as it used to be. My part throttle acceleration doesn't seem to be quite as zippy as it was, wide open throttle feels about the same as before. I am wondering if the fuel has changed, like maybe they are diluting it with alcohol or something. I purchase from the same local stations I always have. Still starts and runs fine, good idle, no stumbling, surging or anything like that. No trouble codes or anything.
Lee Richardson

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
zark wrote:

Have the codes read. You could have a bad knock sensor which will retard the timing and not light the CEL.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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.