Bad mileage... bad, bad mileage

[95lesabre]

I've posted a couple of times on this forum (just the other day - no heat on passenger side - haven't found the problem yet, but got advice as to where to look - thanks, HotZ28.) I appreciate all the help that's out there.

I have a 95 Lesabre that gets crummy mileage. I've had it about a year and it runs like a top. Starts fine, idles fine, runs fine, seems to have plenty of power (for a 6) and doesn't miss, hesitate or anything. But...I only get about 13-14 MPG in town, maybe 15-16 on the highway. Just replaced the air filter, but haven't had much of anything else done. Many times in the past, on different cars, I have replaced points, plugs, set timing, "tune-ups," etc. and have only gained moderate improvements by those actions. I think there's something intrinsically wrong and that doing a tune-up or replacing plugs isn't going to net me another 10 MPG. I think most people get a lot better mileage than this.

Any ideas?

Thanks!

[Salestax]

"Just replaced the air filter, but haven't had much of anything else done"
Stuff can always add up, I dont much like the 'mileage' complaints at the office. Not sure how many miles on the vehicle, most of those have the 2x platinum plugs 'good' for 100k in them. If no check engine light, no performance/driveability issues, consider changing the plugs, fuel filter, possibly the O2 sensor (contrary to popular opinion, these ARE wear items and arent good forever until it sets a code). Do your best to calculate your mileage, and not stab in the dark at what you're actually getting. Fill the tank consistantly every time, don't 'top it off' mid-week becuase gas is cheap, keep your foot a little lighter on the go-pedal, and good luck.

[wrightz28]

Oxygen and coolant temp sensor are the main players to setting fuel trim.

Have you tried running some injector cleaner through it? Waht about the fuel filter?

Also, make sure your tires pressures are correct.

My wife drove me nuts with her car once getting bad mileage, and as soon as I went to get a flashlight out of the trunk, the problem was found, too much garage sale-ing.

Btw- where did you find the ponts and how did you set the timing?

[spinne1]

Originally Posted by wrightz28

Btw- where did you find the ponts and how did you set the timing?

His post mentioned changing such items on previous cars he had owned.

[95lesabre]

Yeah, points and such were on previous cars - like the 65 El Camino I have that you can actually see all the spark plugs! And I haven't met an O2 sensor yet that didn't take three men, a boy, and a blowtorch to get loose.

But, it's a good point that all the little things add up. Probably due to change plugs, fuel filter, O2, etc. Maybe the "computer" is compensating and sacrificing mileage for running well. The car has about 150,000 miles on it.
I'm prudent about checking the mileage - full tank to full tank, not topping it off. The last check was 13.8. The best I've got was 15.9 (some highway miles). The car has close to 150,000 on it, so it may have some blow-by, although I don't notice a stench, or a lot of smoke when I start it up.

May have to wait until Spring. More important to get the dang heat thing fixed now - it's cold out!

Thanks for the replies.

[wrightz28]

Originally Posted by 95lesabre

Yeah, points and such were on previous cars - like the 65 El Camino I have that you can actually see all the spark plugs! And I haven't met an O2 sensor yet that didn't take three men, a boy, and a blowtorch to get loose.

Okay, now that makes sense, I didn't pick up on that.

Never really had that musch trouble with O2's. I use a combination wrench, and on the older style 1 wire ones, slip the wire through the closed end and break it free. The heatedsensores, I just cut the pigtail to do the same. Most sensors now come with anitsieze already on the threads, but I still put a extra dab when needed.

[LeSabre97mint]

Hello

I have a 97 and only get 23 mpg. I've changed the plugs, O2 (pre-cat). I'm thinking about checking the timing chain for slack.

Regards

Dan

[wrightz28]

Why, that about in the right area?

[LeSabre97mint]

Shouldn't a 3800 get around 25-30 on the hiway?

Dan

[Whoaru99]

I just drove about 350 miles one-way almost all interstate 60-75 mph and got ~26 MPG outa my 94 LeSabre (80K miles).

As a contrast, my 91 Camaro Z-28 (38K miles) with 5.7L TPI got ~24.5 on the same trip earlier this year - probably had the A/C running on that run though.

[Smith1000]

Does it make any difference on the brand of O2 sensor used? Will the Bosch work okay? I have read that Bosch plugs do not work well in the 3800, not sure about the O2 sensor. I believe I put a Bosch O2 sensor in last time I changed it.

[ChevyWonTon]

Have you considered other non-engine areas as the cause?

I'd suggest looking for transmission problems or dragging brakes. Either of these should be obvious, if there's any issues bad enough to hurt your gas mileage.

Also, make sure the odometer is reading correctly - that could affect your mileage calculations!