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Fuel mileage??

patcal

Junior Member
85
8
8
Gresham, OR.
Buick Ownership
2000 Lesabre Limited
Hey all,

I hate to post this because I know that there are a lot of variable but I need some help. My 2000 Limited with 135k is just not getting the mileage I think it should. I have had it since March. According to my calculations I am averaging 16.7mpg since I bought it. My best was 19.7 & worst was 14.9. I drive mostly rural roads. The car runs good, has all fluids up to date, new plugs & wires, thermostat. I have a OBD2 adapter & Torque pro but not really sure what to look for. Thanks.

Pat
 

squirrel

Member
39
13
8
Sierra Vista, AZ
Buick Ownership
1999 LeSabre
Interesting, I have been getting about 25 over the past 1500 miles in my newly got 99 LeSabre Limited. We live out of town a bit, but it's not a big city, and I have taken several trips to surrounding cities. So, mostly rural, but also mostly highway.

Driving technique can have something to do with it, but I think traffic has more effect on reducing mileage.

Does the car seem to be running ok? Does it coast for a long time without slowing down much, if you're cruising along at 45-55 mph and let off the gas? I've noticed mine just keeps rolling along without slowing much at all, compared to other cars we have (we have a lot of them, and some are real gas hogs, such as my street/strip Chevy II with a blown 427, my 60 year old truck with a 454, etc).

If you are using the brakes a lot, you're not getting as good of mileage as you could. Drive "ahead"....plan your slowing down early, accelerate gently but don't take forever to get up to speed, etc.
 

patcal

Junior Member
85
8
8
Gresham, OR.
Buick Ownership
2000 Lesabre Limited
It seems to run fine. I really like the car. I do notice that it rolls easier then other cars I have had. It does not seem to have any rolling resistance.
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GliderRides

3.8L Member
195
19
18
Buick Ownership
2000 LeSabre
Still getting close to 19 city/30 hwy. Better than 4cyl Accord!

Some ideas:

Dragging brakes, won't know until they are checked, internally collapsing hoses can hold pressure after the pedal is applied then released. Finding one wheel hotter than the other after a drive through town can be a hint, but checking each wheel off the ground is the only way to know for sure. Spin wheel, pump brake, release, immediately spin wheel. You can't tell by looking at the hoses, caliper pistons can also stick. You may not notice the extra rolling resistance until the problem is fixed. I find this most often with poor MPG and a good running engine.

Clogged cat, doesn't always trip a code, easily checked with vacuum gauge.

Fuel trims, running rich, or too rich during warmup.

Wheel alignment.

Engine not making full power. Dead or weak cylinder doesn't always cause rough running. I would do a cylinder short test and read vacuum. Stealthy culprit: valve timing/sloppy timing chain.

Scan for codes just in case. MAF, CTS, CAT, TPS, etc can affect MPG.

Engine temperature, running too cool affects MPG.

Doesn't have 40-50w oil in it?
 

patcal

Junior Member
85
8
8
Gresham, OR.
Buick Ownership
2000 Lesabre Limited
GliderRides: brakes were checked out. They are fine. Coolant temp is 198-220 per OBD2 port. The cat is brand new, old one was breaking up. Oil is 10w-40 Maxlife. No codes as of a week ago. I am not sure the correct procedure for checking fuel trims. I know Torque Pro will show them just not sure proper way to check them.
 

patcal

Junior Member
85
8
8
Gresham, OR.
Buick Ownership
2000 Lesabre Limited
So I took a ride & got some fuel trim measurements. Hope I did this right. First one is at idle after a 12 mile ride at 60mph. The second is at cruising speed.

screenshot2.jpgscreenshot.jpg
 

carlos&carlos

Member
37
3
8
Buick Ownership
1999 Buick LeSabre Custom
Interesting, I have been getting about 25 over the past 1500 miles in my newly got 99 LeSabre Limited. We live out of town a bit, but it's not a big city, and I have taken several trips to surrounding cities. So, mostly rural, but also mostly highway.

Driving technique can have something to do with it, but I think traffic has more effect on reducing mileage.

Does the car seem to be running ok? Does it coast for a long time without slowing down much, if you're cruising along at 45-55 mph and let off the gas? I've noticed mine just keeps rolling along without slowing much at all, compared to other cars we have (we have a lot of them, and some are real gas hogs, such as my street/strip Chevy II with a blown 427, my 60 year old truck with a 454, etc).

If you are using the brakes a lot, you're not getting as good of mileage as you could. Drive "ahead"....plan your slowing down early, accelerate gently but don't take forever to get up to speed, etc.
Interesting.

A similar mileage gives me the 99 LeSabre as well. But only in Highways at 65 plus miles per hour. In the city, oh heavens, at the beginning this car was like a 2008 8 cylinder 6.4L 4x4 Ford f250... barely reaching 12 miles per gallon.

I also use the same trick, to stop using the pedal periodically because the car runs fine by itself after 55 miles per hour, and the RPM goes well under 1,500 RPM and I know it saves me lots of gasoline.

There is a sensor located on the corrugated pipe going to the throttle body. It cost me about 10 bucks. I bought it because the mileage per gallon was very low, and I guess changing it did work as expected.

When I bought this car, in the city as daily driving, the full tank lowered a 1/4 of it at 50 plus running miles. After replacing that sensor, I do the same driving routine and now reaches 90 running miles. I am filling up the tank at the same gas station. I opted to replace that sensor after checking all other options, and after the live scanner showed me spark plugs doing OK and etc. Actually a neighbor who understands those waving lines on the screen told me the spark plus, fuel injectors and others were apparently in good shape. He told me that sometimes sensors will fail a little but not enough to call for engine light, that the car will run fine but not as it should be.

Then, I did check several webpages looking for a possible cause, and that sensor is mentioned as a "remote" possibility for low mileage. I check the price and was the cheaper sensor for my car. I replaced it and I was lucky it did help me doing so. The running mileage per gallon is way better.
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squirrel

Member
39
13
8
Sierra Vista, AZ
Buick Ownership
1999 LeSabre
which sensor was it? Sounds like it might be the IAT (intake air temperature) sensor? That is located in the air duct that connects the air cleaner assembly, to the throttle body. And it is rather inexpensive (probably $10 online, but more like $20 at a parts store)

 

Frisbee

New member
20
9
3
What I'm about to mention may or may not be related to your fuel efficiency problem, but it caught my eye.

In your Torque Pro screenshots, I don't know what the "H2OS" graph is actually reporting. If that's supposed to be the voltage on the "upstream" (Bank 1, Sensor 1 -- aka B1S1) O2 sensor, then, for the "engine idling" case at least, that looks completely wrong to my eye. On an idling but warmed-up engine like yours (where it's gone into "closed-loop" operation), B1S1 voltage should be changing very frequently as the PCM alters the fuel mixture. The upstream O2 sensor should be detecting that.

Furthermore, I'm pretty sure that "O2 1x2" graph is showing the "downstream" (Bank 1, Sensor 2 -- aka B1S2) O2 sensor voltage. On an idling, warmed-up engine, I'd expect it to be hovering steadily near the lower end of the voltage range, not showing that odd behavior (ramping up to 0.6 volts and then partly falling off again) near the end of that graph in your screenshot.

For comparison, here's a plot of a 40-second oxygen sensor test performed on a 2005 Buick LeSabre with about 70K miles and with original O2 sensors:
O2-plot.png
The blue line near the bottom is showing the voltage of the downstream O2 sensor and it hovers just below 0.1 volts. That's on an engine which was well warmed up (coolant at 214 degF) at the start of the test, running at idle (about 750 rpm) throughout the test.

That vehicle, run mostly under "highway" conditions, got 27.3 and 24.4 MPG on two recent fillups, so I agree that your fuel efficiency is suspect.

So, if I were you, in addition to any other suggestions you get, I'd do some more monitoring of B1S1 and B1S2 O2 sensors and make sure they're reporting as expected, especially if you just had a catalytic converter replacement. If things are really bad, you might eventually see a DTC (Diagnostic Trouble Code) like this common one:

P0420 -- Catalyst System Efficiency Below Threshold (Bank 1)

BTW, how long ago was your catalytic converter replaced?

So I'd also use your OBD scantool and Torque on a regular basis to keep an eye on any "stored" ("Show logged faults" in Torque Lite) or "pending" ("Show pending faults" in Torque Lite) DTCs. Note that your vehicle is too old to report "permanent" ("Show historic faults" in Torque Lite) DTCs.

Please keep us posted. Good luck!
 

Frisbee

New member
20
9
3
What sensors specifically do I need?
I only have Torque Lite, not Torque Pro, and I don't know how well they correlate, so my advice might not be 100% accurate or current in this regard, but I'll give it a try....

In Torque Lite, you'd add these 2 "displays":
  1. "O2 Volts Bank 1 sensor 1"
  2. "O2 Volts Bank 1 sensor 2"
Hopefully that translates to Torque Pro.

That first one should be the "upstream" (pre-cat) O2 sensor and the other should be the "downstream" (post-cat) sensor.
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Frisbee

New member
20
9
3
Is this the same?
It's hard to say for sure. I don't know what "O2S1LV" refers to. "O2", "S1", and "V" make sense, but what's the "L"? And what units are those 2 displays using? I guess you could just try graphing those 2 parameters and see if they react like O2 sensors, reporting voltage between 0 and 1, with the former changing values rapidly like my graph showed (purple line), all after you've warmed up and are running the engine, of course.

On your original screenshots, you had a graph showing "O2 1x2 V". That looks like what I see for B1S2 on Torque Lite, which shows on the graph with the same header, but without the "V". So if you can somehow get that display back up and add the "O2 1x1 V" (B1S1) version alongside, you should be OK.
 

patcal

Junior Member
85
8
8
Gresham, OR.
Buick Ownership
2000 Lesabre Limited
Well, I am going to take a drive tomorrow. I think I have the sensors I need. I will also try logging my trip. I really appreciate your help.

Pat
 

Merkava_4

5.7L LS1 Member
686
58
28
Clovis, CA
Buick Ownership
2000 Buick LeSabre
I get a constant 28.3 miles per gallon, but I live 32 miles from work and that's mostly all freeway driving.
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Frisbee

New member
20
9
3
Well, I am going to take a drive tomorrow. I think I have the sensors I need. I will also try logging my trip.
Sounds great!

I want to emphasize that this effort might not help with your low fuel efficiency, but I still think it's worth checking, especially since you already have the right tools (OBD2 scantool and software).

I hope others will continue to offer suggestions about the low MPG.

Looking forward to hearing your O2 sensor test results!
 

patcal

Junior Member
85
8
8
Gresham, OR.
Buick Ownership
2000 Lesabre Limited
Well, here are today's results. One was at idle & one was at 2000rpm. Unfortunately, I forgot which one was which. I could not figure out the logging.

screenshot 3.jpgscreenshot 4.jpg
 

Frisbee

New member
20
9
3
Well, here are today's results.
Unfortunately, for O2 sensors, a screenshot with that "display" format (showing just a single data point) is essentially useless. That format can be useful for something like "transmission gear selected", but for O2 sensor monitoring, it's not very helpful.

Sorry for not making this clearer initially but you need to set up those 2 oxygen sensor "displays" on Torque Pro using the "Graph" format, not "Display" format:
Torque-Lite-display-type-selection.jpg
Note that Torque 'Lite' (and 'Pro'?) foolishly uses the same term ("display") for 2 different concepts/things, making things needlessly confusing! It also uses non-standard terms in some cases, like calling "Permanent" DTCs "Historic".

Basically, we need to see a running graph (i.e. over time) of the O2 sensors' voltage outputs.

In the following discussion, I'm forced to assume that Torque Pro is similar enough to Torque Lite, but if it's not, it'll be up to you to figure out where it's different and react accordingly. No pressure... ;)

First off, I'd prefer that you put nothing but the two O2 sensor graphs on a single "page" in Torque, all by themselves. Your initial screenshots in this thread show (via those horizontal dots at the bottom of the screen) that you're on page #1. Don't mess with that setup if it's still there. All of your following screenshots show that you're using page #3. For the O2 tests, whether you continue to use page #3 or a new, clean page, I'd like you to set that page up with nothing but two "graph"-format "displays" for the O2 sensors (upstream and downstream).

Remember (per the earlier screenshot) that when you go to add a "display" to whatever page you're on in Torque, it asks you to "Select type of display". For the 2 oxygen-sensor displays, select "Graph", not "Display".

Please do not add/include displays for fuel trim (STFT or LTFT) to the page with the O2 sensor graphs -- that will only slow down the speed at which the O2 sensors are queried by Torque. We want maximum query speed on the upstream O2 sensor because it should be changing values quite quickly. If you'd like to further monitor fuel trims (a worthy endeavor), please put them on a separate Torque page and do that testing separately. For now, I think you should focus on the O2 sensors.

BTW, there's really no need to drive the car at all when doing this testing. Furthermore, there's really no need to observe things at any engine RPM other than "idle" -- if your O2 sensors are working, it should be quite evident just sitting in the car running at idle, as long as the engine is adequately warmed-up. In fact, you might want to put a "display"-format display (there's that stupid Torque terminology again!) with the engine coolant temperature (ECT) on a page other than the one with your two O2 sensor displays, so that you can "flick" back to check how warm the engine is.

In short, I'm suggesting that you simply configure Torque with two O2 sensor displays (maybe with an ECT display on a different page), start the car, and just sit there watching the graphs of the O2 sensors, taking a few screenshots, especially once the ECT gets to about 195 degF or higher.

That should give you a reasonably good idea of whether your O2 sensors (etc) are working correctly.

For a crude reference, here's a (cropped) screenshot of what I envision your Torque Pro setup to look like, once the engine has warmed up:
Torque-Lite-O2-sensor-monitoring.jpg
Be aware that my screenshot was done with simulated car data. So, although the top graph (upstream O2 sensor) is reasonably realistic, the bottom one (downstream sensor) is not very realistic because (1) it's unchanging throughout -- an unrealistic flat line and (2) the value (0.4 volts) probably won't match your Buick. But it should give you a good idea of what we're looking for.

If I've left anything important out or if you have any questions, don't hesitate to ask and I'll gladly clarify.

I find use of an OBD2 scantool and various apps on a laptop PC or tablet/phone to be incredibly useful when diagnosing all sorts of automotive issues, so I think you'll find that whatever time you spend to learn the "ins and outs" of whatever software you use (e.g. Torque Pro) quite worthwhile.

BTW, don't forget to periodically use your scantool + Torque to check for DTCs (Diagnostic Trouble Codes). Don't wait until you see a "Check Engine Light" (CEL) because DTCs (especially "pending" DTCs) can be present without the CEL being lit.

Good luck and keep us posted, please!
 
Last edited:
Pedal Commander
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