Causes for bad mileage

Can somebody please post a check list of possible causes for bad mileage? I'm getting about 15 mpg in my 94 LeSabre, which is terrible. I already replaced O2 sensor, ECM, fuel filter and spark plugs. What else could be wrong?

Thanks

Ill take a shot. 17MPG city is good. 27 highway is good 30 is great.

:banghead: *Driving conditions
:sorry: *Driving style
:2cents: *Gas leak
:lol2: *Air filter, air flow
:naughty: *Fuel Quality
:1: *Vehicle loading:dogpile:
:licka: *Tire pressures, unequal pressure loads transmission differential
:smokin: *Fuel injectors, piss instead of spray
:eek: *O2 sensor, sends wrong mix adjustment info
:gives: *Air conditioning
:icon16: *Transmission
:disappoin *MAF sensor, misreading intake airflow
:confused: *ECT sensor, says the engine temp is cold ECM adjusts pulse width of injector
:p *Battery condition, :screwy:
:crying: *ECM prom program, performance settings
:chair: *Camshsft sensor, sends pulse info for fuel injectors
:bananadie *TPS sensor
:twak: *EGR valve
*

Ok I slowed down....:dunno:

Good Luck
Bass
94' Lesabre, 94' Park

17MPG city is good. 27 highway is good 30 is great.

17 mpg city is good?

:banghead: *Driving conditions
:sorry: *Driving style

Normal. Actually even better when it comes to gas efficiency, because knowing this car has such poor mileage I try to accelerate much slower than when I drive other vehicles.

:2cents: *Gas leak

If it's leaking to the ground, then I don't think there is any.

:lol2: *Air filter, air flow

Air filter is pretty new, how do I check for air flow?

:naughty: *Fuel Quality

Always BP 87 octanes (which is recommended in the manual.

:1: *Vehicle loading:dogpile:

Just me, nothing heavy.

:licka: *Tire pressures, unequal pressure loads transmission differential

Tire pressure is about 33, I'm not sure what the other thing means.

:smokin: *Fuel injectors, piss instead of spray

:eek: *O2 sensor, sends wrong mix adjustment info

Replaced a few months ago with a brand new AC Delco.

:gives: *Air conditioning

Doesn't work, has a huge leak somewhere, when I put freon it doesn't last for two days.

:icon16: *Transmission

I did a complete transmission fluid flush one month ago.

:disappoin *MAF sensor, misreading intake airflow

:confused: *ECT sensor, says the engine temp is cold ECM adjusts pulse width of injector

:p *Battery condition, :screwy:

New battery, although it's one of those Walmart sells, the mid-grade one.

:crying: *ECM prom program, performance settings

I replaced the ECM yesterday, however as for the PROM itself I just took it from the old computer and put it in the new one. They told me the PROm itself rarely ever goes bad, it's usually the ECM itself that screws up.

:chair: *Camshsft sensor, sends pulse info for fuel injectors
:bananadie *TPS sensor

:twak: *EGR valve

Replaced that with a brand new ACDelco in March of 05.

Thanks for your reply. I'll check into the other things. Are all these things supposed to show codes in the scanner if they're failing or not? I checked thecodes yesterday and it says no codes present.

NOPE... Just soz you know...

CORRECTION:: Some are SUPPOSED to show codes.. yes.. sometimes dont.

Bass

You replaced the spark plugs, but how about the wires?

Just a comment on WIRES... wires is usually are noticed rythmatic missing unless at a higher speed or really load only.
If you pulled the plugs you could look at the old ones and check for the color of them.


But the basic is being clean and on the moca side of color.

Some also say you can fine tune even this moca color on the ground strap changes from lighter to darker about the first 1/8th inch part of the end of the strap.

A nice web page I found.

http://www.angelfire.com/fl4/pontiacdude428/Readplugs.html



BASS

You replaced the spark plugs, but how about the wires?

Yes, the wires too, at the same time.

some of those emission sensors would show up in the trouble codes...

another cause: worn engine/ test via compression/leakdown... but as other posters stated that V6? engine is around the ballpark for mileage...

carbon buildup in combustion chambers, causing predetonation, but knock sensor will pick this up & retard the timing a bit, producing less power...

clogged cat

ECT sensor, says the engine temp is cold ECM adjusts pulse width of injector

agree w/ the engine coolant temperature sensor: but if it's reading cold/ due to corroded or open wire, the ECM/PCM would just stay in "open loop mode" neglecting the readings of the o2 sensor & would run from the PROM readings instead-fail safe mode---> you'll be running slightly rich as well, wasting gas...

these other stuff i listed are just more of the extreme sides...

agree w/ the engine coolant temperature sensor: but if it's reading cold/ due to corroded or open wire, the ECM/PCM would just stay in "open loop mode" neglecting the readings of the o2 sensor & would run from the PROM readings instead-fail safe mode---> you'll be running slightly rich as well, wasting gas...



Is there a way to know if the car is running all the time in open loop mode, or if it's using the fail safe mode?

Sure.. Get the codes read...but you checked that and no codes.

RESPONSE TO YOUR POST:::If you have irregular tire pressue or different sizes of tires on it your transmission differential would be working too hard and proubbly heating up..

The engine runs in the closed mode when all the sensors it uses are warm(O2), and responding reaonably well. HOWEVER.. all engines are a bit different and your engine has its own best response stored which are different from another exact vehicle. It uses them as a good place to start when starting.

You might try disconnecting the battery for a period. Let the computer reset and then see if it relearns (runs a little badly for a bit) and after a few starts gets better. Its a cheap try anyway.

Good luck..
15 MPG isnt horrible.. could be stop and go traffic only I would expect almost that.

Sure.. Get the codes read...but you checked that and no codes.
15 MPG isnt horrible.. could be stop and go traffic only I would expect almost that.

Do you mean that if the scanner is not giving me any codes then in theory the car is running in close loop?

Well, according to fueleconomy.gov, this car is supposed to have 19 city, 28 hwy and 22 combined. Because of where I live my driving is more like combined. It should be like 22. But doing some simple math, when I bought this car in Feb 05 it was giving me 370 miles on a full tank and now it's giving me 270, a 100 mile difference. If I'm right, this car has an 18 gallon tank. So it went from 20.55 mpg to 15 mpg. So something is definitely wrong there.

mebbe the change of formulas of gasoline are starting early this year from summer blend to winter blend???

~~~~~~~~~~~

hmm, OP didn't state if read the codes or not...

PS: Y did you change out the car's PC/ ECM? was it faulty from the git-go?

~~~~~~~~~~~~

GM Trouble Code Info
Accessing Trouble Codes



* Turn ignition switch to OFF position
* Locate Data Link Connector (DLC), see image below.
* Jumper the A&B terminals(a paper clip or a jumper wire work ok)
* Turn Ignition switch to ON position.
* Count the flashes on the "CHECK ENGINE" or "SERVICE ENGINE" light.
* FLASH, pause, FLASH, FLASH = code 12
* NOTE: Some 94 & 95 models do not have the B terminal. In which case a scanner is required.
* NOTE: Some 94 & 95 models that DO have the A & B terminals still require a scanner.
* All vehicles after 96 are OBDII,and require a scanner to access them.

GM Data Link Connector
12 Pin DLC
A - Ground

F - TCC
B - Test Terminal

G - Fuel Pump
C - Air Injection

H - Brake Sense Speed Input
E - Serial Data

M - Serial Data
Clearing Trouble Codes

Diagnostic trouble codes may be cleared by disconnecting the battery ground cable for at least 20 seconds. Reconnect negative battery cable and recheck codes to confirm the repair.


you can access the trouble codes w/out a scanner...

paper clip is a good jumper to put on terminals A & B, then read them again... reset pc... drive until the computer "relearns" your driving style for about a week or so... read codes down the line to see if any is stored...

http://www.troublecodes.net/gmobd.gif

------------------------------

my sis' case was an open thermostat, which never brought up the operating temps & so was wasting gas mileage as well... another cause you can look @ easily if your car is equipped w/ a temp gauge on the cluster...

it's a 94... how many miles? and was a compression test/ leakdown test done to see what the mechanical health of the engine is?

- hmm, OP didn't state if read the codes or not...

I did, at Advance Auto Parts. It shows no codes.

- PS: Y did you change out the car's PC/ ECM? was it faulty from the git-go?

I replaced the ECM last Saturday for an AC Delco. I swapped the PROM from the old one.


- it's a 94... how many miles? and was a compression test/ leakdown test done to see what the mechanical health of the engine is?

It's close to 100,000, and I have no idea what a compression test\leakdown test is.

Man, cars are just a big headache :(

How many miles are you guys getting to a half tank cauz i am getting about 200 or more. jw thanks

My Guage really drops fast after half. I dont think its very linear..
I cant go by the guage.. just the calculations of input gallons to mileage traveled.

Im getting that 22MPG in town.
Maybe you have a valve burning out. or something similar. Maybe a compression problem. Hope not.
These engines are pretty hearty. Some have trouble with the plentum.

Sounds like you need a tuneup SEBAZ..

Hang in there

Well, my mechanic told me that a common cause for bad mileage could be dirty injectors. However, new injectors are very expensive, and have them cleaned is also expensive. Do you guys know if that STP Super concentrated fuel injector cleaner is any good or just a waste of money? Also, some people say that using premium gas is much better than regular, while others say it's a waste of money. This car runs on regular, but it takes premium without problem. Would premium increase my mileage?

yea, that's a possibility

there's a special fuel system cleaner that some shops use... they'll disconnect the main fuel supply...

tap into the schrader valve of the fuel rail (if it has it)

using a pressurized container, they'll add a slightly stronger concentration of a commercial brand cleaner (or you can just try b12 chemtool in the gas tank)
along w/ some regular 87 octane...

and run the engine thru that pressurized cleaner/gas combo on the vehicle until it runs out...

change fuel filter if you opted for it.

50:50 chance of improvement vs taking off all the injectors & having them sonic-cleaned or some other jargon they used... more $ that way, but they'll test the spray pattern & see if you're getting a mist & not a dribble out of those injectors...

Also, some people say that using premium gas is much better than regular, while others say it's a waste of money. This car runs on regular, but it takes premium without problem. Would premium increase my mileage? Fuels with higher octane ratings perform better because they burn more slowly. Less energy is lost to shock waves, and more energy is directed at pushing the piston smoothly through its stroke. Now with all that said, let’s take a look at the “real world” view!:grinyes:

Ok, let’s assume that using premium fuel will get you an extra ½ mile per gallon, then we will do some simple math, to see if there is any benefit to using premium. At an average price of $2.15 per gallon (in my area for regular), 10 gallons @ 15 mpg would give you 150 miles. The same amount of premium @ $2.35 per gal, might give you 15.5 mpg, or 155 miles. Now, 10 gals @ $2.15 per gal = $21.50 and @ $2.35 per gal = $23.50. At this rate, you would use .93 gal less fuel, using premium, in lieu of regular. Sound good so far?

OK, now let’s look at the flipside of the story and see how many miles you could get with .93 gal of regular.@ 15 mpg. .93 X 15 = 13.95 miles. (By the way. .93 gal @ $2.15 per gal = $2.00, which is the difference between the cost of regular and premium in this scenario). Finally, let us add 150 + 13.95 = 163.95, miles on regular, at the same cost as premium would give for 155 miles @ 15.5 mpg. So, actually your wallet would not benefit from using premium! I hope that you were able to understand, in this scenario, the cost per mile, is actually less, using regular in lieu of premium. :grinno:

Is there any cost saving benefit from using premium over regular, in an N/A engine designed for 87 octane? The answer to that is a big fat, NO!:grinno:

OK, that's the octane comparison (which is very good). But what about other factors? As far as I know, fuel companies put a lot more cleaning products in premium gas than in regular. Don't those cleaners prevent clogging and deposits and thus keep the engine and fuel lines at peak efficiency?

Want just an opinion?

Fact.. a bad injector poorly atomizes fuel.
Either *streams or *sprays properly or is *clogged or *inoperative

A clogged injector causes a lean cylinder.
A streaming injector causes bad idling.
A inoperative injector is an obvious miss.

The days of wearing out the injector orafaces are practically gone with new technology and metals.

The chances of it being all your injectors are slim.
If your gas mileage is bad under normal conditions, you can take to an exhaust analyzer and see if its rich.

I would say get an injector cleaner and monitor your calculated gas mileage before and after the treatment.

You either moved to an uphill home. Since you started measuring your gas mileage or you are loosing gasoline somewhere or mistaken.

Good Luck

On modern engines with sophisticated engine management systems, the engine
can operate efficiently on fuels of a wider range of octane rating, but there
remains an optimum octane for the engine under specific driving conditions.
Once you have identified the fuel that keeps the engine at optimum settings, there is no significant advantage in moving to an even higher octane fuel, other than, to enjoy the small benefit of the additional additives.
I guess you would need to do a cost/benefit analysis on that! :confused:

While there may be some disputes amongst the various producers about relative merits, it is quite clear that premium quality fuels, have superior additive packages and that they do help maintain various engine components. These additives have been shown to slightly improve fuel economy, NOx emissions, and drivability as well as help to dissolve existing carbon deposits. :grinyes:

I suppose you could get this same benefit from a bottle of Lucas or Sea Foam additive every other tank full, in lieu of using premium fuel.:rolleyes: