POOR Gas Mileage

[2OOOLS]

Originally Posted by Sparkey56

Go by your local AutoZone store and get them for FREE to scan your car as long as it 96 and up. Copy down all the codes and then have them look it up in the computer. I used to work for one up in Mass.

unfortunately FREE scan at AutoZone store did not pass any codes

[fredjacksonsan]

What size tires do you have? Are they stock or a larger size?

How does the car coast? Does it slow down rapidly or freely stay at the same speed? If you've got some resistance (perhaps in the front bearings, or the Ujoints or brakes dragging, for example) then that would contribute to poor mileage.

[Sparkey56]

first off get rid of the original spark plugs and go with the regular bosch plation plugs. sometimes there is what is called soft codes that come and go and there is a way to recall the history I will have to try and check for you. Also another problem area might be the issue could be a vacuum leak. Mine was running ruff until a friend of mine who is a ASC mech for dodge found a vacuum leak and after we fixed it mine has running great. The last check of my gas mileage was 24.8 for freeway. Granted my average speed to work is 65 and on cruise control. So it is possible to get better. My next step is to get a K&N filter for mine and see how that helps. Hope this has helped.

[jimmytroanoke]

Originally Posted by Sparkey56

first off get rid of the original spark plugs and go with the regular bosch plation plugs. sometimes there is what is called soft codes that come and go and there is a way to recall the history I will have to try and check for you. Also another problem area might be the issue could be a vacuum leak. Mine was running ruff until a friend of mine who is a ASC mech for dodge found a vacuum leak and after we fixed it mine has running great. The last check of my gas mileage was 24.8 for freeway. Granted my average speed to work is 65 and on cruise control. So it is possible to get better. My next step is to get a K&N filter for mine and see how that helps. Hope this has helped.

MOTORCRAFT only on the plugs - Bosch are fine if you want to change them in a year, but Motorcraft are the only ones that last in the Mod V8. I have owned my GM since new and also my 4.6 F150 so I speak from experience. Pay the extra money and get them from the dealer. They work. I have thrown away too many Bosch plugs with 20 K or less on them to count.

[2OOOLS]

Originally Posted by jimmytroanoke

MOTORCRAFT only on the plugs - Bosch are fine if you want to change them in a year, but Motorcraft are the only ones that last in the Mod V8. I have owned my GM since new and also my 4.6 F150 so I speak from experience. Pay the extra money and get them from the dealer. They work. I have thrown away too many Bosch plugs with 20 K or less on them to count.

I am sorry ppl, I am lost

where should I start first?

replace originally installed MOTORCRAFT plugs with new MOTOCRAFT plugs?
with new Bosch plugs?
just replace plugs without doing tune up?
do computer diagnostic even if there is no guarantee that it will bring any results?
put K&N filter instead of filter that I put 1 month ago?

btw, my tires are ok, they stock and inflated according to the manual

i have feeling that my oxygen sensor is not good... there is interesting site located at:

http://www.fueleconomy.gov/feg/FEG2005.pdf

they say that "repairing a faulty oxygen sensor can improve fuel economy by as much as 40%!"

TIA
2OOOLS

[jimmytroanoke]

Originally Posted by 2OOOLS

I am sorry ppl, I am lost

where should I start first?

replace originally installed MOTORCRAFT plugs with new MOTOCRAFT plugs?
with new Bosch plugs?
just replace plugs without doing tune up?
do computer diagnostic even if there is no guarantee that it will bring any results?
put K&N filter instead of filter that I put 1 month ago?

btw, my tires are ok, they stock and inflated according to the manual

i have feeling that my oxygen sensor is not good... there is interesting site located at:

http://www.fueleconomy.gov/feg/FEG2005.pdf

they say that "repairing a faulty oxygen sensor can improve fuel economy by as much as 40%!"

TIA
2OOOLS

Plugs & PCV essentially are the tuneup. A good diagnostic at the Dealer will tell you a lot about your cars performance and find problems even if the engine light is not lit. They can see a graphical trace of the O2 sensors functions and see if they are lazy even if they aren't throwing a code. They can also pinpoint sticky injectors etc. as far as O2 sensors go, if you do decide to replace them, there are 4 and they are about $100 apiece. Just do the two that are before the converters as the rear ones do not contrubute to how the car runs. The rear ones are efficiency monitors for the converters and rarely fail. Use only Ford (Motorcraft) parts here. The dealers diagnostic will pinpoint weak ignition function and show if you need plugs and wires. The tech can also look at long and short term fuel trims, etc and outputs from every sensor on the car. This cant be accomplished with the handheld unit at autozone which is only a code reader. So, if you go for the computer diagnosis (which is usually 1 or 1-1/2 hours @70-90/hr) just go somewhere where they can really do a diagnosis and show you printouts to back it up. Bad gas can also cause a bad converter which will be covered for 8/80 Federal emissions warranty.
I say to run from Bosch plugs and any Ford tech will back me up. Several that I have spoken to have said that they have cured all manner of driveability concerns by removing Bosch plugs. Having put well in excess of 100k miles on both my Fords, and having tried Bosch in both with no success is my basis for this statement. K & N filters are OK but if you put too much oil in them it will kill your Maf sensor. I'll stick with paper thank you.
Your mileage is a little low to need O2 sensors but a tank or 2 of crappy gas can kill them.
Also inspect all vacuum lines for leaks. The PCV line on these cars deteriorates at the intake manifold where the short section of rubber hose joins the hard tube to the manifold. Hard to see unless you remove it and inspect.

[Sparkey56]

Good input there jimmytroanoke, I guess I have been lucky with my MGM and the bosch plugs. I will keep checking them every now and then to see if things change, I drive on the average of 100 miles each day at freeway speeds so I cannot complain on the mileage I am getting. Also another good point on the air filter is if to much oil is used when cleaning the K&N filter. Only time will tell.
Another point to maybe check would be if the emergency brake shoes might be dragging just enough and not to over heat. Just a thought there.

[qliit]

yea i have a problem with mileage too (11.8 mpg) i replaced my old (as far as i know stock) plugs and wires on my 92 a couple months ago with bosch platinum+2 plugs and ford racing wires. it ran better but no more mileage. when i got my car and i noticed some problems with mileage i looked into the o2 sensor but ended up not getting it cause it costed 50 dollars and i needed 2 but maybe now ill make the investment. sounds like its worth it.

[jase386]

our 2000 Marquis was getting about 12mpg around town, but we were using the cheapest gas we could find. We started using BP/Amoco gas at about 10 cents more per gallon, and now we are getting 17 and 18 around town. My guess is you may be using the cheaper gas which is now cut with Ethanol. I lost 5 mpg on my minivan when they started selling the ethanol blend, but i still get decent enough mileage.


so try some Real gas, like Hess or BP. something that isnt cut with ethanol and see what happens, and let us know

P.S. we are still using regular 87 octane

[Hollowcreek]

My 2000 LS gets 20 in the city and 22 - 25 on the highway. I just had it inspected (here in TX it gets an ODB2 emissions test) and all emissions were good. The inspector told me that he sees Ford products all the time with no check engine light on that routinely fail because O2 sensors are not working properly. Don't believe the mechanic that says that nothing will show up if the check engine light is not on, thats BS, you just need more than a code reader.

Your 2000 may just need to go to the dealer and have the computer flashed too. I had to have it done last year after the tps was replaced. It was getting poor mileage and it was really knocking when it got warm.

[Sparkey56]

Hi all, I am happy to report with the K & N air filter in my MGM I have seen a great improvement in the get up and go department and even with high prices for gas I am averaging a solid 25 MPG for mine. The best place to find it is on ebay. I saved over 15.00 dollars vice retail cost that way. :-)
My only other issue with it has been today replacing the starter, it finally died. Not to hard to replace just a bit time cunsuming, she runs great again.

[Hombrero]

On my 95 I get 19 city and 27 on the hwy.That's perfect for V8....

I have heard a lot of stories here and there that gas mileage for Grand Marquis in town average is 17 to 18 MPG.

The fuel economy of my 2000 MERCURY Grand Marquis LS is 12.55 mpg in the city!

I am confused
Do you think its normal? If not, whats wrong? Any suggestions?

TIA
2OOOLS[/quote]
1995 MGM

[jase386]

our 2000 LS averages about that also!!!! what did they change with the new body style that makes them drink so much gas, and have no get up and go??!!

[Hollowcreek]

Its probably the gas if you are not seeing any diagnostic codes. My 2000 was really knocking and getting bad mileage until I went to Premium. The knocks stopped and the mileage is over 20mpg. Also make sure you have the tires properly inflated. My door tag says 26 lbs which is totally wrong if you have the 60 series 16" wheels. I'm running at 36 which has the tires wearing properly and handling much better.

Another possibility is the cracked intake manifold thing. You might just want to have it checked.