2005 MERCURY MONTEREY POOR GAS MILAGE

  • Tiny
  • don22
  • 2005 Mercury Monterey

Engine Performance problem
2005 Mercury Monterey 6 cyl Front Wheel Drive Automatic 75000 miles

I had the fuel pump replaced, and gas milage dropped 3 miles per gal. Eng analizer say mixture is to rich. Mech reset fuel air mix, but the fuel mixture resets itself to a rich setting after car is restarted. I had it reset again, and drove the van 60 miles and got 25.4 MPG. I stopped, shut the engine off, restarted the engine, and retraced the same route. Gas mileage dropped to 20.4MPG. Mech does not know what to do. Help

Wednesday, August 19th, 2009 AT 2:05 PM

14 Answers

  • Tiny
  • ImpalaSS
  • Expert
  • 3,148 posts

Hello -

Can you tell me your engine size in liter and the 8th digit of your VIN?

Sensors that affect an engine to run rich are manifold air temperature sensor, engine coolant temp sensor, O2 sensor and the intake air temperature sensor. Excessive fuel consumption can be a faulty engine coolant sensor.

Have you tried pulling the codes to see what codes are thrown?

If you want to do this yourself before taking it to the mechanic. You can go to Auto Zone (AZ) or O'Reilly's (OR) and for FREE they can pull the codes to the car. Most important: Once they check your codes, if they find something and you don't get it fixed and need to get back with us, please make sure you tell us exactly what the code was, number and all. Example, if the code was E0568 O2 Sensor bad. Then make sure you give us all of that. While there for FREE also they can bring their tester out and check your battery and alternator.

I can advise you on the codes if you receive any. The common sensor for running rich and fuel consumption is your engine coolant temp sensor.I would have that checked out.

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Thursday, August 20th, 2009 AT 12:01 AM
  • Tiny
  • don22
  • Member

The eng size is 4.2L. The 8th digit is the #2. I will do as you suggest

don22

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Thursday, August 20th, 2009 AT 8:41 AM
  • Tiny
  • don22
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Why would the computer reset itself after it was adjusted to lean the fuel out.

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Monday, August 24th, 2009 AT 9:20 AM
  • Tiny
  • ImpalaSS
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Hello -

There can be several reasons. It can be resetting (which it appears it is) once the key is cycled (on/off) Sometimes the check engine light can come on and once you cycle the key it goes off. The code is still there but it resets the light.

Obviously it is reading a sensor or something that we need to figure out that will keep it from resetting.

Once you do go to AZ or OR and they check the codes. Again, make sure you get all the info on it if it gives codes. The code number, what they say it is etc and give that to me. When they have done that have them clear all codes.

Let me know what you find.

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Monday, August 24th, 2009 AT 10:52 PM
  • Tiny
  • don22
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I had the analizer hooked again last night, and there are no codes. I am going to replace the eng coolant sensor.

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Tuesday, August 25th, 2009 AT 8:42 AM
  • Tiny
  • ImpalaSS
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Hello -

Please let me know what you find out after the replacement

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Tuesday, August 25th, 2009 AT 9:28 PM
  • Tiny
  • don22
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After replacing the cyl head temp sensor, I drove 2 days, 300 miles each. The AC was off, and cruise was on. Speed was 70 MPH, on 4 lane road. Gas milage was 21.8 first day, and 21.2 the second day. The route was the same both days. It seems that the temp sensor was not the problem. There is no eng code.

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Thursday, August 27th, 2009 AT 10:15 AM
  • Tiny
  • ImpalaSS
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  • 3,148 posts

Hello -

Well. We still aren't there BUT. It is a little better. Only a little but that is a positive.

Have you had the mass air flow sensor checked and or the Intake air temperature sensor checked?

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Thursday, August 27th, 2009 AT 10:47 PM
  • Tiny
  • ImpalaSS
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Hello -

One last note..........try cleaning the Mass Air Flow sensor with some electrical cleaner. Go easy.


http://www.2carpros.com/forum/automotive_pictures/248015_6_23.jpg


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Thursday, August 27th, 2009 AT 11:07 PM
  • Tiny
  • don22
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I wrote down some reading's from analizer. At idle, 640rpm the eng load is 19%, with a/c on load is 23%. The eng temp reads 16,800 F. The timing reads 22 to 24 degrees. Air sensor, O2 sensor, egr sensor, all check ok. A few of the injectors show they stay open periodically a little longer then the should. Timing and eng load seem high to me. The eng temp used to read 30,000 F before sensor was changed. I also noticed on this last trip that I now go the same MPH at 100 rpm less.

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Sunday, September 6th, 2009 AT 2:00 PM

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