Sudden change in MPG

Comments

• ogwagon Wagonist

  February 2010

  Have you bottomed out your car recently? Raise up your car and do a quick visual inspection of the fuel tank for possible leaks. Also inspect the fuel lines in the engine compartment from the fuel filter to the fuel rail while the engine is running. It sounds silly but check your fuel cap also. Make sure the seal is good. Do you notice unsual amounts of black smoke from the tail pipe? Black smoke from the tail pipe that smells like raw fuel is an indication of poor/incomplete combustion in the engine. Check the gap on the spark plugs, since you just replaced them. Are you sure you adjusted the valves correctly? Have you done this before or first time?Did you remove the distributor during your recent repairs? If so check your timing and make sure its still on. You may have accidently damaged a vacuum hose during your last repairs. Inspect the vacuum lines on the intake manifold especially the ones going to the map sensor and fuel pressure regulator. A cracked/broken vacuum hose at either of these components will cause your symptoms. Inspect the map sensor itself and its electrical connector for damage or corrosion. Inspect the oxygen sensor on the exhaust manifold. Check the electrical connector/wiring and make sure it has not burned from coming in contact with the manifold. Even if the wiring to the oxygen sensor is ok, the sensor itself could be bad especially if it is the original part. If none of these apply, remove and inspect the distributor cap. Check for excessively burned contacts. If so replace the distibutor cap and rotor w/OEM parts. That's all I can think of right now. How does the car feel power wise? Does it still accelerate like it used to?
• wago_dan Wagonist

  February 2010

  No smoke from the tail pipe, though it does smell of fuel in the bay. there is no sign of leakage along the fuel lines or at the filter. the plugs came pre gapped but I did check that they were all the same.
  
  I have never adjusted valves before, but I followed the chiltons manual on how to do it, and I am familiar with using feeler gauges.
  I have not removed my distibutor but I did remove the cap and check the points and rotor, They looked fine.
  
  I will check the vacuum hoses when I get home from work. that does sound like a possibility.
  
  I am getting a CEL only once in 10 times i drive the car. Code 1, o2 sensor. Its on my list to replace as its probably the original.
  
  The car is an automatic so it never really accelerated well. Um I would say it feels about the same as it always has.
  
  Thanks for the suggestions.
• doitdub familEE

  February 2010

  My first thought was O2 sensor....

  wago_dan wrote:

  I am getting a CEL only once in 10 times i drive the car. Code 1, o2 sensor. Its on my list to replace as its probably the original.

  Also something to note is if you live somewhere cold, winter gas mix sometimes effects MPG, along with warm-up time. Something some people forget to consider. Not as much as you're stating though. I'd get that O2 sensor replaced.
• SiWagon Council Member

  February 2010

  Did you goto a thicker oil?Did you goto a wider tire?
  
  The tires can cause a 2-3 mpg drop.The winter gas ...3-8 mpg drop.The valve adjustment 1/2 to maybe a 1mpg drop.
• wago_dan Wagonist

  February 2010

  There were 175/65 on the 13s and when I got the fat fives they are 195/50/15. Shouldn't cause that much of a shift by themselves?
  
  I do need to change the o2 sensor.
  
  Doitdub, I live in socal and while it has been colder than usual, I don't think its been cold enough to affect the milage.
• wago_dan Wagonist

  February 2010

  Replaced the o2 sensor. The wire was shredded by the heat shield and only the wire core was still attached. Also replaced the terminals and cleaned the battery. Car drive much better, as it used to die every once in a while as I came to a stop. Seams to accelerate much better now. Hope this solves the milage issue. Thanks for all the help guys, I'll let you know.
  
  Dan
• SiWagon Council Member

  February 2010

  wago_dan wrote:

  ... were 175/65 13s... I got the fat fives 195/50/15. Shouldn't cause that much of a shift by themselves?

  
  It's not the height of the tyre ,but the width.It causes a lot greater rolling resistance .Once you pass 185 it drops a lot.I've done a lot of testing.
• judebert familEE

  March 2010

  SiWagon wrote:

  wago_dan wrote:

  ... were 175/65 13s... I got the fat fives 195/50/15. Shouldn't cause that much of a shift by themselves?

  
  It's not the height of the tyre ,but the width.It causes a lot greater rolling resistance .Once you pass 185 it drops a lot.I've done a lot of testing.

  
  Whoa, really? I thought going with a low-profile wider tire would offset the difference, because the sidewall wasn't as flexible.
  
  Sorry to resurrect such an old thread, but this is really near and dear to my heart.
• wago_dan Wagonist

  March 2010

  Just got 25.5 out of my last tank... Car is is much better than it was but still has a dieing issue SOMETIMES when I come to a stop or go from park to D or R. Idle is set properly, vaccumm lines to the map and fpr are good, replaced a bunch of parts... I'm at a loss.
• Eagle Beagle familEE

  March 2010

  using ac?
  voltage check...
  
  
• wago_dan Wagonist

  March 2010

  No AC,
  Car shows 12.8 volts and all grounds show the same voltage.
• SECURITY Band Wagon

  March 2010

  PCV valve hasn't froze up?
  
  Run fuel injector cleaner through lately?
• wago_dan Wagonist

  March 2010

  haven't checked PCV. Will do in the AM.
  getting 16In of vaccum.
  I have used seafoam recently. half can in the oil, half can in the gas tank. oil has been changed since. This was a method on their website. It didn't make a noticeable difference for or against.