big drop in MPG
08-27-2009, 01:30 AM
#1
2nd Gear Member
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Join Date: May 2008
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Posts: 206
big drop in MPG
For the last couple of days I've noticed when the car sits overnight or during the day at work it takes a couple of seconds to start when I first get in. Before it used to fire right up, but now has a slight hesitation before starting, the RPM's are bouncing between 840-1000 and my MPG have dropped from 19 to 15. Sound like a fuel pump? No CEL's, the air filter and MAF were just cleaned and I have a new set of plugs, injectors and COP's. What's the deal?
08-27-2009, 02:58 AM
#2
5th Gear Member
Join Date: Feb 2007
Location: Hawaii
Posts: 2,211
have your battery checked.
the alternator might be engaged alot more than it should have to because of the battery.
if the electricity isn't needed, the alternator isn't used and basically free wheels and engages as needed depending on electrical load. since you are saying it takes a few seconds to start up and the idle is erratic, I'm a bit suspicious of the battery...or even perhaps the alternator itself.
the alternator might be engaged alot more than it should have to because of the battery.
if the electricity isn't needed, the alternator isn't used and basically free wheels and engages as needed depending on electrical load. since you are saying it takes a few seconds to start up and the idle is erratic, I'm a bit suspicious of the battery...or even perhaps the alternator itself.
08-27-2009, 02:49 PM
#6
3rd Gear Member
Join Date: Apr 2008
Location: Merritt Island, FL
Posts: 996
Maybe the your MAF is dirty. http://www.muscularmustangs.com/maf.php
Read something like this in one of the mustang magazines about a year ago.
*EDIT* Ignore - I should probably learn to read the entire post before replying...
Read something like this in one of the mustang magazines about a year ago.
*EDIT* Ignore - I should probably learn to read the entire post before replying...
Last edited by JasperGT; 08-27-2009 at 02:52 PM. Reason: Didn't read the full post :(
08-27-2009, 04:13 PM
#7
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Join Date: Jun 2006
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Posts: 912
Its the sure fire sign of a failing battery. When a cell or two in the battery fail, the computer reconizes the loss of voltage. It compensates the voltage loss in the ignition, or firing system by forcing the fuel injectors to add more fuel. The loss of mileage is the giveaway. Have the battery tested. I'll bet at least one cell is dead. A new battery will get you back to the previous mileage you were producing.
08-28-2009, 12:36 AM
#8
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Join Date: May 2008
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Posts: 206
thanks for the suggestions. I'm going to take the battery over to Auto Zone tomorrow and have it tested. The alternator is less than 3 months old. The OEM was replaced w/ a 200 amp to compensate for the aftermarket system. The fuel filter was done also about 3 weeks ago. Thanks for the help.
08-28-2009, 12:50 AM
#9
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Join Date: Nov 2006
Location: Detroit Rock City!
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Do you have a CAI and tune?......might need to reflash the tune you had previously.....the battery sounds like the culprit.
Oh which COP's did you get?
I have found that many of the COP's out there actually suck compared to the stock COP's....many wont even advertise the voltage output.....40,000+ would be great!
Nineinchnails1024 can help if it is a COP issue....started out fine and great and ended bad and went back to stock....I believe he had FI at the time but could be wrong
Oh which COP's did you get?
I have found that many of the COP's out there actually suck compared to the stock COP's....many wont even advertise the voltage output.....40,000+ would be great!
Nineinchnails1024 can help if it is a COP issue....started out fine and great and ended bad and went back to stock....I believe he had FI at the time but could be wrong
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