Why is my 996 getting 12.5 MPG?
03-08-2019 | 04:16 PM
#2
Rennlist Member
Joined: Apr 2010
Posts: 5,972
Likes: 1,208
From: Ormond Beach, FL
Which plugs and coils did you replace with? Why did you replace the plugs and coils? Try disconnecting the negative battery lead for 30 minutes to reset the DME, then do some drive time to establish new values on the new plugs/coils.
03-08-2019 | 05:24 PM
#5
Rennlist Member
Joined: Oct 2010
Posts: 6,516
Likes: 4,947
From: Alabama USA
It's probably due to aging 02 sensors. They are designed to run for at least 120k miles under normal circumstances. But sometimes will last longer( sometime not), but the aging will slow response time and bias the fuel trim.Get you a bluetooth (or wifi for IOS) OBDII adaptor and a phone app and read your fuel trims. Fuel trims should be near zero , if too far from zero means something is amiss and is being compensated for.
How many miles are on your engine?
How many miles are on your engine?
03-08-2019 | 05:43 PM
#6
Drifting
Joined: Sep 2005
Posts: 2,528
Likes: 175
From: Glenview, IL
I have had my car since 2000 and 4,000 miles. Around town it has always gotten 12-14 mpg. On the highway cruising at 80+ I can get 25-28 MPG. So if you are getting 12.8 mpg around town it does not surprise me.
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03-09-2019 | 12:43 AM
#9
Burning Brakes
Joined: Jul 2018
Posts: 1,100
Likes: 127
From: Casselberry Florida
Was the battery reset when the coils and plugs were changed?
i only ask because doing so resets the AVG MPG calculations. Allow me to explain. My car is typically only driven on the highway back and forth to work 1 day a week. Its 50 miles round trip and all highway. When i purchased the car i reset the AVG MPG in the cluster. Right now it reads AVG MPG as 22. This is because the last time i reset it it has only seen the avg high mpg from the highway. If i were to clear it again and do more local in town driving it would instantly read very low MPG AVG.
At work we see this complaint from people who do a lot of highway type driving. Then they come in and we do some repair that requires a battery reset. Then for the next few days or even weeks the AVG MPG is messed up until they put some time on the car for a better calculation to see a true avereage. Hope that makes sense.
i only ask because doing so resets the AVG MPG calculations. Allow me to explain. My car is typically only driven on the highway back and forth to work 1 day a week. Its 50 miles round trip and all highway. When i purchased the car i reset the AVG MPG in the cluster. Right now it reads AVG MPG as 22. This is because the last time i reset it it has only seen the avg high mpg from the highway. If i were to clear it again and do more local in town driving it would instantly read very low MPG AVG.
At work we see this complaint from people who do a lot of highway type driving. Then they come in and we do some repair that requires a battery reset. Then for the next few days or even weeks the AVG MPG is messed up until they put some time on the car for a better calculation to see a true avereage. Hope that makes sense.
