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Fuel economy down 5-7mpg after dealer replaced cats/downpipe with P042

Haus_Z71

By Haus_Z71
in Troubleshooting & Recalls

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Haus_Z71 Enthusiast

Haus_Z71

Posted
Posted

I can't get a break with this truck.

 

After having a recommended Direct Injection valve cleaning done, the truck threw check engine light with code P0420.

 

Dealer replaced cats to fix the code.

 

Since then I've noticed a huge drop in my fuel economy. Down to around 10mpg around town. 14mpg on my 400mi average. But, oddly enough, my highway driving while cruising at 60mph still results in around 20mpg.

 

So what the hell could cause only city driving to suck? I am driving like a grandpa.

 

Here's a short clip of the mpg while slowly accelerating, which may mean nothing but seems odd that it shows that low mpg while slowly accelling.

 

https://youtu.be/Rgbf2Y8QdWM

Haus_Z71 Enthusiast

Haus_Z71

Posted
  • Author
Posted

Just read a couple other topics and around this time the temps dropped by 20 degrees. Sounds like cooler temps, along with 2 minute remote start in the morning may be accounting for some of this decrease. I didn't notice this last winter though. Still doesn't seem quite right.

TJay74 Senior Enthusiast

TJay74

Posted
Posted

Lower outside temps means more fuel into the mixture, also winter fuel shipped out last month to all refineries, add to that remote start events and you can kill fuel mileage pretty quick.

truckguy82 Senior Enthusiast

truckguy82

Posted
Posted

My truck gets horrible mileage when cold and in city traffic.

 

If I'm just driving to and from the office in the cold, which is 10 minutes away in 25mph residential streets, I probably average 10mpg babying it.

 

The same truck has averaged 25mpg on flat surface at 60-65mph

  • 3 weeks later...
vacuman Enthusiast

vacuman

Posted
Posted

My mileage readings dropped after installing a catback system. Disconnecting the negative battery cable for 10 minutes brought the readouts back to previous levels. Don't take the readout for gospel. Do the math. Divide miles driven by gallons used for the REAL gas mileage. If it isn't at least 16mpg, you've got a problem.

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