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Lost MPG after custom tune

mxzretta

Full Member
Joined
Oct 5, 2014
Messages
9
Had a custom tune done and I went from 15 mpg down to 11 mpg. My truck has had the cats gutted so it was always throwing 420 and 430 codes. I had him make it so it wouldn't throw the codes. Wondering if the computer is not getting any readings from the o2 sensors thus causing the poor mileage. Tune was dome with EFI live. Thanks for any help
 
P0420-P0430 only tell that the converters are not working properly, turning those sensors readings off does not affect the air fuel ratio.

The questions are???

1. Have you been driving it like you stole it checking the performance after the tune.
2. Who tuned it.
3. Was it a performance tune or a mileage tune.
 
When I first got the tune of course I drove it like I stole it. But that was over a month ago. Drive like I always have. The tuning was done by a very reputable tuner up here in Edmonton. He mainly does diesel tunes. As for performance or mileage tune never asked. He rode with me made some changes flashed it and had me drive to see how I liked it. More than happy with the tune. Just wondered about the mpg.
 
The ECM's can be programmed for performance, towing,  mileage and low/high octane. Talk to your programmer and let him know, they usually give a few re-tunes a year at no charge.

Something else could be wrong also, if you have allot of miles on the spark plugs and/or upstream O2 sensors a performance tune may not perform..


Good luck
 
Performance tune or not, you shouldn't be getting that much if any of a mileage hit unless he changed the part-throttle shift points a lot.  Does it upshift at around the same speed as before?
 
Also in Edmonton and get about 400km to a tank of gas in the city. This is with a 6.2 however. Did you go to Moretto?
 
New plugs and wires this summer as well as 02 sensors. Also a new transmission. Went to Coopers Custom Solutions. Just east of Beaumont. I'm getting about 550kms out of a tank with the 5.3
 
To me that doesn't sound that bad. Back when I had my 5.3 and 5.7 I was in those areas. Did you get a new converter put in with the tranny? Maybe a higher stall?
 
It would be interesting to know what year and model he has. Along with what other mods he has done.  ???


Also why did he gut the cats
 
Other mods are magnaflow exhaust, AFE cold air intake. Had the tranny replaced on holidays. It went in Merrit,BC. When it was in getting the work done they discovered one of the cats was plugged so I had them gut them instead of getting them replaced to keep the cost down. Old converter was installed. Btw don't do business with Murray GM very poor customer service. Took them 3 weeks.
 
I'll let the other folks address your tune, but since it's getting cold outside your mileage will be worst in winter.
 
My mileage gets worse in the winter also, additives in the fuel and extra ideling.  Are you able to go back to stock with your programmer and see if the numbers come back up?  Or is the Ecu just flashed.
 
I have had this truck for couple years and never got this bad of mileage. Even in winter I would get 500kms out of a tank. Out of my last tank I got 350kms out of 88 liters of gas. Think I will go back to my tuner and see what he can do.
 
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