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Discussion Starter #1
Hey guys my car had been getting worse than worse gas milage for the past 3 full tanks.
I am getting less than 400km on a full tank. About 375km per tank on average. Converting for u guys is around 19mpg. I'm not sure exactly what is causing it but I feel like it all started after I was trying to fix a rattle in my exhaust which turned out to be just one of the heat shields. My mechanic cut my exhaust before the cat and put it back together. I've already asked them to check exhaust leaks twice. May be they weren't thorough enough on checking? I'm on full bolt ons and tuned but that was in the summer. Could it be the cold weather ? I also had my engine breather hose that connects to the air intake disconnected for a while (like a week) because I didn't notice it slipped off. Can this damage my engine enough to give me such low gas milage ?? Also my o2 sensors have been on incomplete on my obd2 reader ever since the exhaust was cut (>1000km driven). What do you guys think is the problem ?? I don't want to keep asking my guy to check for exhaust leaks I think he is getting fed up with it (but I hope that it the only problem )

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I'll go with no damage, but you have a few things that are designed to keep the engine optimal not in working order. The O2 reads rich and lean, and corrects the values it receives, cold in general changes fuel ratios correct by a good O2--sounds like that is missing in your vehicle?. I'd look at the O2 situation and less to an exhaust leak.
 

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Since it is cold outside, are you having your car warm up before driving? Having to defrost the windshield? Sitting for 15min just running will add up over time and drop mpg.
 

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Discussion Starter #6
Hey guys just to update, my spark plugs are brand new so are both my primary and secondary o2 sensors. (<10k on them). No cel, I do idle quite high when my engine is still cold . Idle is at like 2.2k then it goes back down to regular . I do warm up my car but up to 5 mins max and on average about 30s-1 min

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I had frozen rear calipers that were dragging. Check and see if you can feel heat from the center of your wheel after driving.
 

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Discussion Starter #10
So I checked tires exhaust and did an oil change with Castrol edge 5w30, gas is petro 94 , brakes seem like they are not heated after a long drive (rear ones at least) haven't checked vacuum leak or thermostat but looks like my thermostat is working ( no engine overheating issues ? ). Perhaps it could be my tune ( it is quite aggressive ) together with the winter weather ?

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I'd double check that primary o2, change it again if you can. Go back to a stock map and see if anything changes.
 

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Discussion Starter #12
Currently trying to use seafoam and maybe that will help.. I have just put it in the fuel tank but have not gone through the vacuum line or oil yet as I just changed my oil . Going to have to wait till my next oil change but I will probably be doing my vacuum line soon .
Update : car is running pretty smooth on Castrol edge 5w30 with seafoam in my fuel tank . Hoping I will see some MPG gains . Will see what happens when I refill my tank . Will update after tank is finished.

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Discussion Starter #13
Currently trying to use seafoam and maybe that will help.. I have just put it in the fuel tank but have not gone through the vacuum line or oil yet as I just changed my oil . Going to have to wait till my next oil change but I will probably be doing my vacuum line soon .
Update : car is running pretty smooth on Castrol edge 5w30 with seafoam in my fuel tank . Hoping I will see some MPG gains . Will see what happens when I refill my tank . Will update after tank is finished.

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On second hand , does anyone have experience with ktuner's RBC/I/H/E basemap ? Perhaps a less aggressive tune than my custom tune ? I might end up just using that as a long distance driving map and my custom tune to **** around on on the highways.

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Discussion Starter #16
For some reason the CEL only goes on after my car has warmed up to max operating temperature. When I check readings on my torque 2 OBD2 app, I am still getting readings for my AFR until the check engine light comes on , then my AFR just stays at 14.7 and my car starts driving like the AFR sensor has turned off .. what is going on ?? I forgot to pull the codes but I'll get them .

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Discussion Starter #17


I'm hoping for a cleanable O2 sensor that just got caked with carbon from the seafoam. Im guessing that's not good for my cat either.

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