Lost 3.6 mpg, what'd I do??? - Fuelly Forums

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Old 09-30-2009, 04:03 AM   #1
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Lost 3.6 mpg, what'd I do???

My blazer is running great, no engine light, just as smooth as it always is.The only difference between this fill-up and the last was I just changed the oil. 5w-30 conventional was used (which is what was in there before). I've never had this bad of a mpg, went for 19.2 last week to 15.6 this week. Previous worse was 16 last winter. Tire pressures are all at 38psi as always. Tune-up items all have less then 10k miles on them. I'm I possibly accelerating TOO slow???
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Old 09-30-2009, 05:02 AM   #2
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maybe an oxygen sensor or the EGR valve. I know my EGR was getting clogged and I lost a few miles per gallon and couldn't figure it out. my engine finally threw a code.

I have actually found that if you briskly accelerate to get up to running speed, it is actually better for your efficiency. just stay out of WOT and also close to WOT as to not go into open loop. that is where the ECU will just use a preset fuel map and just start dumping fuel in the motor. I have had pretty good success with doing this.
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Old 09-30-2009, 06:06 AM   #3
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I lost 2 MPG after getting my radiator flushed. I'm not sure that it is related. It is a bit of a guessing game for me with regard to effectiveness of some of the techniques without my scanguage. I am so looking forward to that instand feedback.
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Old 09-30-2009, 08:09 AM   #4
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CHVYPWR, with an automatic it can be inefficient to accelerate too slowly; with a closed throttle and low RPM, the transmission may wait in a low gear instead of shifting when it should, and it may not lock the torque converter until you're in high gear. Sloshing the ATF in the TC can waste energy.

Brontegirl, your radiator may have been clogged and not working as well, which could increase fuel economy in some circumstances...but it's still better to have it working right.
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Old 09-30-2009, 09:54 AM   #5
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How much have the temps and winds changed since your last fillup?

I know here in MN and WI the winds this last week and the temps have been really cold and windy. It'd hurting my mileage as well.
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Old 09-30-2009, 11:43 AM   #6
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CHVYPWR, with an automatic it can be inefficient to accelerate too slowly; with a closed throttle and low RPM, the transmission may wait in a low gear instead of shifting when it should, and it may not lock the torque converter until you're in high gear.
Well, I'll try giving it some more pedal then. The trans does like to hang a little before shifting, if I let off it shifts, or give it more it shifts (a typical 4L60E). The lock-up kicks in at 45mph no matter what.
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Old 09-30-2009, 11:45 AM   #7
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How much ahve the temps and winds changed since your last fillup?

I know here in MN and WI the winds this last week and the temps have been really cold and windy. It'd hurting my mileage as well.
Temps for this tank were still summer like. I hadn't drove it over the weekend when it got cold out.
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Old 09-30-2009, 11:53 AM   #8
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Well, while I'm logged in, I figured I'd ask my wife if she filled up the Jeep yet. She did, and her fill up was 3mpg lower too!!!! I'm thinking they must have started with the winter blended fuel here in Michigan already! The Jeep has been rock solid at high 26 to low 27 since we got it in April. A change in fuel seems to be the most logical idea for both vehicles to drop like this. Thoughts?
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Old 09-30-2009, 03:09 PM   #9
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no idea about winter blend fuel but i'd change the fuel and tranny filters(and tranny fluid of course), especially if it's been a while. the only thing i can think of besides tune-up, which you already eliminated.

my wife's chevy w/ AT seems to get sluggish when those services get neglected.
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Old 09-30-2009, 05:15 PM   #10
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I track every tank.
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