Really bad gas mileage?
07-08-2009, 08:56 AM
#1
Really bad gas mileage? So I filled my tank up yesterday with 11 gallons, so it was pretty much completely full. I just got the idiot light on right now saying to put gas in, and I;ve gone 86.3 miles. Thats 6mpg, its been getting worse every day for a week or two now. Anyone have any idea why it would be so bad? No codes, car runs fine, just terrible gas mileage. Nothing has changed since the last few weeks where I was getting 25+ on the highway and a little less in town.
07-08-2009, 09:53 AM
#3
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check your air filter. My mpg went from 22 to 10 in a week because they were working on the roads near me and the air filter was clogged. I got damn near a cup of dust out of there when I cleaned it LOL. it could also be fuel filter causing the bad mileage.
07-08-2009, 09:54 AM
#4
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Yeah either someone is siphoning your gas or you have a leak. I cant imagine the car would run correctly if it were burning that much gas. Did you go 160mph for 86 miles? Lol
07-08-2009, 01:04 PM
#5
Well, heres the scoop. Its been getting progressively worse over the last, say, 3 weeks. I started by cleaning my K&N which was somewhat dirty but not bad. There are NO leaks. I cleaned my maf off with the spray, looks good. I changed the oil. I changed the spark plugs and noticed 2 were very fouled up, and found that the plug wires going to them were bad, broken off in the boot. After I replaced all those, I got about 2 tanks of gas with good mileage, and it started going back down again. I'm thinking maybe those 2 coils might be shot as well? The car does not drip gas at idle.
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07-08-2009, 02:50 PM
#9
It feels fine to me, exactly like it has been. But I also couldn't tell that the two plugs were fouled up and they were really, really bad. I might have to get it on HPtuners and see if one of the O2's is bad, I may have it set to not show an SES light even if they go bad.
07-08-2009, 03:19 PM
#10
It can be misfiring without throwing a code. When my knock sensors went bad I saw really bad gas mileage (less than 10) for a tank and no codes, but the car did feel down on power...
HP Tuners can tell you a lot of good info and save you a lot of searching though. Hope you get this sorted out.
HP Tuners can tell you a lot of good info and save you a lot of searching though. Hope you get this sorted out.
07-08-2009, 03:35 PM
#11
I'll have to look at this. My engine has less than 20k but I had to reuse my old knock sensors. The car doesn't feel like its lost too much power, but I rarely got WOT. I'm going to re-check those plugs that were fouled up and see about getting some scan done with HPtuners and see what its doing.
07-08-2009, 06:51 PM
#12
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I was using the Bosch O2s and they were causing my plugs to foul as well due to too much fuel being dumped. Were these plugs on the same side? My car wasn't throwing any codes but it was behaving strangely, good luck figuring it out!
07-08-2009, 07:46 PM
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This is strange. And yeah, you'd know if there was significant knock retard or something like that. A car that feels like its running fine doesn't get 6 mpg. Hope you find something soon. Stuck injector?
07-08-2009, 10:44 PM
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check for leaks around the mass airflow sensor and in the airbox assembly. unmetered air can be a bad influence on your mileage. it can also build up trash in your top end. scary s***...
07-09-2009, 05:07 PM
#18
Sounds like O2 sensors to me. I had bad O2's on my DD and it is a 4 cyl that gets 27 consistently and it dropped to 10-12 mpg until I replaced it. And it would be your upstream O2's that would make it get bad gas mileage if that were the case. Could also be fuel injectors.