05 GT getting 7MPG, smell unburnt fuel, no CEL and all sensors normal. Help? - Ford Mustang Forum
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post #1 of 19 (permalink) Old 07-06-2019 Thread Starter
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05 GT getting 7MPG, smell unburnt fuel, no CEL and all sensors normal. Help?

2005 Ford Mustang GT, 105K miles stock, bought last month. I get 7MPG city, 9MPG highway. Car smells rich, possibly from the driver side exhaust. Here's what I looked at so far:

- Spark plugs and fuel filter changed
- Cleaned MAF sensor - the readings before and after were identical (sits around 4.8/s at idle, increases with revs)
- O2 sensor 1 voltages oscillate normally between 0-0.9, sensor 2 voltages steady around 0.8V
- Tested fuel trim levels, short term hover around +/- 3% at idle, long term hover around -4% (slightly rich, but not sure if this is enough to decimate my MPG)

I then took it to my mechanic and they also said the sensor readings are 100% normal, plugs are firing, etc. He also checked the exhaust and said he couldn't find a leak. He said he can try shots in the dark like fuel injector cleaner, induction cleaner, etc. but says it'll get expensive quickly.

I'm thinking of doing a ghetto smoke test with a vape, but wouldn't a vacuum leak show up on the fuel trim levels? I'm kind of stuck here.

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post #2 of 19 (permalink) Old 07-06-2019
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Are you calculating MPG manually or relying on the dash display reading? Is the car stock or are there any mods such as CAI, performance cams, forced induction, charge motion deletes, etc? How did the old plugs look? Did they look rich? Were they wet with fuel?


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post #3 of 19 (permalink) Old 07-06-2019 Thread Starter
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Are you calculating MPG manually or relying on the dash display reading? Is the car stock or are there any mods such as CAI, performance cams, forced induction, charge motion deletes, etc? How did the old plugs look? Did they look rich? Were they wet with fuel?
I calculated MPG manually. Filled up to full tank, did road trip, then filled up again to get litres used. No mods according to previous owner. I had mechanic change the plugs and they said they were seized (hadn't been changed since factory). Also said the old fuel filter had lots of dirty fuel in it.
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post #4 of 19 (permalink) Old 07-06-2019
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When you figured MPG, did you use liters or gallons? Also, how about miles or kilometers? I'd do some serious inspection to see if there is a fuel leak in the supply since you can smell a "rich" mixture. If your engine is actually running rich, you should have a code set and a CEL on. Also, a heavy foot on the gas pedal will lower your MPG.
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post #5 of 19 (permalink) Old 07-07-2019 Thread Starter
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When you figured MPG, did you use liters or gallons? Also, how about miles or kilometers? I'd do some serious inspection to see if there is a fuel leak in the supply since you can smell a "rich" mixture. If your engine is actually running rich, you should have a code set and a CEL on. Also, a heavy foot on the gas pedal will lower your MPG.
I use litres + kilometres. I thought it was just a heavy foot, so I went on a couple of hundred KM roadtrips where I used nothing but cruise control on highways (RPMs under 2000 most of the way), and my MPG was 9 at most. I've visually inspected for drips around the pump, injector, and spark plugs and found no leaks, my mechanic said the same.
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post #6 of 19 (permalink) Old 07-08-2019
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That makes your fuel consumption ~26L/100km, which means you'd go from a full tank down to 1/4 in just ~175km or 110 miles.


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post #7 of 19 (permalink) Old 07-09-2019 Thread Starter
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That makes your fuel consumption ~26L/100km, which means you'd go from a full tank down to 1/4 in just ~175km or 110 miles.
Yeah, that about right. I just finished a full tank with 250km on the trip reader. 24L/100KM...
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post #8 of 19 (permalink) Old 07-09-2019
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hmmmmm . . . obviously it is running crazy rich, the question is WHY . . .

Do you have a tuner and a laptop so you can datalog? If yes, here's a thought: you could contact "Lito" (Manuel Pazo) at [email protected] . . . he normally does remote tuning using datalog to fine-tune, but if you could send him a datalog, he might be able to figure out what is going on, and if it is a tune-related issue, he might be able to correct it. Obviously he would not do that for free, but his charges are very reasonable.
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post #9 of 19 (permalink) Old 07-09-2019 Thread Starter
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hmmmmm . . . obviously it is running crazy rich, the question is WHY . . .

Do you have a tuner and a laptop so you can datalog? If yes, here's a thought: you could contact "Lito" (Manuel Pazo) at [email protected] . . . he normally does remote tuning using datalog to fine-tune, but if you could send him a datalog, he might be able to figure out what is going on, and if it is a tune-related issue, he might be able to correct it. Obviously he would not do that for free, but his charges are very reasonable.
Its a 100% stock, no mods on it as far as I can tell it. The previous owner said there was no tune on it as well. He also said he would get between 10-15L/100KM, so I don't know what's going on here. I unfortunately don't have a tuner.
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Something doesn't add up here, and I'd be willing to bet that one of the upstream O2 sensors (driver's side is bank 2 sensor 1) is at fault.
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Does it coast freely? To get that kind of economy, it sounds like you've got serious drag like brake calipers stuck.

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post #12 of 19 (permalink) Old 07-10-2019 Thread Starter
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Something doesn't add up here, and I'd be willing to bet that one of the upstream O2 sensors (driver's side is bank 2 sensor 1) is at fault.
The voltages oscillate normally. Is there any other way to see if it's gone bad?

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Does it coast freely? To get that kind of economy, it sounds like you've got serious drag like brake calipers stuck.
How do I test this? For what it's worth my RPMs hover constantly between 1500-2000 when using cruise control on the highway (60-70MPH).
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The B2S1 O2 sensor hovering around .8v tells me its not functioning properly. It should be constantly adjusting the AFR hence why the B1S1 is swinging between 0~.9v constantly.

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Quote:
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The B2S1 O2 sensor hovering around .8v tells me its not functioning properly.
My thought exactly as per post #10.
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post #15 of 19 (permalink) Old 07-11-2019 Thread Starter
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Originally Posted by Jeremy Weigel View Post
The B2S1 O2 sensor hovering around .8v tells me its not functioning properly. It should be constantly adjusting the AFR hence why the B1S1 is swinging between 0~.9v constantly.
Both bank sensor 1s are oscillating. Sensor 2s are constant.

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