Worsening MPG and Raw Fuel Smell

Singlefin · 11-13-2008, 03:41 PM

Guys,

I am experiencing something with my modded 04 FXT and was wondering if anyone has an idea where I should begin to troubleshoot. The MPG on the car is deteriorating, I used to get about 19-20mpg combined, now it's probably down to around 15mpg. I also noticed that there is often a strong raw fuel smell after I park the car. This had been going on for maybe about 3-4 weeks now.

At first I thought it was my wife's driving style, as the car is now her daily driver to and from work, about 20 mile round trip. And I am sure she doesn't push the car like a maniac. I used to drive it for my daily commute and get better mileage.

FYI, the car is heavily modified, i.e. bigger injectors, Aquamist meth kit, vf39, Perrin TMIC, Perrin EBCS, TBE, Cobb AP ver1, protune, the whole works.

What do you think? a bad CAT? O2 Sensor(s)? if these go bad, I should get a CEL but the only CEL I get from time to time is P0245, which has something to do with the boost control solenoid, and I think this CEL might be caused by some wiring issue with my Aquamist or a failing ECBS unit. Also checked the tire pressure and are ok.

How about a stuck injector? but I would hear back fire if something like that happens or the car would idle crapy right?

Any input is greatly appreciated...

Thanks

Firdaddy · 11-13-2008, 05:28 PM

if you had a stuck injector, the car would hesitate to start, or even a leaking injector.. this is for two reasons.. 1. the cylinder of the stuck or leaking injector would be loaded up with fuel not not want to fire form being flooded.. and 2. you would have zero fuel pressure when you turned the key... so if you can rule out hard starting, you have ruled out the injectors..

secondly.. the boost control solenoid.. do you have a boost gauge on the car? is it running normal levels of boost? do you hear any boost leaks? if so the maf could be calibrating for a certain amount of air, stick in the appropriate amount of fuel and make it run uber rich.. similar to a problem with a vented bov.. this could cause the horrible gas mileage and since its running rich, the unburnt fuel could be loading up in the cat/ exhaust and cause that smell

third.. the o2 sensor scenario.. while this is highly likely and possible to create your problems, i'd think you'd throe a c/e light by now.. if the o2 sensor goes bad and the ecu detects it, it will run the car pig rich to try and save the motor against any damage from running lean, since the ecu is controlling the fuel purely by the input of the maf and map sensor..

this is truly all speculation, however i'm just trying to help you start to rule things out.. if it was me, i'd stick in the boost gauge, go for a drive, get on it and see what kinda boost it runs vs. the target boost

g00fy · 11-13-2008, 06:07 PM

I've got a similar problem, i don't think my gas milage has dropped, however when i first start the car and sometimes when i get in the car after it's been parked for a while i smell fuel inside the car. I can't find a leak anywhere. I hope one of us can figure it out or i hope someone on here has already figured it out. Oh and my car is also pretty heavily modded: Short ram intake, full exhaust, headers, TGV deletes, big injectors, 20g turbo, etc... Also the problem only seemed to have come about with the cold weather.

Firdaddy · 11-13-2008, 06:25 PM

Quote:

Originally Posted by g00fy

I've got a similar problem, i don't think my gas milage has dropped, however when i first start the car and sometimes when i get in the car after it's been parked for a while i smell fuel inside the car. I can't find a leak anywhere. I hope one of us can figure it out or i hope someone on here has already figured it out. Oh and my car is also pretty heavily modded: Short ram intake, full exhaust, headers, TGV deletes, big injectors, 20g turbo, etc... Also the problem only seemed to have come about with the cold weather.

under cold weather starts, the ecu dumps extra fuel in the engine since the air is more dense.. and from that reason and because you have larger injectors.. thats just might be par for the course, especially if you are catless... just exhaust smell coming in.......

to the op though.. i forgot.. whens the last time you cleaned your maf???

Real Lyte · 11-13-2008, 06:42 PM

I know on SF's its common for the fuel neck to corrode excessively because the shield perpetuates it, not sure on your models but that's a start

Another thing is the vapor box (the actual name escapes me) that recirculates fumes, the pipes that lead into that can get disconnected when doing exhaust work easily.

BAC5.2 · 11-14-2008, 05:18 AM

Does it go away once it gets warm?

Check hose clamps going to the fuel rails, and then check the injector o-rings. If you reused your stock o-rings when you swapped injectors, then that is a likely candidate.

TheEmrys · 11-14-2008, 08:13 AM

Don't overlook an easy one. Has the fuel filter failed? I had this happen before. Not on a Subaru, but I had to stop at a Wal-Mart and buy a generic Fram one.

Singlefin · 11-17-2008, 12:18 PM

I think the problem may be intake temperature related as Firdaddy suggested. I had just moved from Los Angeles to New Jersey, and the winter air temperature rarely dips below 50s in LA. But air temp has steadily decreased over the past month and is now mid-40s to mid-50s here in NJ. So, it may be that the ECU is dumping more fuel given the colder intake air temp and since I have 740cc injectors, it may explain running richer than I had been tuned for while out in LA. I hadn't noticed this problem before while I was living in LA, so the probability of temp/fuel compensation seem higher than other potential issues.

The car starts smoothly every time so it doesn't appear to be a stuck injector. Fuel filter was also replaced about 4 months ago and doesn't appear to be leaking. Boost levels appear to be normal, although I haven't heard any leaking noises, I have yet to check all the piping. The stock injector O-rings were replaced with the ones that came with my Deatschwerks injectors and the problem doesn't seem to go away after the car warms up. I smell the fuel after driving home and parked in the garage, it is especially noticeable when I walk around the tailpipe of the car, there's also noticeably more soot than before around the edges of the tailpipe.

I haven't cleaned the MAF in maybe 8-10 months, but it's worth a shot so I'll try it this week. Will report back if anything changes...

Thanks

Firdaddy · 11-17-2008, 04:56 PM

if you have fuel smell in the exhaust and more soot than normal, i'd bet anything its running rich...also was there a notable change in elevation between your old home and new one? it takes way less fuel at higher elevations to run the same amount of boost.. i'd just say your tune is way off if its running rich... if you have a wideband o2 unit i'd check the af/r's.. also since its so rich, your o2 sensors are most likely covered in soot as well... so .. clean the maf.. see if it still persists, if not time for a tune

11-13-2008, 03:41 PM	#1 (permalink)
Singlefin Join Date: Feb 2006 Location: was SoCal now NJ Posts: 225 Gallery: 0 iTrader: 4 / 100%	Worsening MPG and Raw Fuel Smell Guys, I am experiencing something with my modded 04 FXT and was wondering if anyone has an idea where I should begin to troubleshoot. The MPG on the car is deteriorating, I used to get about 19-20mpg combined, now it's probably down to around 15mpg. I also noticed that there is often a strong raw fuel smell after I park the car. This had been going on for maybe about 3-4 weeks now. At first I thought it was my wife's driving style, as the car is now her daily driver to and from work, about 20 mile round trip. And I am sure she doesn't push the car like a maniac. I used to drive it for my daily commute and get better mileage. FYI, the car is heavily modified, i.e. bigger injectors, Aquamist meth kit, vf39, Perrin TMIC, Perrin EBCS, TBE, Cobb AP ver1, protune, the whole works. What do you think? a bad CAT? O2 Sensor(s)? if these go bad, I should get a CEL but the only CEL I get from time to time is P0245, which has something to do with the boost control solenoid, and I think this CEL might be caused by some wiring issue with my Aquamist or a failing ECBS unit. Also checked the tire pressure and are ok. How about a stuck injector? but I would hear back fire if something like that happens or the car would idle crapy right? Any input is greatly appreciated... Thanks __________________ Sleepers of the World Unite!

11-13-2008, 06:07 PM	#3 (permalink)
g00fy Join Date: Mar 2006 Location: Lake Hopatcong, NJ Posts: 1,041 Gallery: 0 iTrader: 2 / 100%	I've got a similar problem, i don't think my gas milage has dropped, however when i first start the car and sometimes when i get in the car after it's been parked for a while i smell fuel inside the car. I can't find a leak anywhere. I hope one of us can figure it out or i hope someone on here has already figured it out. Oh and my car is also pretty heavily modded: Short ram intake, full exhaust, headers, TGV deletes, big injectors, 20g turbo, etc... Also the problem only seemed to have come about with the cold weather. __________________ 20G powered 05XT CGM w/fully built IPT 4EAT

11-13-2008, 06:42 PM	#5 (permalink)
Real Lyte Join Date: Sep 2007 Location: Southern Tier, NY! Posts: 882 Gallery: 0 iTrader: 0 / 0%	I know on SF's its common for the fuel neck to corrode excessively because the shield perpetuates it, not sure on your models but that's a start Another thing is the vapor box (the actual name escapes me) that recirculates fumes, the pipes that lead into that can get disconnected when doing exhaust work easily. __________________ SF '99L A/T (Mine) & '95LS Legacy A/T (hers)

11-14-2008, 05:18 AM	#6 (permalink)
BAC5.2 iMod Contributing Member Join Date: May 2006 Location: Gaithersburg, MD Posts: 7,356 Gallery: 0 iTrader: 3 / 100%	Does it go away once it gets warm? Check hose clamps going to the fuel rails, and then check the injector o-rings. If you reused your stock o-rings when you swapped injectors, then that is a likely candidate. __________________ The Aggressive™ -- You don't know about it. 1998 Forester S - Big brakes, Big Tires, 5-gears.

11-17-2008, 12:18 PM	#8 (permalink)
Singlefin Join Date: Feb 2006 Location: was SoCal now NJ Posts: 225 Gallery: 0 iTrader: 4 / 100%	I think the problem may be intake temperature related as Firdaddy suggested. I had just moved from Los Angeles to New Jersey, and the winter air temperature rarely dips below 50s in LA. But air temp has steadily decreased over the past month and is now mid-40s to mid-50s here in NJ. So, it may be that the ECU is dumping more fuel given the colder intake air temp and since I have 740cc injectors, it may explain running richer than I had been tuned for while out in LA. I hadn't noticed this problem before while I was living in LA, so the probability of temp/fuel compensation seem higher than other potential issues. The car starts smoothly every time so it doesn't appear to be a stuck injector. Fuel filter was also replaced about 4 months ago and doesn't appear to be leaking. Boost levels appear to be normal, although I haven't heard any leaking noises, I have yet to check all the piping. The stock injector O-rings were replaced with the ones that came with my Deatschwerks injectors and the problem doesn't seem to go away after the car warms up. I smell the fuel after driving home and parked in the garage, it is especially noticeable when I walk around the tailpipe of the car, there's also noticeably more soot than before around the edges of the tailpipe. I haven't cleaned the MAF in maybe 8-10 months, but it's worth a shot so I'll try it this week. Will report back if anything changes... Thanks __________________ Sleepers of the World Unite!

11-13-2008, 05:28 PM	#2 (permalink)
Firdaddy Join Date: Nov 2008 Location: Dickinson TX Posts: 54 Gallery: 0 iTrader: 0 / 0%	if you had a stuck injector, the car would hesitate to start, or even a leaking injector.. this is for two reasons.. 1. the cylinder of the stuck or leaking injector would be loaded up with fuel not not want to fire form being flooded.. and 2. you would have zero fuel pressure when you turned the key... so if you can rule out hard starting, you have ruled out the injectors.. secondly.. the boost control solenoid.. do you have a boost gauge on the car? is it running normal levels of boost? do you hear any boost leaks? if so the maf could be calibrating for a certain amount of air, stick in the appropriate amount of fuel and make it run uber rich.. similar to a problem with a vented bov.. this could cause the horrible gas mileage and since its running rich, the unburnt fuel could be loading up in the cat/ exhaust and cause that smell third.. the o2 sensor scenario.. while this is highly likely and possible to create your problems, i'd think you'd throe a c/e light by now.. if the o2 sensor goes bad and the ecu detects it, it will run the car pig rich to try and save the motor against any damage from running lean, since the ecu is controlling the fuel purely by the input of the maf and map sensor.. this is truly all speculation, however i'm just trying to help you start to rule things out.. if it was me, i'd stick in the boost gauge, go for a drive, get on it and see what kinda boost it runs vs. the target boost

11-14-2008, 08:13 AM	#7 (permalink)
TheEmrys Join Date: Oct 2007 Location: Northern Colorado Posts: 311 Gallery: 0 iTrader: 0 / 0%	Don't overlook an easy one. Has the fuel filter failed? I had this happen before. Not on a Subaru, but I had to stop at a Wal-Mart and buy a generic Fram one.

11-17-2008, 04:56 PM	#9 (permalink)
Firdaddy Join Date: Nov 2008 Location: Dickinson TX Posts: 54 Gallery: 0 iTrader: 0 / 0%	if you have fuel smell in the exhaust and more soot than normal, i'd bet anything its running rich...also was there a notable change in elevation between your old home and new one? it takes way less fuel at higher elevations to run the same amount of boost.. i'd just say your tune is way off if its running rich... if you have a wideband o2 unit i'd check the af/r's.. also since its so rich, your o2 sensors are most likely covered in soot as well... so .. clean the maf.. see if it still persists, if not time for a tune

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