Bad MPG

[keeler]

I did search but couldn't find any answers.

I'm getting between 10-15 mpg. I have replaced the plugs, wires, air and fuel filter, o2 sensors, boost leak test came back good, compression was good, new tps, new iac, seafoamed the car a couple times, cleaned butterfly valve, idles around 1300rpm which it always has. It just randomly started running rich. No particular reason why. I'm running stock fuel setup, stock boost, and a few minor mods. It's running pretty rich as I can smell it but I've found no leaks of anything. Anyone have any ideas? I'm at a lost and it's killing me driving 40 miles to work everyday. The car runs fine otherwise and has been doing it for about 3 weeks.

 

[sureshot971]

have you tried running to a autozone to see if you are running any codes?

 

[keeler]

have you tried running to a autozone to see if you are running any codes?

Not pulling any codes and I haven't seen a CEL. Also couldn't find an vac leaks.

 

[want_a_gsx]

are you venting the bov?

 

[sureshot971]

I highly doubt venting a bov can affect the MPG that much i mean yea you run a little rich with most vented bov's but could it really affect it that much? ( not trying to sound like a prick i really wanna know ### i vent mine)

 

[sureshot971]

You said you had replaced both 02 sensors right? ### both of mine had gone out and my MPG dropped to 10-15 like yours.

 

[-TunedDSM-]

hmm, tried the ecu?

 

[keeler]

are you venting the bov?

I am however I have hooked it back into the intake and ran it for a couple days and reset the ecu with no luck.

hmm, tried the ecu?

Also have used a spare one

 

[sureshot971]

man seems like you have tried everything i am stumped also, did you do any mods and then this happened shortly after or immediatly after?

 

[keeler]

man seems like you have tried everything i am stumped also, did you do any mods and then this happened shortly after or immediatly after?

Nope, I haven't done any work on the car for about a month except clean it....I always monitor my gas mileage and was getting about 22 normally. Then I filled up noticed I got about 19. So I figured it might be a fluke but then my next tank was about 15mpg.

 

[mhuffman]

I did search but couldn't find any answers.

I'm getting between 10-15 mpg. I have replaced the plugs, wires, air and fuel filter, o2 sensors, boost leak test came back good, compression was good, new tps, new iac, seafoamed the car a couple times, cleaned butterfly valve, idles around 1300rpm which it always has. It just randomly started running rich. No particular reason why. I'm running stock fuel setup, stock boost, and a few minor mods. It's running pretty rich as I can smell it but I've found no leaks of anything. Anyone have any ideas? I'm at a lost and it's killing me driving 40 miles to work everyday. The car runs fine otherwise and has been doing it for about 3 weeks.

Have you checked:
- Exhaust restrictions?
- Mass airflow sensor?
- Base timing?
- cam timing (t-belt skipped some teeth...)?
- fuel system incl. fuel pump and fuel injectors?

 

[twocanewayne]

Yhea like mhuffman said check fuel system injector could be stusk open, timing could be off (to advanced). Also check 1g recalls , 2g has a leaky f/p recall.

 

[Eric_7810]

Ive got a similar problem. Can an O2 sensor go bad without triggering a CEL?

 

[keeler]

- Exhaust restrictions 3 inch, turbo back about 2 months old
- Mass airflow sensor - just tested
- Base timing - Normal
- cam timing (t-belt skipped some teeth...) - looks good, to spec
- fuel system incl. fuel pump and fuel injectors - Freshly cleaned with new pump, and filter.

I have new 02 sensors first thing I replaced.

 

[mhuffman]

Ive got a similar problem. Can an O2 sensor go bad without triggering a CEL?

Yes, O2 sensors can start to fail and not throw a code, especially if your trips are short.

 

[Isphius]

If you got the cheap bosch sensors, I used to use those on my supras and have had a few out of box or very short failues with those. Its cheaper to get the real one, than replacing the bosch one 5 or 6 times, If you did buy that one. Take the o2 sensors back to the shop you got them, and see if they will give you new ones. Just tell them your getting an o2 code still so they must be bad, and see if that fixes it.

 

[VanIsleDSM]

just turn up your boost to burn up that extra fuel

 

[shaunman1979]

If your knock sensor fails it can pull timing and cause you mpg to go way down.

 

[Eric_7810]

If his knock sensor failed he'd be on here complaining about spooling up to max boost and going no where. A failed knock sensor will completely disable a car from making power under boost. I'm stumped at this one though

 

[dsmdragon]

ok like he said The knock sensor will max your boost and that's about it besides runing like crap. If there isn't a check engine light on the autozone can't check if there are any codes on your ECU. But If this is a turbo Gs-t or GsX we are talking about then it might have to do with the ECU. The number one reason why more gas/fuel is put into a motor is becuase the ECU or something going to the ECU like tps,air temp, or o2 sensor is telling your car you don't have enough to do the job. So in this case you have replaced everything thing besides the brain of the veichle. becuase I don't thinck your air temp sensor is doing all this hell to your car. also The more mods you have on your car the less mpg you get, but you probably already knew that. if you have the stock caty. converter on your car then that really isn't the o2 sensonr that goes out first. normally it's the first bank or up strem sensor doing all this problem. You can try moving the o2 to another location in you down pipe if it is to close to the turbo exhaust elbow, but that might just be stupid to do at first.
So I'll give you a little brake down of what sensors you might want to check or parts that might be working improperly.
first mass-air-flow sensor
second TPS
third Air temp sensor
fourth crank and cam sensors
fifth check to see if you have replaced the fuel filter in the last 50000m
6th o2 sensors like bosch o2 sensors suck. you would be better of buying ngk or denso o2 sensors. they go for cheap on ebay and they work. just read-up on which one will work for you.
last if none of those problems work then it would be the ECU, becuase all of which I just listen work for the ECU.
(Autozone can test your sensor for you unless they are stupid and don't know there store. I work there i should know.
let me know if that helps

 

[vr4gasmtt]

Not really answer to the thread, but.... How do you reset the ECU, I unplug my negative battery terminal for about 15 mins, and when I jump backin my car and start it up, the clock in the cd player is still the same and hasn't reset it self.

 

[keeler]

I've tried all of the above and I've replaced the ecu with a known good to no avail. I guess I'll go over the injectors one more time and see what I find. I'm just at a lost and I won't have a wideband until the end of december

 

[sureshot971]

Maybe you should bring your car into a shop and see what they got to say?

 

[dsmdragon]

yeah take the car to a shop if you Have done all you can to try and fix the problem. It might have something to do with the internals of the car and I don't know if you have the tools or no-how to tell that for sure. so Let them do it for you man.

 

[da_reeseboy]

Wouldn't a bad injector cause it? If it didn't close, just kept draining fuel, that would cause it possibly, wouldn't it?