Replaced all plugs and coils, still getting 13mpg

My mechanics are having a hard time with this one. The first time they checked it they secured a nut that was loose on one of the coils and I was getting 20MPGs for a week then as soon as I filled up it was back to 13. Had all the plugs and coils done, cleaned gas lines and injectors twice, I'm driving like grandma and I'm still getting 13 MPGS. Any ideas?

I guess you have no CEL's ?

 

Have you cleaned the MAF sensor with a short spray of MAF sensor cleaner ?

 

Can you data log so we can view the data ?

 

Have you searched the local forums for someone who may help you ?

 

Sounds like you need to get the car to a Tuner so they can figure out what's not right.

No CEL

haven't cleaned the sensor

don't have means for data logging

I could take it to Subaru and see what they can find

haven't cleaned the sensor

don't have means for data logging

I could take it to Subaru and see what they can find

 

Post in your regional forum here. There's gotta be somebody local with a vag-com or tactrix cable that can help you log.

 

And if your mechanic is stumped, I'd take it to another mechanic before the dealer.

Is it stock? Are you burning any oil or coolant? Noticeable loss of power?

 

I would also check out WRXAtlanta.com - it is a great regional forum and there are a bunch of shops that are active on there that specialize on Subarus and I am sure they can help. I got my start with turbo charged Subies with that group and am still moderately active (even though I have since moved to Seattle...)

i had a pretty noticeable jump in mpg after PCV replacement. but I was nowhere near 13.

Yes, don't take it to the dealer. It's to old for them. $$$.

 

Check your local forums.

Seafoam, or GM upper intake cleaner. Remove throttle body, clean, replace... then suck one of those up through the BPV line.

Running really rich, need to figure out why the A/F ratio doing that. O2 sensor bad?

Has anyone checked the fuel pressure to make sure it's within spec?

The fuel pressure regulator could be bad.(pressure to high)

There are a massive amount of things that can cause problems like this, so guessing is frequent without having a log to use as a base for the evaluation. The CEL is only good for something that is definitely detected as wrong, but there are so many things that can be almost wrong but still be within specs that can cause trouble.

 

A random pick of stuff:

 

• O2 Sensors (any of them)
  
• MAF
  
• MAP
  
• Air leak
  
• Bad cam timing (jumped belt)
  
• Compression problem
  
• Fuel pressure
  
• Clogged cat
  
• Forgotten rag in the intake (or some animal that has built a winter nest there)
  
• Dirty throttle body
  
• Crank case ventilation problem
  
• Bad ignition coil
  
• Fuel theft
  
• Dragging brakes
  
• Plastic underbody acting as an air brake.
  
• Thermostat stuck open.
  
• Bad temp sensor.
  
• Wastegate problem.
  

Take your pick(s).

The only odd thing I notice is it's a little shaky when I stop after a cold start but after I drive it it goes away and the power delivery seems to be inconsistent. The car is stock although they said there was an aftermarket MAF sensor, haven't checked the fuel pressure or o2 sensor.

an aftermarket MAF sensor

 

ORLY!?

 

 

Is your intercooler broken?

Got the car tuned about 2 weeks ago, I told them I was having bad fuel economy and now it's worse, I'm getting 9MPG! However it has been very cold out which I heard affects mpgs and I've been buzzing around town more than usual. This week I've been going easy on it. Going to clean the MAF tomorrow and see if that helps.

i'm down to 17 mpg but it could be the snow tires and temps around 0 F. I get about 19 mpg in the summer with BBS and better rolling resistance tires. I thought my gas mileage was shitty until I read this. 9 mpg is clearly a problem. o2 sensors would be the first thing I would think about.

mweiner said it.

 

Aftermarket maf sensor? I'd only go OEM only for one of those.

 

Have you reset the ecu after new parts?

holy cow!!! some of you guys have it bad!

 

i would also caution you on the seafoam treatment in hopes that it will help anything. i did that on my car just before installing new plugs and oil change. i dropped an immediate 2mpg!!! i suspect it was the deposits that got cleaned out through the motor built up in the up pipe cat. im going to be removing that asap!!! this took me from 22.6 down to 20.4mpg.

 

i would not rule out a blocked catalytic converter, replace and or ditch those (at least U.P. even if only for turbo safety) and get new o2 sensors. probably problem solved.

 

since you say you got tuned are you able to log info now?

i'm down to 17 mpg but it could be the snow tires and temps around 0 F. I get about 19 mpg in the summer with BBS and better rolling resistance tires. I thought my gas mileage was shitty until I read this. 9 mpg is clearly a problem. o2 sensors would be the first thing I would think about.

 

holy cow!!! some of you guys have it bad!

 

i would also caution you on the seafoam treatment in hopes that it will help anything. i did that on my car just before installing new plugs and oil change. i dropped an immediate 2mpg!!! i suspect it was the deposits that got cleaned out through the motor built up in the up pipe cat. im going to be removing that asap!!! this took me from 22.6 down to 20.4mpg.

 

i would not rule out a blocked catalytic converter, replace and or ditch those (at least U.P. even if only for turbo safety) and get new o2 sensors. probably problem solved.

 

since you say you got tuned are you able to log info now?

 

I'm assuming the ECU should have the right settings after the tune. Got new o2 sensors with the UP/DP and the UP is catless. I'll get a cable if cleaning the MAF doesn't help or I'll just replace the stupid thing since it seems to be root of my problem. Ya it sucks I can't afford 9MPG car

Instead of hanging an assload of parts on that thing thru guesses, have you considered buying a handheld code reader with data parameter listing or more specific hardware for you car (ie: cobb ap or tactrix op and rom raider logger)?

 

You really need to check some of the onboard information, whether there is a code or not, you will likely find something that help. I wonder what your fuel trims are showing.

 

The aftermarket MAF is a huge concern in my book, there is a reason the OE part costs more. You don't happen to have your BPV vented directly to the atmosphere do you?

holy cow!!! some of you guys have it bad!

 

I agree - I think it sucks now when I'm approaching 30mpg, but I shouldn't complain compared to the reports I see. 17-18 seems to be decent, when I was driving my friends STi I was really nursing it for a try and got it up to 25.

 

But 9mpg is horrible - and definitely worth to check out in detail.

Whoever owned this car before me didn't take good care of it, the tires are really cheap Falkens and they're very noisy, there's dents, dings and scratches all over it, there's claw marks in the rear seats and a chewed up seat belt (dog).

 

Obviously he just got a cheap MAF so I'd rather replace it with an OEM one.

How much should I expect to pay for one? I'm seeing them anywhere from $170 to $350 which sounds like a little much.

Bummer, why did you buy it ?

There were only 2 in a 50 mile radius, this one was $8,800 with 98k miles and the other was $13k with 130k miles so it made more sense before I found out what was wrong with it. I test drove a few times and it seemed fine but I didn't pay attention to things like mpgs and shit tires.

Buy the MAF from someone like ...

http://www.fredbeansparts.com/subaru-performance-parts

 

Call them.

Nobody noticed the part about him getting it tuned?

 

Who tuned it and didn't notice an obvious problem with the car? How are you determining the MPG, the dash display?