[pdxmike]

Looking for ideas on what else to go after to solve my MPG problem. 

 

My mileage has been atrocious during the entire year I've had the car. Granted, it gets daily driven, about 3 miles each way in moderate traffic. Lots of stoplights, lots of stop-and-go. It's pretty rare that I get any extended driving opportunities away from the city. 

 

On a good tank I get about 12-13 mpg. This last tank, I tried really hard to go extra light on the throttle and shift before 3K. 9.6 mpg- WTF. 

 

The car drives GREAT - good power, no hesitation, idles decently. Quantity and nature of exhaust at idle appears pretty much normal. I mean it has a little more exhaust at idle than your typical Subaru but that's to be expected. I'd be hard pressed to tell it was running richly if not for the MPG figure. 

 

I have put in a new O2 sensor, changed distributor cap/rotor/leads/plugs, tried non ethanol vs ethanol gas. Had the injectors cleaned by Witchhunter. Just checked fuel pressure which is spot on.

 

I read today that the Bosch universal O2 sensors need to be crimped not soldered so I'm planning to re-do that this week. I have looked at the Durametric graph and the O2 sensor seems to be oscillating normally. It's definitely getting a signal at the DME. So I'm doubting the O2 sensor has anything to do with it. 


As a baseline for comparison - on the same route, in my wifes Honda, I get 21 mpg. Vehicle is rated for 31 city. I do flog that car though.

 

Manual, 124K, all stock. Other ideas? Live with it? (Do NOT say drive the Honda...)

 

 

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[pdxmike]

#1 plug below - certainly doesn't look sooty. 

 

   

 

O2 sensor screenshot (steady throttle just above idle)

 

   

 

 

 

 

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[Spokayman]

Mike, have you taken the car on a longer drive (not in stop and go traffic) to see what highway-only fuel economy you are getting?


The reason I ask is because my wife has a 3 mile commute to work through stop and go traffic in her Acura MDX and we see about 12 MPG. Out on the highway, we easily see 22-24 MPG. Almost a 100% difference between city and highway.


Older vehicles with their less sophisticated warm up controls may produce even worse city vs highway numbers.


Also, have you checked your thermostat and/or verified that youre coming up to operating temperature quickly?

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[Waylander]

Check your blue topped temp sensor values, if it's out of whack it will be telling the ECU cold map while the O2 sensor is telling it your too rich,


A world in conflict


And I am not a fan of platinum tips in combustion chambers that were not designed for that burn pattern, cheap old Bosch WR7DC work as the engine was designed

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[pdxmike]

I agree that I need to get it out on a nice constant-cruise highway drive to get a comparison.

 

I thought a lot about this overnight and maybe the engine is fine and I'm simply expecting too much. The numbers are low but my daily drive is optimized to waste fuel. The coolant temp comes up to temp normally but my oil gauge indicates that my oil temp isn't getting to operating temp on my morning drive (ie, I'm still at 3-4 bar pulling into work). Couple that with the fact that I'm running 20w50 and its possible the car is just doing a lot of work. And - this last tank I filled at a place that seemed to have suspiciously cheap premium. Maybe there was a reason for that...

 

I will take a look at the DME temp sensor to see what it's reading. Good tip. The Durametric - which I grudgingly bought to address my airbag light - has turned out to be an incredibly useful diagnostic aid.

 

I'm not sure the iridium plugs are contributing but they're easy enough to swap out for a few tanks. I wasn't aware that the non-copper plugs could be a problem.

 

As a side note - the last tank on the Honda was 17.3 mpg. Even worse percent-wise than the 968. Indicating again that I should probably just be biking to work.

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[MCL968]

I noticed my MPG dropped when I went to the lower temp fan switch. Perhaps these engines like to run warm? I had the injectors cleaned, installed a K&N filter, and did a few other things (changed plugs, wires, etc.) and I expected an increase, instead MPG dropped.

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[Waylander]

Did you change your shoes for heavier ones?

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[Chris Vais]

You might try cleaning MAF sensor. My fuel consumption dropped dramatically as the MAF performance fell off. I eventually had to replace it. My typical mileage around town, low speed stop and go is between 15 to 18 mpg. Freeway driving 28 mpg or better. My yard stick is whether or not I can drive from the Bay Area to LA on a single tank.

 

I am inclined to think that your short commute drive may be the problem. The car may not be getting up to full operating temperature. Find a longer route to work. When my 968 was my daily driver, I found a longer route to work that let the engine get up to full operating temperature.

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[ds968]

Given the nature of the commute , I don't think 12 -13 mph is really all that poor of a gas mileage . It's a bit more that one would expect but not by so much so as to cause alarm. However, sub-10 mpg is a sign something may be off ; MAF is always suspect so just for safe measure cleaning it can't hurt.

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[pdxmike]

MAF cleaning is a good idea. I did it over the summer but we of course had a lot of wildfire smoke in the fall and it's easy enough to do. I should probably clean and oil the K&N air filter while I'm at it.

 

I can live with 12-13 mpg. Not expecting miraculous MPG, just want to have my engine running as well as possible.

 

Plan is:

 

plugs

re-crimp O2 sensor

check DME temp sensor

clean MAF

clean air filter

maybe lighter oil

tank of good gas

step on it on the highway

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[pdxmike]

Did a couple of the fixes and took it out for a Friday fun run - got 18.6 mpg over 130 miles. This was in no way an "economy" run. Hard to keep it under 4K on the twisties so Im sure I left a few mpg on the table.


I re-crimped the O2 sensor and the response seemed a little smoother on the Durametric. Honestly though it runs about the same and Im guessing my "problem" was just an artifact of driving short distances on a cold engine.

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