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Discussion Starter · #1 · (Edited)
I drove a 97 900 Talladega for 10 years, and loved it.
Two weeks ago I sold the Talladega and bought a 9-5 wagon to accommodate my growing family. 110,000 kms, looks great.
I live in a residential neighborhood in downtown Toronto. Lots of stop signs and stop lights.
Still, I was shocked to see how much gas this car was using. When I refilled the first quarter tank, I averaged just over 10 mpg. No check engine light. I took it back to the dealer, and they adjusted the spark plug gaps, and swapped out the mass air flow sensor, and said they were then getting around 19 mpg on the SID display driving on city roads around the dealership (which are much longer blocks, far fewer stops or lights). They sent they even sent out two drivers with different driving styles.
Took it home, filled it up again, and averaged 12.5 mpg on the first quarter tank.
Am I doomed to get horrendous mileage, or can something be done here? (It's 15% worse gas mileage than my 16-year old Talladega was getting).
I haven't taken it out on the highway to see how it fares - I thought I'd do that tomorrow night.
Thanks for any help!
 

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Discussion Starter · #3 ·
I am using actual numbers. I'm sure the trip odometer works fine, so I'm relying on that and the actual amount of gas I'm putting back in the tank when I fill up.
 

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How long are your average city trips? If you never run the car long enough to get it out of open loop, or if you have a faulty O2 sensor, you'll have horrible mileage and the car will run ridiculously rich.

If everything checks out, and you're still getting bad mileage even on longer trips, start checking for physical issues like a leaking fuel connector at the rail, or a small leak in the tank.
 

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Do the typical fuel system cleaners, check for boost/vacuum leaks.
If you're a car guy that likes to tinker, you should have an OBDII logger.
Torque is a great android app. pair it with a bluetooth OBDII plug, and you are armed with the most information possible.
You can watch O2 sensor voltage cycles, engine temps, ignition advance, long and short fuel trims as well as many, many other things.
This will help you fix your lower MPG's without guessing and spending lots of unnecceasry $$.
 

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I have an 08. Likely your sid is displaying wrong numbers. They are not too reliable. Use actual numbers.
I am not sure about the newer 9-5s, but all my SID MPG readings (9-5, 9-3, 900) have been almost dead on and off by perhaps a tenth.
 

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Buy some silicone vac hose and check all the lines. Specifically the bitch to get at one between the fuel pressure regulater and wherever it goes. (forgot) It is only about 2 inches long and was the most brittle on my 07.
 

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Discussion Starter · #9 ·
Thanks for all the replies and suggestions. I have some more questions.
I took the car out for an hour on the highway at 75 mph and the SID was pretty steady around 27 MPG, which was encouraging... and it pretty much lines up with how much gas I seem to have used (I didn't fill up to confirm, but the fuel gauge has been pretty accurate so far).
Mike S - most of my city trips are 10-20 mins, in stop and go traffic, with some idling. I'm not really getting the point of an engine running in open loop. But more importantly - is there any way to get it to closed loop faster? Would letting the car warm up for 5-10 mins before taking it out be helpful?
Craig - I get that having an OBD2 would give me info like O2 sensor voltage cycles, engine temps, ignition advance, long and short fuel trims (still getting clear on what those all mean) - but I'm not clear how it will help fix the lower MPG? Is it about quicker and more precise identification of where the problem is? Also, do you have a recommendation for an OBD2 logger and bluetooth OBD2 plug?
Thanks,
Daryl
 

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I can answer all: 27mpg highway is still pretty low. I have a short commute, and my SID reads a pretty consistant 24mpg mixed. part of this is because of tune, and part because of how I drive, but if you're not driving a modied 9-5, you should expect 29-31mpg highway. (maybe more)

Open loop and closed loop are just the different operating climates of the ECU.
Closed loop is when the ECU ignores Everything but the oxygen sensors. The ECU is making adjustments to fuel trims based soley on the feedback from the Oxygen sensors to reach 14.7:1 air-fuel, or Stoichiometric...
This is typically in operating situations of low-risk. (full operating temp, no load, low RPM, low vehicle speed, little-to-no throttle) these are situations where the ECU thinks it's safe to run less fuel because there's no chance of engine damage. This is your idling, your highway cruising, and really low throttle imput (no boost) for the most part, the ECU can compensate for bad sensors, but there are things like exhaust leaks and some vacuum leaks that can cause fuel trims to go way-off. for instance, a leak in the exhaust before the first o2 sensor will allow clean air in, and trick the sensor into thinking the car is running lean, so it will add fuel to compensate. This will cause MPG's to be off. A failing oxygen sensor could be cycling slowly, or reporting incorrect information back to the ECU. again, it'll throw off fuel-trims.

Open loop, the ECU is reading the multiple sensors to calculate the air mass entering the engine and fuel accordingly. This mode ignores the oxygen sensors and fuels accordingly to reach a target Air-flow ratio, which has been user-entered (factory entered).
This is where you ECU is when your car is too cold, too hot, is loaded (boost/acceleration) is in high MPH, or >20% throttle position. This is what tuners tune.
The down-side is that while reading the air temps, the inlet pressure, the engine temp, knock, and barometric pressure if any of those sensors are reading incorreclty, it throws off the air-fuel ratios and causes the car to run poorly.(too rich/too lean) depending on the sensor, it can cause the ECU to run in open loop when it's not supposed to, and THEN run poorly, on top of that.

Having the scanner allows you to see the sensors operate, and if you know what you're SUPPOSED to see, you can tell if a sensor is reading incorrectly. I will post the plug I bought from ebay in a few minutes. Gotta get back to work.

here's more info from a mustang forum. the basics apply.
Definition of Closed Loop vs Open Loop
 

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Im also from Toronto, my stage 3 aero gets about 9-10 L/100km on the highway on cruise and 11-12L/100km city but i always drive fairly aggressively, the best things i can think of, is check for boost leaks, fuel filter, bad plugs and a failing 02 sensor. I also had the temp sensor slowly fade causing the car to think it was warming up constantly and that wastes A LOT of gas.

When was the last time you had a CEL and what was it?
 

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Discussion Starter · #12 ·
I haven't actually seen a CEL yet, but I've only had the car 2 weeks. The fuel level sensor failed two days after I bought the car, but that's since been replaced. When your temp sensor was failing, how did you know?
 

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I haven't actually seen a CEL yet, but I've only had the car 2 weeks. The fuel level sensor failed two days after I bought the car, but that's since been replaced. When your temp sensor was failing, how did you know?
I had a CEL come up, and the temp gauge would go cold while driving at random with heating or no heating. my level sensor is off ever since i replaced my pump :(
 

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Discussion Starter · #14 ·
Thanks, Craig.

You wrote: "This is where you ECU is when your car is too cold, too hot, is loaded (boost/acceleration) is in high MPH, or >20% throttle position. This is what tuners tune." What/who are the tuners you refer to? Does that mean that tuners can adjust engine setting so the car gets into closed loop faster (and stays there) for city driving?

Also, when you have a chance, could you please post the details on the OBD2 logger and bluetooth OBD2 plug? (Are these two separate devices?)
 

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Before tuning, I'd have someone with a Tech 2 check the coolant temp sensor and the intake air temp sensor.

Back in the old days (gets pipe, settles down in rocker)...coolant systems were a bit more primitive and used to develop scale and deposits just from the interaction of the chemicals and the metals. Sometimes the thermostat would stick open and make the car take much longer to warm up, keeping the car in open loop a lot longer. Might be a good idea to also check/replace the thermostat.
 

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Is your temp gauge at half? If not, you probably have a bad thermostat.

If it is at half, you could still have a bad thermostat. Tech II can read actual temperature. Where modern temp gauges on the dash peg right to the middle as long as the temp is within some predefined range.

Don't even think about tuning or even google "tuning" until you get everything running right
 

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Also worth trying, next time you go on a long trip, try clearing your SID or calculating your mileage to see where it is.

If your trips are short enough that you never get the car warmed up, yes, you will burn more fuel, but probably not to the point of 12 mpg.
 

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keep in mind warming up the car to get into "closed loop" is going to use gas just sitting there which will defeat the purpose of doing it.

also remember it has the two options for a reason so you dont cause major engine damage.

do you drive agressively light to light? with acceleration to fast speed each stop and go? or just simple driving.

stop and go city is the absolute worst on MPGs and will be very low if that is all you do. also the grade of fuel you use will make a difference.
 

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you can buy lots of obd scanners. When I had my Volvo and DSM, I used an old m105 palm pilot and obdgauge.com's software.

Now, I use the Android app "torque" and a bluetooth adapter. I'm able to look at all the car's stuff on my phone. You could use a tablet, too. and I'm pretty sure there's an Ios version, too.

This is the OBDII adapter I purchased. People have said it's a knock-off and whatnot, but mine works perfectly. Amazon.com: Super Mini ELM327 V1.5 OBD2 OBD-II Bluetooth CAN-BUS Auto Diagnostic Tool for Windows XP, Vista, Win7, OSX and Android: Car Electronics
...something about 1.5 not being a real version or something. Either way, mine always connects, and always shows everything I need it to.
 

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Discussion Starter · #20 ·
The city driving we do is just regular stop and go; not usually in a hurry to get to the next stop sign. And I also don't believe that would (on its own) cause 12 mpg. We put in premium fuel (which is 91 here in Canada).

I just ordered this OBD2:
 
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