The Random E46/ZHP Question Thread

[3LiterStraightSix]

What are the common causes of poor gas mileage? Today i put in 15 gallons after 302 miles and been getting 20-21 consistently, probably since i've had the car. Seem to remember getting mid 20s (24-26) in my previous zhp?

I'm in the same boat. Think my DISA is shot.

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[az3579]

What are the common causes of poor gas mileage? Today i put in 15 gallons after 302 miles and been getting 20-21 consistently, probably since i've had the car. Seem to remember getting mid 20s (24-26) in my previous zhp?

Really depends on a number of things. Do you have any codes?

Things that can cause poor mileage include:
* Intake leaks
* Clogged fuel filter
* O2 sensors nearing or surpassing 100k
* Bad MAF
* Spark plugs / ignition coils (unlikely though)
* Clogged catalytic converter (this one is my issue)

And the most important one:
Non-fuel efficient driving (driving style)

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[3LiterStraightSix]

Really depends on a number of things. Do you have any codes?

Things that can cause poor mileage include:
* Intake leaks
* Clogged fuel filter
* O2 sensors nearing or surpassing 100k
* Bad MAF
* Spark plugs / ignition coils (unlikely though)
* Clogged catalytic converter (this one is my issue)

And the most important one:
Non-fuel efficient driving (driving style)

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Interesting! I know for sure my o2 sensors are originals, at 137k. How do they cause bad mileage? Providing an incorrect Fuel/Air mixture?

And how do you determine that your Cat is clogged?

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[John in VA]

The winter fuel blend also result in fewer MPGs vs. summer blend. Nice that regular is $1.88 & premium $2.18 currently!

[az3579]

Interesting! I know for sure my o2 sensors are originals, at 137k. How do they cause bad mileage? Providing an incorrect Fuel/Air mixture?

And how do you determine that your Cat is clogged?

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Yes, the O2 sensors are very sensitive pieces of equipment. They help with adjusting for air/fuel mixture.

My car has clogged cats, with a serious loss of power/torque and a huge hit on fuel economy. Where I used to be able to easily hit 30-31 mpg highway, before O2 sensor replacement I struggled to hit 24, and a Prius can out-accelerate my car. Acceleration also feels funky; sometimes it's a little choppy. Here is a video I took on accelerating on to an on-ramp. 3rd gear, 45 mph to almost 75 mph took that amount of time.

https://youtu.be/MH4jsI4EOFo

Replacing my O2 sensors allows me to at least maintain 25-26 mpg, even with the clogged cat.

The winter fuel blend also result in fewer MPGs vs. summer blend. Nice that regular is $1.88 & premium $2.18 currently!

It doesn't make that much of a difference with a well running vehicle, in my experience.

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[NYRhockey]

Really depends on a number of things. Do you have any codes?

Things that can cause poor mileage include:
* Intake leaks
* Clogged fuel filter
* O2 sensors nearing or surpassing 100k
* Bad MAF
* Spark plugs / ignition coils (unlikely though)
* Clogged catalytic converter (this one is my issue)

And the most important one:
Non-fuel efficient driving (driving style)

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No lights on dashboard so no codes that I’m aware of. Car drives fine and the same way since i got it so just confused as to what it could be. Turns out there are various reasons for it. I’m pretty sure previous owner did spark plugs but o2 sensors I believe are original.


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[papa_g]

Which O2 sensors should be replaced? precat or post cat? Is it a pretty easy job?

[Sockethead]

Pre-cat. Yep it’s easy. They are right on top of the manifold

[ComradeNick]

The winter fuel blend also result in fewer MPGs vs. summer blend. Nice that regular is $1.88 & premium $2.18 currently!

Aw man I’m paying close 4 bucks a gallon for 91 octane. And that’s CA 91 which is diluted with ethanol -_-.


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[az3579]

No lights on dashboard so no codes that I’m aware of. Car drives fine and the same way since i got it so just confused as to what it could be. Turns out there are various reasons for it. I’m pretty sure previous owner did spark plugs but o2 sensors I believe are original.


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Well, you're local - we can do a drive cycle with me driving and I'll let you know what I think.

We have to discuss your lighting situation, by the way.

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