Z3 Roadster (E36/7) Going through gas way to fast.

I have a 96 z3 1.9, and lately i have been getting some garbage numbers when it comes to miles per tank. I remember when i was younger me and my father use to be able to get at least 300-350 miles on a tank, but now, i am barely getting over 200. Do you guys know what this could be? I have read some guys saying that it could be the o2 sensor, but is that the only thing it could be? Could there be other things wrong with my baby to?
Any help is greatly appreciated.
-Jason

Originally Posted by Jortiz96

I have a 96 z3 1.9, and lately i have been getting some garbage numbers when it comes to miles per tank. I remember when i was younger me and my father use to be able to get at least 300-350 miles on a tank, but now, i am barely getting over 200...

Same car here.
So you are driving 200 miles, and find that it runs the 13.5 gallon tank down close to empty, so you refill with 12 gallons or so, and you divide the 12 gallons into the 200 miles, and get like 16 mpg?
If that is not exactly what is happening, please tell us what you are doing.

Yes, i will drive for about 200 miles on a full tank driving as conservative as i possibly can and still get these horrific numbers. The most i have ever gotten was about 230, and yes after the 200 miles i am filling up when i am dangerously low on gas.

Originally Posted by Jortiz96

... after the 200 miles i am filling up when i am dangerously low on gas.

Please fill up now, drive until below the 1/4 mark, and then tell us how many gallons it takes to fill up. We need to hear your actual miles per gallon which you have not said. The actual miles per gallon based on long division is an important number. Please wait until you have an actual figure.

I will share that I just only acquired my 1997 1.9L eight weeks ago. I was appalled at how fast the gas gauge sank after the 1/2 mark as I roared around town. But when I did the long division, the mpg came out to the high 20's.
17-Nov-12 32,754 275 10.8 25.4 City, suburb
25-Nov-12 33,024 270 9.3 29.0 City, suburb, rural, I-state
9-Dec-12 33,184 160 5.9 27.1 City, suburb

So please, do share your actual miles per gallon.

Yes sir, i will fill my gas tank when it hits below the quarter full mark and i will get back to you.

How many miles are on your air filter and spark plugs? What maintenance has been done in the last 30,000 miles?

Automatic or manual?

It's a long shot but is there a chance your engine coolant temp sensor is bad? Could be telling the engine computer to rich up the mixture because the engine is cold (when it isn't). Sensor is located on the side of the cylinder head on the left side just above the oil filter. Might be worth a scan to see what the sensor is reporting to the computer.

I think he should wait until he knows that his actual mpg is bad before replacing a costly O2 sensor or coolant temperature sensor.
If either of those were defective, they would trigger a warning, which he has not reported.
And since the coolant sensor likely reports to the temperature gauge through the ECU because the needle is buffered, a sensor problem would show up as low temperature on the gauge, which he has not reported.

If there is no record of air filter or plugs being changed, they should be looked at regardless. I had no records on my car, but also no problems. My air filter looked OK so I left it in. I looked at my plugs and they looked OK but were the wrong kind. They were the popular NGK BKR6EIX single electrode Iridiums, which NGK emailed me had the wrong resistance and tip (firing position) for the 1.9L. They recommended the dual electrode NGK BKR6EK, which I installed.

All good points which is why I'd put a scan tool on before replacing anything. The 1.9 Z3 uses a dual temp sensor; one for the temp. gauge on the dash and the other for the ECU, they're built into the same unit. This setup can allow the dash gauge to read properly even though the ECU is getting bad data. The sensor (P/N 13621703993) is readily available for under $15 and takes about 10 min. to replace if it is the source of the problem.

Sorry i took so long guys, i was away on vacation, Merry late Christmas by the way. But i finally filled up my tank, i went 214 miles on 10 gallons. And it is an automatic. And could you guys link me to scanner?

Harbor freight tools sells a good inexpensive scanner. I paid 120.00 for mine. But if your car isn't throwing any check engine coeds the scanner useless. If your o2 sensor is bad your car will also tell you. But that scanner does do live read outs. So you can read your maf and o2 sensors to see if they are working within spec

Here is the scanner I use
http://www.harborfreight.com/can-obd...ner-98614.html

Originally Posted by Jortiz96

... i finally filled up my tank, i went 214 miles on 10 gallons. And it is an automatic...

That 21.4 mpg might not be unusual if an automatic is driven on short hops or on aggressive-traffic commutes in cold weather in mixed city and suburban traffic on winter blend gas.

The first dealer fill up of my manual 1.9 was in November, and after gentle driving on 10-mile trips in suburbs and rural roads,when I filled up the car got 25.4 mpg.

After changing the plugs and putting in my favorite 93 octane gas, with gentle driving on 15-miles mixed suburban/rural trips, the mpg rose to 27.
I choose my driving routes for pleasure (easy joy rides out of traffic), and drive gently (old guy).

Hi Vintage. So, you are saying that you get better mileage if you use premium gas? That does make sense, especially with the gas they feed people in some states.
The driving mellow part I already do, most of the time!

Originally Posted by vintage42

That 21.4 mpg might not be unusual if an automatic is driven on short hops or on aggressive-traffic commutes in cold weather in mixed city and suburban traffic on winter blend gas.

The first dealer fill up of my manual 1.9 was in November, and after gentle driving on 10-mile trips in suburbs and rural roads,when I filled up the car got 25.4 mpg.

After changing the plugs and putting in my favorite 93 octane gas, with gentle driving on 15-miles mixed suburban/rural trips, the mpg rose to 27.
I choose my driving routes for pleasure (easy joy rides out of traffic), and drive gently (old guy).

The engine is built for high-octane gas. It performs best on 89 octane or higher. It can run on lower octane fuel, but the engine computer has to retard the timing to prevent knocking, which results in lower fuel economy. Generally, between high- and low-octane fuels, the loss of economy is greater than the difference in the cost of the fuel.

Usually BMWs have the octane requirement on the inside of the fuel door, but I haven't looked at my Z3 to verify.

I never buy anything other than 93 octane, or the highest possible at that gas station.

Originally Posted by rudyrov

... you are saying that you get better mileage if you use premium gas? That does make sense, especially with the gas they feed people in some states...

The second sentence does not make sense ;-) because premium is going to be the same in any state.

If an engine can take advantage of 93 octane, it will perform better than on lower octane. Performance includes more power from the same amount of gas, which translates to mileage. But the increase in mileage is very small.

Many engines, like my 2006 Scion xB, cannot benefit from anything more than 87 octane. Many other engines are rated at mid-octane 89, and some of those can either tolerate 87 or take advantage of 91/93, or do both.

It all depends on the engine's ECU and how much it is designed to retard or advance the ignition timing based on the inputs it receives from the knock sensor.

Whatever the case for a particular car, the Owners Manual will say. And our 1997 Z3 1.9L Owners Manual says that the engine can run alright on regular 87, is "rated" on premium 91, and that super premium 93 "will produce slightly higher levels of fuel economy and performance."

It is nice to have an engine that can run on any gas. If you want economy of cost and don't need the max power, use 87. If you want max power and don't mind paying an extra 20 cents per gallon, use 93.

Edit: I did some rough math comparing 87 and 93, assuming 93 was 20 cents and 1 mpg more. Ten gallons of 93 will go 10 more miles at a cost of $2.00 more. So it's about a wash on cost, while the 93 will make max power and fun.

Hi Vintage, Sorry if my second statement didn't register, I was referring to the gas "Blend" that different states use. I live in AZ and have been told by friends in the industry that for example our neighbor California uses very different gas blends than we do.
I assume that this also applies to premium because my friends have large engines and need the high quality gas to prevent detonation or pinging.

It is nice to have a gas that will give a little more when we want to have some fun, I do agree with that.

Originally Posted by vintage42

The second sentence does not make sense ;-) because premium is going to be the same in any state.

If an engine can take advantage of 93 octane, it will perform better than on lower octane. Performance includes more power from the same amount of gas, which translates to mileage. But the increase in mileage is very small.

Edit: I did some rough math comparing 87 and 93, assuming 93 was 20 cents and 1 mpg more. Ten gallons of 93 will go 10 more miles at a cost of $2.00 more. So it's about a wash on cost, while the 93 will make max power and fun.

Originally Posted by rudyrov

... I was referring to the gas "Blend" that different states use. I live in AZ and have been told by friends in the industry that for example our neighbor California uses very different gas blends than we do.
I assume that this also applies to premium because my friends have large engines and need the high quality gas to prevent detonation or pinging....

Blends may refer to seasonal or altitudinal or ethanol additives, and these will vary as suitable for their location and regulations. These blends are not a matter of quality and the octane(s) of the blends are maintained.

Some people do not like some blends and prefer plain straight gas. That may be possible in AZ. However, some states require gas with ethanol, some big cities require expensive "reformulated" gas to meet air quality standards, and in winter the refineries serving most of the country put in additives for better starting and moisture absorption. Here is Louisville, KY, we get all three blended in our gas. Those things affect the cost and energy content (mileage) but not the octane(s).

High quality gas is not a meaningful term, and not related to octane. I think the terms premium and super premium make people think they are better or of higher quality than regular. 87 and 93 octane gas do not differ in quality, only in resistance to knocking. Likewise the difference between straight gas and blended gas is not a quality issue.