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Going through gas way to fast.

Z3 Roadster (E36/7) 
5K views 19 replies 8 participants last post by  vintage42 
#1 ·
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
 
#2 ·
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.
 
#3 ·
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.
 
#4 · (Edited)
... 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.
 
#8 ·
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.
 
#9 · (Edited)
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.
 
#10 ·
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.
 
#14 · (Edited)
... 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).
 
#12 ·
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
 
#16 ·
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.
 
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