My 18is is consuming way to much fuel...

[MTD]

Strange, try to put on an emission tester, maybe the lambda sensor has gone bad.
No engine fault codes?

Emissions should be ok, it was tested the other day when i took the car to get inspected and certified to drive another year, at the inspection center

no fault codes

[MVincken]

Strange, try to put on an emission tester, maybe the lambda sensor has gone bad.
No engine fault codes?

[MTD]

Hey, sorry i forgot to mention the results.
So, last saturday i filled up again... and the results where disappointing. 22.5mpg. 1mpg of improvement, but that's probably cause i did a trip with 70kms of continuous freeway.

This problem is really annoying, and is driving me to bankruptcy. Filling the thank every 7 days, with the gas prices here in europe is insane.

Other suggestions as to what might the problem be?

[word is bond]

Hey - any follow up on this? I've had a similar issue for while. Replaced the O2 sensor, but no difference...

[916e30Dave]

I'm interested to hear your results

Sent from my SM-N910T using Tapatalk

[MTD]

So the car is back from the mechanic. The temp sensor was gone, so he put in a new one. Let's hope that was the problem! Filled a tank today, i'm gonna report in a week or so when i fill again and get the mpg calculation!

Also, thanks for all the tips guys!

[5Toes]

^ no. there are two separate senders. one for the DME and one for the gauge.

[MVincken]

but when the coolant sensor is broken, won´t the coolant gauge also give a bad value?

[bmwman91]

Makes sense, good call on testing at the DME. If the temp sensor is anything like the sender, the wires by the connector might be prone to breaking.

[5Toes]

I dont think a bad coolant sensor will throw a CEL because as far as motronic knows its just -100 degrees outside and the engine is never warming up haha.

The sensors go bad with age. when you test them make sure to use the DME harness pins so you know the wiring in between is good. I used to be the type to test them at the sensor itself but thats actually harder than pinning out the dme!

[MTD]

Fingers crossed dude. Fingers crossed!

Just FYI, the OEM Bosch coolant sensor is $19 from RM European, and the aluminum o-ring is $0.05. Just so you know if the mechanic gives you a quote for a lot more $ or something.

Thank you, i'm in Europe so the prices might be different... No problem though, my mechanic is my uncle, he wouldn't charge me extra or anything!

[bmwman91]

Fingers crossed dude. Fingers crossed!

Just FYI, the OEM Bosch coolant sensor is $19 from RM European, and the aluminum o-ring is $0.05. Just so you know if the mechanic gives you a quote for a lot more $ or something.

[MTD]

Regarding the coolant temp sensor, wouldn't you get a CEL / fault code if it was open circuit or way out of range? I am actually having the same issue as the OP, have been for years. Damn near everything in there has been replaced in the fuel system, and sensors...BUT I have never replaced or tested the coolant temp sensor. I would assume that they just go open circuit when they die, but do they just start to drive farther and farther from the expected value instead? That would explain why my mileage has just gotten worse and worse over the years, and nothing that I have replaced has made a difference.

Sorry to thread-jack OP. I hope that you figure it out, because maybe it will help me too!

No problem man, your post is actually helpful. My mpg is also getting worse wverytime, so if the only thing you didn't check is the coolant temp sensor that must be it

[MTD]

MTD pull off the intake boot and check it for cracks! once the intake boot is off the throttle body internals will be visible and DER E30's post will make alot more sense lol. I could try to explain it better but I think once you see it yourself you'll completely understand. but if your driving habits have not changed then this is certainly not the problem.

My top 3 things to check would be:
1. fuel pressure, get a gauge on there and observe what it does while underway. 43psi at idle and under wide open throttle it should bet closer to 50-53. If the pressure is too high that would cause the bad fuel economy

2. coolant temp sensor. located under the intake manifold (usually blue in color). Get a digital multimeter and open the glovebox up. Pull off the ceiling panel and take the harness connector off the DME. You can find the pinout online at e30zone (http://www.e30zone.net/e30zonewiki/i...s#Motronic_1.7). test the resistance between pin 78 and 34 (ground). should be 1-3000 ohms stone cold and much lower after a good drive with the engine warmed up. If this sensor is broken the engine will run rich all the time because it thinks it is stone cold even when warmed up

3. oxygen sensor. if your car has one its probably really old. if your fuel economy were down a couple mpgs it could be the o2 sensor but since its a considerable change your problem probably isnt from this. they arent too expensive to change and it would be a good idea to change it anyways.

good luck!!

2.

Thank you so much for this! Unfortunately I don't have the tools to check this myself, but I will tell my mechanic everything on the post so he can check it for me!

[bmwman91]

MTD pull off the intake boot and check it for cracks! once the intake boot is off the throttle body internals will be visible and DER E30's post will make alot more sense lol. I could try to explain it better but I think once you see it yourself you'll completely understand. but if your driving habits have not changed then this is certainly not the problem.

My top 3 things to check would be:
1. fuel pressure, get a gauge on there and observe what it does while underway. 43psi at idle and under wide open throttle it should bet closer to 50-53. If the pressure is too high that would cause the bad fuel economy

2. coolant temp sensor. located under the intake manifold (usually blue in color). Get a digital multimeter and open the glovebox up. Pull off the ceiling panel and take the harness connector off the DME. You can find the pinout online at e30zone (http://www.e30zone.net/e30zonewiki/i...s#Motronic_1.7). test the resistance between pin 78 and 34 (ground). should be 1-3000 ohms stone cold and much lower after a good drive with the engine warmed up. If this sensor is broken the engine will run rich all the time because it thinks it is stone cold even when warmed up

3. oxygen sensor. if your car has one its probably really old. if your fuel economy were down a couple mpgs it could be the o2 sensor but since its a considerable change your problem probably isnt from this. they arent too expensive to change and it would be a good idea to change it anyways.

good luck!!

2.

Regarding the coolant temp sensor, wouldn't you get a CEL / fault code if it was open circuit or way out of range? I am actually having the same issue as the OP, have been for years. Damn near everything in there has been replaced in the fuel system, and sensors...BUT I have never replaced or tested the coolant temp sensor. I would assume that they just go open circuit when they die, but do they just start to drive farther and farther from the expected value instead? That would explain why my mileage has just gotten worse and worse over the years, and nothing that I have replaced has made a difference.

Sorry to thread-jack OP. I hope that you figure it out, because maybe it will help me too!