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

[MTD]

Hey guys, my 18is is consuming way too much, I do not know what's going on ... Lately I will always get 11 l/100 (Or 21.5mpg for the US folks). For the type of driving I do, and the engine that it is, it's way too much. 70% of my driving is in the freeway, in 5th gear at 2200/2500rpm. little traffic. Shifting at 3000rpm. Etcetc. I may do 1 or 2 agressive starts each tank of fuel, but thats it.

Given my type of driving, i should be getting much less fuel comsumption. I have no idea what it may be, since the car was revised and changed filters 1 month ago. Do you think?

[5Toes]

only 1 or 2 aggressive starts? lol I cant say the same :)

start with getting injectors rebuilt. does your car have a o2 sensor?

[MTD]

only 1 or 2 aggressive starts? lol I cant say the same :)

start with getting injectors rebuilt. does your car have a o2 sensor?

How do i check that?

[5Toes]

look at the exhaust piping for a plug coming off of it with some wires. its visible from the passenger side of the engine bay (if vehicle is LHD)

[uturn]

Check all your fuel lines. Pull the rear seat and remove the fuel pump access cover to see if it's leaking there. The driver's side in front of the rear tire at the fuel filter. The two lines below the brake booster up to the fuel rail.

[MTD]

thank you guys, i will try to check that. 5Toes, what am i supposed to check on the o2 sensor if i find it?

Any other tips?

[DER E30]

Maybe the Air flow meter? O2 sensor good start though. I'm not sure how to check it though.

When you cruise do you use only the little throttle body or do you go fast enough to use the big one? If you feel the pedal there's a spot where it gets a tiny bit stiffer. I almost always sit on the max opening of the little one without cracking the bigger under cruise...

I drive mine fairly hard when in the mood once its warm and I've never gotten less than 24mpg on a tank, I've gotten 32mpg on runs to school on the highway ~65-70mph with 4.10 rear so something is wrong with yours for sure. I'd say 27 average is normal for my driving habits

[MTD]

Maybe the Air flow meter? O2 sensor good start though. I'm not sure how to check it though.

When you cruise do you use only the little throttle body or do you go fast enough to use the big one? If you feel the pedal there's a spot where it gets a tiny bit stiffer. I almost always sit on the max opening of the little one without cracking the bigger under cruise...

I drive mine fairly hard when in the mood once its warm and I've never gotten less than 24mpg on a tank, I've gotten 32mpg on runs to school on the highway ~65-70mph with 4.10 rear so something is wrong with yours for sure. I'd say 27 average is normal for my driving habits

I never noticed what you are talking about on the pedal. I'm gonna check it later tonight. Anyways, if i only press the pedal to a certain point, ill get better mpg?

[5Toes]

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.

[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!

[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!

[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

[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]

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!

[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!