High fuel consumption - 520iA

[fo3]

My 525i was using about 14/100km when i got it, and it was worse in winter. Currently it uses 11.3l/100km when I use if for a school run to pick up my kid for a week - 30km round trip - though it gets worse if I only do short drives as they run really rich when cold - short trips only it uses just over 12l/100km average after a week.

What I did to fix it was:

The ECU temp sensor was broken - I fixed that for a small improvment
Thermostat was missing - fitted one (along with addressing vacuum hoses and leaks) this got it down to 12.7L/100km

Mine didn't have a mechanical fan as the previous owner fitted an electric thermofan but they had the fan cutting in very low. I set the thermostat to not switch the fan on until almost 1/2 gauge. This helps it warm up even faster on cold days and short drives. Small improvement I think.

Bought new injectors - this made a huge change with more modern, clean, better spray pattern and new style of injectors. That got it from ~12.5 to ~11.5l/100km.

[bjkbarann]

thanks bro

[bjkbarann]

Hello to everyone,


We were able to connect to the car's brain and read the error codes.
As engine codes;


50 Injector Code, but this was about the coil pipe I took care of it,
200 Lambda sensor I will either replace or clean this, waiting for your advice.


We also got the following error codes from the Gearbox;
104 DKT Temperature Information
105 DKT Throttle information


There are no problems with my transmission, I would be very happy if you share your experience. Thanks.

[Simmo2222]

You could put a vacuum gauge on the engine to try and diagnose a blocked exhaust. Stranger things happen, I had a neighbour that I had a feud with once and I emptied a whole can of expanding foam into his exhaust.

https://www.ericthecarguy.com/using-...to%2021%20INHG.

My M50 B25TU does about 7-10 litres per 100km in traffic but I have only had the car for about a month.

[bjkbarann]

Thanks for reply quick

I've tried with a lining spray before, but I couldn't find a leak

@simmo2222 i will try dude, thanks

[bjkbarann]

Any idea , for gearbox system?

[Simmo2222]

Hello to everyone,


We were able to connect to the car's brain and read the error codes.
As engine codes;


50 Injector Code, but this was about the coil pipe I took care of it,
200 Lambda sensor I will either replace or clean this, waiting for your advice.


We also got the following error codes from the Gearbox;
104 DKT Temperature Information
105 DKT Throttle information


There are no problems with my transmission, I would be very happy if you share your experience. Thanks.

DKT refers to throttle Position Sensor but 104 specifically refers to temperature received from the engine. This thread describes it and, as described by WhiskyChaser, you need to consider whether there is a complimentary fault on the engine temperature sender or, if not, it may be wiring between the two control modules. The 105 throttle information is basically the engine speed from the DME to the transmission. If that is coincidentally failing, I would strongly look for a wiring fault in the loom between the DME and transmission module, especially if you don't have a load of codes related to your engine.

https://www.bimmerforums.com/forum/s...r-Code-DKT-104

[bjkbarann]

Thank you for your answer man, my car is at 400,000 km and I think I need to replace all the temperature sensors. I will also change the tps sensor and try it like that. I'll rewrite it after trying it.

[Simmo2222]

OK, I would clear those codes and run it for a bit to see if they come back straight away or if they are more transient. You can always test all of the temperature sensors by measuring their resistance and compare against the listed values before junking any. Parts are expensive and there's no need to replace them if you don't have to.

[bjkbarann]

Friend, thank you for your return,
If you have it, can you share a file like a resistance chart?

[Simmo2222]

Have you got a copy of the Bentley service manual? Section 130-6 covers fault finding on the DME fuel injection including testing all temperature sensors and throttle position sensor.

http://www.mediafire.com/file/eyz2yd...anual.pdf/file

[bjkbarann]

thank you so much dude , i am very happy now, I will try all of them one by one , thank you

[bjkbarann]

I've made a lot of innovations and the fuel has finally run out, I wanted to share with you


I replaced the cam and crank sensors with the originals,
I thoroughly cleaned the oxygen sensor and installed it,
I had the exhaust leaks fixed and the last muffler replaced,
I fixed the brake booster hose,
Oil maintenance was done again,
Oil was leaking from the rocker cover gasket to the spark plugs, I changed them.
Temperature sensors checked, no problem.


After doing all these, my fuel dropped from 20lt/100km to 16km/100km, the traction and driving of the car changed noticeably. There is an aftermarket flowmeter left on it, I can't replace it with a 033 coded flowmeter, although the one on it works fine, but it is often said to replace it.


All 6 of my coils are original, how many thousand kilometers are their lifetimes?
I'm using bkr6equp ngk 4 prongs as spark plugs, but someone said, "Original coils won't have them, use double prongs" can you tell how accurate it is?

[circuit.heart]

Did not see any mention of engine compression in your diagnosis, so I'll bring that up - even if all your fuel, spark, and air delivery are working properly, 16L/100km is still bad and I'd be checking everything.

[bjkbarann]

I will have it done as soon as possible, do you have any other suggestions or advice?

[circuit.heart]

I think you've gone through most of the other stuff. Engine efficiency is:

Fuel delivery (amount, pattern, timing)
Spark delivery (timing)
Cams (timing and lift)
Compression ("is it there")
Airflow (intake restrictions, exhaust restrictions)
Friction (stuck seals, wrong oil, misalignments)

I'm sure I've missed some, but hopefully that's a helpful list to check off.

[bjkbarann]

how do i check them? bro

[bjkbarann]

I noticed yesterday that the throttle was not fully opened, when I adjusted the fuel consumption was around 13 liters, I guess it's not even harder to go down? I think it's solved.

[bjkbarann]

And of course I couldn't solve it, I know it's a long topic, but I want to try all the ways to solve it. I bought an original flowmeter and installed it, I did the flowmeter bellows, the oil maintenance, I checked the vacuum leaks again, but unfortunately my fuel consumption does not decrease below 16 liters. I'm about to hate the car. I guess I'll take the catalyst off and try that. There is nothing else I can do about the engine. I have read the live values, all the sensors are working, the responses are good, smooth.


by the way yesterday the car's advance setting is low, a mechanic said, and did a small software install, the car got better gas, I think the vanos played with the timings, it doesn't matter, the car provides good torque in the early revs.


I will write the fuel consumption again after the catalyst change and cancellation.


In the meantime, I would be very happy if you can write an idea that comes to your mind.

[Pink120]

Have you done anything regarding the lambda sensor? Deleting the cat won't do much, in fact, you should keep it, unless it is clogged.

[bjkbarann]

my friend, the only thing I need to answer is the catalytic. If you say why, I read the live values of the engine from the original device, all the sensors are working, there is no error code, there is no problem in the engine, there is no problem in the transmission, all wheels turn easily, but on my wheels 205/65/15 4 seasons michelin , the friend who opened the topic also has tires of the same size, I wonder if it is because of him.

[circuit.heart]

Installing a wideband O2 sensor into the exhaust (before the catalytic converter) is what I use to figure out if the car is setting the correct air-fuel ratios, but that is kind of a waste of money just for a little data.

The spark plugs can have small effects on fuel consumption, I did the best using 4-prong Bosch plugs (about 9-10L/100km). A clogged catalytic converter can have a large effect (adding resistance against the engine) so you could try checking that out, just take the car to a shop and replace them with straight pipe.

[bjkbarann]

yes, the catalytic has been cancelled, the car has gotten a little stronger, I will change the all season tires and write again. Thank you for the feedback.

[bjkbarann]

I fill the tank of the car every 300 km, average speed is 19 km / h, fuel consumption is 16 liters / km. Has anyone seen this fuel consumption with this average speed?

[dennistgt]

I fill the tank of the car every 300 km, average speed is 19 km / h, fuel consumption is 16 liters / km. Has anyone seen this fuel consumption with this average speed?

you're not alone
i have e34 1993 manual non vanos m50b20
fuel consumption 1L/5.5km (average)

no vacum leak (already smoke test)
new camshaft sensor
compression all 6 cylinder around 160 psi
rpm idle 750
new fuel pump bosch
new fuel filter
new air filter
oil follow bentley manual recommendation
new thermostat
new waterpump
new sensor for temp gauge (instrument cluster)

rich on cylinder 1 and 6


any ideas guys?