Fuel Trim Error Code issue

[inkey$]

Hi all.

During a long run a few weeks ago, I got an EML appear after around 150 miles into the journey. After scanning it was telling me I had fuel trim levels being exceeded on bank 1. Fast forward another 200 miles and the EML appears again, this time bank 2.

Im now experiencing the EML light again and its telling me both banks are running lean. On occasion the scan would also tell me I had a misfire. Replaced the fuel tank breather valve too as I was getting another code related to that.

Any ideas? I dont appear to have any vacuum leaks and all pipework looks intact. I had thought it may be O2 sensor related, but on both banks? Other than the EML the car seems to be running fine.

 

[ChrisD]

The usual cause of a lean running condition is air leaks. If you're 100% certain that you have eliminated this potential cause then you should then look at the fuelling. It looks from the data that the O2 sensors are at least switching and not showing faults so I'd trust the information they are providing and look elsewhere for now. I'd start with a fuel pressure measurement to check that the fuel pump and pressure regulator are working ok.

 

[ChrisD]

Also, particularly if this fault is only appearing after replacing the purge valve then check that this has been installed correctly as it is connected to the intake and could be a source of unmetered air.

 

[inkey$]

The usual cause of a lean running condition is air leaks. If you're 100% certain that you have eliminated this potential cause then you should then look at the fuelling. It looks from the data that the O2 sensors are at least switching and not showing faults so I'd trust the information they are providing and look elsewhere for now. I'd start with a fuel pressure measurement to check that the fuel pump and pressure regulator are working ok.

Thanks for the response. Was happening before the purge valve change, so not linking it to that. The lean running defintley pointed me towards a vacuum leak in the first instance but all the usual suspect pipes seem in perfect order and passed the smoke test. Fuel pump and pressure regulator are a good call. As you say, the sensors seem to be operating fine.

 

[NZ00Z3]

The adaption mixture Multiplicative (long term fuel trims) are 14% and 12%. This is saying you are running lean all of the time.

Read: https://www.e46fanatics.com/threads...how-to-diagnose-p0171-p0174-and-more.1284608/

 

[inkey$]

The adaption mixture Multiplicative (long term fuel trims) are 14% and 12%. This is saying you are running lean all of the time.

Read: https://www.e46fanatics.com/threads...how-to-diagnose-p0171-p0174-and-more.1284608/

Thats a really handy article. Reads to me that my issue is either ’lazy’ O2 sensor(s) or the fuel pump is on its way south.

 

[NZ00Z3]

There is a Schrader valve on the fuel rail. Check the fuel pressure with the key in position 2 and the engine off. It should be 50 PSI +/- 3 PSI.

 

[Lee]

Check the purge valve is shutting also check the brake booster line non return, had sticky valves causing a leak recently on these. Blow down and you shouldn't be able to.

When you say don't appear to have any vacuum leaks how have you proven this ?

 

[colb]

Smoke test usually finds air leaks, whats the Maf doing in live data can you see it reacting with throttle movement, if thats misreporting it would have an effect on the fuel trims. Also check the pre cat exhaust sensors in live data to see if they are ranging up and down the voltage scale. The ECU will be comparing what they are picking up compared to the airflow passing through the Maf and calculating the fuel trims required.

 

[inkey$]

Smoke test usually finds air leaks, whats the Maf doing in live data can you see it reacting with throttle movement, if thats misreporting it would have an effect on the fuel trims. Also check the pre cat exhaust sensors in live data to see if they are ranging up and down the voltage scale. The ECU will be comparing what they are picking up compared to the airflow passing through the Maf and calculating the fuel trims required.

Just checked the MAF live data and it’s working as it should be on idle and at revs. Next stop, pre cat sensors. Ordered a small endoscope too so I can check for tiny leaks as I don’t have a smoke tester.

 

[colb]

More positive way to find air leaks rather than an endoscope would be to spray carb cleaner or brake cleaner around the engines intake and vacuum hoses to see if the engine note changes if it sucks the mixture in through any holes or splits.

 

[inkey$]

More positive way to find air leaks rather than an endoscope would be to spray carb cleaner or brake cleaner around the engines intake and vacuum hoses to see if the engine note changes if it sucks the mixture in through any holes or splits.

I'll do that too

 

[t-tony]

Once you can identify where the leak is by using Carb. cleaner etc. then an Endoscope could be useful.

Tony.