Guys
Just my 2cts on my journey to sort out fuel trim issues just in case it helps other people.
This will be valid for the M54B30 engine maybe other M54 like the 2.2
Note that I was not getting any lights or any codes, car was running fine, good power across the rev range although maybe slightly higher fuel consumption. There will be more comprehensive guides on other forums on the M54 on how to troubleshoot this but I am going to try to make this short and informative.
It all started while checking the fuel trims on INPA - Values - Lambda
It will give you three values there - Lambda integrator - Additive values and multiplicative values for the two banks
Normally after driving the car for a while those values stabilise and you get a number on the additive (which has mainly an effect on idle or low load fueling) and multiplicative (higher loads fueling) - the lambdaintegrator is an average of the lambda readings but it helps also with the troubleshooting and this value changes all the time - you need to check this values when the car is running and at operating temperature (closed loop)
My particular problem was that I was getting higher than expected multiplicative values. Ideally those should be zero but anything below 2.5 is considered very good - I was getting 4 to 8. Additive were close to zero.
That prompted me to start investigating - the troubleshoot sequence that I recommend people with fuel trims or codes for lean values - positive values on fuel trims / car is trying to inject more fuel to compensate for more air - is the following -
- Check for vacuum leaks - ideally with a smoke tester - normally problems are around the intake boots, good practice to replace anyway, also the small vacuum tubes that come from the F fitting on the upper intake boot perish, it can also leak from the valve cover gasket, the DISA o ring or the DISA itself if diaphragm ruptured, the PCV valve, the dipstick tube area, the vacuum port blanks at the rear of the intake and the pipes that go to the fuel filter / pressure regulator (underneath the car) operated by vacuum and also for cars with a flap on the exhaust that's also vacuum operated and you might have leaks - if you have vacuum leaks and they are big they will throw engine codes, if they are small you will see the lambda integrators go positive at idle (after you do an adaptations reset on INPA F4 then reset adaptations lambda) - but when you accelerate the lambdaintegrator values decrease (meaning the leak is small and has less relevance once the engine uses more air) - small leaks will give you positive values on both multiplicative and additive but it will be more significant on additive.
If you are confident you have no vacuum leaks
- Check your fuel delivery system - starting with measuring the fuel pressure (50 PSI) should stay there at idle, under load etc and if you have the opportunity check;clean your injectors and maybe replace your fuel filter which also contains the fuel pressure regulator in these cars - if the pressure is not good or the injectors are not delivering the right fuel then the ECU will start increasing the additive/multiplicative values to compensate and add more fuel.
if this is all good
- Check your MAF and lambda sensors - the fuel mix is controlled by the ECU with the readings from the MAF and the lambda sensors when at temperature in closed loop - if your MAF is no good (my case) or the lambdas are not measuring properly you will get odd fuel adaptations.
Best way to tell what's what is to check what the adaptations tell you - if you get good values on one bank but not the other chances are one of the lambdas is had- you can also see the LAMBDA values in INPA and figure out what's going on as the values should be comparable on both banks.
If values are comparable on the LAMBDA readings then chances are the culprit is the MAF - the MAF is difficult to test properly but it can be done - some people say just test the value at idle - mine was reading OK at idle if a tiny bit lower than expected - that's why my additive values were OK - but it was apparently under reporting when cruising or at load that's why this test is not definitive- this took me a while to figure out. - if you want to test MAF properly you will need to use a data logging software like TESTO and then plot the MAF readings on a curve with RPM and see if those values first are linear and then see if they align with the expected volumetric efficiency for your engine on the RPM range (there's charts and explanations on the web on how to do it) - I didn't test further my MAF and I just took a known working one (from a car with good fuel trims) and tested in my car - straightaway values came back to normal after a fuel trim adaptation reset and stayed within spec.
If you want / need to replace your MAF I can recommend the VDO one (continental) part number 13627567451 5wk96132 this is for the 3.0 - they are the OEM supplier and the one I got worked flawless - note that there are COUNTERFEIT MAFs around and they won't work buy from a reputable seller - the one I got cost around 130 GBP and it was definitely genuine - there are other MAF from reputable brands (HELLA etc) but why chance it on something this important for the engine and its performance.
Sorry for the long post but I thought this might help someone in the future
Just my 2cts on my journey to sort out fuel trim issues just in case it helps other people.
This will be valid for the M54B30 engine maybe other M54 like the 2.2
Note that I was not getting any lights or any codes, car was running fine, good power across the rev range although maybe slightly higher fuel consumption. There will be more comprehensive guides on other forums on the M54 on how to troubleshoot this but I am going to try to make this short and informative.
It all started while checking the fuel trims on INPA - Values - Lambda
It will give you three values there - Lambda integrator - Additive values and multiplicative values for the two banks
Normally after driving the car for a while those values stabilise and you get a number on the additive (which has mainly an effect on idle or low load fueling) and multiplicative (higher loads fueling) - the lambdaintegrator is an average of the lambda readings but it helps also with the troubleshooting and this value changes all the time - you need to check this values when the car is running and at operating temperature (closed loop)
My particular problem was that I was getting higher than expected multiplicative values. Ideally those should be zero but anything below 2.5 is considered very good - I was getting 4 to 8. Additive were close to zero.
That prompted me to start investigating - the troubleshoot sequence that I recommend people with fuel trims or codes for lean values - positive values on fuel trims / car is trying to inject more fuel to compensate for more air - is the following -
- Check for vacuum leaks - ideally with a smoke tester - normally problems are around the intake boots, good practice to replace anyway, also the small vacuum tubes that come from the F fitting on the upper intake boot perish, it can also leak from the valve cover gasket, the DISA o ring or the DISA itself if diaphragm ruptured, the PCV valve, the dipstick tube area, the vacuum port blanks at the rear of the intake and the pipes that go to the fuel filter / pressure regulator (underneath the car) operated by vacuum and also for cars with a flap on the exhaust that's also vacuum operated and you might have leaks - if you have vacuum leaks and they are big they will throw engine codes, if they are small you will see the lambda integrators go positive at idle (after you do an adaptations reset on INPA F4 then reset adaptations lambda) - but when you accelerate the lambdaintegrator values decrease (meaning the leak is small and has less relevance once the engine uses more air) - small leaks will give you positive values on both multiplicative and additive but it will be more significant on additive.
If you are confident you have no vacuum leaks
- Check your fuel delivery system - starting with measuring the fuel pressure (50 PSI) should stay there at idle, under load etc and if you have the opportunity check;clean your injectors and maybe replace your fuel filter which also contains the fuel pressure regulator in these cars - if the pressure is not good or the injectors are not delivering the right fuel then the ECU will start increasing the additive/multiplicative values to compensate and add more fuel.
if this is all good
- Check your MAF and lambda sensors - the fuel mix is controlled by the ECU with the readings from the MAF and the lambda sensors when at temperature in closed loop - if your MAF is no good (my case) or the lambdas are not measuring properly you will get odd fuel adaptations.
Best way to tell what's what is to check what the adaptations tell you - if you get good values on one bank but not the other chances are one of the lambdas is had- you can also see the LAMBDA values in INPA and figure out what's going on as the values should be comparable on both banks.
If values are comparable on the LAMBDA readings then chances are the culprit is the MAF - the MAF is difficult to test properly but it can be done - some people say just test the value at idle - mine was reading OK at idle if a tiny bit lower than expected - that's why my additive values were OK - but it was apparently under reporting when cruising or at load that's why this test is not definitive- this took me a while to figure out. - if you want to test MAF properly you will need to use a data logging software like TESTO and then plot the MAF readings on a curve with RPM and see if those values first are linear and then see if they align with the expected volumetric efficiency for your engine on the RPM range (there's charts and explanations on the web on how to do it) - I didn't test further my MAF and I just took a known working one (from a car with good fuel trims) and tested in my car - straightaway values came back to normal after a fuel trim adaptation reset and stayed within spec.
If you want / need to replace your MAF I can recommend the VDO one (continental) part number 13627567451 5wk96132 this is for the 3.0 - they are the OEM supplier and the one I got worked flawless - note that there are COUNTERFEIT MAFs around and they won't work buy from a reputable seller - the one I got cost around 130 GBP and it was definitely genuine - there are other MAF from reputable brands (HELLA etc) but why chance it on something this important for the engine and its performance.
Sorry for the long post but I thought this might help someone in the future