BMW 120D idling issue - smooth running test?

[thatdude]

Hello everyone,

My wife's BMW 120D (2005 model, pre-DPF, automatic) has a bit of an iffy idle, and on occasion appears to "miss-fire" (which I know isnt possible but is what it feels like). It runs ok when not idling, and the idling issue is far more pronounced when the engine is in "D" and under some load when stationary. I have a small hunch that it could a a leaking injector - the car has been checked for codes (although no dash warning lights), and did have some thigns but nothing that would cause rough running. The fuel filter has been replaced, and it's improved a little but not eradicated the issue. It's also more prominent after a run at good speed (e.g. national speed limit), for say, 1 - 2 hours.

I'm aware of diagnostic software that can be used via the OBD port that can show the injectors in real time, which I understand is part of a "smooth running" test. can anyone of you recommend a workshop in the north london area that might be able to do this? I'm looking to get diagnostics run first, before going forward - I have some hypotheses on the cause (I also want to check the coolant temps via the secret menu). I'm not sure it's the EGR, and the exhaust is clean, even when giving it some heavy right foot.

Any help / advice is appreciated. If an injector is leaking, I;d like to get it sorted soon.

Thanks

Edited by thatdude on Monday 28th July 11:02

[anonymous-user]

You need someone with the BMW diagnostic tools, either the OEM INPA/EDIBAS or a quality aftermarket equivalent. With these you can look at the smooth running fuel quantity adjustment for each cylinder, and that will show up any dodgy injectors. It's also very easy to do a "leak back" check on the injectors to see if one (or more) are out of tollerance.

[thatdude]

Ok, thanks for that. I'll have to ask around...as far as I am aware, the issue doesnt throw up an error code or give any dashboard warning lights - I've only gained this hypotehsis from scouring BMW-specific forums and saw some images a guy posted doing a test on his BMW showing the relative levels od fuel each injector was supplying

[anonymous-user]

thatdude said:

Ok, thanks for that. I'll have to ask around...as far as I am aware, the issue doesnt throw up an error code or give any dashboard warning lights - I've only gained this hypotehsis from scouring BMW-specific forums and saw some images a guy posted doing a test on his BMW showing the relative levels od fuel each injector was supplying

Eventually, the idle fuel quantity adaption (smooth running) will set a non MIL code when they get too large, but you will need a specific BMW code reader to spot / determine this as it is not an EOBDII mandated (< #1000) code.

The simple "return pipe off into a bucket" test is worth doing to determine if you have an excessively leaky injector, which can cause idle misfires.


If you don't want to buy a leak off test kit, you can buy the little plastic elbows and short length of return pipe from BMW and they are pretty cheap (iirc ~£10) which enables you to "T" into each injector return spill pipe without letting any air into the system.

[thatdude]

Thanks M_T for your input - I'll explore these options and see what information I can gain