B3 3.3 Rough on initial start

[Pete Atkins]

Hi Guys
I've had a problem with my 2001 B3 3.3 since about April. I've had it in two local garages which I can normally rely on but they were unable to find the problem so I ended up taking it to my local BMW dealer where it has been for just over two months now and they are running out of ideas so any help would be greatly appreciated.
On start up from cold it misfires and nearly stalls but as soon as you put it in drive it drives as it should. It will start up fine all day long after the initial problems until I leave it over night and try again in the morning.
BMW initial diagnosis indicated a mixture adaption issue, the mixture was too lean. They replaced the crank case breather valve/numerous perished vacuum hoses/inlet manifold gaskets but the issue remained. They did a smoke test on the inlet side with no signs of a leak. Tested a donor air mass meter but it is still doing the same. fault code still indicates mixture too lean.
Thank in advance
Pete

[Charles]

Sounds like it might be a fuel starvation issue after the fuel system has depressurised overnight.

I had a similar problem and once I changed the fuel filter all was fine.

A cheap part and easy to change. If this does not work then you might want to check for leaks in the high pressure rail that feeds the injectors.

[greenelekta]

I was also thinking fuel pressure. Maybe also look at the fuel pump

[AG]

unfortunately I don't believe a BMW dealer these days is the best place to work on a 16 year old car let alone diagnose a problem.

Can't help with the faul though I'm afraid.

[shaziman]

Alot of E36's can do this. Do you turn the key straight to start the engine?

My solution to this is to turn the key to position 1, as if it was an old diesel and you are waiting for the glow plugs to go out, wait until you hear the fuel pump stop priming and then try and start.

Also, do the same but don't start, and see if it try's to prime again.

If so, you need a new fuel tank lift pump.

[rc944]

you really need access to inpa to get some decent diagnostics and live data... could be numerous issues but easy to throw parts at something like this and get nowhere....

i expect the above has been done but unless you have the fault codes and live data printed off its hard to be precise with the diagnosis

you can test fuel pressure on feed and return easy enough and buy the gauges relatively cheaply...

fuel filter cheap to buy and fix diy

did they rule out cam position sensors and lamba/02? they wouldnt be the obvious choices but if there are no vac leaks and no unmetered air entering the system, the issue is likely not air related but air/fuel mixture or fuel pressure

[Pete Atkins]

Thanks for all the useful info.
I am waiting for them to check the fuel pressure now, would you believe they had to buy a new test set! Fuel filter is getting changed.
will let you know what happens.

[MichaelC]

Maybe a red herring, but my B6 developed a rough idle recently but was driving fine until the revs dropped. I took the car in to MJF last week, it could have been a number of issues according to Mark, any of spark plugs, coils, but on hearing the chugging sound the engine was making thought it more likely to be a failed sensor or vacuum leak. On testing sensors he found one of the two cat sensors had failed. Duly ordered a new sensor and with luck that will be fitted on Friday and nothing else will be found to be the problem. I guess what I am getting to, after poor experiences with a main BMW dealer in the past with my old M3 go to an independent versed in BMWs.

[Oneball]

If it's doing it on starting from cold it's unlikely to be O2 sensors as it doesn't use them until its warmed up a bit. It runs open loop and the mixture isn't adjusted. Find out if they think it's running lean because the adaption values suggest so or if there's an error code for being too lean.

As it only does it when cold/left standing the two classics that cause this are a faulty temp sensor and a faulty fuel pressure regulator on the fuel rail