Missfire with 528 e39

[gav2612]

I am having major missfire issues with my 1996 e39 528 runabout.

I had a vaccum leak around the inlet.
I replaced the inlet manifold gasket but there still sounds like a leak someplace else around the inlet that I cant find either visually or by spraying carb cleaner about.
Two of the coils appeared to be faulty, so have been replaced along with the spark plugs.
I have had out the ICV and cleaned and lubricated it

The car still has major issues. It will run great when cold, but after running for 10 - 15 minutes, it will missfire and occasionally stall at lights, once hot it will then be very hard to restart. A few questions.

1. Would a vaccum leak cause this? I would imagine a vacuum leak would also make the car run equally as bad when cold as hot?

2. Could it be a bad o2 sensor? I believe the o2 readings arent used by the ECU until the car reaches operating temperature?

3. Any other ideas?

I have a code reader, but cannot find any obd port inside the car. Not sure if euro 96 e39 would have an OBD 2 port?

Many thanks for any input

Gavin

[HRG]

My local BMW dealer read out all the faults on mine and told me what they were along with a parts list for £30. Money very well spent IMO.

[Welsh]

If they do have diagnostic sockets it will prob be a round socket under the bonnet.

[gav2612]

I have been doing a bit more research and it seems that a intake leak would probably be worse at idle than through the rev range. Bar the odd time the car stalls, it idles very steadily at around 700rpm with no fluctuation. The missfire is then evident under load through the rev range only when the engine is hot. The fault performs consistently 10 - 15 minutes after starting the car from cold, and will then be present until the car cools down again where it disapears until the car has heated up again

[phelix]

Although the oxygen sensor input isn’t used by the ECU until the engine’s up to temp they don’t usually cause a big problem as they only fine tune the mixture and expect the basic air fuel ration to be pretty close. You can always try unplugging it to see if there’s any change.

You might still have a bad coil that plays up when it gets warm/hot. How did you identify which coils needed to be replaced? Hard starting doesn’t tie in with a single bad coil though.

Is your valve cover gasket secure with all bolts in place and tight? Use a 2 or 3 foot section of garden hose as a stethoscope to find the source of any hissing sound. Works a treat but the neighbours may think you’re mad. I found a loose fixing nut that way.

Getting the codes read can be very useful as the car does have a fair bit of self-diagnostic capability.

[gav2612]

Thanks Felix,
Was quite tricky to find faulty coils, as it is mostly under load it missfires. Disconnected one at a time when it did missfire at idle and tried to idetify that way. I am waiting on an adapter to fit the 20 pin BMW port in the engine bay, to connect to carsoft. with the car being 1996 it doesnt have an OBD2 port. It is just very strange that it runs well when cold and is almost like clockwork on missfiring when warmed up. I initially thought it was still a vacuum leak causing the problem, but I would have thought that would have been as bad or worse when cold? Thats what made me think of the 02 sensor or temp sensor as they should obviously start working at a set temperature. Will disconnect the 02 when warm to see if that makes a difference(I presume the ECU will just revert back to default readings if disconnected?)
Gavin

[phelix]

Yup, the ECU will default no adjustment if the oxygen sensor is disconnected. It may log a fault code as well.

The temp sensor is certainly one to check - if the ECU thinks the engine's still cold when it's actually hot it'll probably be running rich. What does the temp gauge say? (Although there may be multiple temp sensors.)

Next time the car's idling hot and running rough try this: rapidly pump the brake pedal. This allows unmetered air into the engine via the brake booster. If the car's running rich the idle speed will increase and if it's running lean the idle speed will decrease. Normally you should get a slight drop in idle speed.

[gav2612]

Thanks Phelix,
More confused now than ever. Tried disconnecting O2 sensor. No noticeable difference. Rapidly pumping the brakes provided only a very small drop in revs. Opened the bonnet while it was running rough again to try and listen for vacuum leak with stethescope, still sounds like it is from round the inlet manifold, no noise from valve cover. Could possibly be from the CCV under the manifold? strange thing is, switched car off, started again straight away first time and then ran smoothly again straight after. This shouldnt happen if it was relating to the temp sensor or 02 sensor as the car was still hot. I am now back to possibly another faulty coil or electrical fault. Will need to get it diagnosed, at least find out which cylinder is missfiring(if it is just one)and try and swap out the coil