XSeries-forum

Hi All,

It's been a while since I've been on here which is a good thing as I've had minimal issues!

However, I thought I'd report something odd which I've been experiencing with the 4.8 N62 unit. When I first bought the 2nd hand car, I've never had a V8 before, only I6 petrol or diesel (3.0 E39 form) was the closest prior to that. Sitting and driving in the X5 seemed to me that there was more power available than those, but comparable performance due to the power to weight ratio. I enjoyed the power and noise well enough for me.

A couple of months ago I was doing the usual thing, as it seems to consume a bit of oil (might be PCV, or dread to think valve stem seals). Anyway I topped off the oil level as the car was asking for more at the end of the week, and come Monday started the car and it had a rough idle. Didn't think much of it and thought that it would settle down. I drove it somewhere and back, not to far and it still had a rough idle. Had a look under the bonnet and was horrified to see that I embarrassingly didn't put the oil cap back on properly, I guess causing a vacuum leak. Promptly wiped the small amount oil that had leaked out from the cap and replaced it back correctly. Started the car and the idle was as smooth as cream. Drama over. Remember to never do that again.

When I got into the car the next day and drove it, I slowly realised that the 4.8 engine under the bonnet had somehow turned into a beast . The low end torque was now immense, and it gave a massive grin each time I accelerated and it shoved huge amounts of torque to the wheels at low RPMs I've never experienced in this particular car. I could only explain it like it felt like a new engine.

Unfortunately the "repair" that I did on this car lasted a couple of weeks.

So that got me thinking. Before all of this excitement, I had already done the following on the car a couple of years ago for other reasons:
1. Usual services including air filters, oil filter etc. (done on a regular basis)
2. Changed throttle body harness (Symptom was horrendous idle hunting, limp mode)
3. Changed MAF sensor (replaced for same reason as above)

After the oil cap incident, I started watching Timm's BMW and repair information as he has some fantastic videos on the same engine, explaining things like Valvetronic, VANOS and the like. I had a closer look at this via INPA and it all seems to show that these systems are responding to throttle etc. One thing that I don't know might have a bearing is the DISA on the inlet manifold, as there isn't anything that I can see on INPA that diagnose that part of the system. I know the TU engine has a 2 stage system of inlet manifold controlled by servo motors on the back of the manifold and I don't know if any of my symptoms are related to this. I also managed to remove, inspect and clean one of the VANOS solenoids that I could get to. I didn't notice any dirt on it at all. There are no engine codes recorded, only a more recent one to do with the tank valve which is intermittent anyway.

By removing the oil cap for a while and replacing it seemed to put something back into place in the engine, causing it to behave as new. I haven't tried this again as it seems like a silly thing to do, not to mention the mess it can make. If anyone has any idea on what I should do next to try and improve the situation on a more permanent fix basis, it would make me very happy.

Possible ideas: VANOS solenoids, DISA server motors?


Cheers,
Rehan.

Hi All,

As an update to this, I have been occasionally getting a fuel tank ventilation valve error intermittently. say once a week. I didn't think much of it, as what's the worst that could happen if that valve isn't sending petrol fumes into the combustion chamber? Reading up more about it, it can regulate the fuel tank pressure if there is ambient temperature, or when fuel gets consumed there will be a vacuum. I was thinking if the valve isn't working that if a vacuum gets created, potentially it could be affecting fuel pressure causing a lean mix and therefore performance. Anyway I've got a part on order and will be fitting it in the next few days. Let's see if it makes a difference.

Cheers.