E39 530i not running well

[bramley]

Hi folks.

Right, car is a 530i touring, 2003, with 107k.

A couple of months ago the yellow engine light came on and my local garage used their Snap-on scanner which came up with intermittent lambda sensor fault. The live values were apparently all ok, so they reset it and off i went.

Then it came back on, so they've scanned it again today and I was expecting to have o2 sensor(s) replaced, but it's thrown up more fault codes now (haven't had any new parts yet).

They were:
- 02 Bank 1 and Bank 2 deviation (iirc)
- misfires recorded on cylinders 2, 3, 4, 5 and 6

The car has a noticeable misfire at idle, speed is ok but feels a bit rough. At one point (while I was watching) all 02 readings went to 0.00 briefly while engine was running, then back to normal. The live readings the rest of the time were all ok apparently, all doing what they should do. The garage suggest maybe it's an electrical gremlin and suggested going to a specialist (they've been helpful, done their best and not charged me. As they aren't experts on BMWs they suggested going elsewhere would end up being a cheaper solution than them replacing parts willy-nilly).

Trawled bmwland forums and others have had similar symptoms which turned out to be a dodgy vac hose. Others found coil pack issues, but my misfires were recorded against cyls 2-6 inclusive - though that was after 10 mins running. After 2 mins it was just 4 and 6 i think.

If anyone has any suggestions or advice I'll be very grateful, I guess I'll have to go to bmw but would like to get help from people on here and at least go to BMW armed with some knowledge.

Thanks!

P.S. Oil pressure light still flickers at idle, they were going to pressure test the engine but haven't yet. Only mention it in case it's all connected to another fault.

[sparkythecat]

I'm not usually an advocate of going to the dealers, but in this instance, I would.
They should be able to diagnose it quicker than anyone else.
OK, you'll pay a premium, but you could spend a lot of time and money exploring other avenues to know avail

[bramley]

I think that's sound advice. Hopefully the proper BMW diag machine can be more specific than the snap on one at my local garage. Thumbs up to my local garage though, they've been very good.

Just registered online for Cotswold BMWs discount scheme for cars over 4 yrs old, then I'll book it in.

Cheers

[Gallen (BPH)]

2 suggestions from me:

MAF Sensor (unplug it - if the remedies then get a new one, if not, then its not that).

Cam shaft position sensor?

[bramley]

Bit of an update, I got the INPA diagnostic software running my laptop, and also the car went into a main dealer this morning. They told me there was no conclusive data logged as fault codes, reset it and told me to come back when it's back on and they'll get a senior technician to look at it. Not surprisingly it came on again between the dealership and home...

I've just spent some time looking at the diagnostics through INPA and I got the following errors:

202 - Lambda regulating limit Bank 1 - mixture rich
203 - Lambda regulating limit Bank 2 - mixture rich
227 - Lambda control tolerance Bank 2
228 - Lambda control tolerance Bank 1
242 - Burning fail cyl 5
240 - Burning fail cyl 3
243 - Burning fail cyl 6
239 - Burning fail cyl 2
241 - Burning fail cyl 4

Now, I'm way out of my depth when it comes to interpreting this data, but wondered if someone on here could make any sense of it.

Other observations: mpg is down, misfire evident at idle but not when driving. On INPA the lambda readings struck me as odd, but I have no knowledge on them at all! At a constant 2,000 revs the pre cat lambdas were fluctuating between 0.08 and 0.80 (both sensors doing this) whereas the post-cat lambdas stayed at a constant 0.64 (again, both of them). When I switched from analogue data mode to digital I noticed Lambda Control Bank 1 and 2 both briefly went off for a split second as I came off the throttle then they gave a signal again. This may be normal, I don’t know.

Hopefully the senior tech at BMW will get to the bottom of it, but I’m just not 100% confident in them and would welcome any help. I had a quick look for vacuum leaks and some other things suggested by people on this forum, but haven’t had much time to be sure of anything. Need it sorted, getting fed up hence deciding to take it to BMW, but all they’ve done is say computer says no and sent me home!

[dan101smith]

To me that reads as though a lambda sensor has failed, is providing false readings to the ECU which is changing the mixture to match.

But I'm not an expert.

[wezzer-45's]

I'm not really a BMW expert but the pre cat lambda's will switch from rich to lean fairly quickly (approx 0.08v is lean and 0.85v will be rich). This is normal operation of closed loop fueling.

The post cat sensors just monitor the cat efficiency and should stay fairly stable when hot, normally approx 0.4v to 0.6v. This stable reading shows the damping effect of the cat.

If the post and pre sensors mirror each other, this shows that the cat is not working and will generally flag a cat efficiency or cat faiure code.

you really need to get the missfire fixed first as this will cause a rich mixture and will normally result in missfire codes, a rich code and cat efficiency codes being logged.

just my £0.02p worth.

[bramley]

Thanks Dan and Wezzer.

It's odd how it's ok one minute and not the next. My indy reckons there might be a multiplug connector somewhere that's got moisture/corrosion in it that's causing a problem, or an intermittent fault with one of the sensors. The trouble with it being intermittant is that it's gonna be hard to pinpoint reliably without changing parts willy nilly.

Re the suggestion to unplug the MAF, should I do that when engine is running or before I switch it on? And should I clear the current fault codes before trying that?

Thanks very much

[SJobson]

My indie plugged a known good MAF into my 540i when he thought it may be at fault. I ran around for a couple of weeks with his MAF in, which cured the problem (in my case it ran fine but the check engine light kept coming on). He ended up selling me the MAF rather than ordering in a new one.

So, offer him a couple of beers to borrow one from his stock, perhaps?

[bramley]

My indy isn't a BMW specialist so won't have one to hand Simon. I may order one online, try it and stick it on ebay if it doesn't cure the problem, so it wouldn't cost me much to do it. Determined to try and cure it before it goes to BMW next Tuesday!

[SJobson]

Try to source a proper BMW OEM fit one. There's a bloke on eBay who sells E39 MAFs which are actually for Ford Transits, and you may remember Jayell going on about how VW MAFs are exactly the same, but he's subsequently replaced them rather more quietly...

[bramley]

If i get one I'll get it from www.airmassmeters.com, they're OEM but apparently a fair bit cheaper than BMW. Probably worth a punt.

[welwynnick]

MAF sensors don’t last forever and cause all sorts of problems.
You can sometimes clean them with carburettor cleaner, but I wouldn’t count on it.
Watch out for cheap parts on e-bay.
I bought one for my 540i and it took out my ECU.
I wouldn’t want it to happen to any one else.

Nick

[bramley]

BMW diagnosed this as a sticking crankcase breather valve, total bill £270 + VAT. If that does cure (time will tell) I'm a happy man. Not something I would have undertaken myself and although poss cheaper at an indy, BMW seemed to have diagnosed it fairly quickly.

If this doesn't cure it I'll report back.