540i with misfire (?) on idle

[jochen 4]

Hi all,

My E39 03/1997 540i with the M62 V8 engine has a slight idle problem.

When idling, under load, the engine will every now and then give a little 'lurch' that shakes the car a bit. Just once, by itself, and then be nice and smooth again. You feel it in the steering wheel, gear level, and the car body. Happens when not moving (so its not a pothole).

I thought it was a misfire, but I'm not sure, as everyone tells me I wouldn't feel a misfire on 1 cylinder in a V8. It would have to be more than 1 cylinder to be noticable, and that doesn't sound plausible with the E39 M62 motor.

The engine idle is a smidgen over 500 RPM, and nice and stable, never surges, doesn't vary any more than you'd expect with the DME controlling the idle speed (slightly higher with A/C on, higher when cold, etc)

The 'lurch' happens with A/C turned on or off.

Doesn't happen with trans in neutral, only seems to be when engine under load (in Drive sitting in traffic, with or without A/C)

Doesn't happen when driving or under throttle (that I've noticed), I've never had any problems at any speeds other than idle.

I've just had 2 x trips Akld - Ruapehu and it drove beautiful and smooth all the way there and back.

BM Workshop have used their DIS to check error codes.

Only thing noted was a 01 Constant Voltage fault on the DME, so we threw in a new DME relay (just in case the relay contacts were dropping out) But I don't think that would be the problem of the Lurch.

Before we replaced the relay the Constant Voltage fault was cleared on a Friday and had re-appeared on the Monday, so we replaced the DME relay on that Monday.

Next time we checked we had no more Constant Voltage faults logged, but I'm going to pop in again tomorrow for another fault code readout (it will have been 10 days & 2 x trips to Ruapehu, plus another 20 'lurches' over the last 3 days since the last readout)

It's had about 4 x tanks of BP 98 Ultimate in it, so fuel has stayed the same.

We've changed the plugs to a new set 10 days ago, but the symptoms are still there.

Anyway, anyone got any clues as to what could cause it?

I come to the conclusion that:

1. Cannot be fuel, as any fuel delivery problems would show up under load and at speed

2. Not sure about ignition - with a separate coil per plug, it doesn't seem plausible that multiple coils would fail occasionally, and only at idle

3. Not the AC compressor clutch slipping, as it happens with AC on or off

What on earth could it be?

Ross said the ICV (idle control valve) needed cleaning, but would it cause these sumptoms?

Would a failing O2 sensor cause any symptoms like this?

Look forward to all and any ideas and experience...

Thanks, Jochen

Edited August 24, 2006 by jochen

[cainchapman 0]

I'd think it is the ICV or PCV (same thing, different term).

[martyyn 2]

I'd think it is the ICV or PCV (same thing, different term).

Hmmm Im not sure thats the fault Cain. Happy to be proven wrong but I had that last year and what happened for me was that the engine would simply stall when idling not 'lurge'.

The biggest sign is the smoke pouring out of the exhaust when you start the car !

The fault given by the decoders for the PCV can often be mis-diagnosed because its a 'generic' code on most cars but not on the M62. I cant remember the details of the fault unfortunately.....it will come to me....but not tonight !

Im also not sure how you 'clean' the PCV ? After all you have to take half the engine apart to get to it and even then you can only find out if its damaged by smashing it to bits to get at the filter in the middle. Its the filter that fails and sometimes its a simple as the outer edge has worn.

As you dont get any trouble when driving Jochen Id rule out the cats, that also causes a misfire but you'd notice that believe me !

I find it strange everyone tells you you wouldnt notice a single cylinder misfiring. The M62 is such a smooth engine I wouldve thought it would be obvious.

Not much help Im sorry but as with alot of things on these engines you have to start at one point and work your way through

[my_e36 43]

Could it be fuel pressure? (per BMW TIS RA 13 31 029)

[jochen 4]

Hi all,

Thanks heaps for the advice.

I popped in to BM Workshop yeasterday, put the car on the DIS, and not a single fault code logged on the car anywhere - which is a good sign. At least my Constant Voltage fault has not re-appeared.

Had a chat with the Workshop Manager, he thought it would be a good idea to clean the Idle Control Valve - easily accessible on the M62 engine, he showed me where it was.

Theory is that if it is sticking the DME might be making the mixture too rich or too lean at idle momentarilly and thus causing it to struggle, and then the ICV would suddenly open and it would be OK again.

Symptoms support the theory - problem only at idle, never unde driving conditions.

So that's todays job.

Otherwise, if not the ICV, next thought would be to change the O2 sensors...

But cleaning the ICV is much easier, and something I'll do today (and then drive it for a while to see what happens)

I'll keep you all posted....

Jochen

[jochen 4]

Hi all,

Well some good news.

On the M62 engine the ICV is at the front of the engine above the thermostat. Take one rubber air tube of it, unplug the wire, and the ICV pulls out of its socket. Easy to remove, easy to re-install.

I have just cleaned my ICV inside (and out). checked the movement of the valve before I cleaned it, it was slow and sticky. When you opened the valve it would close only very very slowly.

And it was covered in black carbon and soot etc

A bit of cleaning with engine degreaser, carb cleaner, and a rag, and now it is spotless, shiny (inside and out :-), and the valve closes nice and fast, and moves easily open and closed. Sprayed a bit of CRC as lubricant inside it as well.

Reinstalled, and will keep a close eye on the engine over the next week.

It has to be better, the ICV was very sticky and slow, so I'm looking forward to a noticable improvement....

Cheers, Jochen

[martyyn 2]

So if the ICV sits at the front and you can pick it off and clean it what am I thinking of thats at the back of the engine and is a

b!tch to get to ?

I thought that was the PCV ?

[Huttey 0]

Jochen, I had a similar problem with my 540, the engine would surge at idle (a little tricky when in gear at the lights) and then a couple of times the engine just died when I stopped at lights. It appears to have cleared itself and hasn't done either for last few weeks but I will have a look at the ICV tomorrow and see what it is like

[jochen 4]

Hi Huttey,

Surging is normally sign of a vacuum leak - check your vaccuum hoses for cracks and old, deteriorated rubber. Replace any that are suspicious, and with new hose clamps :-)

Best way though is to do a vacuum test with a smoke machine

But hey, the ICV is really easy to remove and clean.

Here's the ICV:

http://www.realoem.com/bmw/showparts.do?mo...hg=13&fg=15

Item #23 is the ICV "T-SHAPE IDLE REGULATING VALVE"

Don't drop it, it costs $390 USD !!

Watch the rubber holder #14, when I put mine back in it cracked where it goes through the bracket.

The internals of the valve should swing open and closed nice and freely... spray on de-greaser and carb cleaner did the trick for me.

Jochen

[jochen 4]

Bugger, cleaning the ICV did not change my "misfire" problem - it is still there.

Now to check O2 sensors and crankshaft sensor.....

Which one is easier?

Jochen

[kiwipetrolhead 1]

Please let us know what you find, once it's fixed. I have a 540i too, and you never know.. one day I might have the same problem in mine.

Best of luck

Paul

Hi again,

Had a we think about this, sounds to me most likely a vacuum leak too. If hoses and things check out OK, what about leaking manifold gasket?

I think it's most likely not electric, like you say... but sometimes things aren't quite what they seem. The coils are easy to replace, so any chance you can borrow one and try it on each cylinder one at a time? Might be worth a go if you can't find any vacuum issues.

One thing else, it might be a sensor. I've not played with mine so I can't guess which, but these things do sometimes cause problems like you describe. BM's tests should've found that though.

Paul

[jochen 4]

Hi Paul,

Thanks for your info. The guys at BM Workshop now reckon it's a coil on it's way out, and recommend waiting until it has failled sufficiently for it to log a fault in the DME.

Jochen

[kiwipetrolhead 1]

Hi Paul,

Thanks for your info. The guys at BM Workshop now reckon it's a coil on it's way out, and recommend waiting until it has failled sufficiently for it to log a fault in the DME.

Jochen

Pity to have to wait tho - you might be waiting for a very long time - i.e it might not be a coil, and what if whatever it is does not deteriorate further?...

Doing the coil switching trial as I suggested would help speed up the process.

P

[bekker 7]

Hi,

Does the 540 V8 has a coil per cylinder?

If so, my Honda has the same set up and on the Legend you diagnose a faulty coil simply with a multi meter. If the resistence of the coil is outside factory specs (high or low) its faulty.

Could the 540 be tested the same way?

Just a matter of finding out what the normal resistence range is for the coil.

Dont know if that helps or not.

Cheers

[kiwi535 538]

i was going to suggest a coil.....The pcv is a crancase ventilation device on the back of the enging which directs "cranckase air" back into the inlet manifolds to be burnt.Thats what you had Martyn,relatively common i beleive on the M60 and prolly m62.

Whatever i hope it turn out to be a coil Jochen,test them then see if you can beg steal borrow one to see if that solves your problem.I also beleive valve cover gaskets can leak oil collects in the valley and can affect the coils/spark plugs.?

[jochen 4]

Thanks for the info

I will probably take the covers off and start measuring and recording resisitance of all coils to see if any are dramatically different from each other.

Yes, there is a coil per cylinder - mounted directly on top of the plugs

I can see it would be a long slow process to fit a known good coil in turn to each of the 8 cylinders and wait to see how the car performs.... by trying 8 in a row, murphys law states it will be the last one you try.... but if you try the last one first, it'll still be the last... etc... etc...

I have seen the plugs sitting in their sockets, and there is no oil there.

But I'll try to take the covers off this weekend and inspect everything closely, look for signs of arcing, carbon deposits, poor resitance, poor / dirty insulation, poor contact with the plugs, etc ...

I'm not entirely convinced it is an ignition fault however as today it 'blipped' 4 times quickly, - but then again - with an idle speed of 600rpm, that's 10 revs per second, which means (I think) every cylinder firing at least once per second at idle (is that right..??)

Jochen