Extreme Hunting

[NigelB]

My engine is in, and running, It sounds great with the exhaust now complete and most of the time it's fine. It idles around 1000rpm which is a bit fast but no great concern.

However, every now and again (2,3,4 mins intervals but fairly randomly) the engine starts to die, the revs drop back to 300-400rpm and then pick up to 2500-3000 rpm. It oscillates like this 2 or 3 times and then settles back to about 1000rpm.

I guess the idle speed being a bit high could be an air leak somewhere in the induction side but I don't think that would account for the wild oscillations?? (could be wrong??). I've had the idle control valve out today and given it a good clean with some throttle body cleaner and that hasn't helped. (in fact, at a push, I would say it happens more frequently...............)

Does anyone have any ideas. The oscillation always seems to start with a reduction in revs followed by an overswing in compensation. It normally settles down after two or three oscillations but sometimes the engine dies. What could be causing the drop in revs that starts the oscillations. It doesn't appear to be temperature dependent.

If the air side is OK, ie no significant leaks and the idle control valve doing what it should (I guess the ECU is controlling that and that's what's changing the revs) then should I be looking at fuel supply. Could it be the injectors, or the fuel pressure regulator or do I need to be checking my ECU.

Any thoughts would be very welcome.

Nigel

[Grey V8 Pete]

Not sure what engine you have but I had a similar problem (one of many!) with my fuel injected Rover V8. Cleaning the idle valve made little difference but a brand new replacement one solved the problem. Maybe you could borrow and fit a known good one to check before spending money. Also check and clean all electrical connectors on the idle valve, injectors etc. Peter.

[Mike]

Originally Posted by Grey V8 Pete

Not sure what engine you have but I had a similar problem (one of many!) with my fuel injected Rover V8. Cleaning the idle valve made little difference but a brand new replacement one solved the problem. Maybe you could borrow and fit a known good one to check before spending money. Also check and clean all electrical connectors on the idle valve, injectors etc. Peter.

Nigel

I have a spare ICV if you would like to try it, to identify if that is the cause?

Mike

[NigelB]

Originally Posted by Mike

Nigel

I have a spare ICV if you would like to try it, to identify if that is the cause?

Mike

Mike,

That would be great, if nothing else but to eliminate it as a possible cause. Thanks very much.

If you are happy to mail it to me (I'll cover the cost) I'll give it a try send it straight back.

You have probably got my address after sending me the dual servo but if not, drop me a PM / Email and I'll send it through.

That should really help. I need to thoroughly check all the wiring to the injectors, coil packs etc as Peter suggests and if it's not that, at least I can get to narrow down the potential causes.

Nigel

[GreatOldOne]

Oh - I was expecting a conversation about bagging Tigers with nothing but a safety pin...

It's not intermittant fuel starvation is it? When the revs die, that is. If it starts drop off, doesn't the ECU try to compensate by cracking open the ICV increasing the fuelling?

Apart from that, I'd be checking all the induction hoses.

[peterux]

If your car is OBD-I and you can wire up an engine light, you might be able to read the fault codes.....

http://www.pelicanparts.com/bmw/tech...de_Reading.htm
They may not give you the full answer but might point you in the right direction.

In the meantime, like Pete above, I would start by checking all electrical connectors.

[morris]

Hi Nigel, one thing to consider is the general condition of the hoses overall. I cleaned all mine out the other day and though most of them were ok they were chock full of grungy oily stuff from 150K worth of crank/cam case ventilation.

you may not necessarily have a leak at a joint but the hoses could be a bit blocked. I also noticed that the thin one between the cam cover outlet connector and the connector immediately behind the intake manifold had the consistency of bluetack. I'm going to replace mine as I have no confidence of its ability to pass air through reliably. the same goes for the one connecting the manifold to the fuel pressure regulator. for a vacuum hose it was pretty squidgy. If either of these is collapsing under vacuum it could cause a problem, particularly the fuel pressure regulator one. I think the other is just a thin bypass for when the throttle plate closes completely to provide a very draw through of crank/cam vapour rather than the big suck when open.

the hoses would be number 5 in this diagram
http://www.realoem.com/bmw/showparts...84&hg=11&fg=15

and number 11 in this diagram
http://www.realoem.com/bmw/showparts...69&hg=13&fg=15

[NigelB]

My hunting is sorted at last.

I dismantled the induction side of the engine again and replaced all the vacuum hoses and the connectors into the inlet manifold and the camshaft cover. The fuel regulator was secured properly and the fuel regulator vacuum hose which had gone hard and powdery and had a hole in it (although I may have made the hole when I disconnected it!!) was replaced. I replaced the six inlet manifold gaskets and thoroughtly cleaned the idle control valve.

And it all made b--gar all difference!!

So today I have electrically checked all the main sensors as per the Bentley manual and they were all fine too. Except for the O2 sensor. I had excluded that as a problem because of a number of things I had read on the web that say the O2 sensor doesn't play any part in engine management until it had reached its operating temperature in the exhaust. My idling problem started as soon as the engine was running so the perceived wisdom is that, in those circumstances, you can ignore the O2 sensor.

But the E36 sensor is a 4 wire sensor with a heating element, heated by a 12v supply from the ECU relay and a switched earth provided by the ECU (once the engine is running). My ECU is not switching that earth so I have no heating element so effectively have had no O2 sensor.

But I have now hard wired the earth and all seems to be fine.

Which is great. Except that if that is the full explaination, why was the engine not previously idling correctly once it had come up to normal operating temperature.........................

Something to keep an eye on!!

[peterux]

Hi Nigel,
very pleased to hear that you have solved your idle problem.
Like you, I have no idea what would cause this problem but I'm wondering if the ECU has other switched earths?
As you have hard wire grounded one of them, maybe you have also grounded other switched earths by the internal connections inside the the ECU.

It's also worth thinking about why this switched earth was not switching? I guess it could be a fault in the ECU but i'm wondering if there an input to the ECU that it needs to see before it switches the earth. I don't have an e36 Bentley manual but IIRC in the e46 manual there is a table that describes all the ECU inputs and outputs?

But maybe if it works OK, why worry

(P.S. anybody want a secondhand e46 Bentley Manual?
E46 models and engines covered:
323i/Ci (M52 TU, 2.5 litre engine)
328i/Ci (M52 TU, 2.8 litre engine)
325i/Ci/xi (M54 / M56, 2.5 litre engine)
330i/Cis/xi (M54, 3.0 litre engine)
M3 (S54, 3.2 litre Motorsport engine)

Half price plus postage )

...peter

[morris]

Hi Peter, I may have that manual off you, what's half price? Last time I looked for a new one it was about £80 or something daft like that.

Nigel, how did you remove the hose from the manifold to the pressure regulator? I was going to do mine but it looked like the bit on the manifold was liable to snap if I got it wrong. My alternative was to just snip the hose and run some copper brake pipe between the two points.

Did you also manage to find a cheaper non-BMW source for the intake and throttle body seals. it adds up to around £50 for the genuine parts and although I know I really ought to change them....£50 for a handful of little rubber seals!!!

glad you got the engine running smoothly though. I've a feeling I'm going to be hassling both you and Mike for even more info over the next few months.

[Mike]

Originally Posted by morris

Hi Peter, I may have that manual off you, what's half price? Last time I looked for a new one it was about £80 or something daft like that.................

Ian, it is for an m52?

Originally Posted by morris

glad you got the engine running smoothly though. I've a feeling I'm going to be hassling both you and Mike for even more info over the next few months.

Nigel's your man - I just learn from him!!

[NigelB]

Originally Posted by peterux

Hi Nigel,
very pleased to hear that you have solved your idle problem.
Like you, I have no idea what would cause this problem but I'm wondering if the ECU has other switched earths?
As you have hard wire grounded one of them, maybe you have also grounded other switched earths by the internal connections inside the the ECU.

It's also worth thinking about why this switched earth was not switching? I guess it could be a fault in the ECU but i'm wondering if there an input to the ECU that it needs to see before it switches the earth. I don't have an e36 Bentley manual but IIRC in the e46 manual there is a table that describes all the ECU inputs and outputs?

But maybe if it works OK, why worry

Thanks Peter.

And the very same thoughts are bouncing around my head. (And the more I try to understand what is going on in the ECU, the more I realise just how much room there is in there for those thoughts to bounce around in.............!!)

Looking at the diagrams I am fairly comfortable that the swithed earth that I have hardwired is dedicated to the O2 sensor (as was the case to my hardwiring solution to my fuel pump problem). But what I do not understand is what swithes the earth on. In the case of the fuel pumps I can look at the diagrams and convince myself that the swithed earth is provided by the immobilisatiion system (and that makes a lot of sense) but I am not so sure for the O2 sensor. The Bentley Manual says that you need to measure the voltage (I was missing) with the engine running, not just with the ignition swithed on, so probably the switching for the O2 sensor earth occurs once the ECU detects the engine running (ignition, cam position sensor, crank position sensor etc.) Given that all those must be working for the engine to run, I too suspect a minor ECU fault.

But at the moment I am firmly ignoring that, leaving it to one side and getting on with building!!

[NigelB]

Originally Posted by morris

Nigel, how did you remove the hose from the manifold to the pressure regulator? I was going to do mine but it looked like the bit on the manifold was liable to snap if I got it wrong. My alternative was to just snip the hose and run some copper brake pipe between the two points.

Did you also manage to find a cheaper non-BMW source for the intake and throttle body seals. it adds up to around £50 for the genuine parts and although I know I really ought to change them....£50 for a handful of little rubber seals!!!

glad you got the engine running smoothly though. I've a feeling I'm going to be hassling both you and Mike for even more info over the next few months.

Hi Ian,
I grabbed the hose with a pair of pliers and pulled while rotating it and it came away very easily. I think I probably put a hole in the hose as I removed it but as it went straight in the bin it didn't matter.

I bit the bullet and bought the genuine BMW parts. A good seal at those points is so important I went ahead even after what I though was a price for all six turned out to be an 'each' price.....................!!

[morris]

Hi Mike, my daily driver is an E46 325 with the M54 engine so it's for that rather than the marlin.

[peterux]

Originally Posted by NigelB

........I too suspect a minor ECU fault.

But at the moment I am firmly ignoring that, leaving it to one side and getting on with building!!

Good plan!!

[peterux]

Originally Posted by morris

Hi Peter, I may have that manual off you, what's half price? Last time I looked for a new one it was about £80 or something daft like that.

Hi Ian,
OK, i'll send you an email later.
...peter