850 2.5L 1996 intermittent stalling

Hi All,
Just putting this out there in case anyone has heard of a similar case and there is a straightforward answer.
I have an 850 2.5L 1996 (Fenix 5.2 fuel system) which this last week has
begin stalling intermittently during normal driving. There is no common conditions - hot, cold, uphill, on the flat - the engine stalls.
It happened to my wife at first and I had thought it was perhaps due to something simple like the idle speed being too low but tonight it has happened twice to me during normal driving conditions. Then engine just dies at normal revs.
It is a bit disconcerting of course. The second time it happened tonight it was difficult to start again. When the engine did take it was not idling smoothly for a couple of minutes but that might have been becasue it was too rich. The engine actually runs beautifully so i don't think it is related to plugs or HT leads.
I checked the ECU for the fuel injection reports 1-1-1 - no error.
I need to investigate more tomorrow when it is daylight but would an clogged airfilter cause this sort of behaviour?
Any other suggestions would be appreciated!
Cheers NK
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NK wrote:

Does the tachometer drop like a rock when it stalls, or does it follow the engine RPM down? Does the ignition system display any codes? A clogged air filter will normally make the engine feel low on power, but random stalling is not a problem I'd expect from that.
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Hi,
If you haven't had this problem before, it's probably time. It's the rubber elbow on the alternator end of the inlet manifold, which is very hard to see and reach. It connects to the other side of the manifold near the flame trap. The rubber elbow perishes and goes soggy and sticky and eventually gets a hole which lets air into the manifold. You will eventually get an error code (I got 2-2-1 "long term fuel mixture too weak in part-load stage"), but before that the idle speed will play up.
Mine eventually started making a lot of noise which is what led me to it. Before that I had unusual idling problems.
I bypassed the original piping layout due to it's inaccessiblity and ran a piece of rubber tubing over the top of the manifold to the flame trap, and held it in place with cable ties.
To check it, try poking it with a thin stick, or try and get you hand in there when the engine's not too hot.
Regards Barry
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On Sat, 17 Jul 2010 16:26:42 +1000, Baz wrote:

Many thanks Barry for your excellent insight.
I had a good root around the engine today and I think I found the elbow/ tube you meant (see http://picasaweb.google.com/lh / photo/8ctZn9vdvaVtDaVco2TkwQ?feat=directlink) but it looked fine to me other than a little orange/brown residue in the tube - is that normal?
Is that cylindrical part the 'flame trap'?
I also noticed the similar pipe heading off from the manifold to a sensor above the radiator which reads the manifold pressure (the 'Manifold Absolute Pressure Sensor'). I am suspicious of this because it has the capability to stop the engine immediately.
I dismantled the MAP setup and everything seemed to be in order (see http://picasaweb.google.com/lh/photo/EsFCWVqDuXvkvB_w3PpLSA ? feat=directlink)
After I disconnected the sensor I got correctly got a 1-2-1 error about the MAP in the ECU and the 'lambda' sign on the dash. Previously I have only got 1-1-1.
So would a faulty sensor be able to stop the engine and *not* register an error with the ECU?
I reassembled everything and took the car for a test drive but only got about 100m down the road when the engine cut out without warning. I then started it again and took it for a 15min ride without incident.
Still scratching my head so any ideas gratefully received,
Many thanks Noel
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Hi Noel,
No the hose you are pointing at is the vacuum line to the fuel rail pressure regulator. (It is in my car anyway.)
The elbow I'm referring to is more to the left and lower down. Look in the small gap just to the right of the power steering fluid container and the left end of the inlet manifold where the 5th inlet runner pipe (not quite shown in your picture) joins to the "large round part that goes to the throttle body on the right". Under the top radiator hose. It is hard to reach with your fingers.
The elbow is also larger in diameter to the one in your photograph.
I wouldn't expect much residue in the pipe from the fuel pressure regulator unless the regulator diaphram has a leak. Much like the pipe to the MAP sensor. There shouldn't be much airflow back and forth. Shouldn't stop the engine suddenly anyway.
As your engine is actually cutting out whilst driving, I think you might have a different fault to the air leak I suggested you check for. Mine when leaking badly didn't stop the car, merely brought up the engine fault light and mucked up the idle.
I have a copy of an article from an English magazine from about 10 years ago which describes the Fenix engine management system on the Volvo 850 in detail which I can email to you if you give me your address (about 8.5MB). It might help you.
Most engine sensors are monitored for readings which are out of normal range and the ECU will report a problem. But the ECU can only report what the designers have told it do, and they can't foresee all the problems that might occur.
A sudden engine cut out like you describe seems to me like an electrical fault, and you do really need to find the actual fault itself rather than try things and hope you fix it. You need to know that it is fixed, and to do this you need to locate a fault. Intermittent faults, particularly in a (moving) car can be very difficult to locate. You probably realise this by now anyway.
I live in Western Sydney, Australia, a very mild climate and very kind to cars. I wonder where you are and is your car likely to suffer from corrosion due to weather conditions. There are many connectors in a modern car that can give trouble, including earthing points for various components. The earthing for the "ignition amplifer" is a known problem in the 850. The article I mentioned points this out. I believe the ignition switch itself can be source of problem too, particularly if a heavy load of keys is regularly swung from it.
Lastly, and this also won't stop the engine immediately is the ignition leads. I had a slight miss when my car was about 6 years old, which got progressively worse. It turned out the plastic tubes that fit inside the engine to carry the current to the spark plugs were progessively breaking down and arcing to the engine. Worth checking occasionally. Also have you had the ABS module fail yet? It is a do-it-youself repair if you're competent with electronic printed circuit board repair. Merely needs some joints resoldered. Also the airconditioner evaporator (the inside the car bit) should have needed replacing by now :-))
regards Barry (barvic139_at_internode.on.net) remove the "_at_" and replace with @
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On Sun, 18 Jul 2010 13:56:14 +1000, Baz wrote:

Thanks Barry. I had to leave the car at someone else's house but I'll try and track down this pipe later when I cycle up there. I think you are right though that the issue is not the same.
I took the car for a spin yesterday and it was fine until the return leg when the engine cut out whilst climbing a hill. An interesting clue which (I had noticed previously but could not be sure about) was that the engine seemed flooded when it was restarted. Really flooded - very strong smell of petrol and the engine was struggling to idle. If you put any revs on the engine it cut out so I had to let it idle for a minute or so until the richness had cleared and the engine settled down.
So I am thinking now that there is a problem with the fuel mixture or the perhaps a fuel blockage or something? Fuel pump stopping?
I live in London and the only problems we have ever had with the Volvo are when we have had very hot summers (ie not very often!). The car has always been very, very reliable.
I'll read around the fuel system I think although I guess there should be something logged in the ECU for a problem like the fuel pump cutting out.
Cheers Noel
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Hi Noel,
Don't forget the obvious (and cheapest to fix), the fuel filter.... Also you'll probably find some details on the wed re problems with the fuel pump relay. I've seem them mentioned before, but they might not refer to 850s.
Though I wouldn't expect a fuel stoppage to cause engine flooding. See my previous mention of your vacuum pipe to the fuel pressure regulator. It should be clean inside unless there's a (fuel) leak in the regulator diaphram itself. That could cause richness problems, as petrol would be sucked into the inlet.
Anyway these are just thoughts, hope you locate your problem.
Barry
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Is that white /grey colour on the pipe you have in your picture a sign of arcing from some electrical source ? I once had issues with old rubber boots on the spark plug leads shorting out in a V6 Volvo they had become conductive with old age .

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Fuel pump relays often have dry joints (usualy volvo thing) - can you hear the pump prime when you switch the ignition on?? It is on the underside of the fuse box, accessed from under the bonnet..
And secondly, ignition switches themselves can get intermittent. Especially if your keys are a large heavy bunch. With the engine running- try wiggling the key around - if it splutters you've found the problem.
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