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Discussion Starter #1
Hello all, Ive have a 2003 156 2.0 JTS and I need help with fault finding a misfire at idle.

The misfire occurs about 10 seconds or so after start up and it occurs when a scraping sound starts. The area where the scraping noise is coming from from the catalytic converters. The misfire is only at idle and when coasting along, off throttle, and there is no misfire when accelerating.

Given the location of the scraping noise, I would think it has something to do with the catalytic converters or one of the sensors?

No fault codes when scanned with Multiecuscan.

Here is a link to a video I made. You can hear it run fine then the scraping noise and misfire starts:


Any advice appreciated.
 

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I can detect no misfire. The engine speed remains unchanged. I think it is more likely a pulley bearing. Try removing the auxiliary drive belt to see if the noise disappears.
 

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Discussion Starter #3
The misfire starts near the end of the recording. I’ll take a longer recording and upload it.

It runs fine for about 10 seconds then that scraping noise starts and that’s when the misfire also starts.
 

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Discussion Starter #4
Here is a link to another video. Don't worry about the high idle or steam, I just started it up from cold.


You can't see the engine misfiring because of the iPhone image stabiliser but you can hear it at the exhaust tip.

Good suggestion about a pulley bearing as that is what it sounds like but the noise not coming from the side of the engine, definitely the front of the engine. So I highly suspect something is going on with the cat converters or the sensors making the mixture too rich or lean at idle. So can anyone say what I should I be looking on the Multiecuscan regarding the lambda readings?
 

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That is normal JTS engine idle when using the lean burn strategy (at 1400rpm or less).
I had my JTS remapped so it now runs a stoichiometric fuel mixture all the time. A side effect of that is a more regular engine idle. I see 1.5 volts from the pre-cat wideband O2 sensors at engine idle. It is likely your car records a higher voltage though.
 

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Not sure about noise.

Misfire could be something simple like vacuum leak, spark plugs. If it's just running rough, poor idle it could be throttle body dirty.

JTS engines can have issues with worn cam lobes, depending on mileage and service history. Worn lobes I guess won't be doing a car any good. I have no idea of the symptoms of that however, so hopefully it's not that.

Being direct injection they can also have issues with intake valves having excessive carbon deposits. I'm not sure on the symptoms of that either.
 

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Discussion Starter #7
I put the Multiecuscan on and at operating temp at idle, the pre-cat lambdas are reading in the 2.3 to 2.5v.

937715
 

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The noise sounds a lot like a belt pulley bearing is worn. I'd remove the aux belt and briefly start the car to see if the noise is gone. If it's still there it could be the balance shaft belt or cambelt. For the misfire start by pulling out and checking all the coils and their wiring, then remove and check the spark plugs.
 

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Discussion Starter #9
Would a faulty coil pack throw a code? No codes have been recorded. Seems like It could be a coil but only misfires at idle. It has good acceleration and I would of thought if a coil was faulty it would miss under load which it doesn’t. Plugs were replaced about 1000ks ago. I might give the MAF a clean and see what happens.
 

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I listened again and there could indeed be a bearing sound. As suggested by @sprint_veloce, remove the auxiliary belt. It may be the tensioner or possibly alternator. I guess my ears aren't so good to hear stuff on a recording.

BTW, how did you get the screenshot of MES up?
 

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Turn the AC off, Does the noise go away? If so it is the AC pully/bearing.
Now, Rock the steering wheel from side to side. If it changes then it is likely to be the power steering pump.

If neither of those make a difference, remove the auxiliary belt completely and start it back up. If the noise is still there then you can rule out all Auxiliary components and bearings.

When was the timing belt last changed? While you have the aux belt off, remove the covers and have a look at both that and the balancer belt.
 

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Discussion Starter #13
All good suggestion which I’ll check. However, there is no noise or misfire for about the first 5 seconds after starting up. When the noise starts, so does the misfire. Coils were replaced a few years ago. Plugs changed last service. Cam belt was replaced about 6k kms ago I think.
Hit control and print screen together and then paste to upload screen shot.
 

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Bad coils from my experience occur under load, or when the car is hot. If they have been replaced I would think they are ok, unless they were too cheap to be true.
 

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Discussion Starter #15
Had another look today. The noise is def coming from the front of the engine, almost like it’s coming from inside the plastic coolant housing that runs next to the head. It’s not coming from the side by the belts nor the top. The title is probably a little misleading as the sound is best described as “like” a scraping sound. I’ve done the long screwdriver up against the ear diagnoses but can’t pin it down. Maybe the noise is coincidental that when it starts, the miss starts? Is there anything between the exhaust manifold and the block, under the aircon compressor?
 

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Discussion Starter #16
So I think this is coolant related which would explain the noise coming from the black plastic housing area. It was replaced a few years back and I replaced the thermostat about 6 months ago. When I raise the revs slightly above idle, the noise is there for about 5 secs and then disappears, this suggests to me that something is not cycling properly (coolant system) at idle. I just drove in heavy traffic and the temp raised a bit so I’m wondering if there is air trapped in the coolant system (maybe inside the black housing causing the noise). When I did the thermostat, I read that it’s a self bleeding system is this true or is there a correct way of bleeding this bleeding thing?
 

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Hard to diagnose via internet. I think the time for looking and listening is over and some spanners will help. First thing would be to remove the aux belt and eliminate that. If it's not that, remove the cambelt covers and check all's well in there. Hard to do much except look at the balance and cambelts, but you could start the engine and confirm the belt runs as it should.

Sometimes exhaust manifold leaks can make odd sounds at odd times. Maybe remove the heat shield and see if there are any cracks, and check tighten the manifold bolts/nuts at the head and flange joint to the rest of the exhaust system.
 

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Discussion Starter #18
SOLVED!

There was actually two faults. Firstly there was no oil seal between the dipstick holder and the block, secondly the PCV had failed. So having a faulty PCV, caused the crankcase pressure at idle, to escape the easiest path - the bottom of the dipstick tube which is where the noise was coming from. I removed the guts from the factory PCV and replaced it with an inline one and now no more weird scraping sound. New dip stick seal also fitted. Reset all the adaptations and the idle has now improved substantially.

So it wasn't coolant related and regarding the overheating, well it wasn't. I just wasn't waiting long enough for the fan to come on. When the fan came on, the gauge returned back under halfway. Im just use to a BMW gauge that stays at 12 o'clock once it reaches temp and stays there no matter what the driving condition.
 

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Glad you got it sorted. There should be no crankcase pressure at idle by the way, should be a very considerable vacuum, and it would have been sucking air through the failed dipstick tube seal, which would have made for a very bad idle.
 
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