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Camshaft Deviation


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#1 PILFILR

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Posted August 28, 2011 - 02:41 AM

What are normal values for Camshaft Deviation? MKI and MKII values the the same? Where do you start to worry about potential IMSB failure based on these values?


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#2 logray

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Posted August 28, 2011 - 07:10 AM

0 +/- 6 degrees is normal. The readings should hold steady regardless of RPM. I've seen some readings beyond that, indicating bad sensors, off by a tooth or two, bent sensor pickup flanges, etc. - but the engine still runs fine (all of those conditions should be addressed regardless). I've read that if the values fluctuate that is a sign of IMSB failure, however I don't believe most people would have enough time to use that indicator as a method to prevent or diagnose IMSBF before it happens.... there are "better ways" that have been developed. Why do you ask?


Edited by logray, September 19, 2011 - 07:18 AM.

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#3 Newfarm

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Posted August 30, 2011 - 03:19 AM

If you have values outside what the car thinks is normal, you'll get an errorcode. P0011 for bank 1, P0021 for bank 2. I'm in the middle of trying to figure out why I have a P0021 myself while the car itself is running fine. Durametric shows a deviation of about -12,7 for bank 2 on my car.


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#4 logray

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Posted August 30, 2011 - 10:16 AM

The theory is, that one can see a preemptive IMS bearing or gear/tube separation before it happens by monitoring the camshaft deviation values. If the IMS tube is moving all over the place then the cam timing is going to change. That is the theory at least.

My stance is, once those things start to go, for example you lose a bearing or two or the gear separates from the tube it is going to be a matter of miles not days or even weeks of driving the car. So for one to pop on their Durametric and happen to find that their camshaft deviation values are fluctuating would be akin to a hole in one in golf. Or maybe an albatross. I'm not saying it hasn't happened, but unless you are really in tune with your car and on the slightest abnormality in running you stop the engine and fire up your laptop to monitor camshaft deviation is an exercise in hypochondria for your vehicle.

Fortunately someone has developed a better way to determine IMS failure perhaps many many hours before it happens. It will be interesting to see what Mr Raby has developed.

Your reading of -12.7 at the crank means your bank 2 cam is -6.35 degrees retarded. It could be that someone at the factory set it this way lazily, or perhaps that this is how the cam is degreed (machined or possibly even warped)? I've also read that the 4-6 sprocket can slip a little over time

Another possibility is that 6 degrees might indicate 1 tooth off.

Anyhow 6 degrees AT THE CRANK, which is what Durametric reads (3 degrees at the camshaft) is the maximum deviation from 0 permissible (factory setpoints). Now will the car run ok beyond that, possibly - but at what point are you going to have interference between the valves and pistons (and lots of other badness), who knows.

It could also be that your variocam actuation is stuck or has a problem.

A deviation that big is not likely to be cam pad wear if you have the early 3.4L system, I would guess that once you get to the 12 degree range your cam pads would have already snapped in two.

There is a really good thread about camshaft deviation if you've read it before here it is:

http://www.renntech....c-readingerrors


Edited by logray, September 19, 2011 - 07:17 AM.

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#5 Newfarm

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Posted August 30, 2011 - 11:51 PM

Thank you for the thoughts on cam deviation logray, very interesting indeed! I have read the thread you link to before and it does have some good pointers. The car is running fine with my values, but something is definately wrong somewhere. I'm wondering if perhaps a pad could be worn out on bank 2 (I think the pad on bank 1 was replaced at around 109.000 km, earlier this year) or if the sproket has loosened. Or any of the other things you've mentioned. My car is a 3,6l x51 though, wonder if it changes things. I couldn't find a variocam activation in durametric to play around with, I can only activate the lift and they're both called the same. If I do activate those drive links, the engine sputters to death instantly. This car has variocam pluss though, I presume that might have something to do with it? Would've been nice to be able to test the cam actuators as well, but kind of hard to do with nothing to activate.


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#6 mattatk

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Posted September 19, 2011 - 05:30 AM

Sorry to jump on the thread but having just checked my camshaft deviations, my bank 2 is a steady 0 but bank 1 is s steady -8.02. Is that indicative of bank 1 being out of limits or a bad sensor? Thanks in advance, Matt


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#7 logray

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Posted September 19, 2011 - 06:31 AM

Yes, it could mean the allocation is off by a tooth, the variocam pads are very badly worn, the camshaft flange that the sensor picks up is bent, or perhaps just the timing is off by 8 degrees (crank) and 4 degrees retarded at the camshaft for cylinders 1-3.. Can you also post your actual angles (camshaft) at idle and 3000rpm? Also year of car. Thanks.


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#8 mattatk

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Posted September 19, 2011 - 03:39 PM

Firstly thanks Logray for the reply. My car is 2001. All the way up to 3000RPM & above, the camshaft deviation readings stay fixed, bank 1 @ -8.02 (second test -7.94) & bank 2 @ 0.00.


Edited by mattatk, September 19, 2011 - 03:40 PM.

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#9 logray

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Posted September 19, 2011 - 04:25 PM

Firstly thanks Logray for the reply.
My car is 2001.
All the way up to 3000RPM & above, the camshaft deviation readings stay fixed, bank 1 @ -8.02 (second test -7.94) & bank 2 @ 0.00.


Thanks for the info. If the camshaft deviation is changing, generally that is some cause for concern, from what I understand. For example it could indicate an IMS bearing about to go pop, but possibly/more probably just sensor wear, campad wear, variocam actuator problem, chain stretch, tensioner problem, or something else.

That being said, a 0.06 degree difference between your tests might just be within limits limits and none of the above problems are apparent, just the sensitivity of the cam position sensors and Durametric.

Also since you have a 2001 car, it would be helpful if you could log the "actual angles" (camshaft) value from Durametric at idle and at 3000rpm.

Depending on how many miles are on the car and what you get back on the actual angles depends on whether there would be further action recommended.

Regardless, I would probably verify timing and correct it (all possible with the engine in car). Then continue to monitor the deviation to see if it fluctuates.

If it were me I would pull off the green plastic camshaft cap at the front of the engine (rear of car) drivers side on the bottom of the camshaft cover. Then rotate the crankshaft to TDC. The scribe mark in the end of the exhaust camshaft should be aligned vertically with the camshaft cover if the timing is correct. Here is a good website describing what you should see when you pull that camshaft cover cap off.

http://986forum.com/...ead.php?t=26418

OH, also if you do pull that cap off you should have another one to put on, they cost about $8-10 at your dealer.

-8 degrees off is a fair bit of deviation (1 degree more retarded at the camshaft than the factory recommendation) and the timing is beyond the factory limitation of 6 degrees retarded or advanced.
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