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YOUR RESEARCHHow does camshaft position sensor work?
Leading reported evidence
Check "exhaust cam
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Performed · outcome unconfirmed
Since your Mechanic has triple checked the "exhaust cam to crank timing", he needs to triple check the "intake cam to exhaust cam timing" (14 pins/rollers between timing marks as shown in pictures).
Leading evidence: 'Check "exhaust cam' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Check "exhaust cam' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
Since your Mechanic has triple checked the "exhaust cam to crank timing", he needs to triple check the "intake cam to exhaust cam timing" (14 pins/rollers between timing marks as shown in pictures).
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Suggestion
Also check the cam advance" actuator" for the presence of the little green o-ring that fails with mileage.
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Suggestion
Does the shop doing the work have an oscilloscope to check the output signal of the sensor?
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Suggestion · Original poster
I get that the camshaft position sensor is checking the position of the camshaft.
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Check "exhaust cam
No successful repair reported for this finding.
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Read evidence and context
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Performed · outcome unconfirmed
Since your Mechanic has triple checked the "exhaust cam to crank timing", he needs to triple check the "intake cam to exhaust cam timing" (14 pins/rollers between timing marks as shown in pictures).
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
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Suggestion
Since your Mechanic has triple checked the "exhaust cam to crank timing", he needs to triple check the "intake cam to exhaust cam timing" (14 pins/rollers between timing marks as shown in pictures).
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Suggestion · Original poster
The mechanic swears he has triple checked that the timing is set correctly, and he is next going to try installing a new intake camshaft on the relevant side of the motor.
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Tried some searches and found a lot of hits on camshaft sensors, but not quite what I am looking for . . .
How does the camshaft position sensor in a 3.4 996 work? Specifically, what is the sensor �reading� to get the position? Is there a mark on the camshaft?
If you look at a picture of the intake cam for a 3.4, you will see a metal washer on the end with a tab hanging off the side. The sensor via DME reads the tab's position in relation to the 60-1 teeth on the crankshaft flywheel to determine the position of the intake cam.
.....and that's basically how every other cam position sensor works too in every other engine out there. The camshaft trips the sensor to let the ECU know where the cam is. The sensor's name tells you what it does.
What raises the issue is that my car is currently in a shop for an engine rebuild (
https://rennlist.com/forums/996-foru...-filter-2.html
). After the rebuild, the car is showing a CE code for a camshaft out of alignment (I forget the specific code, maybe P0021). What brought the car into the shop in the first place was the same code and my Durametric showing the camshaft off by 18 degrees. After a rebuild, why is this still showing??? The mechanic swears he has triple checked that the timing is set correctly, and he is next going to try installing a new intake camshaft on the relevant side of the motor.
I'm just wondering how it would work that the timing is set properly (sprockets all aligned with marks, etc.) and the camshaft is not aligned properly. Seeing from previous posts where the sensor picks up the signal, I guess it is possible that the sprocket for the chain and the tab that trips the sensor are out of alignment??? Thus, the timing would appear to be set properly, but the computer would think it is not? Mechanic says the motor seems to be running properly.
I get that the camshaft position sensor is checking the position of the camshaft. The question is, can the referenced part of the camshaft be out of whack with the timing chain sprocket? Looking at the picture posted by Coopduc, it is hard for me to imagine how the reference tab would change in position by 18 degrees relative to the timing chain sprocket, but maybe it's possible?
I imagine there can be other causes, such as a problem with the sensor.
Has the sensor been replaced?
A failing sensor could be off if the magnet has come loose and shifted inside.
They're not THAT expensive.
Certainly cheaper than the work done so far.
Did the shop also replace the chain guides and tensioners?
Faulty sensors can appear to work, but output faulty signals. I just went through this with my girlfriend's Lexus; total PITA. Does the shop doing the work have an oscilloscope to check the output signal of the sensor?
Long story short, but with over 100K miles on the car and me wanting to continue to do DE in the car, I decided to go ahead and do Nickie cylinders, new pistons and connecting rods, etc. Chain guides and tensioners have all been replaced. I will check to see if anything has been done with the sensors.
The pic I posted shows the intake cam relative to the exhaust cam. The 2 light colored chain links are lined up with 2 dots on the sprockets. The cams also need to be set correctly with TDC of the #1 cylinder. There is a sequence to do this with a special tool. I don’t have pics of every step, but set the crank at TDC with a pin in a hole in the pulley and engine block. Then install the tool in the cams and adjust by loosening the bolts in the sprocket intel the tool fits properly. i suspect this is where the problem is. Unfortunately I didn’t take a pic showing that tool in position.
Have a look at this thread:
https://rennlist.com/forums/996-foru...e-p1397-2.html
Took us some time to figure out that the intake cam actually was off by 1 tooth. You can see the process/testing that it took to come to this conclusion. You mechanic should follow the same main steps that we took to properly diagnose the issue and not just start replacing parts like the cam shaft. Our "Ah ha" moment was the display on of the oscilloscope.
Since your Mechanic has triple checked the "exhaust cam to crank timing", he needs to triple check the "intake cam to exhaust cam timing" (14 pins/rollers between timing marks as shown in pictures).
Also check the cam advance" actuator" for the presence of the little green o-ring that fails with mileage. Did you find any bits of light green rubber in the sump or filter? There are some pics in the "cam timing" threads of this little green o-ring that has caused many a problem with cam codes..
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