Porsche 986 Variocam Plus deviation P0021 code
 

First the background, and then the questions. I have been struggling with a P0021 code for several months attempting to get the problem resolved without the dealership coming between me and several thousand of my best friends.….MY 2004 Boxster S, 62000 miles with the M96/24 and Variocam Plus, only on the cam timing, not the later lift as well. I purchased the car with the check engine light (P0021) on from a non-Porsche dealership. It ran strong on the test drive, but I was concerned, and convinced the dealership to be concerned as well that is was an early indicator of a failing IMS bearing. I had them trailer it to my garage as part of the deal. Put it up on stands and cracked her open to replace the bearing, clutch, pressure plate, RMS, cam solenoids, and install a DOF. Upon opening the IMS flange I discovered the later oversized single row bearing in place and the car has a replacement engine. I closely examined the bearing, all seals were in good shape and there was no play or movement in the shaft running through the bearing. I removed the bearing seal facing the flywheel and installed the DOF for the large bearing as extra peace of mind. This did not solve the P0021 code, so I purchased a Durametric tool to see if I could determine what the issue was regarding the P0021. Logging the deviations bank 1 was -3.39 and bank 2 -12.3 both steady and solid. After considerable research I came to the conclusion the timing needed to be adjusted in order to get the deviation to within 6 degrees of each other so the P0021 code could be reset. I am not a Porsche mechanic and I have not done the procedure before but I pulled the plugs and gave it the old gear head try. I locked the cams into position with the Porsche 9686 cam locking plate that locks both the intake and exhaust cams, insuring they were at TDC #4, then used Porsche special tool 9685 to loosen the bolt on the intake cam and then loosened the 4 bolts on the exhaust cam adjuster, then I moved the crank pulley to TDC as indicated on the block. Logic tells me all the marks are in place, so it should be dead on, so I snugged everything back down, buttoned her up, and reset the codes with the Durametric. P0021 came back on, reading bank 1 -3.19 and bank 2 -11.69….progress, but not quite there. If at 1st…you know…time for a second attempt, same procedure, everything locked down, intake cam bolt loose, exhaust cam bolts loose. This time I used a dial indicator to make sure I was at exact TDC. Once at TDC I locked the crank down, then moved over to the exhaust cam adjuster. This thing does not appear to move very easy, maybe it is the tension from the timing chain, or maybe it is the stuck to the cam, but I placed a socket on the slot for the oil scavenge drive and placed some tension on the timing chain pulling it as tight as I felt comfortable from the crank, thinking if there was any chain stretch this would move it back toward the intake came and around to the tensioner. Snugged everything back into place, reset the code with the Durametric and it appears to be holding. Bank 1 reads -3.44 and bank 2 reads -9.64, must be close enough to the 6 degrees of separation for the DME to tolerate. P0021 code has been off for the last 1000 miles and the Durametric is still holding solid….the car runs much better now that the DME allows the adjustable timing to work, so I am enjoying the little extra boost in performance.
Here are my questions / concerns. Why can I not get the cam timing closer to the target of 0 degrees? Should the adjustment sprocket on the exhaust cam be easier to move in one direction or the other? I see that I am nearly out of room for adjustment on the exhaust cam sprocket, do I have to pull the cam cover and skip a tooth or 2 on the adjuster to provide any future adjustment? Did Jake Raby ever come out with a timing chain that has a master link in case my issue is timing chain stretch? Is my logic correct, I do not think it is a tensioner issue since the Durametric is rock solid on the deviation readings? Would you not see some movement in the readings if the tensioner was allowing the chain to move thus permitting the intake came to deviate?

Yes, I have custom, master linked chains.

Just an idea. Not shure if it makes sense.

The plastic chain ramps tend to wear. Even if the chain tensioners work correctly, maybe this could cause not to get needed tension.

Also the chain tensioners tend to fatigue. Over here in germany there were some problems like this reported that could be fixed by replacing all tensioners at one time.

Shure, also the chains can be lengthened.

Regards
Markus