Dharn55

I was helping a friend clear some codes on his car with my Durametric and decided to put it on my car and check some actual values. Came up with two deviations on the Cam Position Sensors

Cam Position Sensor 1 -10.86
Cam Position Sensor 2 -2.14

I am thinking that this is from when I set the cam timing without the OEM tool. Does anyone know if this is degrees, percentage or how to interpret?

Pac996

First of all I'm not certain and I'm sure you know a Durametric or a no BS Porsche mechanic or better yet Porsche in real world Germany would be best for the answer.

I'm not sure if the following information is pertinent to your data but I'll tell you anyway. Some of the race motorcycle bikes pull tricks for getting the 200+hp out of a 1 liter engine. One of the tricks is instead of running the engine as a full balance of every firing being the same the engine is tuned off balanced instead of 1-2-3-4 going off at exact intervals. One of the physics they are playing is crank flex since higher rpms are being run. So the engine runs and the vehicle flys by at 200mph and somebody notes the difference in engine sound of one of the teams bikes. While working on figuring out what the guys were doing like if they were running a non standard firing order and other things.....through experimenting to find the mix of great performance like the odd sounding bike one outstanding fact was found. In an engine that is putting out a lumpy impulse the lumpy inpulse transfers to the wheels then road and better tractions is derived. Finding this lumpier vibration gives better traction some of the guys figured give me a break it just doesn't figure right. But possibly the relation between front and rear receiving the impulses at different timing is where the traction is improved. But, anyway....

I really don't see much Porsche engine facts online. Tomorrow I'll ask Scott the expert that worked on my car this week. He has a Masters degree from Porsche I'm also pretty sure he has stats like sensor readings available from memory. He's got his own race car and a real nice guy. http://www.germanautospecialists.com/Racing.html

PS I think your valve timing is off but we'll see and good luck.

Dharn55

The valve timing is defintely off, on my friends car, which has never been apart, the sensors showed 0. The question is how far off. Is it 10.86 and 2.14 degrees? And advanced or retarded. The engine runs pretty well, maybe a little rough. 10.86 degrees seems like alot. I need to pull off the green plugs on the cam covers and check the timing, but I work in an unheated garage and it is a little bit cold these days to be jacking up the car and crawling around underneath it. I have a shade tree method that I used to set the timing, but I did not have the pre-tensioners, just the actual chain tensioners. 2.14 degrees is not much, but 10.86 degrees would be alot if that is what the measurement/readout from the cam sensors means.

I was kind of hoping that Jake Raby would jump in and give me some guidance.

Macster

My info is for the Boxster and its VarioCam system but it allows a +/- 12.5 deg. change in intake valve timing. That's 25 degs. total adjustment.

At engine start valves are retarded by 12.5 degs. At 1200 rpms the timing is advanced 12.5 degs. At 5200 rpms timing is retarded again.

My WAG is the numbers are degrees. All references to cam timing and intake valve advacing and retarding has been in degrees not percentages.

Course you have to know. Or not. You are probably faced with opening engine up and resetting timing properly and verifying nothing's amiss just in case the timing's ok and something else in the VarioCam system is allowing the timing to be off.

One thought is to move the Durametric system to another car that has no timing issues and see what the readings are under similar engine temperature and rpm and load conditions.

Sincerely,

Macster.

Dharn55

I had the Durametric on my friends car and at idle it showed 0 for both the cam sensors. On my car at idle it was the -10.86 and -2.14. Now the car was not warmed up so I am going to check it again with the car at operating temp. There is really not that much disassembly required to reset the cam timing, it is a 3.4 VarioCam. You have to set the engine at TDC, pull out the green plugs at the ends of the cams. If the timing is off then you remove the scavenger oil pumps so that you can loosen the bolts on the cam sprockets to adjust the timing of the cams. Then either have the Porsche tool for setting the cam, an aftermarket tool, or try my method again.

I really need to know what the sensors should show at idle. If the setting at idle should be 0, then it advances to 12.5 degrees (I thought this advance took place at a higher rpm than 1200. Thus the feeling of going "on cam" at about 3500 rpm or so) and then it retards at a higher rpm, then the reading should be 0. If it should read -12.5 at idle then the setting should be different. But really the cam timing adjustment tool sets the cams it a certain position when the engine is not running, and this should not vary unless the engine is running. It seems that the cams are now retarded (thus the -10.86 readout) at idle.

I think the advance tensioners are working, but even if they are not this should not effect the cam timing at idle. If it was warm out I wojld just put the car up and take a look, but it is pretty cold out now.

Still hoping I am going to hear from Jake.

Macster

Well, as I mentioned my info is for the Boxster engine so this may not apply to the 3.4l engine in the 911 but the intake valve timing is advanced at low engine speed to create valve overlap, so the intake and exhaust valves are open at the same time. The intake valves are advanced to open before TDC of the exhaust stroke while the exhaust valves are still open.

This forces a bit of the exhaust gases into the intake to reduce combustion efficiency and lower NoX generation which occurs at higher combustion temperatures.

Then at a higher speed the intake valves are retarded to open later and thus remain open longer on the intake stroke to take advantage of the momentum the intake air gathers as it rushes down the intake manifold and ports. By staying open later in the intake stroke cylinder filling is improved.

Not quite sure the dynamics involved in the intake valves being advanced again at approx. 5200 rpms.

If everything operating normally at idle I'd expect to see the intake valve timing reading 12.5 indicating the intake valve timing has been advanced 12.5 degs. from nominal. At some other time, under some other operating condtions, higher rpms, mainly, I'd expect to see the timing read -12.5 to indicate the intake valve timing has been retarded.

I would think the same positive and negative signs would be used to indicate the same direction, either advanced or retarded, as used for ignition timing.

But if you want to hear from Jake that's ok by me. In fact I'd suggest you do so. I may be wrong.

If the VarioCam system operating otherwise ok, if the numbers are real, then it the cam timing adjustment that fine? I mean the one showing -10.86 suggests the timing off by 12.5 degs. plus ...

Oh gotta go. Landlord just called water heater in my apartment leaking into downstairs apartment. I'll finish this later.

Ok, I'm back. New water heater being installed Monday AM.

Anyway, is the cam shaft timing adjustment that fine to be able to adjust a mistimed cam that reads -10.86 to read -12.5? (This assumes of course the sign's right and the timing's not off by 10.86 plus another 12.5 degrees, that instead of reading -10.86 the timing should read +12.5.)

In timing cams in other engines I used an eccentric bushings to advance or retard the timing by a few degrees in probably (can't remember now) 1 degree increments.

If the timing adjustment that fine then that suggests the timing's just a fine adjustment out, not grossly out of time.

Sincerely,

Macster.

Pac996

Valve timing is the opposite of ignition timing for where the benifit of power are delivered. Retarding valve timing optimizes the higher part of the power band. Increasing the duration lets the engine breath better. A cam called a circle track can have a 306 duration or such and give 8k rpms to a stock car type of engine. I'm sure your main concern is valve to piston contact being possible. Does the Durametric track cam sensors while running? Not sure if you had already become comfortable driving the car through the rpms then gotten hit by this surprize.

PS I never asked Scott anything since he disappeared from the club cruise on the last part. You know guys with blondes in their turbo do different things some times.