986 2.7 Camshaft Deviation

[jluetjen]

I recently got the dreaded check-engine light associated with camshaft deviation. The car is a 2001 base model (2.7) with about 135K miles. I've owned the car for about 5 years.

Of course it occurs just before my car's inspection is due. So I plugged in the Durometric tool, which showed the code P1341 (Porsche fault code 174 -camshaft adjustment bank 1 below limit value.)

After the car was warm, I used the Durametric to activate the camshaft solenoids while at idle.
- When I activated the bank 1 solenoid, nothing happened.
- When I activated the bank 2 solenoid, the engine's idle got very rough.

Next I took the Durometric and started data logging and took the car through my test loop, which is about 50% secondary roads, and 50% highway with a couple of engine pulls to redline on the entrance ramps.

I pulled the data out to Excel to see what is going on. First I compared the two camshaft positions to the the engine's RPM.


Than I compared the 2 sides to each other by subtracting the cam2 angle from the cam1 angle for each data point.



In both cases, it seams clear that camshaft 1 is generally about 2-3 degrees higher than camshaft 2, especially when they jump to the ~23 degree setting. Also the "Camshaft position 1 deviation" is obviously about -9.66 degree, but that seems to be more of a flag value that is set rather than a specific measurement. It stayed consistent throughout the test across all of the different engine conditions. The camshaft position 2 deviation is -3.86 degrees, and also consistent in all phases of operation.

Never the less, it seems like the camshaft 1 solenoid system isn't working (given the test at idle)

Is it possible and worth-while to replace bank-1 solenoid actuator to see if that fixes the problem, before I start down the path of pulling the engine and replacing all of the chains, rails, etc?

[Newsguy]

If it hasn't already been done, I guarantee you the adjuster pads are trashed and the chain is stretched. I've had one apart with only 106,000 miles and they were nearly thin enough to break soon.

[jluetjen]

Yeah. I got it as far as the general fear factor. I had the oil tested a few years ago, and I've been cutting open the filter after each change.

The oil tested fairly normal, and there wasn't any colorful debris in the filter.

I'm thinking I'll start with another oil change and grab another sample for testing to see what they find. While I'm waiting for the results of that, I'll most likely try to do the accuator on bank 1 to see if it makes a diffeerence.. if iti fixes the prolem, and the oil and filter are nominal, good. If not, than 've only lost a couplebof weeks of time.

[997_986]

To answer your question first, it is of course possible but I would change bank 1 against bank 2 solenoid to see if failure follows.
Newsguy's hint is also valid, there is a vid from LN-Engineering that shows how to replace these rails. My indie did that for me as well (same engine and mls) with engine in the car, no need to drop it.
You can verify it quite simple by pulling the oilfilter, cut it open and inspect it for brownish particles that point to these detoriated rails. After that replace filter + fill up housing with engine oil until filter is soaked with oil and level does no longer drop (~400ml) and install housing.

[Newsguy]

Thinking some more about this. On the one I tore down, there was a lot of pad debris in the sump. Have you tried looking at that?
The pieces were big enough they dropped down directly and clogged the pickup. I also think a piece jammed the auxiliary pump in the head and wiped it out, as well as a main and rod bearing.

[Homeoboxter]

Something seems off, because the actuator shifts at 2500 rpm and 5500 if i remember correctly, so all your data points below 2500 and above 5500 should fall around zero, while the data points between 2500 and 5500 should be around 23-24. That's clearly not the case.

However, I think both solenoids and actuators are working, because what happens is fairly similar between both banks. So, somehow, they are synchronously bad. Perhaps there's a broken wire somewhere which somehow affects both actuators.

For cam angle values over 20 the values clearly separate, which probably means one bank is not able to move the timing to the target range, probably because the chain pad is shot on that side.

Can you arrange the dataset in a time dependent manner?

[jluetjen]

Originally Posted by Homeoboxter

However, I think both solenoids and actuators are working, because what happens is fairly similar between both banks. So, somehow, they are synchronously bad. Perhaps there's a broken wire somewhere which somehow affects both actuators.

For cam angle values over 20 the values clearly separate, which probably means one bank is not able to move the timing to the target range, probably because the chain pad is shot on that side.

Can you arrange the dataset in a time dependent manner?

Like this?



I think I see that you're saying.
1) They are clearly separated at the 20+ degree step. I'm guessing that it's the intake cam being advanced.

2) Also, it also doesn't look like they are moving together when they shift from the nominal 0 level the 20 degree+ level. This may be a time phasing issue since I wasn't taking a gazillion data points. It looks like the logger was capturing a data point every ~1.3 seconds.

But it looks like it's definitely the ramps.

I guess my project is now to replace them and run another set of data to confirm the solution.

Originally Posted by Homeoboxter

Something seems off, because the actuator shifts at 2500 rpm and 5500 if i remember correctly, so all your data points below 2500 and above 5500 should fall around zero, while the data points between 2500 and 5500 should be around 23-24. That's clearly not the case.

Good point. It seems like the variocam is kicking in about 1000 RPM too low, and turning off about 500 RPM too low. Doing a web search, it looks like the actuation of the variocam is dependant on RPM and load. At lower engine loads, the actuation of the variocam is retarded. Under higher load (such as an entrance ramp engine pull) the actuation is advanced. Initially when accelerating from my driveway and a nearby stop sign, the load was high. Than I was cruising on a 2ndary road with 1 stop-light, in ~3rd gear, so no variocam was activated because the load on the engine was light.

It definitely seems like bank 2 is not advancing as much as bank 1. I guess the variocam system advances the intake cam by 13 cam degrees (or 26 crank degrees. I'm guessing the system measures everything in crank degrees). So the bank 1 intake cam appears to have lost about 1 degrees of advance, while bank 2 seems to have lost about 2 degrees of advance. So maybe bank 2 is the real problem(?). Or is it that both sides are retarded (i.e. 1/4-1/2 degree of wear on the tensioner ramps for the long chains, or the chains themselves), in addition to 1-2 degrees of wear on the variocam ramps?

Either way, I'm going to replace the variocam ramps on both sides while I'm under the car.

[Newsguy]

Good luck doing that in the car. I’m finding it a bit of work on an engine stand! If you are able, I highly recommend you just drop it out. It’s pretty easy.

[Homeoboxter]

Yes, plotting the cam angles in the function of time is more infomative. The graph looks fine, actually, apart from that separation in the high cam angle value ranges. I'm not sure about the load dependency, I usually check these in neutral. In those conditions, when revving the engine over 2500 rpm, the variocams keep the cam angle at around 25 degrees. So I would think your value (22) at bank 2 is showing a malfunction. Which is weird, because your fault code is at bank 1. But that code can be due to your high deviation value also on bank 1. Nevertheless, you need to pull both cam covers and replace all four pads anyways.

[jluetjen]

Yes. I was thinking, why am I geetting alarmed for a Bank-1 error when bank-2 seems to have more wear?

Possibilities?
1. If you look at the "Actual Cam1-Actual Cam2" graph, you'll notice that the data is skewed towards the positive side. This suggests that cam1 is more likely to have a larger value than cam2. You can also see this in the distribution of points away from zero. I wonder if the Bank1 exhausr chain variocam unit is slow to return to 0 (and needs to be replaced).
2) Why does Cam1 have such a large negative deviation number when we don't see it in the numbers. My suspician is the Porsche may be more sophisticated than we give them credit for.. I suspect that "Deviation" is not just a reference name, but rather a statistical deviation calculated within the DMU. If this is the case, than enough data points far enough from the mean will trigger the alarm. I'll have to check this in the data when I get home.

[The Radium King]

cel shows up when deviation hits 9 degrees. if you have been tracking your deviation it is typically a slow degeneration until you hit the magic number. this is pads wearing and evidence is hard brown plastic in the sump.

if the solenoid fails evidence is green rubber in the sump (it's the seal that fails typically - always look to the plastic parts as your weak link as these cars age) and a drastic change in deviation - in my case to 16.

[mikefocke]

Recall that there are at least 28 failure causes in this engine. Do em one at a time and spend your life or your savings. Try to do them all and do both.