Camshaft actuator solenoid???

My CS is about 6 months old with ~2500 miles on him. Last weekend after driving at highway speed for around an hour I exited and immediately got a CEL and the car was idling very rough. I parked the car a few minutes later and went to work for the night. When I went back to my car around 10 hours later it started right up and felt fine but the CEL was still on. I drove home with the light on but everything seemed fine. On Monday I called the dealer and had them look at it on Thursday. Today I got it back and the dealer apparently replaced the camshaft solenoid valve and all of the parts surrounding it (part number 996 105 303 05--item #39 on illustration 103.00 in PET). Can someone explain what this part does? Thanks so much.

Brett, There are two different types of cam solenoids on your engine. One controls valve lift and one controls valve timing. There is one of each for each bank. They are controlled by the DME computer and will operate at different conditions, cold start, mid range rpm and high rpm. The main purpose is to add more power and torque at mid range to higher rpm and then go back to normal operation when at idle. One solenoid will change the intake lobe on the cam from base lift to high lift to allow more fuel and air to enter the cylinder while the other solenoid will change the cam timing of the intake camshaft, to cause it to go into "overlap" (intake and exhaust valves are open at the same time) for higher rpm power and torque increase. The cam timing solenoid is the one that I have seen malfunction occasionally. If it sticks in the operating position it will cause the engine to idle like a 60's muscle car with a large cam. Terrible for emissions and idle quality. Not very common but does happen. Hope this answers your question. Thom

Thanks very much for the very well explained answer to my question. So, if I understand correctly, what must have happened was that the solenoid stuck in the high speed condition after I had slowed down to the threshold where it should have switched back. And yes, a 60's muscle car was my exact thought when I stopped at the traffic light. It's really funny that you mentioned that. Is it common in modern engines to control things like this with solenoid valves? My experience with them in the medical equipment industry was that they had a tendency to fail if the state of the sensor controlling them was right at the threshold where they should switch for an extended time. They would chatter open and closed very fast and then the coils would fry. I would imagine the point where they switch to the faster mode is much higher than the point when switch back to slow mode--similar to the reaar wing control. Is that how they keep solenoids from frying?

The solenoids used in this application is more of a oil flow control valve. When energized they allow oil to flow and that is what actually lets the components operate. So being that these are after the oil filter any little bit of dirt or metal debris can cause the solenoid to not allow oil to flow. In the operating position the oil is under pressure so there is usually not a problem, but when the solenoid is returning to rest position, it is trying to allow oil to return and this is where the slightest bit of dirt can cause a problem. Many manufactures are using these systems on their engines and automatic transmission as does Porsche .

I double checked the part number and it is indeed the cam phase solenoid. Luft911 is absolutely correct in his description of the operation of these solenoids. The solenoid is used as an oil control valve, the engine oil is used as a hydraulic fluid, the amount of oil passing through the solenoid detmerines the cam angle relative to the crank angle. (which is why thin Mobil 1 0w-40 is specificied and why it is important to keep the engine oil clean and relatively fresh. You can see several of the items in this picture of a late 986 2.7 cylinder head. On the right of the picture are the intake and exhaust cams. If you look at the chain sprocket on the intake cam you will see it is much larger. The phasing mechanism is housed inside. On the left upper section of the picture you can make out the electrical plug for the phase solenoid valve. On the lower left you can see the hole in the valve cover where the valve passes through the cover. This engine does not have variable lift.

Bwass24, That's a weird one. I've never seen this failure discussed on the club, which leads me to believe that you just had a bad part. Glad it was an easy fix.

I think as time goes on we will see more of these. The parts have been in service in 996/997 cars for a while now. The failure is rare but we have done a few. We had one even stranger issue with a 996 Turbo where the oil control ring inside the cam phase adjuster on the nose of the cam had broken apart causing the cam to phase incorrectly. In the picture you can see a gloved finger pointing to the groove in the cam where the ring is supposed to be. The ring is sitting below the cam in 3 pieces. The part is a little different on the 996TT engine but it works the same way. I don't expect to see this failure again. In the other pictures you can see the intake valve lifters have two parts, one for the low lift (middle) and the other for the high lift (outer). You can also see the multi-lobe nature of the intake cam.

Hmmm....... I couldn't help but notice that only the intake cam has two lobes. Is this also the case in the M97 engines? Or is this just a Turbo attribute? Also... Wow.... Look a the difference between the mild and aggressive lobes. The mild lobes look round....

The variable lift is only on the intake cam in all cases. This makes sense since the intake cam is the one that lets the engine suck in air and therefore determines to a significant degree the engine power. ( BMW uses a similar arrangement with their throttle less fully variable lift valvetronic system, which is also only on the intake cam) The low lift lobe is indeed very very small. When working with the standalone engine control in the 986 race car with the 987 3.4S transplant we were only able to make 80 rear wheel horsepower with the low lift cam. With the high lift cam and very conservative tuning Tony@EPL and I were able to reach close to 300 rear wheel horsepower on street fuel!

Wow... Only 80 HP on the mild cams.... A very interesting project to say the least, and one that is likely to be a real learning experience. When you guys complete that car, you'll have to give us a full blow by blow.

Thanks all...very interesting. I wasn't aware that they used the engine oil as hydraulic fluid but it makes sense now. So, if the solenoid sticks in the aggressive position the car stays in the aggressive timing mode which is why it was idling like a muscle car. I guess, by extension, if the solenoid stuck in the mild position, or if oil flow was restricted by a clogged oil screen at the valve, you might have trouble accelerating and would reach a plateau very quickly?

bwass24, Yes that description is reasonably accurate. GatorBite, As soon as the car is complete I am planning to post pics of the car, dynos, and a blow by blow of the transplant process.

Drew, Thanks for the very informative photos and explanations.

These solenoid valves have been known to malfunction . They can either fail in that the internal winding shorts or the spring breaks. These are the two most common in use. For a new car they often get stuck from an internal metal shaving that was still in the engine. This shaving lodges in the passageway of the oil side. The shavings are normal and are from any of the machining processes of the heads or block. Best, Scott Slauson

bwass24 - As Scott states these are the most likely failure modes. You will not likely experience any further problems. At least not on the same side of the engine. Someday - You're welcome. I'm glad I could help clarify the problem. I need to get a new photo editor and then I'll be able to put labels on the pics.

Drew and Fairfield County Motorsports, I would like to say hello and welcome you. I think the photos are great !! I have to many to count yet not the time to post them so keep it up. Best Regards, Scott Slauson

Thanks Scott! I finally started cataloging all the photos. I'm sure we will have more to post as time goes on.

Bruce: Aren't you glad that this club has such experts at its disposal? Thanks to PCA-TECH [Scott,] Drew@FCM, and Luft911 [Thom] (who just happens to be my Cayman 's "personal" technician) for their lucid and thorough replies.:thanks: -Dave

Sorry about that, Brett ! D-OH!

No kidding, huh....? That's a lot of Porsche knowledge. And all in our neck of the woods. We're a lucky group.

bwass24 and I had a chat Friday about the cam phase solenoid. I don't know if this detail matters to anybody else but for those who want to know how it actuates here is a basic description: The DME uses a PWM ground signal to control the cam Phase solenoid. A P ulse W idth M odulated ground signal means that the DME is rapidly opening and closing the ground circuit, in this case of a 2 pin solenoid, one side is 12Volt+ the other goes to ground but the ground is switched through the DME. The grounding pulse is set up as a requested duty cycle at a specific frequency to get the solenoid to hold a specific position (say 20% through 80% duty cycle and 150hz, I'm not sure if that is the specification that Porsche uses it is just an example) . By holding a specific position it lets a specified amount of oil pressure/volume pass into the hydraulic phasing unit causing the camshaft to twist relative to the chain sprocket. Once the DME sees the cam angle it is looking for it holds that duty cycle. The DME knows the cam angle relative to the crank angle because there is a cam sensor on each camshaft. What we saw on the Cayman S 3.4 transplanted into the 986 is for good idel we need a 20% duty cycle and in the midrange 60-70% duty cycle for best power and then back to 20% in the high rpm area again for best power.

Not only did I get informative and very complete answers to my questions but on Friday Drew@FCM even gave me a "show-and-tell". He had a 996 engine apart in the shop and now I have a complete visual as well as technical picture of how all of this works. I can't thank all of you enough. I hope I get to return the favors.

Good guys over there at FCM. I told you they'd take good care of you. :cheers: I mentioned in another thread that they'd roll out the red carpet. I should have said "They'll roll out the dissasembled engine...." It's kind of cool to be able to see inside that thing, at least to me. It's amazing how much is going on in there.

Actually it was a 2.7 out of a 986 Boxster . That engine had a relatively catastrophic failure (broken pistons , very ugly ). This week we have a different 986 2.7 in the engine stand due to a very nasty top end noise. We'll let you know what that turns out to be. It should be very educational. I'll start a new thread and post some pics if anyobdy is interested. :cheers:

If you can find time, it would be cool to read a blow by blow of the exploratory surgery.

I'm pretty excited we found something we were not expecting. I need a little time to formulate the blow by blow, it will show up in it's own thread. :burnout:

Hello Drew, Thats a problem with those cast or pressed pistons. Unfortunately not nearly as good as the forged. I'm doing another conversion for a 1999 Boxster from Canada for an intermediate shaft failure. Well actually the bearing that failed in the shaft. The top end problems seem to be broken valve springs, bad or worn camshaft actuators and shattered lifters. Keep everyone informed as I think it would be interesting also. All the Best, Scott

I'll get into the details later but the lifters seem to be the cause of the problem. Very interesting actually. More in a new thread in the next couple of days.

i’ve just been reading the post and unfortunately I have a similar problem and wondered if you might be able to help. First of all I wanted to thank you for all of the fantastic information. I have a Porsche Boxster 2002 2.7 and I am finding that the car has a lumpy idle, and also when I’m driving it sounds like the car is only running on a few cylinders rather than all of them. The issue I have is occurring all of the time, so my question is could this be the veriocam tensioner unit or does this sound like something else? A coil pack maybe - although would that show up as a fault when plugged in? When it was plugged in by my local garage he said the fault reader showed it was the cam shaft Actuator but there was no way to know if it was also the whole Unit that as at fault. Any ideas will be greatly appreciated as I’m quite stuck at the moment