ognils

My 1999 996 C4 Cab 36000m has been experiencing some problems. Firstly it became very hard to start, stalled frequently and sounded awful. A faulty battery was diagnosed, replaced and solved part of the problem. But, the car still sounds awful and struggles to maintain its revs, with the needle bouncing up and down until it finds its level.

My local dealer had the car in and diagnosed a faulty 'varioram' unit, apparently not broken but not functioning fully. It will apparently break at some point, just not sure when. Until this time they tell me the car can be driven with out problem, just inconvenience. Can anyone explain what is the part that they call the varioram unit? Is it a control box for example?

Secondly, the car struggles to accelerate fully, I know that a lack of power is to be expected given the diagnosed fault, but this manifests by seeming to slip the clutch. If I accelerate hard the revs pick up, the car accelerates and then the revs seem to be taken away,only by 500rpm or so but it gives the feeling of a slipping clutch. Is it? If I engage 1st, accelerate (soft or hard) the clutch seems fine, no slack or slipping when pulling away, no other clutch slipping symptons.
Any thoughts greatfully recieved.

JimB

Are you sure he said varioram? As I recall, the 996 uses a flap in manage air volume in the intake manafold rather than varioram. It could be that your mechanic is refering to the flap and just calling it varioram. Either way these are electronically controlled mechanical methods used to vary the amount of air that passes through the intake. Hopefully someone more qualified can give you a more complete answer.

Having said that, are you sure he did not say variocam? On a 99, variocam adjusts the timing between the intake and exhaust cams. They only have two settings. They are at setting 1 up until about 2k-2.5k at which time they switch to setting 2. Then somewhere around 5800 rpms the switch back to setting 1.

If one side (or both) are stuck on setting 2, the car will run very rough under 2K rpms and even worse over 6K. Just a thought.
Jim

ognils

I'm sure he said varioram. The service manager whilst explaining to me did say that 'it' had stuck and was not operating properly. Your explanation about the flap would seem to resemble the problem I'm having though. I'll ask for more information though. Thanks for the reply.

SPR

I would guess vario-cam

ognils

The more I read the more I think its a MAF problem. Seems to explain the stalling, noise symptoms. Doesn't explain the 'slipping' clutch sensation.
Is the MAF an independent unit? Is it a large job? or is this a term to explain a problem encompassed by a whole range if units?
I feel like a hypochondriac who is self doctoring. Still, knowledge is power!

1999Porsche911

Disconnect the wire connector from the MAF and see if you see major change in the performance of the engin. If you do not, then it may be the MAF. IF you do, then it most probably is not the MAF.

JimB

Well I suppose we might as well continue to play armchair mechanic. Why do you think it's a MAF? Is your check engine light on? The MAF will trigger it. I'm not sure Porsche911's check will work. I don't think the MAF fails completely so unhooking it may still change the symptoms even if it's bad. It guess it can't hurt to try though. The MAF is a black unit attached to the tube between the air box and the throttle body. You can pinch on the sides of the connector and remove the wire running to it. Treat this stuff carefully. Its very expensive.

If you want to play along, try this. Accelerate in 3rd or fourth gear. Keep very close track of what is happening and at what RPM. It's pretty easy to see if the problems are happening at the cam switch points. I'm pretty sure these points are affected by the throttle position so you might need to try it a few times accelerating at different speeds.


Good luck,
Jim

ognils

Jim,
I only thinks its the MAF after having read a lot of other posts which exhibit similar symptons. Like I said earlier, I'm self doctoring! Having said that though, it can't hurt to explore the MAF option so thanks chaps, I'll have a play later today.
ps. the engine light hasn't ever come on.

ognils

Ok, I'm an idiot and a deaf one at that!
I called the OPC that diagnosed my fault and they confirmed it was a VarioCam problem not VarioRam. Nothing to do with MAF. All of my symptons (inlcuding the slipping clutch syndrome) are confirmed by the OPC as being likley due to the VarioCam fault.
Thanks for your help.

1999Porsche911

Keep us posted as to what they had to do to fix it and the cost. Good luck.

ognils

I'm in the UK, my OPC quoted me £1300+tax inclusive of parts and labour. Apparently a whole days work. A non franchised local Porsche specialist (who have a decent racing pedegree) has quoted £500+tax for the same job. They too quote most of the day to perform the work, although they say that one side of the engine is easier to work on than the other and accordingly the exhaust and manifold may need to be removed thus taking more time, however, they have quoted me worst case scenario. I wonder if my OPC have also quoted for worst case and if so, would the job come in under quote if the 'easier' side was faulty?
The cars booked in at the end of the month (due to my schedule) with the non-OPC. I have every confidence that the problem will be easily and effectively remedied.
I'll post my comments when its done.
Once again, thanks to all.

JimB

If you are interested, here is how the system works. There is a chain that runs between the intake and the exhaust cams. One drives the other. The chain is somewhat loose. Midway between the two sprockets there is a chain tensioner that can protrude either to the right or the left to tighten the chain. As you can imagine, if the tensioner is on the left, the relationship (timing) of the sprockets is slightly different than if it is on the right. That is how the shifts that I mentioned in an earlier post take place. The tensioner is operated by a 12 volt electrical charge. No charge, it protrudes one way, 12 volt charge it protrudes the other. I assume the tensioner has failed although it could also be the cam sensor.

Either way, good luck.
Jim