Kevin

This past summer I was on a shake down drive with my customer, he was driving. I sat back and watched how he was driving. 4th gear and lugging the engine down to 1500 RPM's.. I asked him if he could feel the engine lug down and become "jerky and surging" I couldn't handle it!! I told him for his crankshaft sake, down**** a few gears. Keep the RPM's up. If you don't want to shift trade the car in for a Tiptronic.

Macster

Exactly.

While to try to help the OP with his issue I did drive my Turbo in higher gears at lower rpms (down to around 1500) but the noise from the car clearly made me uncomfortable even though the noise didn't sound particularly horrendous. It just made me uncomfortable enough that even without my natural desire to avoid too low of rpms I could not make a habit out of driving the car at lower rpms.

I don't drive on the freeway in say 3rd gear buzzing the engine way up the rev range just to keep the revs up but except for first gear and possibly second gear I generally (make that almost always) keep the rpms above 2K and higher.

The engine likes a bit of rpms -- IIRC max torque appears at around 2700 rpms and remains pretty high and nearly flat until 4500 rpms -- and I like to see the oil pressure high(er) at the higher revs to help provide sufficient oiling under load.

By my observation -- and Porsche techs have told me stories that match my observation -- too many Porsche owners drive their cars more like a John Deere tractor or a Mack big rig truck than a sports car.

Sincerely,

Macster.

DesignerGenes

I call this noise the "death rattle," not that it has anything to do with dying hardware, but because it sounds as if the engine is trying desperately to clear its throat. It's similar to the sound you hear from a big Cummings diesel-equipped truck when the driver doesn't bother to downshift at a corner, and in fact it's about the same thing - massive load meeting unstoppable torque. Everything that can twitch at very low frequency in a relatively low mass system vibrates.

I'd be interested in hearing from someone with an active engine mount-equipped 911 about this. I'm thinking the sound is more muffled and the rear end of the car quivers as the peak forces are actively transfered to the chassis.

Receiver

My issue is a a hesitation, almost as if the gas was shut off. It occurs mainly in 4th gear between 3200 and 3600 RPM but never at a consistent RPM level. I thought it may be the variocam but if so, thought it would occur in a narrower RPM band.

I left the caar with my tech for a month in an effort to chase this down without success. That's why I'm thinking it may be normal. I'm going to drive another turbo in the spring tro see if it is the same.

Kevin

Receiver, your shop doesn't understand how the variocam works.

All of our cars will get a bump between 1800 and 2200 RPM's that is the low/high lift intake tappets.

The second surge, bump, hesitation (whatever you want to call it) occurs between 3000 and 3400 RPM depending on throttle position and engine load. It is more pronounced at low load and part throttle.

The ECU is trying to establish MAX torque while moving the intake camshafts.

Receiver

Thanks Kevin.

Bobw56

For what it matters, I have an 01 TT and I would say I have never experience the hesitation you are describing. I tend to keep the RPMs up in all gears and from my perspective it is always very smooth. Going back to some of the early posts in this thread, I live in a rural area and regularly "drive the crap out of it".

Simi_911

+1 Thanks Kevin. I've been experiencing the same thing as Receiver. I've always thought it was normal since the 2nd bump is pretty consistent. However, I was unsure of the first one...now this firms it up. Sounds like I need to mash the pedal more often and keep the revs up!

Receiver

No question that keeping the revs up solves the problem. However, I drive this car every day and it is hard to always keep them up there. No matter how hard you try, you are going to be in the 3 to 4,000 range a lot which is where I get the 2nd bump.

Kevin, because of city traffic, I'm going from 3000 to 3600 then back down to 3,000 then maybe up to 4,000 then back etc a lot. Am I going to have extraordinary wear issues on the cams and related parts? Should I make an effort to keep the revs above say 3600 whenever I can?

Thanks for all your help

Macster

Maybe X50 cars are different, but that doesn't sound normal. And my 03 Turbo doesn't exhibit anything like you describe at any rpm.

As I've mentioned there's a bit (just noticable) pickup when on a grade the engine comes on boost (0.1 to 0.2 bar) at steady throttle. And just a similar drop off when boost goes away.

That the egine is so smooth makes these on boost and off boost events noticable. But not disturbing.

One possible is that the E-Gas system has a 'dead' spot in it. There have been reports of similar behavior with other non-Turbo Porsches. This is quite rare though.

There appears to be a problem that the E-Gas system diagnostics do not catch.

Yet another explanation and one I like better than it is normal or a dead spot in the E-Gas system is the E-Gas mechanical linkage under/in the pedal assembly is dirty and this dirt's interference with smooth mechanical action is causing the symptoms you describe.

Even though my info is this is not a servicable item -- I know of at least one person who removed the pedal and cleaned the mechanical linkage and then lightly oiled it before reinstalling the pedal assembly back in the car.

How does this dirt get into the E-Gas mechanism? Well, one possible explanation is I've observed some Porsche service department personel when after a car is serviced and the car is being cleaned to return the car to the customer the employees use shop air to blow the dirt off the carpets and out of the car. I do not like this technique and request when I see it being done to not use it on my cars. It stirs up a lot of dust and dirt and get the stuff where it shouldn't get and where it would not otherwise get, and one place is into the E-Gas mechanism. I prefer the interior of the car, the carpets, etc, be cleaned with a vacuum.

Sincerely,

Macster.