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Flat spot around 3000rpm

DrSimon

DrSimon

New member
Since picking up my 997 C4S cab a couple of months ago I've noticed a slight flat spot around 3500rpm when accelerating. I've done some trawling on various other motoring sites and I've found several conflicting posts regarding this. Many say it's normal and don't worry, other posters offer other various potential reasons. I guess I should have started the research here as you're all experts. The car came from an excellent independent dealer in south west London and the car is still in warranty. Before I speak to them I thought I'd get your input. All comments gratefully received.
Thanks.
Simon
 
I thought I read that the exhaust needed to be tuned quieter in this rev range and this makes the car sound flat. I think it's the noise change that gives the impression of flat performance.

As a solution some people disconnect the electronic valve which suppresses the noise in this rev range. I've played a little with it, but observed other changes which I wasn't too happy about.

KR Lee
 
If you mean noticed as in 'felt' the engine hesitate then it could be one of a number of things shown below, in order of cost / shock of cost:
Vaccum line in the variable inlet system not opening the second flap until very late.
Depending on when they were last done: Spark Plugs. Should be every four years.
Remote, but could be an indication of coil pack failure. Usually they just fail rather than give a warning.
Variocam (adjustable cam timing) fault. This is unlikely as the system doesn't open up until later in the range, usually 5k and upwards.

If you mean noticed as in 'it soundslike' then this could be the exhaust as if you have PSE - Sports Exhaust, there is a spot at about 3.5 to 4k where the system isn't sure whether to change from 'quiet' to 'rwaaar!!!' especially if you're not using the throttle like you mean it.

If the dealer is as reputable as I think the one in SW London is, then they won't make you feel like a fool for taking it back for a look-see.
 
You don't provide the age or mileage of your vehicle, but it might indicate a potentially defective high pressure fuel pump.
They have been known to fail in 997's - just ask tscaptain of this forum. If it is, I hope you have warranty, since it's about £2K to replace! [:(]
Regards,

Clive
 
Thanks for your replies. I should have been a little clearer on the original post. The mileage is around 45k and the flat spot I was asking about is a very slight hesitation on acceleration. It doesn't happen every time and I'm currently trying to work out the exact RPM at which it happens. I'm going to speak to the dealer this week to get them to give it a check.
 
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