RPMs bogging down during hard acceleration, Help Plz!!

[llll1l1ll]

CDV deleted or not (could be that simple)?

I was thinking about this yesterday. If the CDV slows down the speed of the clutch engagement, then no matter how quickly OP lifts his foot off the pedal, the clutch will just slowly engage with the flywheel, which could perhaps cause this "bogging" sensation. In my E30, I can just shift from 1st to 2nd and it'll chirp the tires if I'm quick. It would never slip like that.

It could also be a faulty piece of clutch equipment, like a pressure plate, fork, TOB, slave or master cylinder. I'm not a mechanic by any means - I'm just saying.

On a side note, if it is running rich, then the SES light is trying to tell you something!

[VA//M3]

I'm surprised you didn't get a 2nd gear tire chirp followed with a slight kick sideways from the rear... Like on the new e90 M3's.

[VA//M3]

I was thinking about this yesterday. If the CDV slows down the speed of the clutch engagement, then no matter how quickly OP lifts his foot off the pedal, the clutch will just slowly engage with the flywheel, which could perhaps cause this "bogging" sensation. In my E30, I can just shift from 1st to 2nd and it'll chirp the tires if I'm quick. It would never slip like that.

It could also be a faulty piece of clutch equipment, like a pressure plate, fork, TOB, slave or master cylinder. I'm not a mechanic by any means - I'm just saying.

On a side note, if it is running rich, then the SES light is trying to tell you something!

That's basically what happens. The CDV will never allow you to up shift properly like a manual car should be able to. It will actually slow your car down.

That's becuase your E30 is a proper manual car without a CDV valve.

Take the CDV valve out and you will be back in command instead of the car commanding you.

[AzkotikBMW]

I had the SES codes checked about a month ago and the only code that was thrown is the O2 sensor failure from having my Ebay headers. BUT there could be new ones since then and I would never know because the light is always on.

I have not done the CDV delete, so that shouldn't be the issue.

I also have been driving this car for almost a year now, and have never had a problem like this until now, so I'm don't think its my lack of experience driving the car/manual trans that is causing this.

I've posted this on 3 different bimmer forums, and the first reaction from everyone (to my dismay) is that it's the clutch slipping. But there are a select few that swear on their life it can't be....so I'm getting a little confused :P

[VA//M3]

I had the SES codes checked about a month ago and the only code that was thrown is the O2 sensor failure from having my Ebay headers. BUT there could be new ones since then and I would never know because the light is always on.

I have not done the CDV delete, so that shouldn't be the issue.

I also have been driving this car for almost a year now, and have never had a problem like this until now, so I'm don't think its my lack of experience driving the car/manual trans that is causing this.

I've posted this on 3 different bimmer forums, and the first reaction from everyone (to my dismay) is that it's the clutch slipping. But there are a select few that swear on their life it can't be....so I'm getting a little confused :P

I would take out the CDV valve if you know how to properly drive a manual. I test drove an 03' M3 which has a CDV valve and it was like I was back in my old car(pre CDV valve delete). Completely different clutch engagement everysingle time. I hated it.

OUr pressure plates are also self-adjusting. Your pressure plate might be stuck and not able to adjust itself again. When I first bought my car the clutch left a lot to be desired but after I drove it without the CDV properly it was much more consistant and more grippy.

I would take the CDV valve out and drive normal. As in pushing the clutch all the way in, shifting and engaging it smoothly right at where the revs match the gear. And also rev match downshift. and very little engine braking less (clutch slip braking) for less than 2 seconds and seeing if the clutch feel improves.

CDV valves are evil. They're like Traction control, and haldex differentials. They take the skill and fun out of driving.

Technically our cars do have LSD but it is a failing concept in the real world

EDL (often referred to as Electronic Traction Control.)
This system is used by most VW models today, many Audis and several other car models, and was first introduced for offroad use in the Mercedes ML320 (AWD) and is undoubtably used by many others today.
It's what I call the poor man's LSD

problem with the way EDL works is that it's pretty harsh. The pulsing of the ABS isn't progressive. If the ABS is on, it applies full braking power followed by zero braking power.. full, zero, full, zero.. The torque from the engine that's being transferred repeatedly all the way across the drivetrain from wheel to wheel a dozen times a second, puts stress on everything. Brakes, rotors, axles, U joints, output shafts, and the differential itself. The left and right halves of the differential in the VW 02A transmission are held together with rivets which if forced to take this pounding too long will eventually fail. Neat huh?

That is why the system is aweful during the snow. It's to crappy. Only reasonable solution.. take your foot off the gas and turn off DSC.

^^ that is why BMW deemed a traditional torsen, posi, or viscous LSD "unnecessary". They really just didn't want to spend an extra 1.5k in fitting a real LSD and used it as a cost cutting measure.

[AzkotikBMW]

Thanks a lot VA!

[VA//M3]

NP!

Also when rev-match downshifting--double clutch. When passing through nuetral take the clutch out to the biting point, blip the gas, and press the clutch back in and downshift. It may help knock some sense into the pressure plate.

[telijah]

Quick and dumb question, but when you start your car, and the dash does it's light check, do you DSC lights come on at all? I am wondering if your shifting too hard, causing slight wheel slippage and thus the car bogging itself out as it usually would when the wheels are loosing traction... Seems like VA is talking along the same lines but your vid doesn't show the transaction light coming on.

[AzkotikBMW]

Quick and dumb question, but when you start your car, and the dash does it's light check, do you DSC lights come on at all? I am wondering if your shifting too hard, causing slight wheel slippage and thus the car bogging itself out as it usually would when the wheels are loosing traction... Seems like VA is talking along the same lines but your vid doesn't show the transaction light coming on.

Yes, it does. It also comes on it I hit the DSC button on the dash.

[telijah]

OK, and is not coming on when experiencing your problem, correct? I know, sorry if thats a dumb question and you're well aware of this. I would then check for a CDV. Did you say your car has always done this, or is this a new development?