Thud in the drivetrain with test pipes and tune

[aussiem3]

I have been experiencing some run-over "burble" and a thud when I take the foot off the accelerator since I installed test pipes and tune. The smoothness that existed with the primary cat when you abruptly took the foot off the "happy" pedal is no longer there.

Is it just me and my car, or anyone else have experienced this too?

I have test pipes with BPM Stage II. This is in no way a criticism of the tune or the test pipes, but just trying to understand whether it's normal. I've been wanting to post this for a long time but somehow have been forgetting.

[SilentAttack]

Originally Posted by aussiem3

I have been experiencing some run-over "burble" and a thud when I take the foot off the accelerator since I installed test pipes and tune. The smoothness that existed with the primary cat when you abruptly took the foot off the "happy" pedal is no longer there.

Is it just me and my car, or anyone else have experienced this too?

I have test pipes with BPM Stage II. This is in no way a criticism of the tune or the test pipes, but just trying to understand whether it's normal. I've been wanting to post this for a long time but somehow have been forgetting.

It's normal, my car does it too. I even asked Mike about it because I was wondering if I was having sudden issues with my car.

[aussiem3]

Originally Posted by SilentAttack

It's normal, my car does it too. I even asked Mike about it because I was wondering if I was having sudden issues with my car.

Thanks for the feedback. Good to know it's normal behaviour.

[Rob-NV]

I have a similar setup but with a different tune. I get a thud or a jerk letting off the throttle at low gears and high gears at mid to high rpms. Is there a way to soften this with the tune configuration?

Thx

[Ilikemike]

Anyone else heard of this? The burble sounds interesting but the "thud" sounds a bit alarming.... Mike, anyone?

[apecush]

The thud is unburnt fuel combusting in the exhaust. You will feel it.

[aussiem3]

Originally Posted by apecush

The thud is unburnt fuel combusting in the exhaust. You will feel it.

So then why do you feel it more in a catless setup?

[Ilikemike]

Just guessing but the front cats seem to add enough back pressure to limit any sudden changes in exhaust gas flow resulting in the 'thud' that is appears when they are removed. if the car was engineered without the front cats then I'm sure there would be no thud, but it seems that we are tinkering with a balanced design..... I just don't get that we haven't heard about this before....

[aussiem3]

Originally Posted by Ilikemike

Just guessing but the front cats seem to add enough back pressure to limit any sudden changes in exhaust gas flow resulting in the 'thud' that is appears when they are removed. if the car was engineered without the front cats then I'm sure there would be no thud, but it seems that we are tinkering with a balanced design..... I just don't get that we haven't heard about this before....

Good point ... just goes to show tinkering does have some down side to creature comfort afterall

[American Dave]

this is news that concerns me as I am about to do test pipes, x pipe swap and tune mods. I need to ride in your car aussiem3.

[Rob-NV]

In my case, the thud/jerk is more pronounced with the tune than with factory software. I have had my car into the dealership and they checked for faults and made sure there was no wear with engine or other types of mounts, therefore I believe it is "normal" for primary cat delete + tune

Is this a symptom specific to 2008 models? Is there any reason to believe this is caused by flywheel in 2008 that was changed in later models?

[aussiem3]

Originally Posted by American Dave

this is news that concerns me as I am about to do test pipes, x pipe swap and tune mods. I need to ride in your car aussiem3.

Let me know when if you can't wait till the next coffee catch up. I am happy to do it sooner

[aussiem3]

Originally Posted by Rob-NV

In my case, the thud/jerk is more pronounced with the tune than with factory software. I have had my car into the dealership and they checked for faults and made sure there was no wear with engine or other types of mounts, therefore I believe it is "normal" for primary cat delete + tune

Is this a symptom specific to 2008 models? Is there any reason to believe this is caused by flywheel in 2008 that was changed in later models?

No idea what the cause is. I am surprised there aren't a lot more observing this change given that a lot of forum members have gone down this path - catless with tune.

[Ilikemike]

Aussie, how about changing the title of the posting to see if others are experiencing this ..... 'Thud in drivetrain after test pipes and a tune, anyone else?

[WickedE93]

I have a tune and test pipes and don't have this issue.

[BPMSport]

Flash the car back to stock, this isn't something the tune should cause. Try normal mode instead of power.

[aussiem3]

Originally Posted by Ilikemike

Aussie, how about changing the title of the posting to see if others are experiencing this ..... 'Thud in drivetrain after test pipes and a tune, anyone else?

Good point. Done

[DaveDee]

Originally Posted by aussiem3

Good point. Done

As well as the comments to date, you might want to check the clamp seals on the track pipes, it might be sucking air causing more of a pop. I tried full catless a while ago and really got some good pops and the occasional flame :-)

Also spoke with Mike Benvo who is not in the slightest concerned, so many M3s have primary cat delete without issue Remember the performance gains from getting rid of those shocking 400 cpsi power robbers.

[Ilikemike]

Sounds like you're saying the 'thud' is not normal, which is a relief but not the feedback from the early days of the post. It never sounded like a tune issue just a mechanical issue, I.e., front cat delete with or without a tune would always result in a thud due to changes in back pressure, un burnt fuel or whatever.... I still have the lingering feeling that if I'm one of the 'unlucky ones' I will have a thud when I let off the gas.....unacceptable. I'd be putting the cats back on right away and flogging the test pipes on the classifieds, notwithstanding the extra power...... Be nice to know though..... Seems what's happening to those with the problem (I think it's a problem, others might not care) should be happening to all those with a cat delete, but that's not emerging, so I wonder, why some and not others?

[aussiem3]

Originally Posted by Ilikemike

Sounds like you're saying the 'thud' is not normal, which is a relief but not the feedback from the early days of the post. It never sounded like a tune issue just a mechanical issue, I.e., front cat delete with or without a tune would always result in a thud due to changes in back pressure, un burnt fuel or whatever.... I still have the lingering feeling that if I'm one of the 'unlucky ones' I will have a thud when I let off the gas.....unacceptable. I'd be putting the cats back on right away and flogging the test pipes on the classifieds, notwithstanding the extra power...... Be nice to know though..... Seems what's happening to those with the problem (I think it's a problem, others might not care) should be happening to all those with a cat delete, but that's not emerging, so I wonder, why some and not others?

I am going to get my car checked out by the dealer for leaks in the header and where the test pipes are clamped to the OEM. I will also reflash the stock 240E. I was driving yesterday and couldn't replicate it. Don't know why. I must see whether it happens in low or high gear as well as spirited and normal driving. I don't somehow think it's a tune issue, and it's more mechanical. Let's see.

[DaveDee]

Originally Posted by Ilikemike

Sounds like you're saying the 'thud' is not normal, which is a relief but not the feedback from the early days of the post. It never sounded like a tune issue just a mechanical issue, I.e., front cat delete with or without a tune would always result in a thud due to changes in back pressure, un burnt fuel or whatever.... I still have the lingering feeling that if I'm one of the 'unlucky ones' I will have a thud when I let off the gas.....unacceptable. I'd be putting the cats back on right away and flogging the test pipes on the classifieds, notwithstanding the extra power...... Be nice to know though..... Seems what's happening to those with the problem (I think it's a problem, others might not care) should be happening to all those with a cat delete, but that's not emerging, so I wonder, why some and not others?

Again maybe check the clamps for leaks, mine are customed and welded in and I've never had an issue at all like many others. In one instance where a SC was fitted and a set of "test pipes" with the clamps, the car was throwing codes and had and a leak was found in the clamps. The pipes were then welded in and the problem went away. it's also worth considering the distance between the header outlet and the secondary cats which must have some effect as cats are usually right up against the headers.
Nearly everyone I know with an M3 has a primary cat delete and tune and nobody has ever mentioned a problem before.

[aussiem3]

Originally Posted by DaveDee

As well as the comments to date, you might want to check the clamp seals on the track pipes, it might be sucking air causing more of a pop. I tried full catless a while ago and really got some good pops and the occasional flame :-)

Also spoke with Mike Benvo who is not in the slightest concerned, so many M3s have primary cat delete without issue Remember the performance gains from getting rid of those shocking 400 cpsi power robbers.

That's what MB told me. Thanks Dave and see you soon.