Limp Overboost and Bouncy Idle after DP

[PanAm]

Hi guys!

I've been referencing this forum for a month now and though, why not sign up.

Got a 2011 BMW X5 x35i e70 with 39,700 miles on it. Absolutely love the car but the little errors, fail codes and bugs keep me in check.

Lately it's been going to limp mode when cruiser regularly. Based on the errors I've gotten, it seems to be related to an "Overboost" situation.
When I did a datalog a week ago using Protools, I did notice that sometimes the actual boost would be higher than the target boost. I've checked vacuum lines and they all seem fine BUT there is one that I'm not sure if it's connected properly. Basically it goes from the chassis behind the passenger lamp and it goes to somewhere in the valvecover
Both pictures attached.
IF I use the car in Sport mode, the limp mode takes a lot longer to go into action if even. I know... solution = use it always in sport mode but sadly the error does come on eventually.

Have no idea why that is as the car was completely stock.... until today.

I just did a catless downpipe install annnnd I wish I could say I love it but... my idle completely sucks. Starts normally and starts oscillating more and more to the point that if I'm driving and come to a stoplight it stalls sometimes. I guess O2 sensors parameters are now out of wack with the new DP... sounds like I'll have to try MHD's stage 1 at least..?

Anyway, recommendations, suggestions or pointers will be appreciated. Oh, this is my INPA screenshot before the DP install. I also did some datalogging but will update the thread later with the results.

Thanks!

[ryansbmw]

If you dont see any obvious signs of a vaccum leak, go to a shop and have them do a smoke test. It will quickly point out any leaks in the system.

I'm no expert, but Im gonna assume you will need some sort of tune to help the engine compensate with the catless downpipes. Your 02 sensors ( the rear in particular) are reading the exhaust stream under the impression you still have cats but they have completely failed. Thats def going to to alter the engines fuel/air ratio calculation, timing, etc.. which may effect your idle.

On a side note, what DP did you get? How was the install?

[PanAm]

Originally Posted by ryansbmw

If you dont see any obvious signs of a vaccum leak, go to a shop and have them do a smoke test. It will quickly point out any leaks in the system.

I'm no expert, but Im gonna assume you will need some sort of tune to help the engine compensate with the catless downpipes. Your 02 sensors ( the rear in particular) are reading the exhaust stream under the impression you still have cats but they have completely failed. Thats def going to to alter the engines fuel/air ratio calculation, timing, etc.. which may effect your idle.

On a side note, what DP did you get? How was the install?

Any advice on where to find a proper vacuum line diagram? I want to make sure they are all routed properly.

Well as an update, today I decided to disconnect both O2 sensors and... the idle runs better. Not great but oscillates a lot less and doesn't bounce as aggressive. Drove for about 10 miles and didn't get any engine limp mode errors on the screen and the car felt like it should with a free flowing exhaust.
Tried to run a datalog but sadly Protools won't cooperate and I haven't had much luck with INPA reading my cars info or viewing anything more than just error codes and clearing them.

I'm guessing with an MHD flash the 2nd O2 sensor correction can be disabled and at this point I wouldn't mind buying a new O2 sensor just to be safe.

I got an Ebay one. I couldn't notice any difference from the VRSF one and it was 150$ less. It's a daily driven, mostly city driven car so I'm not too concern about high temps cracking welds. Worst case I get an exhaust leak that would throw off the O2 readings at some point. I'm attaching a picture of it.

Removing the DP wasn't bad at all. Getting the new one in has been a B*T*H! The clamp that ties it to the turbo is difficult to handle in such a tight space and the screw that holds it together doesn't quite fit.

But this experience has left me not wanting to do much more like upgrading the diverter valve and chargepipe or intercooler.

[ryansbmw]

Originally Posted by PanAm

Any advice on where to find a proper vacuum line diagram? I want to make sure they are all routed properly.

Well as an update, today I decided to disconnect both O2 sensors and... the idle runs better. Not great but oscillates a lot less and doesn't bounce as aggressive. Drove for about 10 miles and didn't get any engine limp mode errors on the screen and the car felt like it should with a free flowing exhaust.
Tried to run a datalog but sadly Protools won't cooperate and I haven't had much luck with INPA reading my cars info or viewing anything more than just error codes and clearing them.

I'm guessing with an MHD flash the 2nd O2 sensor correction can be disabled and at this point I wouldn't mind buying a new O2 sensor just to be safe.

I got an Ebay one. I couldn't notice any difference from the VRSF one and it was 150$ less. It's a daily driven, mostly city driven car so I'm not too concern about high temps cracking welds. Worst case I get an exhaust leak that would throw off the O2 readings at some point. I'm attaching a picture of it.

Removing the DP wasn't bad at all. Getting the new one in has been a B*T*H! The clamp that ties it to the turbo is difficult to handle in such a tight space and the screw that holds it together doesn't quite fit.

But this experience has left me not wanting to do much more like upgrading the diverter valve and chargepipe or intercooler.

I dont have a diagram but if I come across one, Ill post it up here.

Thanks for the info on installing the DP. Once I pass inspection in Feb, I actually plan on putting one of these in and bumping up my tune from MHD1+ to 2 or 2+.

I know the diverter valve is a b*tch of an upgrade on the N55 but the chargepipe on this car is actually really easy. Intercooler is expensive but relatively straightforward as well so dont let this discourage you.

[PanAm]

Well just a quick update... I've been driving around with both O2 sensors disconnected for the past two days and it's better than with them connected. The idle hunt is a LOT less and so far it's only gone to limp mode once. Will keep datalogging and testing and will use this thread as a log.

[aligoodn]

Catless downpipes allow the turbo to spool earlier and faster. The stock tables in the ECU for wastegate duty are expecting the restriction from the stock cats, now that its gone the wastegate needs to allow more exhaust around the turbo to control the boost. Downpipes without a corresponding ECU tune will give you the symptoms you describe.

Your limp mode is likely due to underfueling since the engine is getting more air but the ECU is not delivering more fuel, running with the O2 sensors disconnected is allowing the computer to ignore this and run in open loop. Not a good solution because the engine will be running leaner than before and the ECU will have no idea.

Bottom line, you need a tune for the catless downpipes.