[orbE46]

Good evening all. I installed my CG Precision catted downpipe on my 340i a few days ago. Car seems to run fine for the most part, but now seems sort of twitchy/jerky driving in parking lot speeds and under mild acceleration. Shifts also seem more pronounced. Car doesn't have a tune. Any ideas what could be going on here? Maybe just the car adapting to me driving slightly more aggressive with the pedal these past few days?

Thanks in advance.

[Lego864]

You explained it. "It doesn't have a tune". Sure the car can adapt and run decent without a tune, but to have fully optimized drive ability and power, you need a tune.

[orbE46]

Originally Posted by Lego864

You explained it. "It doesn't have a tune". Sure the car can adapt and run decent without a tune, but to have fully optimized drive ability and power, you need a tune.

Thanks. Is it safe to continue to run it then without a tune and just the downpipe?

[IMS-340C]

I used MPPSK tune for a long time with a catless downpipe without any problems.

Originally Posted by orbE46

Good evening all. I installed my CG Precision catted downpipe on my 340i a few days ago. Car seems to run fine for the most part, but now seems sort of twitchy/jerky driving in parking lot speeds and under mild acceleration. Shifts also seem more pronounced. Car doesn't have a tune. Any ideas what could be going on here? Maybe just the car adapting to me driving slightly more aggressive with the pedal these past few days?

Thanks in advance.

[mike@x-ph.com]

No adaptation period is needed, the tune won't change driveability either.

Check if the O2 sensor is damaged or not installed correctly

[orbE46]

Thanks guys. I was thinking there could possibly be a boost leak at the turbo to downpipe connection. The downpipe didn't fit quite flush all around mating up to the turbo, but the clamp seemed to go on just fine. Does tightening the clamp pull the connections together? I think if I had an exhaust leak up there it'd be obvious, no?

[M4-CPA]

Originally Posted by orbE46

Thanks guys. I was thinking there could possibly be a boost leak at the turbo to downpipe connection. The downpipe didn't fit quite flush all around mating up to the turbo, but the clamp seemed to go on just fine. Does tightening the clamp pull the connections together? I think if I had an exhaust leak up there it'd be obvious, no?

Yup! Pulls it all together nice and airtight. It's a pretty gnarly clamp to be honest.

[Uni-Rapide]

Originally Posted by orbE46

Thanks guys. I was thinking there could possibly be a boost leak at the turbo to downpipe connection. The downpipe didn't fit quite flush all around mating up to the turbo, but the clamp seemed to go on just fine. Does tightening the clamp pull the connections together? I think if I had an exhaust leak up there it'd be obvious, no?

Can it be the orientation of the the clamp?
I remember reading something about that the bolt/nut of the clamp can interfere with the waste gate lever if not in the correct orientation.

[orbE46]

Originally Posted by Uni-Rapide

Can it be the orientation of the the clamp?
I remember reading something about that the bolt/nut of the clamp can interfere with the waste gate lever if not in the correct orientation.

Clamp is out of the way of the wastegate in its original orientation.

Thanks everyone for the help. I don't see any soot around the clamp that could indicate a leak. I think it may just be in my head.

[F30Bully]

Originally Posted by Lego864

You explained it. "It doesn't have a tune". Sure the car can adapt and run decent without a tune, but to have fully optimized drive ability and power, you need a tune.

Actually it's ok to run these cars catless (down pipe) with no tune. It won't run as efficient as it could but it still should be running fine. I think something happened along the way, like a broken vacuum hose or something.

Source: I was running a downpipe and no tune for 1 month and half with no issues.

[apex_crisis_]

My case may be different (2018 car with OPF), but this is what happened:

Installed straight through midpipe and catless downpipe. Obviously threw errors because no cat and OPF is gone. I flashed with BM3 tune removing the errors for both. Car drove fine when slow but under any proper acceleration it was very jerky. Logs showed that the ECU was cutting throttle because the turbo was overboosting. Took a bit of time but the guys at BM3 sorted the tune out and it's all good now.

[F30Bully]

Originally Posted by apex_crisis_

My case may be different (2018 car with OPF), but this is what happened:

Installed straight through midpipe and catless downpipe. Obviously threw errors because no cat and OPF is gone. I flashed with BM3 tune removing the errors for both. Car drove fine when slow but under any proper acceleration it was very jerky. Logs showed that the ECU was cutting throttle because the turbo was overboosting. Took a bit of time but the guys at BM3 sorted the tune out and it's all good now.

How long after did your car start to feel jerky? I'm currently running on BM3 and I think I am experiencing the same issue.

[F30MGM]

Make sure intake is tight and the clamps are new and not leaking. When I didn't use new clamps I smell exhaust in cabin

[apex_crisis_]

Originally Posted by F30Bully

How long after did your car start to feel jerky? I'm currently running on BM3 and I think I am experiencing the same issue.

Pretty much immediately. After start up, first WOT pull felt a little slow but usually not jerky, any pulls after that were very jerky.

[orbE46]

With mine it's smooth under heavier load conditions. Most of the low speed jerking surfaces when the ambient temp is hot (95+) and I'm at parking lot speeds. Sport mode amplifies the problem.

[about94ninjas]

Mine was rough at WOT until I got the EWG harness for my JB4. That helped smooth it out a lot. Idk if you're planning on getting a tune, but that'll probably help if not solve it.

[jakel1995]

Originally Posted by Lego864

You explained it. "It doesn't have a tune". Sure the car can adapt and run decent without a tune, but to have fully optimized drive ability and power, you need a tune.

I can confirm a tune solves this. I see a lot of people saying it won’t affect performance, I can promise you it does. Just because the car might not see any power loss at wide open throttle doesn’t mean you aren’t throwing off the AFR. The computer will do it’s best to adjust on the fly and it may become smoother the longer you’re driving it but every time you turn the car off you’ll notice the problem almost resets. I’m also betting every cold start idles pretty high and takes a minute to drop to sub 1000rpm. For anyone reading this just take my word for it, buy the DP and tune at the same time.

[n55david]

Originally Posted by Lego864

You explained it. "It doesn't have a tune". Sure the car can adapt and run decent without a tune, but to have fully optimized drive ability and power, you need a tune.

This is the worst info I've read in a while...

[n55david]

Originally Posted by F30Bully

Actually it's ok to run these cars catless (down pipe) with no tune. It won't run as efficient as it could but it still should be running fine. I think something happened along the way, like a broken vacuum hose or something.

Source: I was running a downpipe and no tune for 1 month and half with no issues.

The car has a wideband 02.. it'll run just fine regardless of tune or not.

[lens]

Originally Posted by jakel1995

I can confirm a tune solves this. I see a lot of people saying it won’t affect performance, I can promise you it does. Just because the car might not see any power loss at wide open throttle doesn’t mean you aren’t throwing off the AFR. The computer will do it’s best to adjust on the fly and it may become smoother the longer you’re driving it but every time you turn the car off you’ll notice the problem almost resets. I’m also betting every cold start idles pretty high and takes a minute to drop to sub 1000rpm. For anyone reading this just take my word for it, buy the DP and tune at the same time.

Fake news.

There's zero performance loss running a DP without a tune, and the cold starts have nothing to do with it. All colds starts are is to warm up the cat, if you have none, it's useless.

AFR is completely fine as well, plenty of guys run catted or catless DP without a tune for months before getting one, I ran one for 6 months and zero issues, AFR wasn't affected either.

[Cytoplasm0671]

Like Mike suggested, my guess is theres an issue with the o2 sensors, either they weren't reinstalled correctly or they got damaged