Catless X-Pipe Misfire/Torque Dip/Bog [SOLVED?]

[MikeYQM]

I have a 2013 ZCP with the following mods:

- AFe CF Intake with Pro 5R filter
- Bimmerworld catless X-Pipe with 4 resonators
- Alpine Stage 2 with GTS DCT flash
- Carbon Project CF Plenum (not yet installed)
*I am running OEM Axle Back*

Maintenance is all up to date including new plugs and O2 sensors within 10k km.

I installed the BW X-Pipe about 1900 km ago. Immediately there was a frequent torque dip/bog. What happens is at around 2500rpm-3000rpm while increasing from about 30-50% throttle. Once it starts, the RPM hang and the DCT won't downshift in D mode. Almost like a misfire, but with no codes.

I immediately contacted Alex and he put in a fair amount of time helping diagnose the problem, we reset the adaptations, tried a stock map and a varied tune map.

The condition has improved some over the last 1900km and is made better by driving in D4-5 but is still present. And it's driving me nuts.

Ive had some good conversations with some helpful people including Alex, SYT_Shadow and have jumped into a few posts and there are a few possible solutions but nothing has been confirmed. It seems like a common enough issue so I thought I'd compile the info here in hopes that all the great minds on this forum can come up with a solution.

Possible Solutions:

1. Adaptations: the theory is that the ECU needs to learn/adjust to the decreased back pressure from the catless exhaust. After 1900 km, this seems to have helped some but certainly not 100%.

2. Tune issue: the theory is that various tunes are not suited to the catless X-Pipe. I tried an Alpine Stage 2, a modified Alpine Stage 2 which was basically stock below 4000 RPM and Stock. Differences were negligible. I reached out to ESS who said this issue couldn't be fixed by tuning.

3. High Flow Cats: the theory is that adding HFC add the lacking back pressure to the system. I haven't tried this yet.

4. Free flowing axle back: theory is that increasing the flow of the axle back matches better to the free flowing X-Pipe.

5. Change driving style/shift earlier: This has helped avoid the symptom but hasn't corrected the problem. I want a cure, not a bandaid.

Something, as a result of adding the catless X-Pipe is causing the issue, and while avoidable, it's definitely an issue, when it occurs, you KNOW that the car isn't responding correctly.

I'm asking, for any of you with a forward X X-Pipe, and a tune, have you encountered this? Have you been able to correct the issue? If so please explain how you did and what you tried that may not have worked.

Thanks!

[Gossypiboma]

It would be interesting to hear if this happens with the Epic tune that was designed around BW's xpipe. So far all the complaints come from members with a forwardly located X pipe but without the Epic motorsports tune.

[SYT_Shadow]

Calling Scharbag and Audioslave686

Calling dmlf , fsmtnbiker , SupergluedGaspedal , CurbBender'90

[SYT_Shadow]

There are long threads from both the BW xpipe and the ESS xpipe. I have both, their Xs are both forward-placed in the same place. I don't have any issues. The issue is very noticeable, it isn't something you can miss.

On one car I have the BW LT headers + catless BW Xpipe and have zero hesitation. It has used both the AA and the BW muffler.
On the other car I have the ESS catless xpipe and have zero hesitation. It has the Evolve Valvetronic muffler permanently on the ON/loud position.


Two friends have the same BW Xpipe and both added cats in the secondary position, one with the ESS tune and one with the Alpine tune.
The ESS car works perfectly
The Alpine car bogs like crazy

Some have theorized that if you have a stock rear section it is more likely to bog. We are testing that theory out.

[MikeYQM]

Adding onto SYT_Shadow's hypothesis, here is my theory in support:

X-Pipe alters scavenging effect creating a pressure backup at the problem RPM range. At the problem RPM range, exhaust gasses do not flow efficiently.

Members have shown by data logging, where lambda reads rich (low O2) in the problem area leading to cut timing and fuel.

Higher velocity exhaust travels through the restriction free X-Pipe & meets Axle-Back. High velocity = lower pressure = more scavenging.

Once exhaust gasses hit more restrictive Axle-Back, velocity decreases, pressure increases and less scavenging occurs.

When restriction in a pipe is decreased at a certain point, a negative pressure wave is created but when a restriction is increased, it can create a positive pressure wave that travels towards the engine.

In the problem RPM band, this causes a pressure resonance (positive pressure wave traveling up exhaust) and exhaust gasses build up leading to poor O2 sensor readings, timing and fuel cut.

I'm not an expert, physicist or engineer so take this with a grain of salt. If correct, an equally free flowing Axle-back should correct (or at least deviate) the problem.

[MikeYQM]

Originally Posted by SYT_Shadow

There are long threads from both the BW xpipe and the ESS xpipe. I have both, their Xs are both forward-placed in the same place. I don't have any issues. The issue is very noticeable, it isn't something you can miss.

On one car I have the BW LT headers + catless BW Xpipe and have zero hesitation. It has used both the AA and the BW muffler.
On the other car I have the ESS catless xpipe and have zero hesitation. It has the Evolve Valvetronic muffler permanently on the ON/loud position.


Two friends have the same BW Xpipe and both added cats in the secondary position, one with the ESS tune and one with the Alpine tune.
The ESS car works perfectly
The Alpine car bogs like crazy

Some have theorized that if you have a stock rear section it is more likely to bog. We are testing that theory out.

Originally Posted by SYT_Shadow

There are long threads from both the BW xpipe and the ESS xpipe. I have both, their Xs are both forward-placed in the same place. I don't have any issues. The issue is very noticeable, it isn't something you can miss.

On one car I have the BW LT headers + catless BW Xpipe and have zero hesitation. It has used both the AA and the BW muffler.
On the other car I have the ESS catless xpipe and have zero hesitation. It has the Evolve Valvetronic muffler permanently on the ON/loud position.


Two friends have the same BW Xpipe and both added cats in the secondary position, one with the ESS tune and one with the Alpine tune.
The ESS car works perfectly
The Alpine car bogs like crazy

Some have theorized that if you have a stock rear section it is more likely to bog. We are testing that theory out.

Which axle-back are your friends using in the problem and problem free car?

[SYT_Shadow]

Originally Posted by MikeYQM

Which axle-back are your friends using in the problem and problem free car?

Both OEM, I should have said earlier.

The cars are identical and both have high miles, the only difference is the tune.

There are long threads about this issue and one tune comes up consistently: Alpine. I know Alex says there isn't a change under 4k rpm but there seems to be an issue of some kind related to the tune.

[GORDON.M3]

I'd look into another rear section and see what happens from there. Do you have access to test another axle back?

[MikeYQM]

Originally Posted by GORDON.M3

I'd look into another rear section and see what happens from there. Do you have access to test another axle back?

I have a Megan rear I'll be putting on to test on Weds after work. Someone else will be testing a BW rear.

[Gossypiboma]

Originally Posted by MikeYQM

I have a Megan rear I'll be putting on to test on Weds after work. Someone else will be testing a BW rear.

What tune does each car have? I would lean more towards this issue being tune related than rear muffler related.

[MikeYQM]

Apparently MPE was run and didn't cause an issue. Alpine Stage 2 93 Octane.

[MShift]

I recently posted about this same issue in several places and I'm currently talking to Randy from Epic to see if he has some feedback.

My setup is BW x, Dinan exhaust, bpm stage 2 tune. I noticed a big drop in low end torque/response and a terrible rasp around 2k-2.6k rpm immediately after installing it. Wonder if the rasp is proof of this exhaust gas pulse interference since it seems to happen at the same time?

My car doesn't quite bog down or stutters as some of the videos I've seen, but there definitely is a noticeable lack of response as compared to my old TopSpeed x pipe.

I'm not sure if I've gotten used to it or if it has improved over the last 1300 or so miles as the Ecu adjusted, but it feels a better than it did immediately after install.

[MikeYQM]

Originally Posted by SYT_Shadow

Both OEM, I should have said earlier.

The cars are identical and both have high miles, the only difference is the tune.

There are long threads about this issue and one tune comes up consistently: Alpine. I know Alex says there isn't a change under 4k rpm but there seems to be an issue of some kind related to the tune.

I read somewhere one of your friends has an OEM rear and the other has a modded OEM rear. Which one has the problem?

The ESS car works perfectly - Is this OEM or OEM MOD?
The Alpine car bogs like crazy - Is this OEM or OEM MOD?

[SYT_Shadow]

Originally Posted by MikeYQM

I read somewhere one of your friends has an OEM rear and the other has a modded OEM rear. Which one has the problem?

The ESS car works perfectly - Is this OEM or OEM MOD?
The Alpine car bogs like crazy - Is this OEM or OEM MOD?

If i recall correctly they're both modded rears, 2 pipe method.

Hopefully this week we see if changing the rear section does anything

[MikeYQM]

So, I've dug through some of the older posts trying to collect statistical data, maybe help rule in/out possible causes. I'll keep updating this list as info comes in. So far, I've found the following:

X-Pipe with Problem Cars:
- Bimmerworld Resonated & non-resonated
- ESS with and without HFC
- Becker Headers/X-Pipe

Tunes with Problem Cars:
- Stock (no tune)
- Alpine
- BPM

Axle-Back with Problem Cars:
- OEM (most common and severe problems reported)
- MPE (problems less often/less severe from multiple members)
- Dinan (problems less often/less severe from multiple members)
- GT2
- Armytrix
- Billy Boat
- Gintani Race
- Megan/Agency Power
- CNT Racing

Axle-Back without Problem Cars:
- Corsa (maybe... heard both good and bad)
- Bimmerworld
- AA
- Evolve with Valves Open

This isn't to assign blame, but rather to collect data to determine the cause/solution to this problem. I don't think there is anything wrong with any of the tunes or exhaust components, but rather a compatibility issue between various modded parts.

Can everyone who has had the 2500 RPM torque dip/bog/hesitation please reply and provide the following information?

- X-Pipe Type:
- Axle Back Exhaust Type:
- Tune:

[fth001]

I had this issue while running the BW Xpipe, Gintani Race rear, Alpine stage 2 tune, MT. Immediately fely a loss in power in that rpm range. It was VERY noticeable when trying to accelerate hard in 3rd or 4th gear from under 2500K. The car would start bogging down, if I backed off the throttle I would be able to get through it. If I held on the throttle, it would bog so hard that it would send my car into limp mode. I would have to pull over and restart the car to get going again. I read the other ongoing threads and some people were pointing towards the tune so I flashed back to my stock tune.....no go. Because I spend most of my time in stop and go traffic I kind off need the low end. Swapped to a MS Xpipe where the X is farther back and viola, problem gone. For me, this issue seems like it was fully related to the X placement.

[MikeYQM]

So, I had some unexpected free time this evening so I installed my Megan axle-back. Awful!

Not only was the hesitation worse, and much more frequent, the sound combined with the BW X-Pipe was garbage. Too loud, to bassy, all kinds of drone.

Going to put OEM axle-back on tomorrow and live with it for the few weeks till she gets parked for winter and we can find the proper solution to this.

I've been talking with Epic and BW and they both suggest a tune that was developed to correct this problem. I'm still not convinced that there isn't an axle-back that both sounds great and solves the hesitation issue.

[SYT_Shadow]

So now it's all up to the BW catback combo!

[94jedi]

So is the thought that the Epic MS tune somehow adjusts for the forward pos. of the xpipe?

[MikeYQM]

Originally Posted by 94jedi

So is the thought that the Epic MS tune somehow adjusts for the forward pos. of the xpipe?

According to both Epic and BW, the Epic tune does correct this problem. In fact, on the X-Pipe website page, they highly recommend the Epic tune. Not sure why I didn't notice that before.

[MikeYQM]

I have not come across any first hand accounts of people who had the problem, installed the Epic tune and the problem was solved.

So far, I've been told:

From ESS: Tune can't fix it.
From Alpine: Tune can't fix it.
From BW: Tune can fix it.
From Epic: Tune can fix it.

[MikeYQM]

Originally Posted by SYT_Shadow

So now it's all up to the BW catback combo!

Well that and so far your AA and Evolve valve open are problem free too. I think you're one of the few who have experienced both problem and problem free cars.