Repeatedly killing PRE-CAT O2 sensors — 274A / 274B every 1–2k miles. HELP

[charliev68]

Pre cat O2 wiring harness plug. Bend the prong plugs on the sensor side to make a better connection.

[supergoji]

AHH gotcha. sounds like an oem tune isn't going to cut it to test. I sent RK an email, but his last communication was on 12/26.

[omgzirra_exe]

Originally Posted by Redd

Oh I didn't catch that. Forward x-pipe systems are known to cause hesitation/stumbling with some tunes. There's quite a few threads on it and one of the reasons I've never experimented with a forward x-pipe. You may require a forward x tune.

Originally Posted by spammysammich

Can confirm the BW forward X caused driveability issues on my car without a tune. PO was going nuts trying to troubleshoot it.

IMO.

There are key differences between the two setups. The reason the Bimmerworld forward X causes hesitation at low rpm is because it’s a more “true” X merge, where the exhaust scavenges aggressively and the pulses jump from bank 1 to bank 2. That crossover disrupts the pulses at low speed and creates the stumble people notice.

The ARH headers use more of a “kiss merge,” where the pipes meet in parallel. The pulses still cross from bank 1 to bank 2, but the transition is smoother and doesn’t disrupt the flow the same way. Because of that, the “kiss merge” design doesn’t create the same drivability issues.

[kimiraikkonen]

supergoji Any update? I may be having a similar issue, Bank 2 pre cat o2 sensor only though. I replaced my O2 sensors 10K mi ago and the codes came back all of a sudden recently.

[supergoji]

Originally Posted by omgzirra_exe

IMO.

There are key differences between the two setups. The reason the Bimmerworld forward X causes hesitation at low rpm is because it’s a more “true” X merge, where the exhaust scavenges aggressively and the pulses jump from bank 1 to bank 2. That crossover disrupts the pulses at low speed and creates the stumble people notice.

The ARH headers use more of a “kiss merge,” where the pipes meet in parallel. The pulses still cross from bank 1 to bank 2, but the transition is smoother and doesn’t disrupt the flow the same way. Because of that, the “kiss merge” design doesn’t create the same drivability issues.

RK was saying the Bimmerworld forward X can cause issues, but I have the ARH system.

I think it comes down to if you know how to manage airflow or not.

If you're having issues with a tune, and your tuner doesn't ask for logs right off the bat to see how the car is operating, what would you do?

Originally Posted by kimiraikkonen

supergoji Any update? I may be having a similar issue, Bank 2 pre cat o2 sensor only though. I replaced my O2 sensors 10K mi ago and the codes came back all of a sudden recently.

Going with Randy at Epic.

[omgzirra_exe]

Originally Posted by supergoji

RK was saying the Bimmerworld forward X can cause issues, but I have the ARH system.

I think it comes down to if you know how to manage airflow or not.

If you're having issues with a tune, and your tuner doesn't ask for logs right off the bat to see how the car is operating, what would you do?




Going with Randy at Epic.

I don’t really trust RK when it comes to the S65. He might tune other BMW engines well, but there are some red flags with his S65 tunes. I’ve even seen cases where people somehow ended up losing power.

As far as forward X / headers, it also depends on which headers you’re running.

If you have the ARH triple-step headers, the stepped design helps maintain exhaust velocity for scavenging and then increases the primary diameter in stages to support better flow across the RPM range.

The non-stepped headers are basically straight primaries into the collector, which is conceptually closer to the OEM S65 equal-length layout, so the pulses coming out of each bank are already fairly even.

That’s where X-merge style and placement starts to matter. A more “true” forward-X placed very close to the collectors lets the pressure waves from each bank interact very early. At lower RPM that crossover can disturb pulse timing a bit, which is where the hesitation people talk about can show up.

The ARH setup is more of a kiss-merge style, so the transition between banks is smoother and tends to preserve drivability better than a very aggressive forward-X.

And yeah, logs should always be the first step with tuning. But even with good logs, certain exhaust layouts can still introduce quirks, which is why some people end up moving away from the forward-X setups.

Also +1 for Randy

[supergoji]

well said. now i just need to find a dynojet in the lower NY/CT/NJ area. so i can get this baby running right.

[supergoji]

headed to the shop CT today to get some baseline pulls of where im at.

took it to the shop CT with a dynojet.

[supergoji]

Post tune, no more hesitation.

Randy also found that I have a code 2B59 - Tstat code. No other scanners found this. even my $1k scanner.

Will replace, send logs post repair and update sheet when possible.

[darren p.]

Originally Posted by supergoji

Randy also found that I have a code 2B59 - Tstat code. No other scanners found this. even my $1k scanner.

What was the $1k scanner that didn't? What were the others? I found the same code using ISTA and it turned out my tstat was stuck open so the car was always running cool as verified on my steering wheel display (BMW Performance V2). After replacement it steady at 180 once up to temp.

Did the tune resolve the O2 sensor issue or was that something else that fixed it?

I'm somewhat dissapointed with the numbers on the dyno considering the head work, cams, headers and ITBs. Was it a custom tune from Randy?

[supergoji]

Originally Posted by darren p.

What was the $1k scanner that didn't? What were the others? I found the same code using ISTA and it turned out my tstat was stuck open so the car was always running cool as verified on my steering wheel display (BMW Performance V2). After replacement it steady at 180 once up to temp.

Did the tune resolve the O2 sensor issue or was that something else that fixed it?

I'm somewhat dissapointed with the numbers on the dyno considering the head work, cams, headers and ITBs. Was it a custom tune from Randy?

Topdon, even some other name brand ones didn't pick it up.
02 issue I have to drive and eventually find out.

I think this dyno just reads low, yes custom tune from randy.
If I can line it up with a 992 gt3 and be pretty much even or faster then I'll know.
On rk's tune with the current setup it was matching the previous owners 992 gt3.