[N55Blues]

Hey I had a strange issue today, I was wondering if anyone has had this happen? I have a 2011 335i sedan. 75k, N55, AT, RWD. No mods, except for aluminum CSF radiator, installed approximately 2k miles ago.

I hadn’t driven the car in about a week. It was 40-45F and raining here this morning. Got in to take on 100+ mile mountain road trip. After about 20-30 min, when I would accelerate and the car would shift from 5-4, which would typically raise the rpm’s and increase torque substantially, the car felt totally powerless. I could press the accelerator and the rpm’s would only slowly increase and the car felt like it would almost slow down. At WOT, but not the passing button, the rpm’s would slowly get to 3-4k and the boost would weakly kick in, but no real power. I switched to manual and was able to shift through all the gears smoothly, just no power. Felt like an underpowered 4 cyl. Never had any CEL, and kept doing check control, that came back “check ok”. I climbed a significant mountain pass without any issue, except for the lack of power.

I had read that some people had experienced their car go into limp mode on cold days with the aluminum CSF radiator. Apparently the ecu thinks the thermostat is stuck open because the car is running cooler than anticipated. They said the remedy was to restart the car and allow the ecu to reinitialize.

So when I finally found a safe location to pull over, I turned the car off, and there was an unusual sound. I can’t remember exactly, but maybe a clunk in the transmission?. Not the typical sound when turning it off, and the fans were on full blast.

I turned the car all the way off and waited 30sec or so for the fans to turn off. I restarted the car and the problem was gone. Great power. No clunk, no cel. Ran beautiful the final 17 miles of curvy mountain roads to my destination.

After about 2-3 hours, I got back in the car to drive home. Started up fine. Drove about 40min. Stopped for about 2 hours. Got back in, no problem. Drove all the way back into town without a single hiccup. Stopped at my shop for about 30min before I went home. Got in and started the car. There was a clunk in the transmission (area). Thought that was odd. Shut it off. Started again clunked in the transmission area again. Drove about a mile home. Turned it off and back on again about 5 times. No clunk.

I don’t think it was in limp mode, especially without any cel, but I don’t know.
I scanned it and it returned the codes:

348A - Map thermostat clamped open, which I somewhat expected.

3166 - Fuel tank ventilation system malfunction,
Which I wasn’t expecting at all

Would the ECU cut power for underheating? Could the fuel tank ventilation system malfunction, be connected to the ecu thinking the thermostat is clamped open? I’m going to clear the codes and drive it around this weekend.

With the clunking, I’m not totally convinced it isn’t transmission issue. I know the transmission is due for fluid exchange, and I had already planned on doing it, and the rear diff this winter. But I don’t know if it is a separate issues from the power loss.

It’s just really strange, and I don’t want to drive the car too much, until I know it’s not something serious.

Has anyone experienced anything like this? I really appreciate your help. Thanks.

[Xalithar]

If you think the the radiator is too efficient, you could do a trick that commercial truckers would do up in Wisconsin. During the winter they would put Radiator bras on that would cut the airflow to the radiator in half. For quick troubleshooting you could just block off one of the kidney grille vents and see if you have an difference.

[whyzee125]

That's a strange one. If you have the ability to scan codes, does that mean you have MHD or the ability to view live data somehow? I'd start monitoring the coolant temps from cold and see if they rise too slowly or don't meet the expected range. It's also very possible you actually have a failing thermostat. Keep us posted!

[anjuna]

do you have a way to log requested load vs actual load? I don't think you NEED MHD for this, but I think some more expensive ios scanners (or android) scanners can get some of this data.

I ask this because:
Ignition is retarded when two conditions happen relevant to your description - insufficient coolant temp and (if I recall correctly) insufficient oil temp.

I also believe (if I can recall correctly again) that a lower intake air temp does advance timing, but only if coolant temp has been reached.

Unrelated to your condition - if coolant / oil / intake air temp is too high (I believe coolant temp above 240F? and intake temp above 140F?) it will also retard timing and (AGAIN IF I RECALL CORRECTLY) also lower commanded load%

NOW, I don't believe any of these changes will lead to the power loss you described. I believe the lowest is 0.8x of your base tables. Sure, that would lead to some power loss, but nothing extraordinary as described.

May want to get a scanner that can read inactive codes on the car and see. May also want to invest in MHD as a scanner only. It's on the more expensive side of just regular scanners, but the amount it can scan and report on is much greater than any other "scan tool" for BMW diag.

edit - clunk described could be carrier bearing for the two piece driveshaft. If it's loud enough or rattles around, it could trip knock sensors. I had my entire coupler for my prop shaft come off and was in FWD only (x-drive) where I could manage to get ~15 miles home that way. Engine reported it was knocking like crazy, but it was the prop shaft rattling / bouncing around.