RPM occasionally fluctuates with AC Compressor on

[lemoose]

Yeah, 14V with the AC on or off. It would seemingly randomly drop to 13.5-13.9 for a couple seconds, but never below that and then would go back up to 14V.

And strangely, last night when I put the airbox back on and started it up, the idle was level with the AC compressor running until I kicked the SMG selector from N to 1, and then it started fluctuating for a few seconds and came back to level. Then this morning it was pretty stable overall.

I didn't really change anything, so I can't figure out why it would be behaving any differently. I will drive it for a few days and see if it's still stable, and get with Kassel to re-tune if needed (at least, as a first step since they owe me a tune anyway).

weird. I've found I can sometimes get the idle hunt to settle a bit if I clutch in- but AC off is the only surefire fix- after driving a couple meters though the idle will be stable through the entire driving cycle. Also running the kassell software on an hp-converted dme.

[Andratch]

-- UPDATE --

I did a 45 minute remote diagnostic session with Kessel today. He found that there was a on/off setting within the DME settings "that they have never had to flip before" related to how the engine reacts to the AC Compressor activation. Activating this did not totally smooth out the idle all of the time, but did seem to have about a 75% reduction in the amount of time it idle-hunts, and allows it to recover more easily when it does hunt.

That said, I do still have my idle set to 950 RPM.....when I dropped back down to OEM 870 RPM, it was still fluctuating quite a bit. So, back to 950 RPM as a temporary fix, i suppose.

The Tech Engineer at Kassel's take is that there may be something wrong with something in the PID loop. He pointed out that the "sucked air temp" value was reading almost 70 C (160F), and that the fuel trim was hunting between 2.0 and 3.0 when it was fluctuating, and steady at 2.5 when it was not fluctuating. With the Turner kit, the intake air temp sensor is at the front, right above the alternator....it could certainly be hot in there, but I don't know if 160 degrees is accurate. I am using the OEM Hella temp sensor with Turner's IAT/MAF Sensor Harness.

He said he didn't think an Alpha N tune would help with this. Curious of y'all's take.

[Bry5on]

Confirms what I wrote above if you ask me, your map likely has some issue that it can’t compensate for when combined with your long term fuel trims. This could actually be related to the non-idle parts of your map as the car learns from and adapts to your normal driving conditions. If you reset adaptations and the idle hunt goes away after a brief <5min short drive and ignition cycle (to essentially just reset cam adaptations), this would be one way to support that theory.

I regularly see 60-70C IATs at heat soaked idle with my factory-like CSL setup, even with the valve closed and drawing air from behind the fog light. 70C certainly isn’t outside the realms of possibility at full operating temp idle with AC on. This was last weekend for me during an autocross:

[heinzboehmer]

I do think I remember seeing a table in the DME that modifies the idle when the AC compressor comes on, but can't remember the details off the top of my head. There's also a setting you can change with NCS Expert in the IHKA which makes it send an additional torque request to the DME when the compressor is turned on.

70C sounds about right for the stock sensor location once things are nice and hot. You should double check that they haven't scaled the tune for the incorrect sensor though.

If I'm being honest, I still don't fully trust that Kassel knows what they're doing and I don't buy this "PID loop" theory. I highly doubt they messed with the gains for the PID control of the ICV or the throttle actuator (and if they did, my next question would be why?) so unless a sensor is dying then this should not cause the issue you're seeing.

Quick test to rule out Kassel's changes in the tune would be to flash a stock CSL binary on. Sounds like your car is SMG, so no need to modify it for manual or anything. Just double check if you're running the CSL bootloader or the stock one.

Full binaries for CSL and stock bootloader can be found here: https://github.com/saildot4k/MSS54-X...mps%20-%20Full

If you're on the stock bootloader, flash the stock binary first and then do the Terra thing: https://nam3forum.com/forums/forum/s...asher-csl-tune

Do NOT flash the CSL binary if you have a stock bootloader (and viceversa) or you'll brick your DME and will need bench flashing hardware to recover it.

Also probably a good idea to do a full binary read first so you can have a backup of the Kassel stuff.

[Andratch]

Confirms what I wrote above if you ask me, your map likely has some issue that it can’t compensate for when combined with your long term fuel trims. This could actually be related to the non-idle parts of your map as the car learns from and adapts to your normal driving conditions. If you reset adaptations and the idle hunt goes away after a brief <5min short drive and ignition cycle (to essentially just reset cam adaptations), this would be one way to support that theory.

I regularly see 60-70C IATs at heat soaked idle with my factory-like CSL setup, even with the valve closed and drawing air from behind the fog light. 70C certainly isn’t outside the realms of possibility at full operating temp idle with AC on. This was last weekend for me during an autocross:

My "tune" is the standard BMW CSL software on a Kassel HP-upgraded DME. So, just factory BMW stuff for CSL. I did reset adaptations last week, I can't recall much of a difference. All of the videos I've posted in the last few days are post-reset of adaptations.

You mentioned the Mullet tune - that's your developed tune, right? I can't find any details on how to buy it. I'm interested, though. I have a laptop and USB/OBDII cable that has worked for all of my BIN updates thus far, happy to turn you loose with it.

Your comment on "stock airbox reliability" is exactly what I'm looking for. I have the Turner intake but non-csl cams. I'm not really concerned about capturing every possible fraction of a horsepower, if I can find a tune that's reliable and steady on idle, I'm down with going that direction. I live in Houston, so temperatures are "balls hot and humid" all the time, not that much variation.

I do think I remember seeing a table in the DME that modifies the idle when the AC compressor comes on, but can't remember the details off the top of my head. There's also a setting you can change with NCS Expert in the IHKA which makes it send an additional torque request to the DME when the compressor is turned on.

70C sounds about right for the stock sensor location once things are nice and hot. You should double check that they haven't scaled the tune for the incorrect sensor though.

If I'm being honest, I still don't fully trust that Kassel knows what they're doing and I don't buy this "PID loop" theory. I highly doubt they messed with the gains for the PID control of the ICV or the throttle actuator (and if they did, my next question would be why?) so unless a sensor is dying then this should not cause the issue you're seeing.

Quick test to rule out Kassel's changes in the tune would be to flash a stock CSL binary on. Sounds like your car is SMG, so no need to modify it for manual or anything. Just double check if you're running the CSL bootloader or the stock one.

Full binaries for CSL and stock bootloader can be found here: https://github.com/saildot4k/MSS54-X...mps%20-%20Full

If you're on the stock bootloader, flash the stock binary first and then do the Terra thing: https://nam3forum.com/forums/forum/s...asher-csl-tune

Do NOT flash the CSL binary if you have a stock bootloader (and viceversa) or you'll brick your DME and will need bench flashing hardware to recover it.

Also probably a good idea to do a full binary read first so you can have a backup of the Kassel stuff.

I don't know how to determine if I'm running the CSL bootloader - how do I check?

I do have a backup of the .BIN file from right after kassel did the HP update on the DME, and the one they did today - so there are some backups.

[heinzboehmer]

I don't know how to determine if I'm running the CSL bootloader - how do I check?

MSSFlasher will tell you if click the "Identify ECU" button. 32300 is stock, 32500 is CSL.

[Andratch]

Hey Folks,

Another update - I loaded the Mullet Tune into the car over the weekend. Bry5on's Mullet tune is awesome! The car just generally seems happier, and Bryson was able to identify some "questionable tweaks" from the prior tune that Mullet corrected.

As for the AC fluctuation, unfortunately it's still there right now. I'm going to replace spark plugs and pre-cat O2 sensors since they're on my list anyway, and Bryson noticed that my Lambda readings are kinda wonky. I did also read over on E46 Fanatics that some folks had fluctuations at idle with the AC on, and replacing those two items fixed it. We'll see!

I did a data log over the weekend with HRTuning's "BMWLogger" software, letting the car start from cold, warm up for a couple minutes, and then turn the AC on and off. You can see the green boxes below indicate where I turned the AC on. 2 of 3 times, RPM fluctuated. 3rd time, it held stable (though the rpm did bump up a bit and could feel the load). Strange.



I also took a screen grab video of the sensor data while the fluctuations were happening that Bryson and I are reviewing - if anyone else sees anything interesting, let me know:

Since this fluctuation also happened with the intake off, and now with the Mullet tune, I'm wondering if perhaps the issue stems from the AC system being overcharged or something. I will order some cheap AC gauges and check pressures on the high and low side.

[0-60motorsports]

Hey Folks,

Another update - I loaded the Mullet Tune into the car over the weekend. Bry5on's Mullet tune is awesome! The car just generally seems happier, and Bryson was able to identify some "questionable tweaks" from the prior tune that Mullet corrected.

As for the AC fluctuation, unfortunately it's still there right now. I'm going to replace spark plugs and pre-cat O2 sensors since they're on my list anyway, and Bryson noticed that my Lambda readings are kinda wonky. I did also read over on E46 Fanatics that some folks had fluctuations at idle with the AC on, and replacing those two items fixed it. We'll see!

I did a data log over the weekend with HRTuning's "BMWLogger" software, letting the car start from cold, warm up for a couple minutes, and then turn the AC on and off. You can see the green boxes below indicate where I turned the AC on. 2 of 3 times, RPM fluctuated. 3rd time, it held stable (though the rpm did bump up a bit and could feel the load). Strange.



I also took a screen grab video of the sensor data while the fluctuations were happening that Bryson and I are reviewing - if anyone else sees anything interesting, let me know:

Since this fluctuation also happened with the intake off, and now with the Mullet tune, I'm wondering if perhaps the issue stems from the AC system being overcharged or something. I will order some cheap AC gauges and check pressures on the high and low side.

Thats great. FYI i have the fluctuation but not as bad as you and ive had it for YEARS. I have checked the AC system and thrown parts at the car and have given up and just live with it now as its not as bad as yours. The only thing i think i never changed are the precat O2 sensors. Might do those with black Friday prices.

[Andratch]

Thats great. FYI i have the fluctuation but not as bad as you and ive had it for YEARS. I have checked the AC system and thrown parts at the car and have given up and just live with it now as its not as bad as yours. The only thing i think i never changed are the precat O2 sensors. Might do those with black Friday prices.

If it was a small fluctuation, I could deal. But this is enough to where the lights dim when it comes down, and that's a bit irritating.

Today's task is to take off the AC belt and see what happens. I want to spin the compressor by hand and make sure that it's not failing. I notice that the engine drops down to like 600 rpm and then recovers back up to 870 when i disengage the compressor, so I have this suspicion that it's creating extra drag even when it's off, WAY more load when it's on, and the engine is trying to compensate. I have noticed that the car 'vibrates' a bit more at idle than I recall from earlier in the year, regardless of whether the AC is on or off...If things get less vibratey when the belt is off, I may have narrowed down my problem. If not, then I'll proceed with spark plugs and O2 sensors

[Andratch]

-- UPDATE --

I took off the AC belt this morning and ran the car. The general idle vibration was about the same, frankly when it was warming up it felt a little bumpy....no codes, but maybe a very minor missfire? I'm replacing spark plugs shortly so that should give some insight there.

Anyway, when turning on the AC compressor (without it spinning), the idle bumped up like you'd expect and settled back down.

When I turned it off, the idle dropped to like 600 and recovered more slowly, with minor fluctuations while it was recovering...which is kinda weird (seen at 1:05). It did the drop-and-recover with the belt on as well, but I wasn't expecting it to do this with the belt off too.

I also noticed a minor fluctuation when engaging SMG from N to 1, so I'm suspecting this is NOT related to the compressor itself, but some other behind the scenes issue. Spinning the compressor clutch by hand, it doesn't really feel like it's scraping or otherwise faulty. The pulley feels very smooth, and the clutch feels like turning a pump.

https://youtu.be/U8wzRgXJMTg

Anyway, There's no fluctuations at all, ever, in the first 2 minute of cold start.....so I'm curious if it's getting bad readings from the pre-cat O2 sensors. Spark plugs, coils, and O2 sensors are next...no idea if they've ever been replaced, so this is a good way to cap off my baselining.

[Andratch]

Tested AC pressures -

COMPRESSOR RUNNING:

LOW: 32 psi
HI: 200 psi

COMPRESSOR OFF:

LOW: 50 psi
HI: 150 psi

As far as I know, this is within normal ranges.

i don’t see a *major* smoking gun with the spark plugs or coils, but the coils are definitely original.

[0-60motorsports]

Try Changing the coils and plugs and lets see what it does, they would have to be really bad or some of them really bad for the car to be doing this.

[Andratch]

Try Changing the coils and plugs and lets see what it does, they would have to be really bad or some of them really bad for the car to be doing this.

After I took that picture, I did notice something interesting about the third coil from the left. The rubber boot is soft on the other 5, but that one is rock solid hard, and has shrunk. On the others, the spark plug would click in nicely. On that one, I couldn't get the spark plug to click into place. The boot actually broke off while I was trying.

I don't really think that's all of the problem, and I wasn't getting misfire codes, but it could be something. The coils had an 11/06 date code on them, so they're pretty ancient and ready for a replacement. At any rate, new spark plugs are in, new Eldor coils going in this afternoon, we'll see what that does.

New O2 sensors arrive today, so they'll be up for replacement tomorrow.

[0-60motorsports]

After I took that picture, I did notice something interesting about the third coil from the left. The rubber boot is soft on the other 5, but that one is rock solid hard, and has shrunk. On the others, the spark plug would click in nicely. On that one, I couldn't get the spark plug to click into place. The boot actually broke off while I was trying.

I don't really think that's all of the problem, and I wasn't getting misfire codes, but it could be something. The coils had an 11/06 date code on them, so they're pretty ancient and ready for a replacement.

Also don't forget the new Bosch coils do not click anymore when seated.

[Andratch]

Also don't forget the new Bosch coils do not click anymore when seated.

I ordered Eldor ones because they were consistently very highly regarded across a few forums. I know Bosch is an industry standard, nothing wrong with them, but folks were actively singing the praises of Eldor versus saying "Bosch are fine too" so I'll give Eldor a shot.