Unusual Loss of Power

[Kdubski]

Following completion of some engine work (head gasket creating misfire like issues, and fresh rod bearings), some loss of power has returned to plague my car. When I was having the head gasket issue (compression bleeding into other cylinders) there was a distinct loss of power acting like a misfire. I noticed this through things like engaging the clutch in 1st gear, where the car would jutter, squeek, and sometimes stall out. Around the same time (fall 2019), I completed some engine work where I disconnected the battery, coils, spark plugs and the issue went away for a few driving cycles.

Following the engine rebuild, the car was incredibly ALIVE, it felt like the sport mode button was engaged at all times. But again, following some driving cycles, so within 130 miles of driving the car again, the loss of power returned. It feels like when you turn the sport mode button off, except the stock driving mode was sport mode. I can easily feel the loss of power now because of how alive the car felt the 2 days prior to the loss following the rebuild.

The engine runs silky smooth now, no check engine lights, no issues, idle is perfect.Things I've recently done that would effect the power:

• coils (<6,000 miles)
• sparks (<6,000 miles)
• New fuel filter
• Vanos full rebuild (helical gears on sweet spots)
• Fresh oil
• Fresh gaskets
• Cleaned cam sensors
• Fresh oil & coolant
• All valve shims within spec
• Fuel pressure @ 5/5.5 BAR
• Fresh air filter
• MAF Cleaned
• Compression test following new head gasket - GOOD
• Header to engine block gaskets new (no leaks - all bolts tightened on engine stand)
• Head to section 1 gaskets - GOOD

I don't know where else to look. I found a thread that referenced this exact issue on the old forums (http://www.m3forum.net/m3forum/showthread.php?t=498767), on a discussion on M3Cutters, however the link is inaccessible. Does anyone recall this discussion or have had a similar issue with solution?

[enjoy_m3]

Do also a leak down test & Check your valve shim clearances. If you can plug in bmw scanner and run tests (vanos test/throttle calibration/ecu reset)

[Kdubski]

Forgot to mention, valve job done while engine was out, all clearances within spec. Can rule out compression as it seems to be a variable issue. What I mean by that is sometimes I turn the car on, it has this very alive feel and will have it for the ride, other times when I'm experiencing this issue it will have it for the duration of the ride, it's not something that happens while driving.

[Slideways]

Maybe check the adaptation values. Can you try another ECU?

[ATB88]

Very interested to see where this goes. A couple months ago after doing a little work on the intake side, my car felt *amazing* for about 3 days. Like it had come alive (akin to difference between sport button vs not, except no button pushed!). Finally felt excited about the car! Then it went back to normal old boring mode that it's usually been in my last 2 years of ownership. I really wonder if there are subtle things that no error code or CEL picks up on that substantially change how this car feels/behaves, because that what it often seems like...

[jbfrancis3]

Given all the mechanical work you've done, you have a BMW software product to pull the codes right?

[Kdubski]

Very interested to see where this goes. A couple months ago after doing a little work on the intake side, my car felt *amazing* for about 3 days. Like it had come alive (akin to difference between sport button vs not, except no button pushed!). Finally felt excited about the car! Then it went back to normal old boring mode that it's usually been in my last 2 years of ownership. I really wonder if there are subtle things that no error code or CEL picks up on that substantially change how this car feels/behaves, because that what it often seems like...

Yes, that's exactly what I am experiencing. The difference was extremely dramatic, I was wondering if this is what everyone elses feels like? Did you have coils unplugged? Hard to go about diagnosing something that does not prompt any codes...

[sapote]

Feeling the power each day is subjective; one sure way is run dyno test.

[Kdubski]

Feeling the power each day is subjective; one sure way is run dyno test.

Hopefully I don't have to resort to that. This feels like sport mode on/off, very noticeable.

[Icecream]

Hopefully I don't have to resort to that. This feels like sport mode on/off, very noticeable.

Does the car pull strong or is the pedal not as sensitive? At 5k and above is the throttle response good or still sluggish? You could try o2s if you really think you are having an issue, particularly if they are old. You could also reset all adaptions and see if your car drives well again. Mine seems to be more sensitive after a reset then settles into its old ways. Maybe that is what you are experiencing. Maybe bad gas. Has it been hotter/more humid?

[Arith2]

We need to know exact circumstances of this power issues. Also have you tested your TPS? Do a sweep just to measure what it's commanding. Also make sure it's opening the throttle bodies properly.

[eacmen]

unplug the MAF. You'll get a code but see if power returns. you mentioned the MAF was cleaned but sometimes that isn't enough.

Alternatively log the engine data doing a second gear pull when its good and when its lagging and compare the data.


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[Kdubski]

Does the car pull strong or is the pedal not as sensitive? At 5k and above is the throttle response good or still sluggish? You could try o2s if you really think you are having an issue, particularly if they are old. You could also reset all adaptions and see if your car drives well again. Mine seems to be more sensitive after a reset then settles into its old ways. Maybe that is what you are experiencing. Maybe bad gas. Has it been hotter/more humid?

It's not a throttle response issue. I noticed the issue when I engage clutch with no throttle input in 1st rolling out of my driveway. It feels like the torque of the clutch engaging severely bogs down the motor. I get chirping, bogging down, and sometimes even stalls. A few days ago, the first few rides after rod bearings the clutch would engage and car would lurch forward with no throttle input. When I first experienced this sensation, I thought my clutch was failing! Have a brand new clutch and flywheel now so can confidently rule this out.

What this tells me is that it's likely an ignition, fuel or air issue...

[Kdubski]

We need to know exact circumstances of this power issues. Also have you tested your TPS? Do a sweep just to measure what it's commanding. Also make sure it's opening the throttle bodies properly.

Unsure of how to test it, but just replaced TPS under the airbox.