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F20 125d Onset of turbo lag

7K views 33 replies 12 participants last post by  OK51MON 
#1 ·
Hi Guys,

Just looking for opinions on why my car could be suffering loss of power and turbo lag at the lower end of the rev range. It used to pull hard from 1200RPM but now is gutless compared to its former self and I actually find the car slow if for example I need to nip out of a junction quickly. It seems fine once you've got at least 2300 RPM on the go. That virtually instant low down torque has done a runner. If I gave it the berries in first it used to just spin up and the traction control would do its thing, now it just drives away.
Anyone got any ideas? No warnings showing. No loss of MPG. 66000 miles on it (F20 125D). Car does short commuting trips most of the week and then longer ones at the weekend, never had any DPF issues with it. I just put 1000 miles on it in two days and it hasn't improved but fine on the motorway.
I was thinking possibly the EGR valve might want cleaning. Maybe it is not sealing shut. No whistling from escaping charge air that I can hear.

Any ideas greatfully received.
 
#3 ·
I've not touched it yet, I was wondering where to start with it really. I've got no manual or anything (Does anyone do one for these cars because I've never found one)
One weird thing the car does (I live on the top of a hill) is when the car is stone cold in the morning and I drive off down the hill, it makes a kind of weird whistling noise when no throttle is being applied and the engine is on overrun. It only does that when stone cold and then it stops. Not sure if that is related or not.
 
#5 ·
cossied said:
whistling on a turbo car is a clue to air leaking somewhere.
I'd agree but it's not doing it on boost which would be charge air escaping through a bad joint, cracked intercooler etc. It only makes that noise when it is stone cold on the over run, say 1800rpm zero throttle.
I'm going to check the actuator pipework tomorrow if I get a chance, see if anything has dropped off or more likely split.

If anyone has any info on the vacuum system then I'd be most grateful....
 
#7 ·
If I get boost issues with my Saab, I plug in an ELM 327 dongle under the steering wheel and I can then see boost pressure (and other stats, using the Torque app for Android (or Dashcommand for Apple phones). If you can find out what the car should be boosting, this would be a big help in diagnosis. Could be boost control valve, bypass control valve, solenoid for activating 2nd turbo (if there is one) etc etc

Others will know if you can plug in a dongle...I've not tried it in my f21 yet.
 
#8 ·
If I get boost issues with my Saab, I plug in an ELM 327 dongle under the steering wheel and I can then see boost pressure (and other stats, using the Torque app for Android (or Dashcommand for Apple phones). If you can find out what the car should be boosting, this would be a big help in diagnosis. Could be boost control valve, bypass control valve, solenoid for activating 2nd turbo (if there is one) etc etc. You can also pull fault codes.

Others will know if you can plug in a dongle...I've not tried it in my f21 yet.
 
#9 ·
marco_polo said:
Weird whistling noises at 1,800 rev/min is classic timing chain territory?
It has got slightly noisy chains actually but it always has had that and thankfully they're not getting any worse as I change the oil way more often than the service schedule. One day I'l get them changed, probably when the clutch and DMF need doing as well.
 
#10 ·
Hmm I want to check my small Turbo.

My boost request on my 125D is 2.7 Bar and it delivers on my Awron from low down but i certainly don't feel torque from 1200 rpm (only 3000 rpm). I wonder if the reason ours feel sluggish is because there isn't enough engine speed.

I have smoke tested from the pre turbo intake.

Can any tell us the protocol checking the actuator and vac hoses. Checking the cracking pressures of the actuators perhaps?

If the OP is local to me (Windsor), you are welcome to bring it over and we can do it together.

Best

Simon
 
#11 ·
Hi Simon,

It'd be great to have another car to test with but I'm afraid I'm all the way down in West Cornwall but thanks for the offer :)
I hope to check all the hoses and clean the EGR valve this weekend. I'll post up how I get on.
One of the things I loved about the car when i bought it was the almost complete lack of turbo lag. Can't wait to get it back as it was.

Out of curiousity, what age is your car and how many miles do you have on it now? Just wondering if they're similar.
 
#15 ·
Ok, so I had a look at this earlier and I found that the EGR system is totally different to the diagrams and videos I've seen on the likes of 120d's.
I was stumped as to what actually does what under there and how it comes apart.
There was signs of no seal where the crankcase breather vents into the small turbo inlet, oily residue around there.
Where on earth is the EGR in that lot and more to the point, how on earth does it come apart? Anyone got a diagram or procedure?
 
#16 ·
I would definitely do a full bore 3rd gear run from 1000-4000 rpm to log the boost and wastegate duty cycles using an OBD2 reader. The logger should have "Specified" and "Actual" values - you're obviously looking to see if the Actual closely matches the Specified. The waste-gate should be fully closed (this may be a positive or negative value - depends on the car) until the Actual approaches/reaches Specified. Then the duty cycle will change to moderate the boost, rather than being fully closed, to stop the turbine from getting any faster.

If the car is whistling more but the turbo itself isn't goosed, you may have a waste-gate that is stuck open. Wastegates stuck open cause underboost, and those stuck closed will cause overboost. Either way, if the difference between actual/specified is significant, the ECU should throw a code and the EML.

A stuck wastegate is likely likely to be a vacuum issue - not sure about these cars though as i havent torn mine apart (yet). Mine is only a 120d so unfortunately cant give you anything accurate to compare against :(
 
#22 ·
Ok so this is still ongoing.

The car went to BMW who replaced the exhaust pressure sensor as it was showing a fault. The car still is nowhere near as good as it used to be but occasionally comes back to full power.
I'm going to get it a new EGR and see if that solves it.

I noticed there are a few other threads here with similar problems on 120/123 and 125's and no real answers.
 
#25 ·
Sorry to bring this back up. I also suffer from this on my 125D. I have had a service today and BMW have come back and marked an "issue" of "exhaust blow near turbo" could this be one of the problems? Annoyingly they didn't tell me this at the dealership to enquiry further. It was only when I got home and looked at the paper work that I noticed.
 
#26 ·
That's interesting. I don't have any exhaust leaks but I haven't solved the problem either.
I'm sick of throwing money at it and getting no answers.
My personal belief is that the small turbo needs to come off and be cleaned. I'd get both done if I had to go that far into it.

1st gear pullaways at full throttle are pretty sedate these days, and everything seems to come back once I'm in 2nd where the car accelerates way faster than it does in 1st. It's like the engine can't react to fast changes.
 
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