F20 125d Onset of turbo lag

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edbutler
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Re: F20 125d Onset of turbo lag

Post by edbutler » Sat Feb 17, 2018 7:29 pm

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 :(

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stevesurrey
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Re: F20 125d Onset of turbo lag

Post by stevesurrey » Sat Feb 17, 2018 7:50 pm

You should find diagrams etc specific to your model here https://www.newtis.info/tisv2/a/en/
E81 120D (N47) SE+Dynamic Package, 2007/57, M Sports Suspension, Montego Blue, Pro HU+HiFi Speakers & Dipstick

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Re: F20 125d Onset of turbo lag

Post by G12 » Sun Feb 18, 2018 10:09 pm

Thanks for the link Steve.
I'll have another look at it this week with those instructions to hand....

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Re: F20 125d Onset of turbo lag

Post by Octavius » Sun Feb 18, 2018 10:42 pm

Could the timing chain have jumped ?
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Re: F20 125d Onset of turbo lag

Post by bpman » Mon Feb 19, 2018 10:30 am

Just had my egr replaced after exactly the same symptoms and back to normal now

125d, ‘66 plate, 22k miles

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Re: F20 125d Onset of turbo lag

Post by G12 » Wed Feb 21, 2018 5:25 pm

Bpman,

Many thanks for the info. It seems like the first place to have a look given that they're prone to getting a bit gunked up.

I will post back here when I find the cure.

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Re: F20 125d Onset of turbo lag

Post by G12 » Mon Mar 26, 2018 5:08 pm

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.

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Re: F20 125d Onset of turbo lag

Post by OK51MON » Tue Mar 27, 2018 10:34 pm

Forget that its your pressure converter valves.


I doing mine at the moment. There are two.

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Re: F20 125d Onset of turbo lag

Post by G12 » Wed Mar 28, 2018 11:35 pm

Pressure converter valves?

I don't suppose you have a pic and/or part numbers do you? Are they expensive?

I changed the EGR tonight anyway and it is still a bag of sh*te.

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Re: F20 125d Onset of turbo lag

Post by Adam-M » Sat Jun 02, 2018 10:57 pm

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.

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Re: F20 125d Onset of turbo lag

Post by G12 » Sun Jun 03, 2018 11:18 pm

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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tweeky
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Re: F20 125d Onset of turbo lag

Post by tweeky » Mon Jun 04, 2018 1:23 am

If your getting full power occasionally then I doubt its the turbo that needs cleaning its more like a air leak boost pipe work, inlet manifold intercooler or if your unlucky exhaust manifold gasket issue.
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Gone 2012 E82 Space Grey 118D Sports Plus standard spec.

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Re: F20 125d Onset of turbo lag

Post by G12 » Sat Jul 14, 2018 7:37 pm

Yeah, that's occurred to me although I've listened hard for any unusual noises and I can't hear anything (with the windows down driving along).
I think it is an actuator or vane problem. The engine is unable to respond to fast changes but once it gets going then it's ok.
It's got even worse now since I started the thread so I'm going to give it one more bite at the cherry and have a full diagnostic Dyno session so we can see what's going on under dynamic load conditions.
Failing that it's getting sold, I'm sick of it. My work van is faster to 30.

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Re: F20 125d Onset of turbo lag

Post by edbutler » Sat Jul 14, 2018 8:10 pm

Have you done what i've suggested before in this thread - log requested boost vs actual vs waste-gate duty?

Wastegates fail safe (low boost) so if you have a lazy vacuum pump or a split in the hose, it will lag.

I wouldn't have thought a boost leak would cause this, as you'd definitely feel that more under high pressure (not in 1st gear).

Edit: Added a vacuum screenshot and Link. Im not sure when the LP turbo yields, but a leak on this turbo could certainly cause lag. The wastegate actuator for the LP turbo looks to be left of (2) on the diagram. The boost solenoid (1) could be a culprit - VW's used to get through these like they were going out of fashion (called an N75)! Make sure all the pipes in this diagram are not split or even kinked.

Image

http://bmwfans.info/parts-catalog/F20/E ... bo_charger

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Re: F20 125d Onset of turbo lag

Post by Adam-M » Sat Jul 14, 2018 10:42 pm

Mine was an upper turbo leak, secondary leak from exhaust manifold, dpf pressure pipe and vacuum lines replaced under warranty.

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