BLT Overboost

[AndyMitton]

Afternoon all.  Been a while since I've posted on here.

 

I'm struggling with intermittent boost issues.  The car is a '56 plate VRS, 1.9 BLT engine 145,000 miles.

 

The car is intermittently lacking power in the low revs, with smoke, but does boost OK other times.

 

Analysis with VCDS leads me to believe that following its replacement, the turbo is producing too much boost and the actuator stem require adjustment

 

I'm after backing these thoughts up please and advice on the best way of adjusting the actuator.  There's many posts and info about on this but the best way I can see is trial and error.  I've a mightyvac so open to suggestions / knowledge of OEM settings (if available...I can't locate them).

 

Background

I changed the turbo last year (August 2017) for a re-con turbo (standard spec).  The turbo was from London Turbos and set-up on the flow bench. Fully understand that there's info out there to say that the actuator may not be set correctly for my car.

 

Ever since fitting the turbo, the car has never run as it did before.  A lot of the time, you put you foot down, and you can hear boost, but no power and black smoke.  And the power eventually comes along.  This seems to get better when warmer but picks and chooses.  It runs OK sometime.

 

No errors logged, no warning lights etc.

 

This happened immediately after fitting the new turbo.  Initially a new EGR actually fixed this.  Then it came back again.  Unplugging EGR vacuum cured this and then eventually it came back again.

 

I fitted another new EGR valve a few weeks ago and it made no difference.

Unplugging the vacuum to the EGR now makes no difference.

I even blanked the EGR exhaust port and this made no difference

 

I've carried out diagnosis according to the workshop manual:

 

https://workshop-manuals.com/skoda/fabia-mk1/drive_unit/1.9/96_tdi_engine_mechanics/exhaust_turbocharger_g-charger/charge-air_system_with_exhaust_gas_turbocharger_part_2/checking_charge_pressure_control/

 

Basic Setting 04, Group 11:

At idle the boost appears to be OK:

I get ambient pressure of 984 mbar and an intake pressure of 1188 mbar, where the max allowable is said to be 1234 mbar

This was derived from the workshop manual stating to add 100 to 250 mbar to the ambient pressure measurement 

 

Logging Group 11

The manual does state to do this in 2nd gear but I've done it in 3rd.  Nevermind, same difference.

So going by the manual, the advised boost pressure at 3000 RPM should be 2100 and 2600 mbar.

Now sometimes it is but sometimes it is over and logging between 2700 and 3000 mbar.

I've attached a plot running up the Revs and one showing boost over a longer period of runs,

 

The first plot shows a run in 3rd gear

 

The second plot shows the expected vs actual pressure over a number of runs, just to show the boost spiking

 

Any advice much appreciated

 

Many Thanks,

 

Andy

 

 

 

Edited 30 December, 2018 by AndyMitton

[sepulchrave]

You definitely need to adjust the actuator linkage quite a bit, it's miles out.

I'm not sure what you're asking since you seem to know already and the graph couldn't be much more obvious.

Edited 30 December, 2018 by sepulchrave

[AndyMitton]

2 minutes ago, sepulchrave said:

You definitely need to adjust the actuator linkage quite a bit, it's miles out.

I'm not sure what you're asking since you seem to know already and the graph couldn't be much more obvious.

Cheers...Just double checking myself and that I've not missed anything before adjusting it, that's all

 

Thanks,

Andy

[JWvrs25]

Yes you want that duty cycle at 4000rpm to be about 75%. It's not too far out, small adjustments is the key. Try just half a turn at a time and log each adjustment. Think you need to lengthen the rod on the turbo to cure the overboost. You will really appreciate the difference after its been done. 

Im surprised your recon unit has lasted so long with it over-boosting so high, my one from london turbos lasted 8 months before it went bang, and that was properly adjusted from when i first fitted it.

 

 

[AndyMitton]

Cheer....Yea looks like it needs lengthened.  Just been reading one of your posts actually on this.  Hopefully not done too much damage, don't fancy changing it out again.  I'll go at it half a turn and see where we are using VCDS.

 

Thanks,

 

Andy

[faboka vrs]

Yeah rod is too short. From personal experience I would aim for the high 60% to low 70% at 4000rpm. Always best to log in 3rd or 4th.

[faboka vrs]