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Other VW Group TD(I)s To keep with the theme of VW Diesels, this message area is for discussion of other VW Group Diesels. Yes, TD's are also welcome.

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Old November 16th, 2018, 12:53   #1
CraigRobbo
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Join Date: Nov 2018
Location: Manchester
TDI(s): B8 A4
Default Power loss Pre-2k - Strange issue!

Hey guys.

I have a very unusual problem with my power loss.

I will try and explain the issue and what I have tried.

My car is an Audi A4 2009 B8 Tdi (CAHA engine)

So I have power loss Pre-2000RPM, the strange this is, its always below 2000RPM regardless of gear, power level, incline, decend its almost "switch-like" (to put it simply)

Pre-2000RPM you really struggle to have any sort of power at all, but its still "smooth" no missing etc its just like you are reducing power!

After 2000RPM the power hits you pretty hard and after 2000RPM there is always an abundance of power, no flat spots no issues smooth and nice.

Now, I am pretty mechnically minded so i tried all the usual stuff first, but the strange thing is, is how its always perfectly at 2000RPM.

*So First port of call was turbo and actuator - Nope these all working great!
*Vaccum leaks? nope All good and sealed.
*Power/Throttle flap? Already replaced.
*VNT? All nice and free moving and hits both end points
*Swirl flaps seem to be actuating nicely with no slop or play.
*I also attempted to adjust the VNT (marking prior so as not to lose its setting) and if I adjust I get Overboost/Underboost errors so it is set right.
*DPF? Well i thought this so I had it removed...No avail here either
*Fuel Pressure logging is all normal with requested Vs Actual
*VNT Actuator position Actual vs requested is good!(which is odd for the next bit)
When Logging the Turbo, Pre 2k The requested boost is considerably higher than actual, talking to an Audi mapper he said this is normal due to lack of spool pre 2k.
*Now The current Map I have is what the mapper calls a "smoke map" so it smokes a little more than usual when under full power, (he said it helps spool the turbo?[I don't want to get into the debate of mapping really here]) Pre 2k No smoke at all almost like the system is holding back here (but again requested vs actual pressures are right) and after 2k when it hits, there is some smoke as to be expected....
*Now, stranger again - Prior to the car having this remap there was NO smoke before or after.. (so the map is doing as it should here) but the problem remains on stock map and post remap ( I have also had 2 different people look at the map and they are happy this is NOT a map issue)

*The car DID have its emissions fix - Initially I thought this was the problem with lag(as many otthers did too) so I had the firmware(not map) reverted by an Audi speciallist...the car became more responsive (after 2k) but the lag pre-2k remained identical.

The strange thing is the turbo, actuator and vanes all working properly!(and the actual vs requested on the vanes are correct!)

So VCDS, Seems No error codes(at least non relating to this or that would be rellevant)
The issue here is I do not currently have access to VCDS.

At first I thoguth this was "normal" when I first got the car but alas no - I went in for a remap and this really pushed the power up but it made the problem "appear" worse because the power loss remained the same but now the hit at 2000rpm is even harder for when the extra power comes in.

What ever the isssue is, It cannot be somthing as simple (eg bad fuel filter[which has been changed]) that would cause issues in other parts of the rev-range or power loss else where.

The issue is too perfectly isolated.

Please HELP!!!

Thank you greatly for reading and hopfully replying!

Last edited by 1854sailor; November 16th, 2018 at 13:08. Reason: Removed duplicate text.
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Old November 27th, 2018, 15:14   #2
eddieleephd
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Join Date: May 2012
Location: Asheville, NC
Fuel Economy: 38mix / 47@70-75
Default

2000rpm's what changes here as far as the ECU is concerned? First thought is the egr closes and causes more boost to hit the cylinder. I know nothing about this engine specifically, if I had this issue on an ALH I'd be looking at timing and timing advance, the egr and asv. How many of these things apply?

Specific RPM range is going to be the tale. Stock map or not same thing happens, often times the map is unchanged until 2000 and this still could be the issue.

What pump system does it have? Is it a manual VE style pump, or PD style? Or common rail design which could be a pressure regulator or draw issue.

Really sounds like an egr power loss until 2000 more than anything.

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