Thread: D2 TD5 surging full acceleration issue

Instead of guessing and wondering what to do next to solve the issue, just wind back the boost to factory range to see if it eliminates the issue. It's fairly fast and free to do and takes it back to a known start point. From there you can consider the many options available but otherwise your going to keep adding layers onto guesses on what the issue is.

If the issue remains at stock boost levels then you've got an issue such as faulty sensor, stuck wastegate, faulty modulator, etc.

If it's gone then you've identified the cause being high boost level. From there the cheapest solution is to gradually increase the boost to find the point that it reoccurs and then slightly lower to the highest point that it doesn't occur. All free.
If you want more, then it's going to cost you. Electronic trickery is one option, but you will need to know which is causing it, seems likely to be the MAP sensor, so a turbo boost box should solve that or having your ECU retuned to take advantage of the maximum output voltage of the stock MAP sensor or to fit an uprated MAP sensor (there's a 3 bar VAG discussed in TD5 updated MAP sensor - anyone using? which is well priced and I've ordered to try).

Originally Posted by steve_a

Worth bypassing the WGM and connecting the hose directly to the turbo outlet and see if you still have the issue.

The WGM only actuates to STOP the boost from the turbo outlet, but it may be getting sticky and getting stuck in the mode where it uses the inlet side to keep it closed.

Am I misinterpreting what you’re communicating?

The WGM keeps the Wastegate from beginning to open at lower RPM to prevent bleed of boost from the turbo as it comes up.

So when the WGM sticks in the ‘bleed to atmosphere’ position boost can peak above ECU thresholds.
Plumbing directly from discharge point to turbo can show if this unit is faulty for sure, with a corresponding loss of bottom end performance.

If the WGM is getting on a bit, it’s worth just replacing it. They aren’t expensive.

Considering the recent disturbance to the area, I’d also be looking at hose condition and potential leaks / splits - or even hoses attached to wrong ports if removed.

The other common cause is sticking Wastegate. Undoing the bolts on the actuator and working the arm back and forth along with some Penetrating spray at the pivot Bush can be beneficial.

Unpowered (i.e. no connection or PWM signal) the WGM port is from turbo outlet to WGA. Fail safe mode. So this is the same as 200/300 and Def TD5 (I'm told).
When being actuated it connects the WGA port to the inlet near the MAF. This provides a vacuum holding pressure to keep the WG closed.

The logic for operation is probably something like this:
if pressure > 1bar
if pressure < max
increase pwm
else
decrease pwm
endif
else
unpowered
endif

It avoids having to keep the WGM powered (with heating issues) and if it fails then you get the same as if it wasn't there.
With no WGM the WG will gradually open to 100% as boost increases, with the WGM the WG should be variably opened based on the control signal to keep boost both under control but not not lost.

The issue is I guess if it gets sticky then perhaps it turns off while keeping WG closed and so it won't open it up because the port doesn't get connected back to turbo outlet.

It's a nice fail safe design in general. You could probably just unplug the WGM to see if it's the second condition, since it now shouldn't overboost unless the rod is set wrong.

If you look at nanocom logs, they show WGM % at 0 until you get above a pressure then operating from 100 down to 0 as pressure rises. No idea what the start point of operation is though, never looked close enough.
The loss of bottom end is no worse than a 200/300 or def td5 in standard form. I never really noticed an issue

So I lengthened the wastegate rod about 3/4 the width of the locking nut. It seems to have helped as the surging is better. I’ll lengthen it a bit more. Still seems to boost 1.3bar before it surges (down from at least 1.4).

I think it had about 15 threads before adjustment.

I’ll repost the results when I drive home tomorrow morning.

Originally Posted by John_D2

So I lengthened the wastegate rod about 3/4 the width of the locking nut. It seems to have helped as the surging is better. I’ll lengthen it a bit more. Still seems to boost 1.3bar before it surges (down from at least 1.4).

I think it had about 15 threads before adjustment.

I’ll repost the results when I drive home tomorrow morning.

Good decision.

1.3 Bar is pretty much the max boost, it equates to 18.85 PSI. 1.4 bar is 20.3 PSI which is technically over boost. So winding it back first is the right call.

Just for the record, I've experienced the same symptoms as you describe even with a boost box. Don't go down that path until you are sure the surging is a result of over boost.

Originally Posted by Jazzman

1.3 Bar is pretty much the max boost, it equates to 18.85 PSI. 1.4 bar is 20.3 PSI which is technically over boost. So winding it back first is the right call.

Sorry to contradict you but the factory set overboos limit is at 1.42 bar calculated by the ECU by extracting the AAP reading from MAP reading...below that value the surging can be caused by too high air flow while the MAF reading exceeds 680kg/hr which is very common, winding back the wastegate would partially cure the symptom cos as the turbo will not spin so fast due to more wasted exhaust gas the sucction will be lower as well... one cause i've seen was low reading MAP sensor compared to a gauge fitted to the EGR blanking port so that would be a relevant test, if the MAP is "tired" and reading lower than the reality the sucction through the MAF will be higher at a certain MAP reading while the real boost is higher as well so it's normal to be higher air flow if you see what i mean... this symptom can be caused by a slight boost leak somewhere, even through the wastegate valve's diaphragm or who knows where

Originally Posted by sierrafery

Sorry to contradict you but the factory set overboos limit is at 1.42 bar calculated by the ECU by extracting the AAP reading from MAP reading...below that value the surging can be caused by too high air flow while the MAF reading exceeds 680kg/hr which is very common, winding back the wastegate would partially cure the symptom cos as the turbo will not spin so fast due to more wasted exhaust gas the sucction will be lower as well... one cause i've seen was low reading MAP sensor compared to a gauge fitted to the EGR blanking port so that would be a relevant test, if the MAP is "tired" and reading lower than the reality the sucction through the MAF will be higher at a certain MAP reading while the real boost is higher as well so it's normal to be higher air flow if you see what i mean... this symptom can be caused by a slight boost leak somewhere, even through the wastegate valve's diaphragm or who knows where

This all started after I’d removed the turbo & gave it to a friend to drill out a broken stud. Until then I had no issues. I would have thought it a bit coincidental if the MAP sensor were to fail at the same time, but I’m not a mechanic (well...until I bought this car!). I haven’t seen my MAP over mid 400’s and definitely not as high as 600 (nanocom readings). I have been wondering if the small rubber hose might be due for replacing as it’s probably 18 years old. That can’t cost much, so I might do that ‘just in case’. I recall someone earlier suggesting sae30 rated hose (?). I’ll see what pirtek have next week.

I bought some silicon hose from supa crap as i needed extra for my boost gauge so did the whole lot simple
No need for flash exy pirtek stuff
Only prob is the colour is blue would have prefered black but it match`s the turbo hoses now Looking a bit ricey now