Mk4 GT TDI Problem

[Skorchio]

Hello All

One moment whilst I dust off my account!


I purchased a Golf TDI 130 back in august knowing that it was not running right and always going in to limp mode (you could hear the boost leaks). Turbo -> inlet manifold fully replaced excluding plastic pipe (2nd from inlet) but including intercooler – It was all knackered and needed replacing. But I’m still having another strange issue.



The Problem:

I never have full power in first gear, as soon as I hit boost the car stutters’ and feels like its trying to stall, with lots of black smoke out the back, if qucily change is to second its exactly the same. It does this in all gears, but not all the time, you can “feel” when its going to do it, mostly when going from < 1500 rpm upwards. If I’m driving enthusiastically, keeping revs high its seems to be OK but will eventually hit limp mode if I sustain a long pull in 3rd gear (2000 –> 4000 rpm) . It very hard to sum up in words.



What have I tried:

Turbo -> inlet manifold fully replaced (pipe work and intercooler)

N75 plumbed with all new hose directly to one way valve / vac feed (no vac reservoir) . N18 + N239 bypassed - EGR + Anti shudder still in situ – I have no EGR delete.

With car ticking over, vac line put straight on to VNT actuator, and it sees to move freely over and over again, so I don’t think its sticky vains, but more on that later.



Logs:

Car performing fine

'001			'011			
Engine speed	Injected quantity	Spec. Inj. duration	Engine speed	Spec. intake press.	Actual intake press.	D.cycle MAP
790-870	3.0-9.0	3-8 °Ck.	2850-3150	2200-2400	2100-2600	35-80%
 /min	 mg/R	 CF	 /min	 mbar		 %
2247	16.2	6.1	2184	1356.6	1497.6	57.8
2436	34.3	11.2	2310	1377	1450.8	56.2
2940	51.1	19.9	2625	2346	2141.1	81.7
3507	49.1	21.4	3234	2346	2983.5	94.4
3990	46.9	22.4	3759	2346	2983.5	94.4
3003	42.5	16.8	3990	1091.4	2983.5	52.6
2856	51.1	19.9	2751	2346	2866.5	94.4
3087	50.5	20.4	2982	2346	2983.5	94.4
3297	49.7	20.9	3192	2346	2983.5	94.4
3507	49.1	21.4	3402	2346	2983.5	94.4
3675	48.3	21.9	3591	2346	2983.5	94.4
3864	47.5	21.9	3780	2346	2983.5	93.6

Car stuttering, not power with lots of smoke.

Engine speed	Injected quantity	Spec. Inj. duration	Coolant temp	Engine speed	Spec. intake press.	Actual intake press.	D.cycle MAP
790-870	3.0-9.0	3-8 °Ck.	80-110°C	2850-3150	2200-2400	2100-2600	35-80%
 /min	 mg/R	 CF	°C	 /min	 mbar		 %
2142	54.1	18.9	85.5	2037	2325.6	2831.4	94.4
2268	53.3	19.9	85.5	2226	2335.8	2925	94.4
2436	51.3	19.9	85.5	2331	2346	2983.5	94.4
2541	51.9	20.9	85.5	2499	2346	2983.5	94.4
2814	51.3	17.9	85.5	2646	2346	2983.5	94.4
2079	0	0	85.5	2688	1387.2	2960.1	94.4
882	6	5.6	85.5	1218	999.6	1836.9	27.5
903	6	5.6	85.5	861	1071	1263.6	24.7

As you can see from the logs I’m over boosting quite allot. So I thought this could be a number of things:

1) Stikky VNT vains, but as I said earlier they seems to move fine when directly connected to VAC.

2) Duff N75. I’m going to try the VAG Com N75 test tomorrow, anyone know what number is it? Is it on output tests?

3) Bad remap



So I’m always over boosting, even when the car is stuttering, so why is the car stuttering and puffing smoke, does the car sense the over boost and do something to try to stall the engine.



Questions :

1) How does the ECU determine fuelling, is it based on MAF + MAP?

2) Is fuelling logged under block 1? If so when stuttering fuelling seems to be the same?

3) There is no dump/reserc valve on these TDIs – Do they not have one?

4) What else could be causing it to stall?



Your thoughts and discussion are very welcome.



Nick

 

[towcester vag]

i would defo check turbo
the actuator may look like its working but does it move fully?
as for trying to stall is it a missfire? as looms in head play up and injector seals can cause problems

 

[Bondiblu]

After having a quick look, you sure are seriously overboosting, you hitting the diagnostic limit, so 2983.5 mBar (Absolute) is the largest value you can see (3Bar MAP), but no way of telling how much past that. From what I can see, you're ECU's not requesting more than stock Max Boost (~2350mBar), so I wouldn't blame the remap too fast. Stikky VNT vains or Duff N75 are a definite possibility, although a faulty MAP sensor looks likely, it may be feeding out garbage looking at your logs and this

903 6 5.6 85.5 861 1071 1263.6 24.7

1263 mBar at 861-903RPM, no, not right, there shouldn't be much boost at that low RPM/idle.

1) How does the ECU determine fuelling, is it based on MAF + MAP?

In basic terms, Fueling is requested by the pedal, and you 2 main limiters are, a range of values programmed in the ECU called the torque limiter and the other being your MAF which restricts IQ (Injection Quantity) accoring to airflow, the more air the more fuel it'll allow until you hit the torque limiter which has the final word. Actual quantities are pre-programmed tables in the ECU done by manufacturer or tuner.

2) Is fuelling logged under block 1? If so when stuttering fuelling seems to be the same?

There are several channels for logging fueling, depending on what you looking for. After a remap I tend to log channels 3, 8 and 11

3) There is no dump/reserc valve on these TDIs – Do they not have one?

No, Diesels work differently the VNT deals with boost control, google will provide you with a detailed answer.

4) What else could be causing it to stall?
the ECU's is going to be panicking about the amount of boost and trying to recify the problem. look a the "N75"duty cycle, it's at max value 94.4%. This rectification is done by a PID controller which gets boost figures from the MAP sensor and then adjusts the N75/vaccum box which then controls the actuator, which in turn adjusts the vanes to release pressure build up or build pressure.

If you disconnect the Vac hose to the actuator, what is the boost sitting at? You say the actuator moves freely, I'd make sure it does?
What faults are logged? There's going to be at least a boost deviation fault.

side note - Check the EGR isn't all clogged up too because this can mess with boost.

 

[Skorchio]

Hello towcester vag :
It does look like its moving fully and freely, I will be ordering some turbo clener and takeing my DP off tho just in case. Can you elaborate on the "missfire? as looms in head play up and injector seals can cause problems "


Hello Bondiblu:
Thanks for the lengthy reply. When i repaced the Intercooler it came with a new MAP sensor, but is it the right one? Maybe i will try and put my old MAP sensor back on and see if this is still an issue (allthought it was before).

The more i think about it i think its the n75, im going to do the n75 check tonight, anyone have ay information on how its done, VAG COM - OUTPUT TESTS - Number?

More questions.
How does the engine achive LIMP MODE. I would guess it opens the VAC lines to the Turbo constantly so the turbo does not spool? If this is the case then LIMP MODE would not enable with a Duff N75?

 

[Bondiblu]

P/N 038906051C for the MAP sensor, make sure it's right, but I'd assume it'll be correct.

Do you know if the turbo has been removed, or replaced? Wonder if the rod length on the actuator has been messed with? A faulty N75 normally will cause underboost, but still possible. More likely sticky vanes stuck in max position. I'd also check the vac pipes are connected up correctly.

Limp mode, generally cuts/limits injection quantity and boost and runs on preset value, enough to get you home basically. Any yes, boost should be cut off.

Simple test is, engine running, pull the vacuum pipe off the N75 valve that leads to the turbo actuator. The actuator should immediately drop back.

Replace the pipe, watch the actuator pull across and then pull the pipe off that runs into the N75 valve the turbo actuator should drop back again.

If any of these tests suggest that the N75 valve is leaking you need to replace it.

 

[Skorchio]

I thought also the Actuator rod might be set wrong, i dont know if its been fiddled with. Also i have replaced all the VAC lines and put the VAC straight on the actuator and it moves fine.

So your saying at tick over the actuator should be reciveing VAC? Does that mean when the car reaches the desired boost (2300) it cuts off the VAC. I thought it was the other way round.....

Let set another thing straight, my understanding is that at tick over the tubo is set to full spool (no VAC) and then when the car hits full boost it sends VAC to the turbo to move the vains so less gasses flow over the spindle?

Is that wrong?

 

[Bondiblu]

Sorry maybe I'm confusing this here

It's a fail safe, so if the N75 packs in and stops working you get no boost, not full boost. If you disconnect the Vac lines, you shouldn't build up boost. So if you have a leaky pipe, Vac doesn't work and no boost, does that help?

 

[Muttley]

Skorchio wrote

... at tick over the actuator should be reciveing VAC? ​

Yes.

Does that mean when the car reaches the desired boost (2300) it cuts off the VAC. I thought it was the other way round.....​

No, the ECU varies the amount of vacuum to the actuator to set the vanes at the required opening so as to control the boost at all rpm. From about 1800 onwards you should be seeing full boost, and the ECU will move the vanes to keep it that way.

Let set another thing straight, my understanding is that at tick over the tubo is set to full spool (no VAC) and then when the car hits full boost it sends VAC to the turbo to move the vains so less gasses flow over the spindle?

Is that wrong?​

I'm afraid so.

The default position of the turbo vanes is wide open, which is the high-flow position i.e. full revs and maximum gas flow. You will also be at full boost, but should have been there for some time.

When you first start the car the N18 valve applies vacuum to the turbo actuator to pull the vanes closed: they don't close completely, but do narrow the intake area, whilst keeping the gas flow steady - the vanes are aerodynamically shaped and are end-on to the gas flow. The result is to increase the gas speed over the turbocharger's turbine blades, which spins it faster and gives you more boost at lower revs than you can get in a wastegate turbo.

The turbo is sized to give max boost at full chat with the vanes wide open, and so does not need or have a wastegate. In between, the ECU varies the vane settings to keep the turbo delivering the required level of boost.

 

[Skorchio]

Thanks guys, Muttley when you say N18 (erg) do you mean N75?

When i get home will start the car up and see if the actuator is reciving VAC. I will also try the N75 test via VAG COM if i can figure out how to do it / google it.

So when my car is hitting its requested boost, either the vains are sticking open or the actuator is still reciving VAC (bad N75). Hence it over boosting.

One thing i still cant understand is why sometimes i have no power and the car tries to stall / missfires. Does the engine sometimes sense there is to much boost and chuckes loads of fuel in as a safety mearure (hence the black smoke) or does the torque limiter sence to much torque and chuck fuel in. I can only presume it chuckes fule in as my logs show boost remains high so what else can the engine do to try and save itsself?

Another question. If my car is flowwing 1250 (maf reading) and 3bar + on the MAP will the car fule it acordingly producing more power or will it be running lean? So when its all fixed will i feel reduced power? (not that i care im not looking for power)

 

[Bondiblu]

http://forums.tdiclub.com/showthread.php?t=312048

 

[Muttley]

Although ours have a pneumatic actuator and no vane position feedback rather than a DC servomotor.

Skorchio - yes, my mistake, I meant N75, turbo not EGR

 

[Muttley]

Sticky vanes usually work fine under no load (going from off to idle) but stick when asked to open up under exhaust load. Since they stick open, the result is that the turbine overspeeds as more exhaust gas is pushed through the narrow vane openings. This results in overboost and limp mode, achieved by the ECU cutting fuel. Remember this is a diesel, power is controlled by varying the amount of fuel injected, a full charge of air is taken in at every input stroke.

Your black smoke is not consistent with limp mode, though.

I know that excessive EGR will generate limp mode and black smoke. Although you've bypassed the EGR, do you know for sure it's staying shut? If it is stuck partly open, it will cause overboost as revs rise, as too much exhaust pressure gets into the inlet side. This also produces black smoke because the exhaust gas is poor in oxygen so not all the fuel can be burned.

I think it would be worthwhile having your EGR valve off and seeing how bad the carbon buildup has got in there and the inlet manifold.

 

[Skorchio]

Morning

Sorry time gor the better of me yeaterday so was unable to check. I shall do it tomoght.

From what your saying Muttley is stick vains, EGR or N 75, i will try and eliminate EGR and N75.

Found this great link Clicky

 

[Bondiblu]

Morning

Sorry time gor the better of me yeaterday so was unable to check. I shall do it tomoght.

From what your saying Muttley is stick vains, EGR or N 75, i will try and eliminate EGR and N75.

Found this great link Clicky

Good link there, nice find

 

[Muttley]

The myturbodiesel site has some useful guides

http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm
http://www.myturbodiesel.com/1000q/a4/clean-intake-manifold-VW-TDI-carbon.htm

And the page below has a good quick summary of decoking a VNT turbo. Scroll down to the bottom where he has a great set of pictures turned into an animated gif showing how the vanes move.

http://www.technologie-entwicklung.de/Gasturbinen/VNT15-Turbo/vnt15-turbo.html

 

[Skorchio]

Hey guys,

Thanks for the links.

I have done the N75 test and its not that, it turns on and off fine. So its now down to sticky VNT (likely) EGR being broken / half open, although I'm not convinced that could cause boost spikes.. but defo the black smoke.

So, 2 options. Do i take the turbo off, strip it down, clean it and refit (this sound fun) or do I buy some turbo cleaner take the DP off and cape it with a cleaner..

I think Im going to take the EGR off at the weekend and clean it all out, test it, if its the same ill take the turbo off and strip it down. This just sounds like to much fun to pass up! Going to call VW tomorrow and order a manifold gasket!

Thanks again guys, I will let you know how I get on
Nick

 

[Skorchio]

Hi Guys,

Spent a lot of time in the garage this weekend!

Bashed up at 160k

The next morning I noticed an oil patch on the drive so took the TIP + EGR off and re seated the oil line, I then started the car forgetting I had taken off the other end!!! TIT

Has fixed my issue tho, I’m a 100mbar over requested but its very constant so I not worried.

	Group A:	'011			
		Engine speed	Spec. intake press.	Actual intake press.	D.cycle MAP
	TIME	2850-3150	2200-2400	2100-2600	35-80%
MARKER	STAMP	 /min	 mbar		 %
	108.18	3066	2346	2468.7	79.3
	108.58	3171	2346	2492.1	82.5
	108.98	3276	2346	2492.1	84.5
	109.38	3402	2346	2480.4	85.3
	109.76	3486	2346	2480.4	86.5
	110.16	3591	2346	2480.4	87.3
	110.56	3696	2346	2480.4	88.1
	110.94	3780	2346	2480.4	89.3

Thanks for all your help guys.

Skorchio

 

[Bondiblu]

Good work there! Not many on here would take on a job like that.