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1.4 TDi losing power

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Hoping someone can point me in the right direction.

My TDi when nipping through the gears feels fine, come to the bypass and put your foot down and by 4th it will loose boost, limp mode. If you flick the ignition off and back on it will pick up again flat out all the way, come to a round about and back up going through the gears and it will do the same. Cannot be the turbo, filters are relatively new and had the same problem when they were new. 

Things I've tried.

All the hoses, intercooler, seem fine. cannot see anything wrong with the pipes around the N75 valve. 

I've put a blanking plate in for the egr, ran with the MAF disconnected, unplugged the N75, unplugged the one to the left of the N75. All of these did nothing and still the same.

I unplugged the connector to the right of the N75 and ran flat.  

 

Really lost on this one.

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Remapped? Get codes read.

If you have k&n filter revert to paper ones as i had nothing but grief with my tdi running one as it messed up the maf very quick.

Mine would also go into limp mode (no eml) stooging up a hill in 4th due to boost out of limits for more than 10 seconds, but fine while on the gas. It hardly ever does it now after reverting to paper filter and tweaking SVBL.

You may just have vacuum line leaks though. Also make sure egr is actually shut, any leak will affect boost.

Best bet is to log some stuff on a run with vcds  and see what boost is doing etc actual vs requested.

Edited by Sausage
added somink

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Completely stock, full service history and seems well looked after for all it's life.

I put the egr blanking plate in at the egr side also. 

What is the best code reader for these or will any of the cheap one's read ok, or use the laptop ( I'm 64bit Win 10)

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Cheap £5 kkl leads off ebay work fine, I would advise to try and find one with genuine ftdi chip in it  and pay the extra but any will actually do the job. You then use vcds lite (google for unlocked v1.0).

I use an old £20 spare laptop for mine.

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Yeah I would invest in a lead and VCDS. I bought a cheap reader and although it seemed to work, it didn't detect any codes. 

Edited by wehey

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Little lost.

 

N75 valve, you got two pipes on the bottom right and one slightly higher on the left.

The slightly higher one on the left where is this supposed to go, mine leads off left across the bulkhead and is not attached to anything. How important is this pipe??????? Anyone got a pic of where it attaches to please.

Thank

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33 minutes ago, rdstars said:

Little lost.

 

N75 valve, you got two pipes on the bottom right and one slightly higher on the left.

The slightly higher one on the left where is this supposed to go, mine leads off left across the bulkhead and is not attached to anything. How important is this pipe??????? Anyone got a pic of where it attaches to please.

Thank

Nope not that pipe, goes to the airbox. 

 

Can I disconnect the pipe to the waste gate?

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Little update.

Got my VCDS working and cleared all codes ( as I went unplugging everything had a few )

After a short drive MAF sensor is throwing up a code every time ( easy enough )

Now when I get it to go into limp mode it's bringing up fault code 17964.

I have a new N75 here to fit ( hopefully it's that ) BUT the N75 on other VAG control the Actuator on the turbo, on the Arosa it goes to the EGR and also another Valve/Solenoid  and this secondary Solenoid then leads to the Turbo Wastegate. Little confused.

 

Any advice on the second solenoid that the N75 leads to.

Also best or what to avoid with a New Maf?

 

 

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There are three valves: the N75 that controls the turbine, the N18 that controls the EGR and N239 that command  variable intake manifold flap.  On VNT (variable nozzle turbo) turbines N18 and N75 are identical in appearance and operation  because they operate on a vacuum basis.  I think you saw something like that in another VAG. At the bypass turbines (westgate turbine) like the one on your car, N75 is different because it works on a pressure basis. in the first pdf you can see on page 5 how the westgate turbine works .

The error 17964 (Charge Pressure Control -Negative Deviation) indicates that the bypass valve has remained open and can not be closed to increase the pressure.

I hope the attached documents will help you find the malfunction.

VARIABLE_TURBO.pdf

N75 Test.pdf

Presure unit Test.pdf

Supercharger Test.pdf

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Free stuff: Try cleaning the maf, double check your pipes are plumbed in correctly with no kinks or blockages. Clean the map sensor while you are at it.

Edit: Same fault code as mine: 

17964 p1556 boost pressure drop, poss n75, boost leak, wastegate stuck. maf sensor

As yours it at high boost (unlike mine) could be intercooler cant hold the boost, look for signs of oil around the plastic end joins as the seals can go there apparently.
 

 

Edited by Sausage

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Well I changed this part first pic what I think is the N75 and still the same. The second pic is that the N18? This os the one that leads to the turbo. I have tried unplugging the MAF so that kind rules it out and that only controlled the fuel not boost. MAP sensor I honestly dont know any tricks for checking this. Intercooler looks in great condition along with he pipes.

I cannot open the files posted the forum wont allow me to.

Going to put it into a fitters hands in the next few weeks to see if he can find the fault. It's really annoying as it would be a nice car if it was not for the fault and I dont plan on spending hundreds upon hundreds on it. 

Give it a while and if still the same may just pass it on, see what I'm offered for it.

 

EDIT: Connecting VCDS Lite, whist parked just revving the car at standstill I can get a boost pressure of 1550 mbar, this is about 22.4 psi, is this way to much, could it be the MAP sensor shot????? 

s-l300.jpg

download.jpg

Edited by rdstars

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N75 is on the right with metal front and goes to turbo, n18 is in the middle and goes to egr, looks like you changed the n18.

 

amf vacuum pipes.jpg

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Your reading of 1550mb is that absolute? might just be including atmospheric pressure so actually means it is 0.5bar boost

edit: good info and tests in here: http://www.vwaudiforum.co.uk/forum/showthread.php/127899-2003-Polo-1-4-TDI-Low-on-Power-Fault-Code-17964-Charge-Px-Ctrl-Neg-Deviation

I need to try some of these again myself as mine still occasionally throws this code.

Edited by Sausage

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Looks like I changed the N18, I emailed a company who on there web site shows that as a N75. Looking all over the web that part comes up are an N75 for all other VAG. 

That other part N75 ( N18 I thought it was ) looks a mare to change, it's not bolted on but some rubber grommets and got all those pain Clic clips attached. There even harder to find on ebay and cannot find them any where else for sale.

Just cleaned out the MAP and it's an original Bosh large probe. Got the part number and there £40 but not sure if that may cause the issue.

My MAF is a solid unit original Bosh but is missing the diode off the side ( but the MAF is not going to cause the boost to cut ) 

The MAP part no is: 038906051 But I cannot find the part number for the MAF.

 

So I may have to decide if to buy the N75 ( what I thought was the N18 ) and also a MAP sensor. Honestly give me a Pug/Cit DW10 motor any day, my 2nd ever Vag and not impressed with there issues they throw.

 

Reading through the link you sent Sausage, he had an injector problem, I don't understand though how an injector can cause the boost to cut. I did look at the deviation of the injectors and there was a difference, think No 1 was close to 0, No 2 was = 0.35 and No3 was + 0.3. So well with in the 1.2 tolerance and thats even with a Maf not 100%

 

  

 

Edited by rdstars

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Plenty of tests to do on n75, maf, map without spending any money. n75 can be tested in vcds (in the link i think) maf and map can be done with multimeter and in vcds (if unlocked version).

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you're spending a lot of time chasing what sounds like a boost leak.

cap it off and do a boost leak test, easy enough to do.

when you're driving it you will find that if you do a rolling bump it will boost again so that will help you diagnose the exact point that it goes limp.

my theory is that it is when maximum boost is achieved and you're pulling in fourth.

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23 hours ago, rdstars said:

Looks like I changed the N18, I emailed a company who on there web site shows that as a N75. Looking all over the web that part comes up are an N75 for all other VAG. 

That other part N75 ( N18 I thought it was ) looks a mare to change, it's not bolted on but some rubber grommets and got all those pain Clic clips attached. There even harder to find on ebay and cannot find them any where else for sale.

Just cleaned out the MAP and it's an original Bosh large probe. Got the part number and there £40 but not sure if that may cause the issue.

My MAF is a solid unit original Bosh but is missing the diode off the side ( but the MAF is not going to cause the boost to cut ) 

The MAP part no is: 038906051 But I cannot find the part number for the MAF.

 

So I may have to decide if to buy the N75 ( what I thought was the N18 ) and also a MAP sensor. Honestly give me a Pug/Cit DW10 motor any day, my 2nd ever Vag and not impressed with there issues they throw.

 

Reading through the link you sent Sausage, he had an injector problem, I don't understand though how an injector can cause the boost to cut. I did look at the deviation of the injectors and there was a difference, think No 1 was close to 0, No 2 was = 0.35 and No3 was + 0.3. So well with in the 1.2 tolerance and thats even with a Maf not 100%

 

  

 

I have a load of random bit left from my Tdi all off a working car.

if any are of any use then pm me and I can post them to you??

IMG_4542.JPG

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Is that canica blue?

Do boost leak test as rich said, no point guessing and buying bits you dont need. 

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If you have a cheap egr delete you may need to seal it with silicone, the original valve has a rubber o ring built into the flange that a cheap kit will not have. My TDI had a very slight leak there that knocked it into limp mode. Very annoying. 

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