Strange power problem TDI 110 please help

[jernjackson]

Hi guys

First post on here as well, i've just bought an audi.

Picked up a 1999 110 tdi last sunday very cheap. Its in good condition but is down on power by a lot.

When I bought the car the guy said it needed a maf and fuel cut off n109, I took my ross tech vagcom lead along and sure enough these where the two faults logged, I cleared them and went on a test drive, the car was down on power and struggled to rev above 2500 rpm and the two faults re-appered so thought its defo a maf problem and drove the car away thinking I had a great deal.

When I got home I decided to take a closer look around the engine and found that the n109 fuel cut off had been hard wired to the battery 12v thus keeping it open. Thought this was strange as if the n109 was knackered then a 12v wouldn't open it. I disconnected it from the n109 and tried to connect to the ECU with vagcom, I was persented with a 'cannot connect to controler' error. When I reconnect the 12v to the n109 I am able to connect to the ECU!

I Replaced the MAF to see if this was causing the loss of power but its the same, it just wont rev. The MAF fault has not come back since I replaced it.

The timing belt seams quite old so i presume the timing is ok and all the vac pipes seam to be in the right order.

I've checked all fuses and the 109 relay, the n109 wire to the ECU is fine but there is no 12v from the ECU pin when there should be.

Im thinking the ECU is a knacker job but just wondering if anyone could shed any light on this problem or suggest anymore tests I can do before I buy a new/e-bay ECU.

Thanks
John

 

[beachbuggy]

Sounds like the vnt part of the turbo is seized. Common problem on vag tdi's . Basically vaines are stuck so the turbo doesn't boost and struggles get any decent rpm. Only real way to sort out and check is to remove the turbo. It's still a cheap fix though if you do it yourself as only part you need to replace is the oil feed, also give you a chance to clean egr and inlet manifold.

 

[s17atw]

Hi, I you back feed the shut off on the pump it can blow the ecu, I have seen this before as a known double letter recovery firm had done this very mod to get it to the dealer

It prob originally just has a faulty 109 relay (ecu power supply relay) quick check if its black its a original if its grey it could have been replaced at some point BUT could still be faulty
as for your lack of power beachbuggy is spot on

 

[TDIQ]

Sounds like the vnt part of the turbo is seized

VNT is probably the culprit. There are various kits and threads on how to clean the VNT mechanism, you can do it with the turbo in place if you don't want to remove it though obviously taking it off allows a more thorough clean.

You may want to check for a boost leak before you start removing the turbo though.

 

[jernjackson]

Hi guys

Cheers for the swift response!

Sorry but I forgot to mention that when I got the car it need a downpipe as there was a hole in the flexi, while fitting that i took the turbo off, cleaned the inlet manifold and EGR/ASV.

While the VNT arm had a little resistance I stripped the turbo and cleaned it. There was a little build up but not much. Both wheels are fine and the VNT moves freely now. The actuator it also fine.

I have also swaped the N75 for the other valve that contols the erg valve to make sure it wasnt the N75 at fault.

Im going to replace all the vac pipes to make sure theres no leaks, but I am really starting to sway towards a ECU fault.

The 109 is a black one, not gray, i have tested it the best i can. Im i right in thinkin that there is a 12v supply to the 36 pin on the relay untill the ignition is turned on?

Any other suggestions?

 

[TDIQ]

Check out this:
VNT TDI turbo: how to adjust actuator & cure boost problems - uk-mkivs

Try and see if you're getting the requested boost, if not then it suggests a leak.

I'm not sure about the 12v to R109 - it may be worth picking up a new one for £10 though.

 

[jernjackson]

Thanks for the link Aaron but im 90% sure its a ecu problem now. Mandged to get a voltage to it without having the n109 jacked to a 12v, its coming back with some strange codes that suggests somethings not right with it.

00668 - Supply Voltage Terminal 30

18008 - Power Supply Terminal 15 voltage too low

Terminal 30 is the 12v out pin on the ecu for the n109, and thats still showing no voltage. My car battery ran low so think thats my 18008 code. I recharge the battery and fiddle about a bit more. Realy want to get to the bottom of this now.

Am i right in thinking the n109 solenoid should be open (12v) whenever the ignition is on? I understand its on a timer when the engine is swiched off?

 

[jernjackson]

PROBLEM SOLVED!!

After recharging my battery for a short while I followed the ECU supply voltage wire back from the 109 relay to find it had snagged on a sharp bit of metal under the dash! Reconnected it and succecss!

All is well again, car starts first time, i have a 12v to the n109 and the car has full power again, and quite nippy at that!

The ECU must have been getting a trickle voltage back through pin 30 via the n109 wire when it was connected to the 12v on the battery. Just enough to start the car and make it drive but not enough to actiave the n75 or get readings from any other sensors. Very strange indeed!! but hey every days a school day!

Just happy I found the problem before i started spending money on turbos and ecus!