01 PD TDI, problem when wet/damp

[jimk04]

My mrs has an A4 Avant 130tdi on a 51 plate, and for as long as we have had it it has had a running problem when it gets wet, or really damp. It will only do it when it is damp or wet, but by no means does it always do it when damp/wet......with me so far?! Then I shall continue!

IT manifests itself as having no power, you can put your foot to the floor in neutral sat on the drive and it'll struggle up the rev range. When out on the road it'll cut out a good few times. Its hard to get the damn thing moving along with the traffic, but it you keep you foot to the floor, when it eventually hits 3000rpm or so it suddenly takes off like a rocket.

While its doing this, the bit where it'll hardly keep up speed, it making a very rattly diesel noise, like a normal diesel rattle but turned up to 11, with a higher pitch, and black smoke pours from the exhaust. (Good innit)!

It wont do it if youve set out in the dry and it starts raining, so its not coming in through the grille, it only does it when its sat in the wet, so my thoughts its getting something wet down the bulkhead? Had a good root around, near the ECU and stuff but all seems dry.

Any ideas folks?
Cheers
jim

 

[Munt]

Hi,
Try putting some dielectric grease inside the plug & socket of the air flow meter. This cured the fault on mine.
Cheers
Munt.

 

[ScottyP45]

Have to agree with Munt mate, theres not much on any diesel that the water can cause problems with, except the MAF. It must be getting soaked during standing due to run-off and signalling no airflow or loads, and getting wild fuelling.

If it does it again, unplug the MAF immediately and it should run fine, the ecu has a default map if the MAF is disconnected, it will throw a CEL light though whih can be easily cleared afterwards.

Use any grease that is non-conductive (dielectric as munt says) and smear all around the plug and socket while connected (and dry inside), wouldn't recommend you fill the socket wi it and then plug in, incase you dont get a good connection from the grease getting on the pins...

 

[jimk04]

Thanks guys. I ought to have put that it did come up with the MAF and on fitting a new one made no difference, but I guess it wouldnt if its the actual connection.

Its just been in again and came up with ' 4623 boost pressure below control' or something, which may not be related.

Thanks again
jim

 

[ScottyP45]

I would then check the N249 valve (if diesels have it??) , the boost path for leaks, the MAF cable to the ecu, then maybe would suspect the ecu if no other fault is found.

Im wondering if the ecu itself is getting wet??

 

[jimk04]

I would then check the N249 valve (if diesels have it??) , the boost path for leaks, the MAF cable to the ecu, then maybe would suspect the ecu if no other fault is found.

Im wondering if the ecu itself is getting wet??

Is the n249 valve what i as a vw man would call an N75 valve; the variable boost controller thing? I had wandered about that. Will check the i/c plumbing but i guess checking from MAF to ECU is nigh on impossible as it all disappears into the loom?

ECU is dry, 1st thing I checked!

Thanks

 

[ScottyP45]

Whoops sorry thats the chappie I meant. the 249 is another bit of the turbo system, but yeah the n75 boost control valve tells the DV to open if the ecu detects overboost or any other reason why boost should not be made, even if the throttle is open - it can cause problems if faulty and some folks "delete" it in the states.

Its maybe the culprit, but if you can find it (sounds like an a-team episode lol) you could remove the vac pipe and plug it, that goes to the DV so the n75 cant open the DV, it might prove thats the fault by running ok, maybe its "fluttering" and making the engine lumpy? and if you pull the electrical plug off the n75 you will normally get a cel and dtc for "n75 missing" or some such code, could very well be the problem (water ingress shorting the signal?)

 

[jimk04]

Just an update chaps, managed to replicate the problem yesterday by putting the hose pipe under the bonnet! And yes, unplugging the MAF stops it! Woo Hoo!

But I dont really know what is actually causing it still. Checked the wiring to the ECU as best I could and all seems fine. Had ECU out and bone dry, all connectors fine, no sign of ever being remotely damp.

Only other thing i found was the last of the rubber boost hoses thats at the back of the engine bay, up near the bulkhead; it turns 90deg to face you if stood infront of the car before going into that big valve thing; wasnt seated very well. It has a big metal clip and this was damaged so only half the pipe was in properly, other half pretty loose. When I got it running like a bag of spanners, I noticed white 'smoke' from here, so i swapped some clips over, got it seated better.

Dont know if this is the problem, but watch this space!

 

[Neil_S]

Sounds like vacuum hoses to me.

 

[jimk04]

Sounds like vacuum hoses to me.

Vacuum as in the one that goes thru the bulkhead to the servo, as I did notice that one doesnt take much moving about to emit a hissing noise, where it goes from stiff plastic, to rubber grommet thru the bulkhead.

 

[Neil_S]

I had similar and it ended up being the vacuum hose from the top of the EGR to one of the controller sensors.

I've ended up replacing all of the vacuum control units N18 and the other one, but not the N75 yet. I've also replaced all the vacuum line.

This is on a 2001 1.9 TDi B6