16V pinks when cold

[roo 0]

I've just got my car through its MOT after rebuilding the engine and everything runs well, although it needs a proper RR tuneup after i've finished running it in.

 

My only problem is that the engine runs fine when warm but pinks at idle when it's cold. I'm assuming it's doing this due to the WUR regulator not richening the fuel mixture sufficiently and so it's running too lean.

 

Can anyone confirm that my WUR is probably not working properly before I go and get a new one?

 

Cheers,

Andy

[bcstudent 0]

These may be obvious questions, but a) what fuel are you using? Standard unleaded or one of the fruitier varieties? and b) are you 100% sure the timing is correct? I'm not trying to imply you'd overlook such obvious causes, but...you know.

 

I'm not sure the WUR is your problem. I'd be looking at the ignition system first, although I'm not sure if there's any engine speed or temperature-related advance/retard in the K-Jet system.

 

With respect to the WUR you could start by measuring the resistance of the heater coil. If that seems normal then (I believe) the only other way to confirm its operation is with a fuel pressure test.

 

The control pressure should rise as the temperature of the engine increases to apply more resistance to the plunger movement in the fuel distributor. There's a linear relationship between WUR temperature and control pressure from 10 decrees C (1.0-1.4 bar) to 40 degrees C (2.2-2.5 bar).

[roo 0]

Yep, i'm using BP ultimate fuel and the timing and CO are both spot on. The reason I suspect it's the WUR is that it only pinks when the engine is stone cold. Do you know off-hand the resistance ofthe heater coil?

 

The engine is now 2 litres and the WUR has not been altered from when it was used as a 1.8, could this be a problem?

[bcstudent 0]

flusted is the man to answer that question!

 

I'd say the WUR could certainly use a tweak to take full advantage of the extra capacity but I can't see that it would cause pinking only at idle solely because it's now a two-litre. If the extra capacity was an issue wouldn't you expect it to pink at all engine speeds when cold?

 

I'll go and measure my WUR heater coil resistance...

 

* EDIT *

 

...it's approximately 23 Ohms.

[roo 0]

Yep, i'd be surprised if a slight capacity increase would affect anything, especially only when cold.

 

I'll go and have a measure of the heater in the WUR and see how it compares.

[sciroccotune 0]

Take it that its 1.8, if that the case the euc does the timing, so there must be a thermo time switch involved...in fact sure that there is, on the gearbox side of the block maybe? hope you get it sorted mate, sorry i cant be more help not so familiar with the 16v kjet but WUR is my bet to.

[roo 0]

It's a 2.0 running on K-Jet. I'm pretty sure that the thermotime switch is related to water temperature so probably wouldn't be the cause of my problem.

 

The WUR heater resistance is 23 Ohms, same as bcstudent.

[sciroccotune 0]

is it k jet from a 1,8 or ke jet as found on 2l16v???

[bcstudent 0]

The thermo time switch operates the cold start valve only, I think.

 

The 2.0 16v (9A) uses KE-Motronic management.

[roo 0]

It's a rebuilt and rebored 1.8 KR block using a 9A crank and pistons with the original K-Jet injection.

 

I'm not sure it's the thermotime switch and cold start valve. When cold starting in cold conditions the engine catches and runs ok for a few seconds. About 5 seconds later it starts to run rough and the pinking starts. My thinking is that when the cold start injector cuts off one or more cylinders are running too lean.

 

I've set the CO at idle when warm to 2% and the timing is correct and it runs well when warm, but still pinks and runs rough when cold. From my understanding the WUR increases fuel pressure (and therefore flow) when the engine is cold to enrichen the mixture during warm up.

 

Any thoughts on dribbling injectors, they have done 149k miles?

[bcstudent 0]

I'm not sure it's the thermotime switch and cold start valve. When cold starting in cold conditions the engine catches and runs ok for a few seconds. About 5 seconds later it starts to run rough and the pinking starts. My thinking is that when the cold start injector cuts off one or more cylinders are running too lean.

 

I agree that it's not the cold start valve or thermo time switch that's causing the problem. I was just saying that I don't think the thermo time switch affects the timing, in response to a previous post.

 

I've set the CO at idle when warm to 2% and the timing is correct and it runs well when warm, but still pinks and runs rough when cold. From my understanding the WUR increases fuel pressure (and therefore flow) when the engine is cold to enrichen the mixture during warm up.

 

That's backwards. The control pressure via the WUR is initially low (i.e. when cold) meaning the counter-force on the plunger in the fuel distributor is also low. With a low counter-force the air-flow flap can move the plunger further for a given throttle opening and allow more fuel through the slits to the injectors. As the engine temperature increases the WUR increaces the control pressure and the counter-force on the fuel distributor plunger is also increased, restricting its free movement and leaning the mixture off.

 

Any thoughts on dribbling injectors, they have done 149k miles?

 

I replaced mine recently (at 119k) and it made a hell of a difference to the way the car started and ran. VW list the mechanical injectors as a consumable item according to GSF; it's recommended they're replaced after 120k. All four inc. VAT from GSF were about £137. They looked slightly different to the ones that came out but work fine. Once changed it took a few starting attempts to create the pressure required to open the sicky seats, which was a bit of a worry initially! It hasn't missed a beat since.

[sciroccotune 0]

I know it sounds silly, but have you checked the wur is getting 12v? when i built my syncro gti this caused problems for ages before i managed to sort it, dodgy connection on the wur. from what i remember it gets 12v all the time.

[bcstudent 0]

That's a good point. It's so easy to overlook the obvious things.

 

The VAG service manual lists these tests for the WUR voltage supply:

 

1) Disconnect the H.T. lead from the distributor.

2) Test for battery voltage at WUR heater connector while the starter is being operated.

 

The heater element resistance specification is listed as being between 20 and 26 Ohms...just for reference.

[roo 0]

Thanks for your replies guys 8)

 

Sounds like my injectors could be a part of the problem then if it's recommended that they're changed at 120k. I'll also check that the WUR is getting the full supply voltage too.

 

Would it seem likely that the WUR mod that stealth do would sort this problem out, assuming that the injectors are good and the WUR isn't broken?

[bcstudent 0]

Sounds like my injectors could be a part of the problem then if it's recommended that they're changed at 120k.

 

Don't take that as gospal; it's what GSF told me so I'm not 100% sure about it. All I know is that mine were definitely past their best at 119k but I never noticed any pinking.

 

Have you seen flusted's 16v tuning guide? I'm pretty sure the WUR mod is in there somewhere.