59 replies to this topic

[LukeFranky]

Hey all,

 

The last few mornings have been fairly cool and damp and my B4 has been starting rough and then idles really badly and almost stalls. If I give it some throttle it evens out a bit and once she warms up the problem mostly disappears. I know it is in tune with the weather as a couple of mornings ago it was a bit warmer and she started and idled without issue.

 

Just returned from a good 16 hour round trip on the weekend and apart from this and a clutch shudder, the car has been buttery smooth. My first inclination is the IACV. What are other possible causes?

 

At the moment it doesn't bother me too much but Armidale will see temps well below freezing this winter so I fear it will become worse.

[Robbks]

Are you still seeing poor battery voltages?
that was the #1 cause of idling/ cold running issues in my TT Legacy

Also Injector seals could be weeping.
As a Test
On it's first cranking, don;t wait for the fuel pump to prime before starting
and hold the throttle wide open until it fires.
See if it starts easier or not

As a second test, 
prime the fuel pump multiple times
then start with no throttle
See if it fires easier.

This helps to see if it's running rich or lean on cranking.
if it makes no difference you can move on to Ignition or electrical issues

[LukeFranky]

Thanks Rob, I'll give it a shot.

 

I have not seen a cam shaft sensor fault since replacing the alternator, but the battery voltages haven't improved massively, at least according to the ECU's reading. Might check it with a multi meter.

 

Also, the injectors aren't old. I do have the old set at home.

[PeeKay]

I love my B4...but damn what a pain in the butthole they can be

[LukeFranky]

I'll give it a clean. Might order a new gasket so I can take it off and do it thoroughly.

 

Tried Rob's suggestion. So far it has started fine once or twice if I let the fuel pump prime. It has struggled to start with WOT. Because the issue is hit and miss I want to try this a few more times to make sure a pattern exists.

[LukeFranky]

I should also mention my intercooler was full of blow by oil. So much so I thought my turbo was on it's way out but the intake pipe was oily too.

 

Put a catch can on the car this past weekend. Will post pics to my build thread soon.

[motoboy76]

Looking forward to the update to your build thread....

[Robbks]

Given your test, it kind of indicates a lean condition when cranking.
This is also a distinct possibility with a un-restricted intake or IACV jammed open.
Or MAF scaling is out due to the mods.

Does it start easier after an ECU reset and slowly get worse as it learns?

Have you confirmed proper Fuel Pressure and Fuel Pressure Regulator operation?

It's also possible that low voltage can reduce the amount of fuel injected when cranking.

ALso with the catch can, make sure it is ONLY between the Crankacse breather Tee out of the block, and the pre-turbo intake.
DO NOT put the head breathers through the same can.

[LukeFranky]

I'll keep trying those tests. Thanks Rob.

 

I haven't tested fuel pressure yet.

 

I didn't hook up the head breathers to the catch can. Left them as is. My crank case breather goes directly to the catch can, then after the catch can I tee out to the intake pipe and PCV valve.

Any issue with this setup? I can't see any problem with it because it is identical to stock just with a catch can inbetween the crank case and the T.

[Robbks]

problem there is you're not catching the blow-by under boost, when it's actually produced.

Under boost the PCV is shut so your catch can is doing stuff all, when it matters

It goes between the Crankcase Tee and pre-turbo intake.

cleaned up 99% of the blow-by on my turbo-subies with the simplest setup
Don;t forget to fill it with air filters for a Lawn-mower to catch the oil.

You can see the two lines running to and from the can which is mounted above the ABS on my MY99 GT Fozz



Fuel pressure is one of the first 3 things you need to check for any issues.
Fuel, Air, Ignition.

Also,
Is the coolant temp sensor OK, and the correct OEM one for your model?
 

[Jimbo]

Rob, is this how you would do it?

[LukeFranky]

Hmm. I woukd have thought that would catch less? My setup means the catch can is always between the crankcase and vacuum from the intake pipe and the manifold.

[Jimbo]

Off boost, both the intake manifold and intake tract draw air through the crank case breather. The PCV valve is only active at this time, effectively doubling the drawing power at idle.

On boost, the manifold valve shuts and the intake tract then draws on it's own with increased vacuum. This is when you need it most. You don't need to do anything with the PCV because it's drawing it straight into the manifold and burning it up anyway.

The valve cover breathers draw in relation to the vacuum of the intake. If you hooked up the valve cover breathers to the same catch can, I imagine it would cause idle issues as your effectively connecting 2 things which should be isolated from eachother. You would have to attach a second catch can on those, hpowever, the volume of vapor is likely far less than that of the crank case.

[LukeFranky]

I didn't attach the valve covers, so no worries there.

I understand your point about burning up the oil in the manifold straight away but wouldn't that still lower the octane?

Regardless, is there any downside of feeding both the intake pipe and PCV through the catch can instead of only the intake pipe?

[LukeFranky]

I guess my point is why is this:

CC -> T -> Can -> Intake
CC -> T -> PCV

Better than this:

CC -> Can -> T -> Intake
CC -> Can -> T -> PCV

At least the second setup catches everything..?

[Jimbo]

It's pointless connecting the PCV valve line as it's only active at the lowest load of the engine. The same time that's open, 50% of the vapor is being drawn through the intake tract anyway. The amount coming through the PCV valve at a low engine speed, is probably so minimal, it wouldn't affect the octane rating.

Being that the PCV valve is only open at low load and drawing straight into the manifold, it's pointless running it to the can. Like Rob said, the important part is when the engine is at high load as that's when the most amount of blow-by is being generated. At this time, the setup I have drawn, is the most effective.

All it does (PCV-valve) is essentially double the vacuum draw on the crank case at idle to give a similar amount of vacuum as if it were on boost (increased vacuum from intake tract).

When you're on boost and it's closed (PCV), your getting a thereabout equal vacuum in the intake tract alone, due to the spool of the turbo/s.
 

[LukeFranky]

I understand what you are saying. I know there may be no extra benefit in my setup but unless there are any side effects I'll leave it as is. I've got bigger fish to fry now.

 

My clutch has started slipping so troubleshooting the rough start is on hold: http://www.subyclub....lutch-slipping/