Engine: 70 T5: LTFT (fuel trims) +18% - vacuum leak through crankcase?

[Jaaap]

Thank you for your time!

- Did the glove test, it sucked the glove in a little, appears to be ok.
- The oil filler cap seal is ok but the dipstick o-ring at the bottom was too flat for my liking so i'll replace it. No smoke coming from it though (when i smoke tested it).
- I'm monitoring fuel trims with Vida and sometimes with a bluetooth dongle and a phone app called "Car scanner ELM OBD2"
- The STFT is all over the place, and averaging out (not just positive or just negative)
- I don't think my car has the plastic tree that you mention (up to '98, mine's a '99)

I'll try the brake cleaner thing.
I'll try to check the turbo boost control valve
And i'll read and watch all your fuel trim info.

Thank you!

[Jaaap]

I also wondered about this vacuum line that goes between the thermostat housing (?) and the bottom of the air intake (where the banjo bolt screws into the intake), it is at the end of the big PCV hose (nr 9470330).

Is it really a vacuum line going into the thermostat housing?
What does it do?

[SteveSarre]

Hi Jaap,

I have a couple of 1999 T5s and I can see that hose. It is short (about 8 cm long) and connects to a metal tube that runs across under the intake manifold.

When you replaced the PCV system, did you take your intake manifold off? That would have been a good time to look! I am 99.99% sure it is not a vacuum hose.

Steve

[SteveSarre]

Hi Jaap

Sorry, just saw your second photo.

So that metal tube is part of the PCV kit. Where does the other end connect to?
I don't remember.

Volvo part number for the kit is 9470330 so I have been looking at the full screen links here.

https://www.volvopartswebstore.com/p...7/9470330.html

but I cannot work out where it goes (and why)

Steve

[Jaaap]

Yeah when i had the intake manifold off is exactly when i wondered about that hose. It's so strange that it goes into (or just below) the thermostat housing.
It must be vacuum since it connects to the intake via a banjo bolt.

I just took the TCV out and benchtested it. It appears to work correctly:

No power: a little air can flow between red and yellow
Power: a lot of air can flow between blue and yellow
It makes a strong clicky sound when i apply power, even at 10V.

[SteveSarre]

The TCV needs power to operate.
One of the vacuum lines controls the vacuum to the other line(s).

Overall, when the engine overruns (ie you take your foot off accelerator) (which causes high vacuum), the TCV switches on (or switches off) vacuum to the turbo so that it doesnt briefly overboost.

Sorry you'll have to do more research for a better explanation.


Hope that helps,
Steve
Steve

[Jaaap]

FOUND SOMETHING!

The middle (thinner) hose/tube that goes from the banjo bolt on the intake manifold to the top of the PCV box has broken loose.

Tomorrow i'm going to (attempt to) fix it.

[SteveSarre]

Hi Jaap

That's great.

Take some photos if you have a chance.

Steve

[Jaaap]

Argh the stupid little tube broke when i tried to bend it back into its hole.
Guess i need to replace the entire PCV hose now.

Solved one mistery though: the "vacuum" line that goes between the thermostat housing and the bottom of the air intake (where the banjo bolt screws into the intake) is not vacuum but coolant!
It goes around the banjo bolt but has no inner connection/hole to it. I guess the coolant goes all the way to the other end of the PCV tube (could not check that)