Blow off valve

[Van Diesel]

I've had my van for a couple weeks now. Last weekend I was going up a very steep hill at the base of Mt Washington and I heard this PSSSSSSSSSSST!

I assume it's the turbo blow off valve but it's the first time it happened. I was doing 60km/h and wanted to go faster. When I pushed the pedal down to get it to drop down a gear and accellerate a bit, I get the pssst sound. If I backed off the pedal a bit, the noise would stop

Am I correct in assuming it's the turbo blow off valve? Is this normal? Does it harm anything to have it do this for more than a few seconds (like 30sec)?

Thanks,
David

[Green1]

Common issue, currently being discussed in another thread, including the method for repair.

leaving the valve "open" while powering up a hill won't hurt it, in fact it may help solve the issue.

[Van Diesel]

Would you be so kind as to direct me to this thread?

I've done some searching and came across something similar regarding L300s called "How to raise Turbo Boost" by preventing the valve from opening too soon.

Is that the one?

[Green1]

http://www.delica.ca/forum/helpful-hint ... -7138.html

[Adrock]

my understanding was a b.o.v. relieves the pressure once the load is taken off the engine. Doesn't sound the same as your problem.

I've also read a blow off valve is completely useless (on most vehicles) but especially on diesels.

[tonydca]

The L400's PRV (pressure relief valve) is a backup device to relieve pressure in the intake manifold in the event of overpressurinzation from a broken wastegate, etc...

On my vehicle, it got gummed up and was not sealing properly, causing to blow off early (I think). It made a steady, loud HISS under load, aimed directly at my head through the firewall.

Since clearing it out, it sits solidly at 11 psi under load, and pulls like a freight train when I goose it.

But as a side note, my gas mileage was significantly (almost 20%) better with the leaky valve, so if you don't need the extra power, it is just compressed air escaping so shouldn't really hurt anything.

[psilosin]

I've also read a blow off valve is completely useless (on most vehicles) but especially on diesels.

A blow off valve (BOV) is a different animal than the turbo wastegate or prv. Blow off valve's dump manifold pressure/vacumn when your foot is taken off the go pedal when switching gears etc to prevent the turbo from an abrupt stop or even spinning backwards. They are pretty much useless on an automatic and are useless on most diesels. The exception are manual trans diesels equiped with a butterfly valve either as part of the EGR system or just equipped for smoother shutdowns (I don't know if teh L300 or L400 has this?). If your engine has this, then a vacumn can be created when you take your foot off the juice and a blow off valve can be beneficial to your turbo health and your 1/4 mile times . If you hate the stupid sound the vent to atmosphere BOVs make you can get recirculating BOVs too...then you don't sound like a Tuner Boiz and still get the benefit.

[Green1]

Although the post is titled "Blow off valve" I suspect that most people don't actually know the difference between the various valves involved on a turbo.
The important part is that it is whatever mechanism makes the "PPPPSSSSSSSHHHHHHHTTTTT" sound when you put the accelerator down, I believe this is officially the "pressure relief valve". more importantly is that it seems this is quite a common occurrence, and seems to normally be caused by a build up of "gunk" in the valve mechanism. Cleaning it out seems to solve the issue generally.

Now for people who want to increase their turbo pressure any, this same valve must be modified not to open at as low a pressure.

[danfromvan]

Sticky Green1's last note. I am no longer confused. Amen!