Blow Off Valve (BOV/BPV or maybe Relief Valve)

[Airgonzo]

Hey Folks,

I've got an obscure "weird noise" question to try to convey in print for those of you inclined to puzzling over the esoteric quirks of the 4M40.

The noise could most aptly be described as a "Hoot" like an owl and it consistently announces itself at very low boost levels, generally just as you apply foot to pedal from zero boost. Just for an instant and as boost increases it vanishes. Seems to be turbo related, but I'm no expert. It's not the "whine" of the turbo.

Some reading from non-Delica sources leads me to speculate that it could be the blow-off valve (I'm not sure if this is the same as the Relief Valve) not functioning properly:

"On your Turbo-charged car, there are a few special pieces that N/A cars do not have, a Blow Off Valve or BOV is one of them. Your BOV acts as a pressure release valve for your car. When your turbos produce pressure(boost), it flows into your combustion chamber. When you let off the gas the Throttle Body plate closes. There is still pressure trapped in your lines leading from the turbos to your Throttle Body. This is where the BOV comes into play. Instead of the pressure flowing back into your turbo and causing backspin or compressor surge (your turbos violently start to spin backward...VERY BAD)your BOV opens and the boost is released through this valve. (That is the whoosh sound) When you are accelerating and you hear a hooting sound, it usually means that your BOV is leaking (releasing pressure when it should be closed)."

Does this sound plausible. If so, does anyone know where I might be able to source a replacement?

Kevin

[Mephisto]

There is no throttle plate on the 4M40, therefore, there is no need for a BOV. The pressure release valve is simply there for over boosting, meaning it only opens when too much boost is being made, eliminating this as a source for the noise you describe. A shot in the dark for an answer for you would be the intercooler piping colapsing under vacuum before any boost is made. I have never seen this happen, but I have heard of it happen and it is plausible that it could make a hooting noise that would be consistent with the one you describe, occuring at light acceleration before boost builds. An easy way to see if this is the issue is to open the hood and watch the soft black hoses going to the intercooler while someone revs the engine from idle, if you can see it collapse this would be your issue.

[psilosin]

The pressure release valve is for over boost protection in the event the wastegate ever gets stuck closed but it is a possibility it has become stuck open slightly giving you the symptoms you describe. That said I have never even looked at where it is located on my L400 so unfortunately I cannot give you any more specifics...

[tonydca]

If I recall, it's on the very back of your intake manifold, pointing rearward.

[Airgonzo]

Yup, Tonydca,

the part I'm thinking of is on the back of the intake manifold. I haven't been able to determine if its the culprit because I haven't been able to reproduce the symptoms with my head under the hood, the van in neutral and someone stepping on the gas, but I've only tried once. My gut tells me its the problem. If that's the pressure relief valve I may just switch it out. Steve at RSI told me $40 for a new replacement and $20 for a used one.

Anybody know anything about replacing it. Seems super-straightforward but does it have to be torqued to certain specs or anything? Basically looks like you just pull it out and crank a new one in. . . .

Thanks for all the ideas everyone,

Kevin.

[Airgonzo]

Picture sucks but, if my suspicions are correct, thats the part in question, in the back, looking like an aluminum mushroom that you'd pick with a pipe wrench.

[Rising Sun Auto Import]

Picture sucks but, if my suspicions are correct, thats the part in question, in the back, looking like an aluminum mushroom that you'd pick with a pipe wrench.

That's the relief valve that used to control or limit the pressure in a system to avoid failure/fire or something.
I have no idea if that is the case.

Steven

[Rising Sun Auto Import]

Yup, Tonydca,

Anybody know anything about replacing it. Seems super-straightforward but does it have to be torqued to certain specs or anything? Basically looks like you just pull it out and crank a new one in. . . .

Kevin.

Hi, you are right. Very simple.
If you think if that is culprit, worth to try it.

Steven

[psilosin]

Before you shell out for a new one you can do a quick check. One of the quick and cheap aussie mods when planning to do some fairly serious overboosting is to zap-strap the valve permanently shut. If the problem goes away then you know the valve was the source of the problem and can get a new one.

[Airgonzo]

Great, thanks for all the advice.

Kevin

[tonydca]

it's a fair big ol' nut and a b*stard of a spot to reach (although a chopper mechanic might have more experience... )

On my rig, I could see it was blowing open (makes a hiss like a compressed air line letting go) because it blows out a bunch of fine black crap from the intake manifold all over my nice clean hood interior... My wastegate actuator was sticking at the time.

[MardyDelica]

you guys sometime need to used diesel fuel conditioner
as sometime it cause by the carbon or sometime need to run it a little bit faster
stick. just need to push it by blowing air from the front line booster actuator.
then from there will see
cheers;
Mardy

[Van Diesel]

Any progress on this? Did you get it fixed?

My van's been hooting too. At least it was while I was driving around the mainland with the family and a bunch of gear. Now that I'm back in Victoria, I haven't heard it.

Somewhere around 2500rpm in 2nd (or 3rd). Only in the one gear at around the same speed mark. Once it shifted, no more hooting.

[Airgonzo]

No progress. I've been too busy to investigate and it's not a huge priority as it seems in no way to affect running or performance of the van. At first I thought our gas milage was a bit low and perhaps wad related to 'hooting' but I've found if I stay at or below 100 km/hr I get around 12 l/100km. So that's normal.

Seems to only make the sound once it's been driven for a while, at low boost, just as turbo is spooling up I think. A few psi. Mostly something I notice in town when accelerating lightly.

It's annoying and definitely doesn't belong but as far as I can tell isn't a major mechanical problem.

Kevin.

[jessef]

Clean it out and put it back in.

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

OK - quick, easy and free test for your Pressure Relief Valve (PRV) which seems to have helped my little hissing problem and power/boost loss.

Firstly, put on some rubber gloves and an old shirt if you have them!

As mentioned earlier, the PRV is a small round spring-loaded device on the rear of the intake manifold, pointing at the driver through the fire wall. In theory, it is set to open up at around 12-14 psi to prevent engine overpressure.

When the engine is at idle or stopped, it is difficult to grip the skinny outer plunger ring of the valve and pull hard enough to open it.

But when you spin the engine up to around 2500 rpm or so (either with a friend on the throttle, or by reaching around with your right hand and tugging the throttle cable) you raise the manifold pressure to a few PSI short of the valve popping open on its own. Now a relatively gentle tug will get it to spring wide open.

When I first did this, the opening motion coupled with the outrush of 12 psi air blew a satisfying amount of evil black oily crud the consistency of lard out of the PRV and onto my hands, jacket, face, etc. in a small cloud.

Popping the valve open and letting it shut again, rotating the plunger, and repeating about a dozen times blew out less and less junk, until now it seems (relatively) clean.

More interestingly, it became slightly more difficult to open as it cleaned itself out.

I believe that 15 years worth of accumulation from crankcase breather fumes, etc. had built up around the valve innards, impairing its ability to seal properly.

It might be wishful thinking, but the van now seems to rev more freely and pull stronger at higher revs. My ears are still buzzing from hugging a revving engine for so long, so I can't tell if the hiss is gone, but it seems to be an improvement.

Time will tell...