Comp surge + Blow off Vent.

[Z2TT]

Hi,

I notice that when I let off the gas sometimes I would hear the compressor surge, and then the BOV will vent, I believe this shouldn't be happening.

Does this mean my Blow off Valve is too small?

[oldcorollas]

how do you know the compressor is surging?
maybe it is just in the wrong place.

[Z2TT]

I know the sound of the compressor surge, As I used to hear it when my BOV never used to vent, this was when the spring was too tight.

Its a much more subtle sound than my Blow off Valve.

The blow off valve is in the correct place, after the inter cooler and before the throttle body.

[oldcorollas]

well.. if it does vent after surge.. then it obviously isn7t venting early enough.

if it was surging DURING venting, then it would be too small... but since it surges and then vents.. your setup is wrong

[Z2TT]

By a wrong setup do you mean that the Blow off Valve is not in the correct place?

I have tried adjusting the spring, but that does not help.

[oldcorollas]

I notice that when I let off the gas sometimes I would hear the compressor surge, and then the BOV will vent,

think for a sec.

BOV will vent when there is no longer boost pressure plus spring pressure pushing the diaphragm closed..

if you let off quickly, then vacuum from manifold reaches BOV quickly and it vents.

if you let off slowly, then you still have either some boost, or no vac + spring pressure holding it closed. and then when you let off fully, then vac reaches diapgragm and bov opens...

how do you know the spring is not still too strong? is your line between manifold and BOV too long/big/whatever.

whatever it is.. you7re doing something wrong just think abotu the conditions that cause it, how the BOV works, and how you have it arranged in your system..

edit: do you have the vac line hooked up to the right spots? after TB, not before it?

[Z2TT]

Yes I have the vacuum line from the Intake manifold connected into the nipple on the BOV, I made sure it is on tight. Might go for a drive now and get back to you.

Thanks.

[Cuzzo]

Did you get two springs with the bov?

if so try the other spring and adjust accordingly.

Is it a new BOV?

[PlacentaJuan]

is this a 2jz i get this also.

[TC1600]

Sounds like a sticking bov, it takes a moment longer to open than it should and it surges, then opens and situation normal. Is there any way to disassemble it to clean it?

[Z2TT]

Hi,

I have a 1g-gte

The BOV has one spring that is adjustable

It surges for a split second then vents.

The blow off valve is not new, it came with the car when purchased so i do not know how old it is.

Last time I tried disassembling my valve, I remember that I could not take it apart.

[MWP]

Are you using a decent sized vac line from the BOV to the inlet manifold?

I replaced my normal (ie, thin walled rubber hose) with a piece of fuel hose, it made a big difference to how the BOV reacts.
I think the normal sized stuff could have been getting sucked closed by the vac.

[Z2TT]

MWP,

Are you trying to say that if the walls are too thin, they would squish together when the vacuum is sucking?

Here are some specs on the vacuum hose going to the BOV nipple.

Internal Diameter : 4.5mm
Wall Thickness : 3mm

Thanks.

[Pure_In_Sanity]

I'd back the spring off a bit if you can. I had to play around with my GFB one to get it in the right spot.
One way it would leak intermittantly, too far the other & it would start to flutter.

(then of course i turned the dial to plumb back & now it's quiet as can be )

[Z2TT]

Thanks,

Today I found out how to take apart my blow off valve.
There was a circular stopper that held the piston in that I never noticed. I pried this out with a screwdriver, the Piston shot up into my nose.

The cylinder (or body of the BOV) was very smooth and so was the piston. I put a thin layer of oil on the piston so it would slide easier.

The Vacuum hose going to the BOV does not come directly off the Intake manifold, it comes off a T piece connected to the Intake manifold, would this be causing a problem?

Would the size of the Blow off valve be an issue? The Inlet diameter to the blow off valve is about 3.5cm. The outlet of the BOV is half of that.

Can mounting position make a difference, I can draw a diagram if it helps.

I will have a play with the spring.

[oldcorollas]

what is the T'd vac line going to? you realyl realyl should check things like that out.. befor eposting

[Z2TT]

what is the T'd vac line going to? you realyl realyl should check things like that out.. befor eposting

T'd vacuum hose that splits into 2, one goes to the Power steering pump, other goes to the BOV.

[YLD-16L]

The BOV should have a dedicated vac line.

Ideally placed it would be just before the throttle body with a nice short vac line.

The BOV's with a larger surface/diaphragm area on the vac/boost side compared to the underside of the piston (the side that releases the pressure) have better response than those with the same surface area on both sides.

Your BOV is plenty big enough in terms of size.

[Z2TT]

I cleaned out the BOV and added some oil so the piston slides easier, made sure the vac line was on tight.

took it for a drive and it was venting real well, no compressor surge, then I began hearing compressor surge again before the vent, and at boost below 5 PSI it would not vent, but just surge.

Here is a picture of how long the vac line is.

http://img401.imageshack.us/img401/9880/bovhoseaw6.jpg

[oldcorollas]

take your foot off the pedal quicker and see what happens,.

if you take off the vac line, when does the BOV start leaking?