Esprit V8 Blow Off Valve

[MD355]

I decided to start a thread about the Blow Off Valve on my Esprit V8.

The previous owner had installed a set of 2 Forge BOV and it appears they almost the same as those sold on PNM.

https://www.pnmparts.co.uk/dump-valve-kit-v8-8928

The problem I have is that I believe that in my car

a) maybe the BOVs are opening sometime under acceleration (is this possible ?)

b) they don't open when I release the gas pedal to blow off the air and allow the turbos to spool freely

 

For a) I hear sometime something like a hissing sound.. not sure if it is the turbine spooling, the wastegate opening or the BOV opening..

If it is the turbo that's fine... If it is the wastegate, either the ECU is allowing it or my wastegate spring are going soft.. If the BOW is opening under acceleration (is that even possible?) then this is a problem..

 

For b) I put below 2 videos... the first is my car and the second is another car with similar BOVs... Check the differences..

Above my car, below another car with working BOV valves... Seem exactly like mine, Forge model

 

 

[mike_sekinger]

Did you take them apart and check the seals?

They do not sound like they are working.  Where are you taking the manifold reference from?

[MD355]

You are right I need to take them apart and check if they are working..

I say a small pipe that leaves the T-connector between the two BOV and goes somewhere round the intake manifold.. I will check with my mechanic..

By the way, is there any chance of BOV to open under full acceleration ? My understanding is that when the throttle body is open there is zero pressure difference, so no way to activate BOV.. is this correct ?

And another question.. If I fix the BOV and they operate correctly, should I expect better response when upshifting ? Does this mean that the turbo pressure will build up faster after the gear change ?

With regards to fueling, my understanding is that the Esprit V8 goes to Open loop when >95% throttle opening which means that it only looks at MAP sensor (not Lamda).. Is my understanding correct ? 

And when the engine works at partial throttle it operates Closed loop which means it check with Lamda sensors if mixture too rich / too lean.. Right ?

(does this mean that if I fix the BOV, when I change gears there will be a "rush" of more air, the MAP will send more fuel, and bang of unburnt fuel will be more ??? I certainly hope so... P.S. I know this part is a little silly, but it just fun)

[mike_sekinger]

What is a dump valve? PH Explains | PistonHeads UK

It is possible that your valve can open, if the manifold reference is not correct but this would only happen when the boost pressure overwhelms the spring.

The principle purpose of the BOV is to remove/reduce any stalling of the compressor when the throttle closes between shifts.   There is a theoretical chance that the turbo response is also better as it is still spinning.  In practice with fast gearchanges, the turbine is being driven again very quickly, especially with small turbos.

 

[MD355]

So basically the article says that at full open throttle there is no chance of air escaping from the BOV as the air pressure is the same before and after the valve..

If the spring is not strong enough the BOV could open at idle or part throttle as this can cause erratic operation of the engine or stalling..

I have to check 1) the connection of the BOV to the manifold and 2) the actual operation of the piston of the BOV

Can someone explain the Open Loop vs Closed Loop operation of the Esprit ? Is it true that at >95% throttle openings it works as Open Loop which means it does not look at Lamda sensor ? Thanks !

[mike_sekinger]

I'm sure that the engine is not running in Closed Loop at WOT.  The o2 sensors are not wideband in nature and you would not want the fuelling to be adapted under full load.

[mike_sekinger]

Any updates/findings on the BOVs?

[MD355]

@mike_sekinger my close buddy insisted that I go buy softer springs for my BOVs and he gave me the address of the Forge importer here in Athens.. 
Since I have infinite free time as my businesses are closed due to covid, I drove there with my Lotus today.
I showed the guy at the Forge shop my car and he offered to sell me 2 sets of springs (green, yellow, blue, red) for 30 Euro each. He said he does not sell individual springs..

But he insisted that maybe something else is wrong with my BOVs..

Maybe the piston is stuck.. He suggested that I bring the BOVs to him, which is difficult for me, since I cannot do anything mechanical by myself, need my mechanic.. LOL

On a another BOV he has at the shop, He showed he how a functioning BOV should work. He pushed with one finger the BOV and used the thumb to close the vacuum opening to see if the BOV would stay open..

So I am going to my mechanic to remove the BOV and test them..

I asked if he could sell me the two kits of springs and allow me to return them to him if I don’t need them.. He said hmm no. 

Edited January 14, 2021 by MD355

[mike_sekinger]

Yes, best test them.  If they are the piston type then they could be seized closed.

[MD355]

BOV update :

So today I went to my mechanic and took out the BOV to check them.

They seem to operate normally, but the spring was kinda hard.

We opened them up and and saw that there was a blue spring.

I called the distributer of Forge BOV and he said that Blue springs are hard and operate over 1 bar.

He said I should go for Green Spring that opens around 0.6-0.7 bar.

Before I go, my mechanic put back the BOV and we tested the car... Guess what ? They opened normally under Full Open Throttle. Check out the videos below.

My mechanic said that I probably cannot hear them when I drive because a) I have removed the cats and mufflers so my car is too loud , b) when you put the luggage area panel and the engine cover back and close the hood, there less of a chance sound coming from the BOV. He explained to me that Japanese rice cars run 1,5-2 bar pressure with large BOV and that's why they sound loud... LOL

 

[mike_sekinger]

I would agree and fit the softer green springs.  You are running stock boost, so don't need the stronger BOV springs.

[cweeden]

Some BOVs also make more noise, my HKS units came with different inserts for the output that change the sound dramatically. I tried the noisy inserts and very quickly removed them, they were embarrassing.