kungfu

Still not found the problem to why my car cuts out when i'm going through the gears, 'quickly'. usually 3,4,5 gear.
It does this with 1/4 & 1/2 a tank of fuel (super) so this can't be the problem.
I fitted a vta dv on sat (turbo xs), and this trouble seems to have happened since.
could it be the air flow meter??

submannz

Could be lack of fuel under high load.

kungfu

Can't be as it does this with even 1/2 a tank of fuel.
Has no-body had problems like this with dumpvalves, as it just seems to be happening since i fitted it.
Really p***ing me off as i want to try and keep the dv on...sounds the part

Brian Swan

Maybe a daft question but here goes anyway, do you need to fit a higher flow Fuel Filter after a dump valve conversion?

In theory as you change gear the dump valve does it's job and if there is low pressure you won't get the fuel in to replace it so should you be looking at the filter or pump for not giving enough pressure in the line?

kungfu

I wouldn't have thought so, surely the dumpvalve can't be that much to do with the fuel.
It feels more as if it loses all it's boost, or stops getting fuel altogether. Also when the car is warm, the revs drop so low that the car stops completely, would this be the same problem??

care3

sounds like your dv isnt working properly

Q: I installed a blow off valve, it sounds really cool but my car stalls when I let off. Why?

A: First of all, the reason this is happening is because the Air Flow Meter on our cars measures
the air coming in through the flapper door. It senses this air and adjusts the fuel mixture accordingly. When you let big rush of air out of the intake system, you are letting out a bunch of air that was just measured. The fueling will still dump the fuel associated with that air and cause an over rich condition. This will cause your car to stall momentarily or in some cases actually turn off. Once the BOV has closed and the intake system will return to it's normal state and work again.

To fix this, you need to adjust your BOV. Most BOVs have a screw or nut to adjust the tension. You can turn the screw/nut to the right and increase the tension. Do this several times with a test drive in between. If your BOV stops letting out the pressure, you have adjusted it too tight. You will then need to start adjusting soft again. You must keep playing with this adjustment until you get it just right. A good adjustment will allow the BOV to release pressure after slight boost, and not stall afterwards. It is not necessary for the BOV to release pressure when you rev the car.

EvoRSX

Care 3,

Just a quick question regarding your theory....

If this is correct then what happens with a standard recirculating dump valve?
The recirculating dump valve still stops the air from entering the engine as it vents it back into the intake side of the turbo and so if your theory was correct then this 'over rich' condition would occur even under normal running with the standard car.

The way that I believe the vent to atmosphere dump valve causes problems is that because the valve opens before you lift off the throttle completely (due to the differential pressure across the throttle butterfly) then air can be drawn into the engine backwards through the dump valve opening, before the throttle has chance to close fully. Because this air going into the engine comes from the atmosphere and hasn't been seen by the airflow meter then you get a lean condition and that is why the car stalls.

With a standard recirculating valve, any air that is drawn back into the engine has already passed the airflow meter and so has been accounted for already.

As always though, I may be wrong and stand to be corrected and flamed

Andy

Jolly Green Monster 2

Yes but the standard BOV recirculates the air into the intake and therefore the engine is not rich with fuel as the air is entering the intake..

You are dumping the air pressure to atmosphere and the ECU is expecting it to go into the intake and injects enough fuel for this.. there is no recirculation so the mixture goes very rich and there is not enough air.. causing the loss of engine revs..

JGM

care3

evo, its not my theory i nicked it from herehttp://www.alltrac.net/tuning/bovfaq.html
http://www.scoobynet.co.uk/bbs/threa...threadid=98711

EvoRSX

JGM,
The standard DV does return the air to the intake but it returns it to a place before the turbo and therefore with a closed throttle, how can this air possibly get into the engine to stop the car from running rich as you describe a VTA doing?

Andy

Jolly Green Monster 2

Not 100% sure to be honest...

My understanding though is that it passes into the cylinders and hence the extra fuel is added.. if you fit a dump to atmos then the fuel is unburnt in the cyclinders and this is often ignited leaving the exhaust outlets... hence flames on decatted and a DTA.


This is IMHO and from what I have picked up from looking at the car and solving a couple of problems on a previous turbo car and reading this board, so I could be wrong...

I must be getting old as I'd rather have the silent recirculation dump valve.. grown out of the noise... still have a HKS Dump to Atmos in the garage which I must get around to selling.
When changing from DTA to standard you notice that there is less or no judder when you come off the throttle.. which makes it clear that the dumped air is passing into the cyclinders and is allowing ignition of the extra fuel which creates a smooth start to the engine braking..

JGM

kungfu

thanks fellas, i put some washers inside the dumpvalve where the spring is, the made the spring tighter and haven't had any problems since (touch wood)

Jolly Green Monster 2

Superb!

JGM

submannz

I was not talking about fuel surge!!!

But lack of fuel. eg injector duty cycle at there limits, fuel pump, need to replace fuel filter.

The other thing it could be is over boost

[Edited by submannz - 6/7/2002 12:41:19 AM]