Decel valve on EFI conversions

[sjf911]

I have had occasional problems with the engine stalling on rapid throttle lift above 2000 rpm with my EFI conversion that seems to be aggravated by the turbo conversion. As a consequence, I tend to run the idle around 1200 rpm. I am wondering if plumbing back in a decel valve (vacuum limiter) would be of benefit here. What has been your experience?
Also, how many replumb their crankcase/oil tank ventilation back into the intake versus using a catch can?

Thanks.

Specs: K27S on OBX headers (GSF HE's being repaired), 964 cams, 46mm Tial WG @ 0.5 bar, 50mm Tial BOV, Carrera intake, 42# injectors, stock FPR, 12X12X3 intercooler, Clewett IAC valve/stepper in stock Carrera location.

[magic930]

Try giving it a little more fuel between 1300-2000 rpm at 0 throttle. If that doesn't work then increase the timing as it falls towards 1000rpm at 0 throttle. For example typically at 0 throttle you will have practically no fuel because of the extreme vacuum on deceleration and that throttle column typically has no or little fuel above the idle point. If you start introducing fuel and or timing at 2000 and increase it as it reaches the idle point then it should catch the falling rpms.


I use a catch can for the oil I didn't want the gunk going back in the engine, it ends up catching mostly water.

[DonE]

I handle mine a bit differently. My car idles at 950 - 975 rpm which is about -45 pka and 5 degrees timing. Below that, I add timing (about 20 degrees) and just a bit of fuel. So, if the RPM's drop below the idle rpm, the additional timing catches the motor and brings the idle back. If I introduced more timing before reaching idle, it would never settle. Also, how do you set idle air? I have a stepper motor that opens a couple steps below optimum idle in case it needs to catch a low idle.

[sjf911]

Originally Posted by DonE

I handle mine a bit differently. My car idles at 950 - 975 rpm which is about -45 pka and 5 degrees timing. Below that, I add timing (about 20 degrees) and just a bit of fuel. So, if the RPM's drop below the idle rpm, the additional timing catches the motor and brings the idle back. If I introduced more timing before reaching idle, it would never settle. Also, how do you set idle air? I have a stepper motor that opens a couple steps below optimum idle in case it needs to catch a low idle.

I see I haven't been adding enough timing. Thanks for that input. Does your EFI/ECU provide idle stabilization via the stepper motor? The IAC control with megasquirt is most consistent as warm-up only. I can't get it to stop at a predictable number of steps below closed so I use the idle bypass screw and the throttle plate adjustment screw to set hot idle.

[Speedy Squirrel]

I agree with the discussion on the timing. It definitely help to kick the idle if you are in danger of stalling by advancing timing. The IAC will not return the same number of steps every time. This is normal. As the engine warms up it needs less power to rotate, so you throttle down the IAC.

[911st]

I like de-accel valves on a Turbo if set up righ.

They do basically the same thing as a blow off valve. They help keep the turbo spinning between shifts and may help keep the turbo from twisting a shaft.

If your BOV freezes up, it may be the only thing that can keep the turbo from going.