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Cold Start Valve

StealthX

By StealthX,
in Engines & Forced Induction

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StealthX Veteran

StealthX

Posted
Posted

Hey guys, just trying to make and install a cold start valve for my X-trail, I had to swap the throttle body from the fly-by-wire QR's, to a cable drive SR throttle body (for tuning purposes), now I have no cold start. The car is MAP sensored with an EMS Stinger controlling it all. I have no MAF or TPS sensors, just a MAP and a cable throttle.

My warm idle is about 1100-1300 rpm depending on how hot the atmo temps are, and that's as low as I can go without it stalling upon cold start up, the cold idle is about 800rpm, if I give it a rev when cold, it'll drop too low and stall, and any load from the air con, power steering pump or alternator causes it to stall, so I almost have to hold the throttle open a little for the first 10 mins of driving (when at idle). As you can guess, it's fvcking annoying.

What I'm trying to do is install a cold start valve in order to reverse these two idles (i.e. warm idle ~800-900rpm, and cold idle ~1200rpm). My car is MAP sensored, so I figure all I need is a small controlled leak in a vacuum line in order to bump the cold idle up a little. I just need to find a device, a small electronic air valve that's activated by a switch mounted in the cabin. Off = valve closed and 800rpm idle, On = small vacuum leak and ~1300rpm idle.

Can I possibly use the factory RB2x IAC valve modified to suit? Or can anyone think of an electronics store that sells such a valve?

Thanks...

Cam.

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scotty nm35 Grand Master

scotty nm35

Posted
Posted
Cheers Scott, any idea where I'd find one? Apart from buying a $400 boost controller just for the solenoid? Haha

Any place that sells air fittings and regs will have one, I have a few here but they are 24v.

An iac valve would obviously be the best but they are variable arent they? A simple on off valve would be easier if you dont have the ecu output.

StealthX Veteran

StealthX

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  • Author
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Yeah the Stinger had PWM 5V relay outputs, they can be configured with respect to RPM, load, throttle position and engine temp, so that's probably the way to go about it...

The RB2X or SRXX IAC valve might be a little complex, I don't think the RB/SR ECU switches the valve straight on or off, i.e. would be hard to implement with a temp switch, the boost solenoid would be a bit easier, so I'll look into it.

Pretty sure the temp switch is the best idea I've heard, thanks Scott, I'll call my tuner tomorrow, see if there's anything else I need to look out for...

I'll post my progress here...

Thanks guys!

discopotato03 Grand Master

discopotato03

Posted
Posted

There is actually a very simple electrically heated air bypass valve that Nissan's have had since the 80's , well I think all the pre electronic throttled ones .

It looks like half a small dumb bell and has an early Bosch injector fitting on one end of it .

How it works is that it contains a metallic strip than when heated flexes and rotates a plate with a hole through it so it slowly closes up the air passage . By slowly I mean approximately 2-3 minutes .

Another clever part of this gadget is that its usually bolted to a surface that conducts engine coolant so if the engine is started hot the internals stay hot and the rotary valve remains closed .

Another nicety is that your computer doesn't need any outputs other than to the fuel pump relay because its that circuit that powers this valve in OE applications .

I can hear people say why wouldn't it be powered by an ignition power supply . The reason is that if for some reason you have the ignition switched on without the engine running the valve won't close up because the fuel pumps power supply is cut other than to initially prime the system .

These devices are merely there to add extra air to a stone cold engine , the "cold gun" effect of cold chambers/valves/pistons means an engine needs more air until it warms up enough internally not to lose much of its combustion heat and efficiency to cold surfaces .

Some non synthetic oils also have a lot more drag when cold so this can add to the cold start woes .

If you search for these valves under AAV or auxiliary air valve you should find some good info .

Note that these are not a controlled IAC or idle air control valve so they can't regulate hot idle speed .

Food for thought , cheers A .

StealthX Veteran

StealthX

Posted
  • Author
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Thanks doods!

Figured out there is an output control designed for idle control specifically.

The Stinger manual explains easily how to set it up and sh!t. Looks easy.

idlecontrol.jpg

idlespeed.jpg

So now I'm thinking the boost controller won't work as well, but an RB or SR item, just need to ring my tuner and ask him which one would work with EMS's system. (anyone know?)

Looks easy enough from there...

Does anyone know how the inputs for a typical idle control valve work? i.e. are there two terminals +ve and -ve? Or are they like a relay where there's positive, negative and a signal?

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