74Adam Posted January 19, 2006 Share Posted January 19, 2006 I just completed the 240SX TB swap and am very pleased with it except for the elimination of the fast idle. Of course I knew this going in but I wasn't sure how much of a difference it would make. If it gets around the mid 50 degree range it takes two or three turns of the key to get it to start and stay idling. If it didn't start doing that until it got down into the 30's I probably would be OK with it. So I was wondering if anyone knows how to incorporate fast idle into this swap? I have a 4 cylinder Frontier (same TB, I think) and thought I would take a look at it to see how it's fast idle works. I figured that if it operates independently of the ECU there might be a way to make it work on the Z. Just wanted some thoughts on the subject. thanks -Adam Quote Link to comment Share on other sites More sharing options...
zcarnut Posted January 19, 2006 Share Posted January 19, 2006 You re-use the stock “fast idle” valve. This is the air regulator valve that is used for the fast idle function. It is a stand alone valve needing a hose connection to the intake and another hose going to the air inlet hose (filtered, metered air supply) and also an electrical connection for the heating element inside the valve. The valve allows air to bypass the throttle when the engine is cold, thus increasing the idle speed. As the heater element warms up the valve gradually closes. There is more info about the air regulator valve in the FSM. Of course if you swap out the stock throttle body with the 240SX one you lose one of the hose connections (the intake manifold one) to the air regulator valve. However, you can make your own intake hose boss and use a suitable hose to the valve as I did: Quote Link to comment Share on other sites More sharing options...
mario_82_ZXT Posted January 20, 2006 Share Posted January 20, 2006 Some TB spacer's for the 240sx TB swap have a hole made for the original flange. Maybe drill and tap yours? Mario Quote Link to comment Share on other sites More sharing options...
74Adam Posted January 20, 2006 Author Share Posted January 20, 2006 Hey guys, thanks for the responses. zcarnut: First of all, I LOVE your clean setup. Someone owns a sandblaster...lol! I have the FSM, read alot of it, and feel like I have a decent understanding of how the circuit works. On your setup you routed the return line through the cold start injector. I will, at some point, get an aftermarket engine management system where I can use the main six injectors for the cold start function (like I assume you are doing?). For now however, I have to use the actual CSI. As Mario mentioned, I could drill through the spacer. I have one of Pallnet's pieces made out of lexan, I believe. I bet I could come up with something. Another question on your setup: My understanding is that with the stock TB, when the engine is idling, the throttle plate is completely closed and all the air getting into the intake goes through the air regulator valve. Is this correct? So on your setup you sort of have a "compromise", so to speak. You control the idle with a screw on the throttle lever but still have an independent "air path". I never considered doing that but it makes so much sense. Last question. I tried but wasn't able to get the stock rubber boot between the air flow meter and the TB to fit, so I used some ducting from an aircraft supply company. Worked well but of course I lost the outlet port for the hose that goes to the air regulator. What boot is that from that you are using? I'm guessing that you aren't using your AFM so I wouldn't be able to do the same thing you have done, but it obviously fits the TB like a glove. Sorry for the long post but I really appreciate the help. It's fun learning about this stuff. -Adam Quote Link to comment Share on other sites More sharing options...
zcarnut Posted January 20, 2006 Share Posted January 20, 2006 .... I will, at some point, get an aftermarket engine management system where I can use the main six injectors for the cold start function (like I assume you are doing?)... Yes. I’m using a Z31 ECU with the turbo 280ZX distributor (for the crankshaft position sensor) and the Z31 air mass sensor. The Z31 ECU does not need the cold start injector, so I used this boss for the intake hose fitting. ..I could drill through the spacer. I have one of Pallnet's pieces made out of lexan, I believe. I bet I could come up with something... The later Nissan air regulator valves (1984 and up) mount directly on the intake manifold and the connection to the intake manifold is made internally in the air regulator body. So no hose is needed. You still need the fresh air hose. You can easily mount one of these later air regulator valves directly to your spacer. This is what I was going to do initially. I was even going to mount the air regulator valve on the underside of the spacer where it would be out of sight. However, I changed my mind and decided to go with a cable for the throttle control and therefore no TB spacer is needed. ..Another question on your setup: My understanding is that with the stock TB, when the engine is idling, the throttle plate is completely closed and all the air getting into the intake goes through the air regulator valve. Is this correct? So on your setup you sort of have a "compromise", so to speak. You control the idle with a screw on the throttle lever but still have an independent "air path". I never considered doing that but it makes so much sense.... I adjust the idle speed by changing the stop position on the throttle lever. By swapping the factory setscrew with a fine pitch screw and spring, you can adjust the idle speed: However, adjusting the throttle stop opening affects the TPS adjustment, so you have to re-adjust the TPS after first setting the idle rpm. Also, repositioning the throttle blade has an effect on the level of ported vacuum that is used by the vacuum advance mechanism in the distributor. But the ZX turbo distributor I am using does not incorporate any vacuum advance so no problem there. ...Last question. I tried but wasn't able to get the stock rubber boot between the air flow meter and the TB to fit, so I used some ducting from an aircraft supply company. Worked well but of course I lost the outlet port for the hose that goes to the air regulator. What boot is that from that you are using? I'm guessing that you aren't using your AFM so I wouldn't be able to do the same thing you have done, but it obviously fits the TB like a glove.... I have a confession to make...The setup pictured is out of my Datsun 810. It has the air box and mass air flow sensor mounted on the side of the engine compartment. So, I am using a boot from a late 1980's Maxima (with a 90 degree bend) which fit my application perfectly. Quote Link to comment Share on other sites More sharing options...
Challenger Posted June 28, 2006 Share Posted June 28, 2006 Hi I recently bought the 240sx tb to make the swap. Im going to be using the spacer from Graytech Software. It has the coldstart valve hole on so Id be good on that but, I read some of the comments by Zcarnut, and Im becoming somewhat hesitant. I was just wondering If anyone could show everything you need to do to make this work. Thanks Quote Link to comment Share on other sites More sharing options...
Challenger Posted June 28, 2006 Share Posted June 28, 2006 I forgot... I have a 1978 280z with stock L28 with stock TB. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 8, 2009 Share Posted November 8, 2009 The stock idle bypass screw from the later ZX's unplug just fine, and with a small torch or heat gun the hot melt glue holding in the large 12mm hoses lets go---allowing you to tap that same valve for a 1/4" barbed fitting, and rig a simple idle speed bypass circuit just like stock. This is the same setup on Euro Turbo cars, they did not use the AAC, just an idle bypass screw with a totally closed throttle plate. With a 1/4" line you can adjust any idle speed from 300 to 2200rpm on most L28's. The larger lines are not needed, you likely could get by with even smaller tubing but I used 1/4" EFI hose so it's good for the boost pressures I'm running. It works just as well on N/A applications. Looks stock, as well! JeffP comments that "I suck" for making it look stocker than his needle valve bypass setup... I might add that using this type of idle bypass circuit allows you to install a simple solenoid into the circuit for initiation of a high idle feature---a direct porting of the 1/4" line with a small restrictor jet in the alternate line will allow 1500 or whatever you desire for fast idle. A magnet valve off a turbo will perform that function, and remain looking stock... Sometimes, I shake my head and leave the SMOG station grinning broadly at what I get by sometimes...All clean and green, yet naughty at the same time! Quote Link to comment Share on other sites More sharing options...
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