at-jefft Posted June 20, 2009 Share Posted June 20, 2009 Hey, I'm sick of cranking my engine(L26 SU's) for 30+ seconds before it starts (cold). I was thinking of putting a switch to control the electric fuel pump in so I can hit the switch and fill up the fuel bowls. First, Anybody see any issues with this plan? Second, This would be my first automotive wiring experience. How would I go about wiring this? I have 2 ideas about wiring it. (remember complete noob) 1. Connect a wire hot when ign switch is "on" to switch then splice it into fuel pump + wire. 2. Wire a relay, again using a wire hot to "On" and then to fuel pump. Would either of these circuits work? if not could you first explain why or why its not the best option. And then a circuit that would work. Thanks, Jeff Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 21, 2009 Author Share Posted June 21, 2009 Its not like HybridZ to have a post up for a day and not have any responses. Any Help would be greatly appreciated Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted June 21, 2009 Administrators Share Posted June 21, 2009 (edited) It's not going to fix your problem. The bowls aren't empty on cold start unless something is draining them. Your cold start problems are likely caused by other issues. P.S. Please refrain from frequent bumping. Edited June 21, 2009 by RTz Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 21, 2009 Author Share Posted June 21, 2009 It's not going to fix your problem. The bowls aren't empty on cold start unless something is draining them. Your cold start problems are likely caused by other issues. P.S. Please refrain from frequent bumping. Woops, I thought I made this thread days ago. I have a ztherapy rebuild kit in the mail. should I readdress after the rebuild? Quote Link to comment Share on other sites More sharing options...
Oddjob Posted June 21, 2009 Share Posted June 21, 2009 This would be my first automotive wiring experience. How would I go about wiring this? I have 2 ideas about wiring it. (remember complete noob) 1. Connect a wire hot when ign switch is "on" to switch then splice it into fuel pump + wire. 2. Wire a relay, again using a wire hot to "On" and then to fuel pump. You might look into a pressure switch (Holley makes them, Summit carries them). This has a big safety function: if your engine has no oil pressure, the pump won't run. The pressure switch has one B+ out, which goes to the pump +. It has two B+ in terminals, a normally closed (NC) and a normally open (NO). The NC contact goes to your + starter terminal so the pump runs when you are cranking the engine, even if it has no oil pressure. The NO terminal goes to any + which is live when the ignition switch is on. The pump runs when the ignition is on and there is oil pressure. The pressure switch comes with wiring diagrams, including one for using a relay, if you like. Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 21, 2009 Author Share Posted June 21, 2009 This has a big safety function: if your engine has no oil pressure, the pump won't run. well, I'm almost positive that the engine will still run with out the electric pump. So I don't think that will exactly have the intended safety effect. I'm just looking to use the electric pump to prime the fuel system so I don't have to sit there and crank it for a good 30sec. Quote Link to comment Share on other sites More sharing options...
Oddjob Posted June 21, 2009 Share Posted June 21, 2009 The primary idea of the safety switch is to avoid feeding a fire in an accident or rollover. If you want a manual primer, you would put a momentary (pushbutton) switch from an always live B+ (eg. the battery) to the NC terminal of the pressure switch, and don't put in the connection from the starter. The pump would run when you held down the button, and would run normally when the engine was running. Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 21, 2009 Author Share Posted June 21, 2009 The primary idea of the safety switch is to avoid feeding a fire in an accident or rollover. If you want a manual primer, you would put a momentary (pushbutton) switch from an always live B+ (eg. the battery) to the NC terminal of the pressure switch, and don't put in the connection from the starter. The pump would run when you held down the button, and would run normally when the engine was running. so basically Idea #1 right? Just checking: battery>switch> fuel pump + wire Sound good? Quote Link to comment Share on other sites More sharing options...
Oddjob Posted June 21, 2009 Share Posted June 21, 2009 Yes, idea #1 is right, with reservations (the devil is in the details). Do not use any switch other than momentary for the primer circuit, and do strongly consider the pressure switch. Check on the current draw for the pump. If it's too high for your switch, you'll need the relay. Be sure to include a fuse right after the connection to your power source. The right value will be about 150-200% of the running current for the pump. Be sure to size your wires to carry this current. Good luck, I hope this solves your problem. Quote Link to comment Share on other sites More sharing options...
at-jefft Posted June 21, 2009 Author Share Posted June 21, 2009 Yes, idea #1 is right, with reservations (the devil is in the details). Do not use any switch other than momentary for the primer circuit, and do strongly consider the pressure switch. Check on the current draw for the pump. If it's too high for your switch, you'll need the relay. Be sure to include a fuse right after the connection to your power source. The right value will be about 150-200% of the running current for the pump. Be sure to size your wires to carry this current. Good luck, I hope this solves your problem. As for the momentary switch, I don't see the need for anything other than a momentary switch. Current Draw? Like see how many amps are flowing/being used/what ever they are doing, and see if that exceeds the max amps of the switch?? yup, planning on a fuse. Where should I get the correct automotive wires? Quote Link to comment Share on other sites More sharing options...
Oddjob Posted June 21, 2009 Share Posted June 21, 2009 Current Draw? Like see how many amps are flowing/being used/what ever they are doing, and see if that exceeds the max amps of the switch?? yup, planning on a fuse. Where should I get the correct automotive wires? The pump itself may tell you its draw (in amps) on a label attached to the pump. If it's the stock 260Z electric pump, you can get the draw out of the service manual. If all else fails, check to see the size of any existing fuse (and wire) and just copy those. An inline fuse holder, fuse and automotive wire are available on the shelf at most any auto supply. They usually have momentary switches, as well. The capacity of the switch will be printed on it, usually on the back. In general, if you size everything for 15 or 20 amps, you will be fine. Quote Link to comment Share on other sites More sharing options...
jasper Posted June 21, 2009 Share Posted June 21, 2009 Fuel pressure/bowl level is not the problem. SU's don't have a real choke/plate. They also don't have an accelerator pump. Choke is accomplished by dropping the main jet to richen the mixture. It has no plate to increase the vaccuum signal in the carb. You have to rely on cranking speed to draw the mixture in. Cold= slow crank, poor fuel atomization also. This system does not work well. I had the same problems 30 yrs ago. I ran 2 batteries in the winter, and sometimes ether to get it started. Try starting your car with jumper cables attached, and see what happens...... Quote Link to comment Share on other sites More sharing options...
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