Fuel Pump Priming Pulse

[jas280z]

I am trying to wire in a way to prime my fuel rail on my 280z to combat hard hot starting problems. Tony D said "Priming pulse will take care of 99.999% of the starting problem. Just bypass your 's' terminal with a spring loaded switch so you can 'crank' the car for a couple seconds without the starter turning. 3 to 5 seconds usually does it. This is VERY simple to fix, and not that big a deal."

 

I will admit that I am a noob when it comes to electrical systems, so I am not 100% sure where to put the switch. Looking at the wiring diagram I see that the wire that leads from the "s" terminal splits and one side heads towards the CSV and ECU, while the other heads to the Fuek Pump Control Relay. If I am correct in my thinking I believe the switch should go after the split, on the side heading towards the ECU/CSV.

 

 

I believe this would allow the fuel pump, and only the fuel pump, to get power when the key is turned to Start and the switch is activated. Does anyone know if this is correct, or would the injectors still fire if I put the switch there? Thanks for any help.

 

P.S. I was unsure if this post was more appropriate here or in the Ignition Electrical section. If the mods feel it belongs in the Electrical section please move it. Thanks again, any help is very much appreciated.

[Tennesseejed]

on a '75 280Z - and I see that you have a '78 280Z so this may not be helpful - the easiest solution would be to put the switch across Pins 36 & 39 on the air flow meter. This way, the fuel pump is tricked into thinking the car is running while the key is in the "on" position.

[jas280z]

Tennesseejed, that is a good idea, I forgot that the AFM was what controlled the fuel pump being on or off when the key is at "on." I would just need to figure out a way to run the wire for the switch into the interior of the car. I wouldn't want to have to pop the hood to flip the switch every time I want to do a hot start, and I also wouldn't want to just jump the pins and eliminate the switch in the AFM. And thank you for pointing out that I have a '78, it is in my sig but I forgot to restate it in my post.

 

I am still interested in the original question as well, so any help on it is still appreciated.

 

Edit: It appears that on a '78 the fuel pump will only run in the "on" position if the alternator is operating and the oil pressure switch is open. So it seems that a switch across those two terminals won't work unfortunately.

Edited August 10, 2010 by jas280z

[Tony D]

Wrong "S" terminal. The "S" terminal on the STARTER.

 

I am interrupting nothing on the ECU power circuit, I am just stopping the solenoid from being engaged on the starter. This will start the fuel pump as long as the car is in the "Crank" position.

 

Jumping the AFM is not recommended---you can manually do that by holding the flapper, and it will continually run the pump as suggested, but my contrivance alters nothing in the fuel control system at all, including the 'stall feature' built into the AFM. If you were to use a non-spring loaded switch and didn't turn it back off the most my modification would do is not allow the car to crank (and you could still start it by jumping the solenoid manually)---if you forget the switch on the AFM, and you get in a wreck...the fuel pump keeps on a-pumping covering the road with fuel and roasting you solwly in your conveyance.

 

No, I think interrupting the starter is easier, shorter runs of wire, and doesn't affect any safety features in the car.

 

It also disables the starter for theives.... But that's beside the point.

 

Look at the "S" terminal on the starter and that circuit. The wires are easily accessed under the hook and routed back inside through any number of grommited holes. No permanent splicing of hte wires is necessary, just a pigtail from the "S" terminal to the switch, and from the switch back to the connector that pushed on the "S" terminal before. Easy, quick, simple. No cutting required.

 

ALL the cars run the fuel pump in the "START" position. This is why I sourced it thus...

[jas280z]

Thank you very much for the description Tony, your help is much appreciated. I hope that you do not mind that I PM'ed you as well, I knew that your input would be very helpful but wasn't sure if you would see my post.

[jas280z]

Results! I located the 's' terminal on the starter and disconnected it. Sure enough doing so allows the pump to run, but keeps the injectors from firing as well as the engine from turning over.

 

I took my Z ou for a good 10 mile ride to get it nice and warm. Normally after a ride like that on a warm (85ish degree) day like today it would encounter the starting problem. I parked the car when I got home and unplugged the 's' terminal, as I have yet to hard wire in the switch. I went back out 7 minutes later, after leaving the hood down and doing nothing to aid the heat escaping the engine. I held the key at the start position for about 5 second (5 buzzes from the door ajar buzzer), then I reconnected the 's' terminal. When I tried to start it after reconnecting the terminal it started right up.

 

To further test the solution I pulled the car into the garage and lt it sit for another 5 minutes, as it was still quite hot. I tried to start it and it encountered the problem. I then removed the terminal again, and held the key at start for about 10 seconds, and reconnected the terminal. Again it started, it stumbled a bit this time, but it cleared up within a second.

 

I wish I had known to do this several weeks ago when the heat problem left me stranded and caused me to miss a track day at Watkins Glen. Oh well, live and learn.

 

I would like to send out one last thank you to everyone who helped me with this problem, especially Tony D.

[Tony D]

Sometimes, the offal I vomit forth is actually tasty enough for consumption, and healthy for you too!

 

 

 

As an ultimate thankyou, you can go down past the Galleria, turn right onto Walden Street and then do a burning clutch-dumping smoky donut in front of Cameron's Main Offices while shouting 'TONY D SENDS HIS REGARDS!' Do it on the Easternmost side of the complex, in view of the training room, Baldo should love it. Don't worry, they will blame me.

 

Remember, this theory was shot full of holes, so 'priming pulse' to return liquid fuel into the rail didn't really work, it was something else! I don't know what, but it was something else...something. Just not what I suggested!

Edited August 11, 2010 by Tony D

[easyguy71]

 

 

Remember, this theory was shot full of holes, so 'priming pulse' to return liquid fuel into the rail didn't really work, it was something else! I don't know what, but it was something else...something. Just not what I suggested!

 

 

Interesting. The way you've strung all those words together to make full sentences, it's just fascinating!

 

The topic content is intersting as well.