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Dan222000

Series II 240Z Factory Electric Fuel Pump - V3 Modification Program

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Hello,

I am in the process of restoring my 1973 Series II 240z and am looking for someone that still has or is familiar with the factory electric fuel pump setup/wiring (AKA V-3 Modification Program).  My car came with the mechanical pump and also an electric pump but the previous owner hacked into the factory wiring and really wired the electric pump in a very strange way.  I want to revert the wiring to factory original.  My car has both relays "A" & B" per the V-3 modification.  I also have the hacked up V-3 Modification Harness B but it's way to hacked up to reuse to I found a new one on Ebay.  I am having an issue with find where two wires go from the new V-3 Modificaton Harness B.  Below is what I have figured out so far.

V-3 Modification Harness B

1. 6 Pin harness connector - Goes to Relay "B"

2. 4 Pin harness connector - Goes to Relay "A"

3. Black Ground Strap - Strapped to Relay "B"

4. 2 Pin harness connector - Goes to fuel harness under radio/console

5. Two wires (Yellow w/Black stripe & Black w/White stripe)  - This is what I cannot figure out where these wires go.  The V-3 modification diagram shows what looks like these wires going up above the dash somewhere but that's it.  Can anyone shine some light here?

 

Thanks,

Dan

Relay diagram at kick panel.jpg

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Where did that "Page 11" come from?  Might be some clues there.  Never heard of the V-3 program myself, but I have a 280Z.  A wiring schematic would show the function of the relays and with that the wiring would be easier. 

Also, you posted in Fuel Injection instead of a carb forum.  No biggy, just not a great intro.  Who are you anyway?

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19 minutes ago, Zed Head said:

Where did that "Page 11" come from?  Might be some clues there.  Never heard of the V-3 program myself, but I have a 280Z.  A wiring schematic would show the function of the relays and with that the wiring would be easier. 

Also, you posted in Fuel Injection instead of a carb forum.  No biggy, just not a great intro.  Who are you anyway?

Zed Head,

first let me apologize for putting this up on the wrong forum. 

I got page 11 from this form.  It came from a 1973 240z to 1974 260z fuel system modification manual I found scrolling through this forum.  The manual has to do with the "V-3" Modification program Datsun introduced for a fuel system modification to add an electric fuel pump to the original manual fuel pump system.  I've attached the whole manual for your reference.  I agree 100% that a wiring diagram would've been easier.  Unfortunately no wiring diagram was provided with this fuel system modification.  But after looking through some of these forms I've figured out where the two wires in question go.  

The Yellow wire goes to the Voltage regular and the black wire goes to the starter solenoid.  At least I hope so!  I will confirm my findings later tonight when I go home and check the car.  

As for who I am,  I'm a Datsun/Nissan enthusiast just like you!  I've owned and driven Z cars since I got my drivers license.  

 

Thanks!

Dan

 

1973 240z 1974 260z fuel system modifications.pdf

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On 7/26/2018 at 2:56 PM, siteunseen said:

fwiw, my 73z had the electric fuel pump installed but I don't think that it ever worked.  It seemed like it was wired up somehow with the alternator.  I think the important thing is that the fuel pump goes off in the event of a crash.  Since I couldn't figure out how to make their scheme work I wired up an oil pressure switch so that if I lose oil pressure the fuel pump stops too.  I override that during start so that during starting the fuel pump runs.  I removed the mech fuel pump 30+ years ago and blocked off the hole.  It helped with the fuel percolation problem.

Thinking back on the wiring I think what they did was sense that the alternator was no longer putting out and it that case they would shut off the elec fuel pump, and of course the wire to the starter solenoid is used just like I did to make sure that the ele pump runs during the startup time.....but I couldn't make that work.

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Hls3073z,

I do believe that I've figured out the missing wires to the "V-3" modification program.  This fuel system was designed to work with both electrical and mechanical fuel pumps.  The electric fuel pump was used to prime the engine than once the engine started the electric fuel pump would shut off and the mechanical pump would do the rest.  This is why in harness A there two are wires, one wire to the starter solenoid to fire the electric pump and one the the voltage regulator to shut the electric pump off once the alternator was running.

I am waiting on a few electrical connectors to custom make harness "A" and give it a try.

 

Thanks!

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If the electric pump shuts off after starting then the mechanical pump would have to pull fuel through it.  Which would increase the possibility of vapor lock.  Plus the mention of the kit in the Troubleshooting section suggests that the electric pump is on while the engine is running.

image.png

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Zed Head,

One of the members (bjhines) on here did specifically state that the electric pump was only used to prime the engine.  

"I have to chime in here on some misinformation on the operation of the ELECTRIC FUEL PUMP WIRING. The 1973 240Z uses ONLY THE MECHANICAL PUMP during normal operation. The electric fuel pump is for priming the system ONLY!!!!! It will not operate once the engine is running. None of this is detailed in the electrical diagrams. There are hundreds of things not shown in any of the wiring diagrams.

There are a bank of relays on the passenger kick panel for the 1973 240Zs. There are 2 relays associated with the electric fuel pump.

Relay 1) cuts the fuel pump OFF once the alternator produces 12v(engine running).

Relay 2) cuts the fuel pump OFF when the starter is engaged(start pos on the key).

The operation of the electric fuel pump is only to PRIME or REPRIME(vapor lock) the fuel system. It will operate when you turn the key to the RUN position. The relays cause it to shut off once the car is running or the starter is engaged.

The electric fuel pump has a filter on the bottom that is often neglected. Check it or change it.

There are many other components on the passenger kick panel that operate flashers, wiper delay, wiper auto run for the washer pump, EGR relay and temp switch, accessory relay, etc. The electrical diagrams only brush over the most basic systems in your car. There are hundreds of wires that are simply not shown in ANY of the available diagrams. This is especially true for the bastard 1973 model 240Zs."

 

I should be able to confirm this once i'm finished with mine.

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It's okay to post the other member's name.  The link would be even better.

Nissan's description does not fit that scenario.  Anybody with a properly installed system should be able to verify what's what.

"Vapor lock" is caused by fuel vaporizing in the lines before the mechanical pump.  It makes sense that an electric pump pushing fuel to the mechanical pump would help.  If the pump's not running it's a restriction, causing lower line pressure, which lowers boiling point.  But, Nissan had a plan.  They just didn't tell anybody what it was.  Who knows.

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zedhed, do you have a copy of the pattern for the heat shield that is suggested?  While my engine is sitting out now is a good time for me to fabricate something.  Is there a source for those 72 carburetor mounting blocks?  I assume that they are some kind heat insulating material, like bakelite. 

Regarding the mech fuel pump.  Back when I still had the mech fuel  when I would stop and let it have a hot soak you could literally hear the fuel percolating inside that fuel pump.

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Nissan provided the patterns in the book.  That book has so much information in it it makes me wish I had carbs.

I think the part numbers might be in the book too.  But there's always carpartsmanual.  It says 1972 production.  Plug in to Google and see what pops up.

Page 72 has the dimensions - https://www.classiczcars.com/files/file/60-fuel-system-modification-plus-73-74/

Here's carpartsmanual - http://www.carpartsmanual.com/datsun/Z-1969-1978/engine-240z-260z/carburetor-240z-(l24)

 

 

 

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I vote with the group that says the electric pump ran when the engine ran. Before I removed the flat top carbs and the electric fuel pump, I could hear the pump running whenever I was stopped with the engine idling.

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I'm in that group too Pat.  I guess quite obviously since I've been running with the electric pump only since 1979.  Those relays do the exact opposite of what was described, they make sure the elec pump is not running in event the engine stops, like in an accident.  Turning on start key enables the pump again.

Has anyone seen a Z with the "competition hood vent".  Actually, that became standard in the zx.

 

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