75 280Z Hands -Free Fuel Pump Primer Circuit?

[HusseinHolland]

Wondering if anyone has done this. I found a thread on HyridZ where the main suggestion was to simply bridge 36/39 w/key on to engage the fuel pump. That appears to be a viable approach, if it comes to that. I need to do this as cold start definitely is impeded by lack of system prime. Hot or warm starts are pretty rapid in terms of cranking time

What I was thinking was more along the lines of a timer/delay circuit that would run the pump for 3-5sec when the key is turned, anywhere in ACC or On, so that no additional input is required. I've found a range of timer relay/circuit boards that would possibly do the trick, the issue seems to be making it only run once with the key on signal & not cycle. 

Couldn't find anything on here, but maybe it's hidden like the AFM/Pot thread.

Example:

[Zed Head]

Are you saying that your fuel pressure is leaking down?

Nissan added automatic pump priming in the ZX's.  It often quit working though.  I'd guess the timer is in the relay.  Maybe you could retrofit a ZX pump relay.

1982 -

[Zed Head]

The forum's search engine is terrible, if you've been trying to find things using it.  Go straight to Google to get better results.

I know that Fastwoman had discussed it in the past.  It's not hands-free but it's close.

https://www.google.com/search?q=site%3Aclassiczcars.com+fastwoman+momentary+fuel+pump

[siteunseen]

I've always had the best search results by typing simple keywords and ending with classiczcars.com. If it's something I remember reading from a member I put their name next to last then classiczcars.com. Most of the time I hit IMAGES and go from what I've seen in threads. Our forum is fantastic but searching within the database is lacking for sure.

I'm about to start using duckduckgo.com. Google has gone to the dark side where the money is, assholes. Maybe I'll use Ask Jeeves on AOL. 

Sorry for the detour.

[HusseinHolland]

5 hours ago, Zed Head said:

Are you saying that your fuel pressure is leaking down?

Nissan added automatic pump priming in the ZX's.  It often quit working though.  I'd guess the timer is in the relay.  Maybe you could retrofit a ZX pump relay.

1982 -

Fuel pressure will always leak down overnight - I don't know how long it is designed to hold, however I've never seen any 'old' EFI maintain rest pressure for more than a couple hours, if that. I put fuel pressure gauges on all my old cars, so I know from personal observation that even with new fuel pumps, regulators, injectors, etc., long term rest pressure is not part of the design.

[HusseinHolland]

5 hours ago, Zed Head said:

The forum's search engine is terrible, if you've been trying to find things using it.  Go straight to Google to get better results.

I know that Fastwoman had discussed it in the past.  It's not hands-free but it's close.

https://www.google.com/search?q=site%3Aclassiczcars.com+fastwoman+momentary+fuel+pump

that search actually just brings up my new thread & few presumably related to fuel pressure issues.

In any event, I'm likely going to add a momentary contact switch for the time being. As it stands, I only need it for cold starts. Though, having said that, it is likely to change 😞

[Zed Head]

11 minutes ago, HusseinHolland said:

Fuel pressure will always leak down overnight - I don't know how long it is designed to hold, however I've never seen any 'old' EFI maintain rest pressure for more than a couple hours, if that.

My good FPR's (edit - and fuel pump check valve) would hold about 20 psi for days.  The bad ones would leak down to zero.

Carry on.  

Edited October 16, 2023 by Zed Head

[HusseinHolland]

2 minutes ago, Zed Head said:

My good FPR's (edit - and fuel pump check valve) would hold about 20 psi for days.  The bad ones would leak down to zero.

Carry on.  

That's impressive. Since many vehicles have a prime feature (for example, my newer Volvo does), I would still say long term residual rest pressure is not expected. 

[Zed Head]

Define long-term.

Hey, you're having fun.  Just keep going.  There's probably a fuel pump relay out there somewhere with an integral timer.  Or try that timer thing in your first post.  My 2003 Ford has a timed prime but I think it's controlled by the PCM (aka ECU/computer).  EFI is all about emissions so the manufacturers went to great lengths to get everything perfect from the first crank.  

 

Have you measured the leak down rate on your system?

44 minutes ago, HusseinHolland said:

Fuel pressure will always leak down overnight - I don't know how long it is designed to hold,

 

[HusseinHolland]

22 minutes ago, Zed Head said:

Define long-term.

Hey, you're having fun.  Just keep going.  There's probably a fuel pump relay out there somewhere with an integral timer.  Or try that timer thing in your first post.  My 2003 Ford has a timed prime but I think it's controlled by the PCM (aka ECU/computer).  EFI is all about emissions so the manufacturers went to great lengths to get everything perfect from the first crank.  

 

Have you measured the leak down rate on your system?

 

It has varied. With the nylon fuel tubing on the rail & the stock FPR, It held  pressure (close to 30psi) for a day or so. After I took it apart again to look for debris, I switched back to standard (Volvo) 7mm fuel hose for the rail junctions & added the Volvo FPR pod. With this setup, pressure typically drops to around 20psi within 4 hours or so, and overnight is down to no registered pressure.

[Zed Head]

I looked around a little bit and it seems like the manufacturers generally went to computer control of a simple fuel pump relay instead of integrating the timer.  But it is a hot topic, so of course, people have filled the need.

https://www.ebay.com/itm/174274213748?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=NmzUBVTDRzy&sssrc=2047675&ssuid=bBzFtXzvTQO&widget_ver=artemis&media=COPY

This on Amazon, below.  The words in search should find it.  I don't like to copy their links they seem full of extra stuff.  Could probably be made to work.

[EuroDat]

On 10/17/2023 at 1:25 AM, HusseinHolland said:

Fuel pressure will always leak down overnight - I don't know how long it is designed to hold, however I've never seen any 'old' EFI maintain rest pressure for more than a couple hours, if that. I put fuel pressure gauges on all my old cars, so I know from personal observation that even with new fuel pumps, regulators, injectors, etc., long term rest pressure is not part of the design.

Mine will hold more than 1.5bar pressure for a least 2 weeks. It took me a while to get it that far, but replacing the check valve on the fuel pump was my eureka moment.