7 minutes ago, Zed Head said:

Considering everything, I would remove the pump, get the proper hose barb for the inlet, take the banjo fitting off of the outlet and see if you can identify the check valve, and try to fix it. It might just be a piece of rust or debris in the check valve seat.

You need to fix that zip tie mount anyway. If that breaks, the hose ends up on the spinning halfshaft and you could easily end up spraying fuel and creating vapor back by the muffler. A fire/explosion waiting to happen.

There shouldn't be an issue with the pump since it is brand new but couldn't hurt. Could you take a picture of how you have the hose routed to avoid the potential of it rubbing on the axel?

I don't have the car anymore. No pictures.

I thought that this whole thread was about finding that there is a problem with the pump's check valve. Do you think that the problem is the check valve in the pump or the leaking hose?

Most intact systems will hold 10 - 20 psi overnight or longer. Your earlier description of air leaking in would have to happen after enough liquid fuel leaks out to relieve all internal pressure. That would be a lot of fuel, especially with fact that the wrong hose probably expands like a ballon. All of that volume has to leak out.

I would fix as much as you can then see where you're at. Your car is a danger to you and the public around you at this point. I remember fixing a coworker's car well enough once long ago to get him home so he could fix the problem correctly. He had overfilled it with oil and the PCV system sucked it up and clogged his air filter. He didn't fix it, just kept driving it and beating on it. One night, about a week later, he parked it in front of the place he was renting after a night out and it caught on fire and burned. The oil had leaked on to the hot exhaust manifold after a night of beating. Luckily the car was parked far enough away that his landlord's family's house didn't catch on fire. He was renting a room.

I think it was a Yugo with a manual transmission. He drove it like an F1 car.

39 minutes ago, chaseincats said:

There shouldn't be an issue with the pump since it is brand new

Edited September 24Sep 24 by Zed Head

2 minutes ago, Zed Head said:

I don't have the car anymore. No pictures.

I thought that this whole thread was about finding that there is a problem with the pump's check valve. Do you think that the problem is the check valve in the pump or the leaking hose?

Most intact sytems will hold 10 - 20 psi overnight or longer. Your earlier description of air leaking in would have to happen after enough liquid fuel leaks out to relieve all internal pressure. That would be a lot of fuel, especially with fact that the wrong hose probably expands like a ballon. All of that volume has to leak out.

I would fix as much as you can then see where you're at. Your car is a danger to you and the public around you at this point. I remember fixing a coworker's car well enough once long ago to get him home so he could fix the problem correctly. He had overfilled it with oil and the PCV system sucked it up and clogged his air filter. He didn't fix it, just kept driving it and beating on it. One night, about a week later, he parked it in front of the place he was renting after a night out and it caught on fire and burned. The oil had leaked on to the hot exhaust manifold after a night of beating. Luckily the car was parked far enough away that his landlord's family's house didn't catch on fire. He was renting a room.

I think it was a Yugo with a manual transmission. He drove it like an F1 car.

Fair point - will do

I have also been reading this thread and been thinking. my early 260z has 4 bolt su carbs and when the engine is off, I can see air bubbles in fuel filter that is in the engine compartment flowing back to the tank. but the early 260z have a return line back to the tank and I think air in the return line is the problem. I also have some type of hard start after sitting overnight. I am also thinking about a fuel check valve to see if it will help with the starting. I always need to use choke a little over night but daily driving it does start right up. [definitely no leaks]

Not sure if you would like to explore the route Houssein took with his car and a 3 second fuel primer circuit: https://www.classiczcars.com/forums/topic/68866-new-problem-fuel-pressure-drops-off-75-280-l-jet-w-composite-injectors-protunerz-rail-3-bar-fpr/#comments

My '76 was also plagued with fuel draining while sitting overnight or even within a few hours. I installed the fuel pressure gauge to monitor it. It seems that all my previous fuel pumps (generic one from Rockauto, MSD 2225 including the current, Walbro 255), did not have the built-in drain check valves. At some point I installed an anti-drain check valve inline past my engine bay fuel filter, it didn't help much. What helped when I switched to Microsquirt which primes the fuel pump for a few seconds before you crank an engine. It builds a nice fuel pressure and the car starts every time.

45 minutes ago, darom said:

Not sure if you would like to explore the route Houssein took with his car and a 3 second fuel primer circuit: https://www.classiczcars.com/forums/topic/68866-new-problem-fuel-pressure-drops-off-75-280-l-jet-w-composite-injectors-protunerz-rail-3-bar-fpr/#comments

My '76 was also plagued with fuel draining while sitting overnight or even within a few hours. I installed the fuel pressure gauge to monitor it. It seems that all my previous fuel pumps (generic one from Rockauto, MSD 2225 including the current, Walbro 255), did not have the built-in drain check valves. At some point I installed an anti-drain check valve inline past my engine bay fuel filter, it didn't help much. What helped when I switched to Microsquirt which primes the fuel pump for a few seconds before you crank an engine. It builds a nice fuel pressure and the car starts every time.

The strange thing is it has the hard starting issue if I prime it, but it doesn't have the hard starting issue when I used the clamp to keep fuel in the rail. That didn't make sense to me since its essentially doing the same thing...

Has the fuel dampener been removed also in the past?

8 minutes ago, Yarb said:

Has the fuel dampener been removed also in the past?

Coincidentally I replaced it maybe 6 months ago because it was leaking and original

16 hours ago, chaseincats said:

The odd thing is if I manually trigger the fuel pump to pressurize the rail, then crank the engine, it still acts as if the rail is completely dry -

It might be that the air (or fuel vapor) that's in the cold start valve line doesn't get fully purged.

The best setup for cold starts is Nissan's original design.

Edited September 24Sep 24 by Zed Head

Can you plug the Cold Start Valve fuel hose and try again? Maybe it is flooding your engine with fuel? You can also remove it and observe how long it sprays fuel for.

On 9/24/2026 at 5:16 PM, darom said:

Can you plug the Cold Start Valve fuel hose and try again? Maybe it is flooding your engine with fuel? You can also remove it and observe how long it sprays fuel for.

The valve is new(ish) and I know it's not flooding the engine because when I trigger it manually (i have a switch in the cabin) the engine fires right up.