Hi all -

Great news - after a very long time of chasing lead after lead, I've finally found the culprit for my hard start - gas is flowing back to the tank, oddly through my new fuel pump overnight.

I ended up putting a clamp on the hose that sits between the fuel filter and fuel rail, waited 24 hours, then cranked the engine and it started right up. 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 - which is confusing to me since the clamp method noted above is in theory keeping fuel in the rail in the same way as priming the rail by manually triggering the fuel pump would be.

This is the pump I have on it now - don't all fuel pumps have check valves or are they external and I simply don't have one?

I'm planning on splicing this check valve between the filter and rail (where my clamp was) which should work I'd think, or is there a better way of going about this?

Edited September 24Sep 24 by chaseincats

I learned from @Captain Obvious that one of the things to consider on a check valve is cracking pressure. Most likely the fuel pump will overcome the cracking pressure on the check valve, but I couldn't find the cracking pressure listed on the Amazon page.

For instance, these Evil Energy check valves have the specs listed on the page: https://www.amazon.com/dp/B0FQHSSLN5

44 minutes ago, SteveJ said:

I learned from @Captain Obvious that one of the things to consider on a check valve is cracking pressure. Most likely the fuel pump will overcome the cracking pressure on the check valve, but I couldn't find the cracking pressure listed on the Amazon page.

For instance, these Evil Energy check valves have the specs listed on the page: https://www.amazon.com/dp/B0FQHSSLN5

That's perfect, thanks!

I talked to one of my friends about it this morning who is an engineer of some sort and he said what is probably happening is a tiny amount of air is getting in the line from somewhere which is letting the pressure out and allowing it to flow back to the tank (like a straw with a tiny tiny tiny leak. That definitely is happening because when I pressurize the line there is a VERY faint fuel smell from the back, and I have to keep tightening the lines. It's so weak that I finally said enough - give me the check valve.

I don't understand why the lines keep getting mushy enough to allow that to happen but as long as its so faint, it should be fine.

Edited September 24Sep 24 by chaseincats

44 minutes ago, chaseincats said:

a tiny amount of air is getting in the line from somewhere which is letting the pressure out and allowing it to flow back to the tank (like a straw with a tiny tiny tiny leak. That definitely is happening because when I pressurize the line there is a VERY faint fuel smell from the back, and I have to keep tightening the lines. It's so weak that I finally said enough - give me the check valve.

Not sure of the logic here but your pump should already have a check valve. If the cause of the pressure loss is a leak then adding another check valve won't solve it.

And SteveJ offered a good example of finding actual specs but that specific example doesn't seem right for high pressure EFI. The call out low pressure applications.

Forgot to say, flow rate is important also. EFI pumps push a lot of fuel. The valve might check but it also needs to flow.

Edited September 24Sep 24 by Zed Head

7 minutes ago, Zed Head said:

Not sure of the logic here but your pump should already have a check valve. If the cause of the pressure loss is a leak then adding another check valve won't solve it.

And SteveJ offered a good example of finding actual specs but that specific example doesn't seem right for high pressure EFI. The call out low pressure applications.

Forgot to say, flow rate is important also. EFI pumps push a lot of fuel. The valve might check but it also needs to flow.

It says on the amazon page it will hold a max of 87 psi - doesn't the pump push ~40? The air leak is back near the fuel pump, that's why a check valve in the engine bay was able to hold pressure I believe.

5 minutes ago, chaseincats said:

It says on the amazon page it will hold a max of 87 psi - doesn't the pump push ~40? The air leak is back near the fuel pump, that's why a check valve in the engine bay was able to hold pressure I believe.

Actually if you suspect an air leak, replacing the rubber lines would be a good start and could alleviate the need for a check valve in the engine bay. If the rubber lines are allowing air in, they can allow fuel out in the future.

2 minutes ago, SteveJ said:

Actually if you suspect an air leak, replacing the rubber lines would be a good start and could alleviate the need for a check valve in the engine bay. If the rubber lines are allowing air in, they can allow fuel out in the future.

The frustrating thing is they are new air lines.

Those are pressure numbers, not volume of fuel. If you restrict fuel flow the leak will get worse between the pump and the valve.

If you put the valve where you clamped the line it would probably work for startup. But you'll still have leaking fuel in the back somewhere. Seems like fixing the leak is the best solution.

Just now, Zed Head said:

Those are pressure numbers, not volume of fuel. If you restrict fuel flow the leak will get worse between the pump and the valve.

If you put the valve where you clamped the line it would probably work for startup. But you'll still have leaking fuel in the back somewhere. Seems like fixing the leak is the best solution.

I've put new lines back there and tightened the clamps a handful of times. I've really had enough of trying to find the air leak back there...

One sign that the valve is blocking flow is if the pump gets louder. It's a common problem when people use the Walbro 255 on the 240Z's after converting EFI. The carb return lines are too small for the pumps 255 liter per hour flow rate.

Anyway, always fun to experiment. I tried to solve a pressure leakdown problem on my car when I was trying to make an adjustable FPR work. They leak down too. Had the same hard start problem.

What brand of fuel hose are you using?

1 hour ago, chaseincats said:

I don't understand why the lines keep getting mushy enough to allow that to happen

25 minutes ago, Zed Head said:

One sign that the valve is blocking flow is if the pump gets louder. It's a common problem when people use the Walbro 255 on the 240Z's after converting EFI. The carb return lines are too small for the pumps 255 liter per hour flow rate.

Anyway, always fun to experiment. I tried to solve a pressure leakdown problem on my car when I was trying to make an adjustable FPR work. They leak down too. Had the same hard start problem.

What brand of fuel hose are you using?

It's standard auto parts 'buy by the foot' stuff. It's standard hose, not EFI hose if that helps diagnose the habitual hose clamp tightening issue.

2 minutes ago, chaseincats said:

It's standard hose, not EFI hose if that helps diagnose the habitual hose clamp tightening issue.

Why would you not use EFI hose? If the leak is on the high pressure side, that might be the reason.

Right after I got my car and got it running again, but before I had given it a good examination, I was out for a short test/tune drive and a UPS driver pulled up beside me and flagged me down right after I had left my neighborhood. He said there was liquid pouring out from the under the back of my car. I pulled over to check it out and found that the hose from the fuel pump had split. It was not EFI hose. A PO had used the wrong hose and it had fatigued and come apart. That UPS guy probably saved my car. And this was after I had made a few high speed runs down the freeway. I got really lucky. There was a guy behind me who cared, I was on a two lane road where he could pull up beside me, and it had split at just the right time.