Need help with fuel pump diagnosis

Feb 18, 2011
Hudson, NH
Finally resolved the hard to start when warm/heat soak problem my 06 Nissan 2.5 S has had off and on since acquisition over a year ago. Turns out the replacement fuel pump assy failed the same way as the original six months later. So I thought it was something else. Just before giving up on this car I installed a third fuel pump assy and it's fixed!!! The starts are normal when the car is warm.

Why did both fuel pumps have the same problem? Best way to describe it is losing prime during a heat soak. Have to turn the key a couple times to get it to start. Looking at the scanner the fuel trim goes positive as if the fuel pumps are getting weak. But it's not the fuel pump. I replaced the fuel pump on the second unit. It's not the fuel injectors leaking down. I replaced them. It's definitely fuel pump related because this third pump resolved the problem.

Anyways here's some pictures that show what I think might be a problem. Inside the housing there are two plastic cases that detach so you can install the fuel pump. It's not super tight. It moves a little bit. It's definitely loose between the (referred to as both damper and regulator) and that black washer. It's barely touching the washer. Behind that washer is a dead end.

Could I be losing fuel pressure from in between the damper/regulator and the black washer? Which is probably the same problem the newer fuel pump had 6 months later. I'm wondering if it's a design issue and something needs to be modified to keep it tight. Or if there's a better washer. Or maybe it doesn't matter. Can anybody help me figure this out. Thank you.


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Any chance the fuel is vaporizing and blowing the seal? If so maybe some insulation around the fuel line/rails? Or some mod to keep the fan running till temps drop lower? This seems more like an issue specific to that engine and best asked in a Nissan forum where others have had to deal with it already.
there should be a check valve in there too. Maybe Nissan calls that metal thing the damper/regulator/check valve??
It is probably the black grommet you mention, losing seal & forcing the pump to work double time when it leaked down .
Usually the 'damper' is a chamber far larger than that plastic housing, but that may be a German/Bosch F.I. habit.
I posted in some Nissan forums. There's nobody there anymore. And the folks on Facebook only care about LED headlights and wheels. The most knowledgeable people are here.

Anyways after researching for a bit this is a returnless fuel system. That means the part in question is not a fuel regulator. Fuel regulation is done by the PCM and the fuel pump. That part is a damper. Which does something different. Does a damper hold fuel pressure or just pass it through? Because if it doesn't hold pressure the entire system is dependent on those gaskets at the end of the line.
A dampner just dampens the high pressure spikes. Mine is on the end of the Fuel rail. Looks like a regulator.