fuel pressure on 88 pathfinder

[bobco]

I've been having issues with my 88 pathfinder with the v6 engine and TBI. trying understand the fuel system. connected up a fuel pressure gauge up to the fuel line feeding the TB( after the fuel filter), when I turn on the ignition key my fuel pressure builds to 35psi hold for 5 seconds and then falls off, for that 5 seconds I hear the fuel pump running and when it stops the fuel pressure bleeds off quickly. this cannot be right? I would think the pressure needs to build and hold at that 35-37psi. I'm thinking fuel pressure regulator and then fuel pump for replacement?? I'm not a mechanic but don't have a bunch of money to dump into this beast, so I'm trying to work through this problem. thanks for any help Bob.

[Terrano1992]

I've been having issues with my 88 pathfinder with the v6 engine and TBI. trying understand the fuel system. connected up a fuel pressure gauge up to the fuel line feeding the TB( after the fuel filter), when I turn on the ignition key my fuel pressure builds to 35psi hold for 5 seconds and then falls off, for that 5 seconds I hear the fuel pump running and when it stops the fuel pressure bleeds off quickly. this cannot be right? I would think the pressure needs to build and hold at that 35-37psi. I'm thinking fuel pressure regulator and then fuel pump for replacement?? I'm not a mechanic but don't have a bunch of money to dump into this beast, so I'm trying to work through this problem. thanks for any help Bob.

If pressure rises to 37psi (it is nominal for Nissan TBI) but quickly falls after a pump stops, there are 3 plausible reasons. One-way valve (buried inside the pump) leak, injector leak or pressure regulator valve leak.

Pinch fuel hose immediately after pump stops, to completely block fuel stream through this hose. If pressure stays high when you pinch the hose between fuel filter and TBI - probably you have a one-way valve leak. Stays when hose after regulator is pinched - regulator leak. Both hoses are pinched simultaneously, but pressure quickly falls - injector leak. Call a helper to switch ignition on/off/on again on your command, while you pinch hoses.

However, if you have stable 37psi until fuel pump running, I don't think pump valve leak or regulator leak can cause any noticeable troubles with running engine. At the same time, injector leak can (air/fuel mixture ratio will be constantly rich).