Stumble when engine is warm

[dkaeppel2000]

seems like maybe a vacuum issue or maybe a gas issue.....does anyone else hear the fuel pump humming while cruising or ideling? If it is a vacuum issue maybe you know a good place to start .....cant seem to find any air leaking ?any thoughts?

[300ZXttZMAN]

There could be any number of things causing the issue. Basically the best way to go about it is to first pressure test the system then work from there.

What have you done?

(Moving to Z32 tech)

[t.mcginley.jr]

You should really only hear the fuel pump prime when you first turn the key to "ON". Other than that you shouldn't hear it at all unless you have a gutted interior or something crazy like that. Even if the pump was running on high due to WOT, you probably wouldn't hear it over the road and exhaust noise.

So if you hear yours priming while idleing or anything, you probably have a fuel leak. This just happened to me a few weeks ago, every once in a while I would hear it, and would smell gas in the cabin. Turns out most of my fuel clamps were loose, and the one at the fuel dampener was so loose that it was leaking onto the valve cover (therefore losing pressure and causing the pump to try and increase pressure). Z32 fuel clamps are notorious for becoming loose when it gets cold out, you should check all of yours before proceeding.

Also, it wouldn't hurt to check for error codes:

http://www.nicoclub.com/archives/nissan ... ostic.html

[dkaeppel2000]

thanks ill try that....here is a little more detailed version i have some time....so bought this z32 last year in piece put it all back together ....it has an aftermarket fuel pump and looks way small than the stock one that mounts to the sending unit....it whines or hums or whatnot all the time....when she is cold turbos open all the way to 9 lbs. when she warms up can only get about 1 to 2 positive pounds....seems to run better the more the tank if full of gas......it really sucks taking such a fast f*** car and have to drive it like a yugo....lol thanks for the advice ill try the fuel clamps any more advice would be great ill let you know how the trip tomorrow is once i tighten these clamps

[t.mcginley.jr]

it has an aftermarket fuel pump and looks way small than the stock one that mounts to the sending unit....it whines or hums or whatnot all the time

This is a big hint, you probably have a Walbro aftermarket fuel pump. They only have 1 speed - High, so yes you will hear it whine. If it's a real Walbro I wouldn't worry about it they are good pumps, if its a knockoff then it could be a problem. However, it also depends how they installed it, since its smaller you usually have to mount it a little different, its possible it isn't sitting deep enough in the tank?