Shift_Speed

when i'm crusing on the highway i go an average 75-85 miles per hour... and noticed that... from 80 - 90 mph ... i have this loud honinh or winding noise... its pretty loud... i have my speaker up to 22 volume but the sound still peirces through... n e ideas why? also i have 3,000 miles on my car now... and i noticed after driving my car for a lil bit... when i go to park it... i hear my engine or something make a lot of noise.... it goes away when i turn off the engine and turn it back on... but i don't think these things are normal... please help me thank you!

1ZFORME

I get the same in the Touring 5 sp auto. between 75-85. drives me INSANE! no idea what it is.

dr_gallup

A lot of people with the tire feathering/cupping problem are reporting an associated noise. Most poeple report this problem starting in the 3,000 to 4,000 mile range. Don't know it is the same noise you are hearing.

D'oh

I have a very slight whine above 80 in 6th gear only. When at 3000 RPM in 5th, or 80 in 5th, the noise doesn't happen. Mine is probably coming from the tranny since it only happens under light throttle and in that specific gear at 80+ MPH. It went away a little bit when I had my transmission fluid changed, but it is still present. Luckily it's not too loud.

I don't know what you are hearing, but maybe it could be something similar. Is it speed dependent, RPM dependent, gear dependent, or what? If you can troubleshoot it a little, you might be able to point a mechanic in the correct place to inspect.

Good luck!

-D'oh!

ares

iTrader: (2)

been discussed, it is the fuel pump, thats why you only get it under load, and at higher speeds. if you downshift, its either a higher pitch than you can hear, or is drowned out by the engine noise.

pushing that much fuel that fast your gonna get a whine, I wouldnt call it "really loud" tho. it was the same way in my last car.

Desmo

I don't think it's not the fuel pump. It's gear whine from the rear differential. At least if you are talking about the same whine that is present in my car. Otherwise why would the sound "bounce" on and off when you are right between accelerating and decelerating? Also, cruising at 80 in 6th doesn't really take that much gas pedal, so I wouldn't call it a high load situation. It's not transmission gear whine because both the autos and manuals do it, and in different gears as long as you are going around 80mph.

John

iTrader: (17)

I still think it has something to do with the tires at that speed or perhaps the aerodynamics of the front of the car.

You can hear the fuel pump while you're idling at a stoplight, it's almost like a little whisper, but pretty much unnoticable.

ares

iTrader: (2)

80mph has you around 3300rpms if memory serves, thats a fair amount of gas being pumped in...

Shift_Speed

i also get it in 6th gear 80-90 and only when i step on the gas lightly... but when i floor it ... the sound fades out... and it is loud if you can hear it piercing even when my volume is up to 22... this is really starting to bother me... thinking about taking it to a nissan tech.. but don't think they will help... you think a grounding kit will solve this???

John

iTrader: (17)

If it was the fuel pump, you'd hear it behind you, and you'd hear it in every gear at that rpm. I know what a fuel pump sounds like since I have a Walbro 255l/h in my previous car, and it's a different sound. This is a speed related issue.

Desmo

No, a grounding kit won't help. I would say with 99% confidence that it's the diff gears.

If it was tires, then the sound would be same if you were on or off the gas. The noise in my car is definitely influenced by the throttle position. Besides, cupped tires (which my car does have) is more of a lowspeed rumbling noise, like a 4x4 with mudder tires.

If it was the fuel pump, then you think it would get louder with more throttle opening, but that doesn't seem to be the case. It only makes the whining noise when you are cruising around 80mph or accelerating just a touch.

It's not the transmission because the noise is present on automatic cars supposedly. Mines a manual so I can't say with certainty, but others on the board have complained about it.

If it was engine noise, then it would happen in any gear, or even in neutral. It's obviously a speed related thing, so that rules out under the hood stuff.

As Sherlock Holmes used to say, once you have ruled out all other factors, the one left must be the culprit, no matter how unlikely. And in this case it's totally likely. It even sounds like gear whine.

Try changing the rear end lube, see if that helps. If the noise is truly way beyond reason (remember this is a sportscar, not a Lexus) then ask your dealership to reshim the rear end gears to adjust the gear mesh. It's a fairly involved process, but they should have the tools, and the service manual spells out exactly how to do it. If they won't help, then go to a specialized axle/drivetrain place and see how much they would charge you to do it.

teh215

iTrader: (8)

My understanding of fuel injection is that the pump will maintain a constant pressure to the injector fuel rail and the pressure regulator will return excess fuel to the tank. If the pump has to increase the fuel delivery by pumping faster, wouldn't that mean that the pump is not quite matched to the injector capacity since the regulator should only return less fuel to the tank rather than causing the pump to spool?

SKiDaZZLe

#1, on the Z33, there is no return for the fuel once it reaches the fuel rail. (Wierd, but true... non-return system)
#2, the fuel pump always pumps the same volume, and it is the fuel pressure regulator that elevates fuel pressure relative to manifold pressure.

m

teh215

iTrader: (8)

Thanks! I really need to get a FSM and study it.

dr_gallup

I'm not sure how the fuel pressure is regulated in this car since it normally is in engine compartment and works by spilling excess fuel to the return line. It has to be able to reference manifold pressure because it (normally) holds a constant differential pressure across the injector. That way the injector flow rate is independant of manifold pressure and the fuel delivery is proportional to the pulse width. Our system may use pressure sensors in the rail and manifold and an electronically controlled pump to maintain the pressure differential? Or does it maintain constant rail pressure and adjust the injector pulse width to compensate for the varying injector flow rate caused by the varying manifold pressure? Major electrical complication to eliminate the simple return line either way.

SKiDaZZLe

you are right... but there are no fuel pressure regulators (risers) as we normally think of on the fuel rail in the engine bay... in the Z33 they are called "Fuel Dampers" and there are 2. one before the fuel rails, and one on the end of the further one. neither of these dampers have vacuum lines connected.

the actual fuel pressure regulator is in the fuel pump assembly (per the service manual)... it goes in-line after the pump, but in my head, i cannot figure out how it can keep pressure up on the engine-bound side, and release excess fuel back into the tank (so the pump doesnt burn out), without being on the return side... and to do this without a manifold pressure feed!

anyone an expert on non-return fuel systems?

oh yeah... for trivia, the stock fuel pressure at idle is: 51psi

m

Shift_Speed

youg uys talking about fuel regulators and this that... hahahaha... i have no CLUE what you guys are saying... but thanks for debating this and trying to figure out the core of this problem... i take it no one has actually taken their cars to nissan to say WTF is this NOISE! ... i think those asses will be like " its supposed to make that sound... yea.. um... it has to do with the blah blah blah and its perfectly normal... "

this problem isn't bad all the time... just when i have a passenger and we drive for a while on the high way the NOISE gets to you REAL BAD..... i hope some car guru in here can figure it out...

Desmo

How Returnless Fuel Systems Work:

They are constant fuel manifold pressure. There is a pressure regulator back in the tank, right after the fuel pump. Excess fuel never makes it out of the tank. The fuel rail and injectors always see the same pressure, in this case 51 psi if Skidazzle's trivia is correct (which it should be because it came from the service manual).

The rest of the story is just electronic magic. The ECU knows what fuel pressure the injectors are at all the time, it knows how much fuel to squirt into the cylinders (based on throttle position, rpm's, manifold pressure, and temperature), so all that's left is figuring out how long to open the injector, or what pulse rate to use if you want to be technical. Computers are good at that sort of thing, and there is a feedback loop via the oxygen sensors in case the first guess was a bit off.

As far as releasing extra fuel without being on the return side, since the regulator is in the tank it can just spit the extra fuel right back into the tank.

As for the Fuel Dampers, I'm not exactly sure what they are, but I have a guess that they some sort of spring loaded diaphram that eliminates transient spikes in the fuel pressure, like when you get off the gas in a hurry. Because the regulator is back in the tank, there is a delay in it's reaction speed to quick changes in the fuel delivery requirements, so you need the dampers up near the injectors to keep the fuel pressure at the desired level. Because the entire fuel system is constant pressure, they don't need vacuum lines or any other means to compensate for manifold pressure. Just set the spring rate so that the diaphram is in the middle of its travel at 51psi, and it'll do the rest.

But none of this changes the fact the the noise is still the rear diff :)

Jer

dr_gallup

I had a look at Delphi's returnless system on their web site. I am assuming that the Z's system is similar but may have important differences. Delphi makes a special point about having an integrated sound isolation system. The fuel pressure is regulated electronically by modulating pump speed with a pressure sensor at the pump. This system has the benefit of reducing the average fuel pump current draw and the return line is eliminated along with the mechanical pressure regulator(s). There are several drawbacks to a returnless system. The fuel pressure has to be higher to prevent vapor lock during hot starts. Also, the pressure at the injectors will fluctate more because the sensor is so far away. The variable speed fuel pump drive electronics are much more complex. There is potential for more noise problems with a variable speed pump. The noise problem that started this thread may be an uncontrolled pump resonance at that particular load & speed.

Having a constant fuel rail pressure makes calculating the injector pulse width (not Pulse Rate - that is syncronized to engine RPM) much more difficult. You now need a manifold pressure sensor because the injector flow rate is a function of the square root of the difference between the fuel rail and manifold pressure. There is an additional complication, albeit small. The injector will take longer to open at higher differential pressure and this effect will vary slightly injector to injector. O2 sensors can not compensate for this type of cylinder to cylinder imbalance.

Overall, it looks like they have traded a nice simple & reliable mechanical pressure regulating system for a much more complex but cheaper electronic system.

Sonny Motts

I can almost relate to the problems you duys encountering, however i decided to go to a Nissan Tech and the said that it must be an aerodinamics. And by the way my car (Track) makes more of a whistle sound everytime i go past about 2,500 rpm and like after 4,000 it disappears in hte sound of the engine and the exhaust. Tech asked me if i wanted to leave the car for a day so they could se what is wrong with it, sorry to say that is the only car i have and i need it everyday.

If i will find something out, i will make sure to post it. Late