About 3-4000 miles ago I noticed that the VQ was getting louder around 2500rpm under load, like going uphill. It may have always done this, or not - that's why I'm asking here. Does your VQ30 get louder at 2500rpm?

 

Mine gets louder the higher the rpms go
I thought this was normal

 

Sorry, my bad.
So let's say at 2000 rpm engine is nice and quiet and you keep accelerating up a hill, rpm keep going up, but the engine is still quiet. But just around 2500rpm it suddenly gets louder with some more rumble to it. Keeping it a 2500 rpm up hill, the loudness /rumble stays constant, almost like a slight knock.

 

Do you have an automatic transmission?

it might downshift while under load.
That would result in the engine turning faster and make more noise.

Now about the knock noises. Are you filling with regular, plus, or premium?

 

Forgot to add, it's a 97 auto.
Downshifting is not the issue here.
Upon further observation, the rumble starts at 2400 rpm and is reduced by 2700 rpm.
I am running 87 octane right now, octane is on my list of possible causes.
But first I want to see if other Maximas are getting this rumble or not.

 

These cars don't run right on 87 Octane. It can run on 87 but 91 or higher is recommended for maximum performance. It should say that on the sticker inside the gas cap door.
It sounds like your car is knocking. Please use Mid Grade of higher.

1995-2001 FUEL RECOMMENDATION:
(Research octane number 96)
If unleaded premium gasoline is not available,
unleaded regular gasoline with an
octane rating of at least 87 AKI (Research
octane number 91) can be used.

For improved vehicle performance,
NISSAN recommends the use of unleaded
premium gasoline with an octane rating of
at least 91 AKI number (Research octane
number 96).

https://maxima.org/forums/5th-genera...ble-check.html

 

I filled up with 91 yesterday morning. 5 starts and 80 miles later, no change in sound. No codes found.
Still no replies reporting whether or not their Maxima gets louder at 2400 rpm under load.

 

It may be beneficial to do a vid showing what you are referring to and post it. Not sure the sound/issue is bad enough to get picked up by a recording device though.

 

Do your rpms increase at the same tume as the noise increases?

This kind of thing might happen as the tran's downshifts when it's under load. Such as going uphill.

 

The transmission shifting gears has nothing to do with it, no sudden jump in rpm.
The rumble is similar to the noise it makes when lugging the engine, at say 1300 rpm in OD with torque converter locked. It also happens at freeway speeds, not only uphill (so it starts around 70 mph).
@Zerodrag - typically the audio has to be off to better hear the noise, I'll try to think of a way to record it though.

 

I'm curious if the noise is related to possibly bad engine mounts.

 

 

If you're going uphill and the transmission is not downshifting, the engine is working harder at 2500 RPM so it may be louder...

If the car is running okay and there are no codes then I wouldn't worry about the sound too much....

 

I have read about some our members experiencing oil soaked engine mounts resuulting from a leak somewhere above it. Like from a valve cover..

A bad engine mount would allow the engine to rotate too much when it is under load. That it turn would cause stress on the flex pipe.

One way to test this would be to have the hood open while an assistant has one foot on the brake, while the other foot blips the gas pedal.

if you see the engine flop around and also hear the noise, you have found the problem.

So the repair would be

1. Fix the real cause of the problem. The leak.

2. Replace the engine mount.

3 Replace the flex pipe.

Failure to do 1 and 2 will cause 3 to re-occur.

 

I'm pretty sure it's a exhaust leak too...

 

Thanks for replying. I take it none of you experince this? (quiet at 2300 rpm, rumble at 2400rpm)
I tried to capture the sound with my phone while driving, but other noises drown it out.
It is not bad enough to bother me in regular driving, but two weeks ago I was driving to a trailhead (9000ft), had to climb a long steep slope and the noise was more pronounced and unnerving.

 

Notice that you are NOT hearing that others have the same issue. This would indicate that there is something wrong with your car.

I gave you instructions regarding how to test your engine mounts and how to listen for the noise while you look under the hood..

Please let us know what the results are.

 

Thanks, I'll do that and post back here.

 

While I didn't get a chance to do a video on the mounts, something else happened to the car.
My wife was driving the car this week and this morning she said it started shaking, smoking and the CEL came on. Over the phone, I walked her throught it and found a P0303 cyl3 misfire.
Will she ruin the CAT driving the car like this for 11 miles?

 

Cat will be fine.

Most likely coil or injector issue.

 

Thanks.
1. Since I'm not near the car right now, is there a way of disconnecting the #3 injector without removing the intake manifold collector?
2. Are Hitachi coils good?

 

Removing the connector will not prevent the injector leak.

 

I believe you are right.
I got to the car (wife had it today) and cyl #3 injector is the only one with no hope of access. Called AAA and while waiting for the tow, I swapped coils 1 and 3 and let it idle for a while. No change: rough running, white smoke and gas spewing out the exhaust. Didn't throw a new code for #1.
After the tow, I idled it some more, and no #1 code. I changed the #3 spark plug with one of the plugs I took out about 10000 miles ago, idled it some more, no change. Unplugged the coil harness connector for #3 - no change. I unplugged the coil harness connector for #1 - slight change. I checked voltage (actually a friend helping me did this) on the harness connector + worked, G worked, IB showed same as +; not sure what that IB does, but my multimeter didn't catch any pulsing on it. After all the idling, there was a strong smell of gas and a puddle of gas under the exhaust.

 

I also read a similar post on Bitog. You have
another name there, yet obviously it's you.

Same advice, replace the injector.
Glad that you are planning or replacing all 3 of the rear ones.
Remove fuel pump fuse.
Run car till it stalls.

Be sure to lube injector o rings with engine oil before installing.

 

I saw that too..he's been a member there longer than here lol
Nothing wrong with asking people who dont own Maximas

 

Notice also that those giving advice about Maxima on the Bitog forum have owned them in the past.

Nothing wrong with going to several sources to get accurate information regarding car repairs. In general, all forums should have similar diagnosis for the same issue.

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Thanks for the advice, I removed them only after reducing the fuel rail pressure.
Yes, I'm a bitog member, who isn't? . I also posted there because it has way more traffic than maxima.org.

 

I only bought this Maxima (my first) in 2014 and promptly created an account here

 

Everything about this problem and almost all others can be found by using the Search button.

Many years of accurate information and procedures are all searchable.

Best wishes regarding this project.

Might as well think of any remaining while I'm in there any way projects. Such as rear valve cover.
I now wish I had replaced mine.

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