Unbootable

This is not a maxima, But i'm here since there are many VQ experts here. And because on some other forums, members will not help and just flame.

This a g35, VQ35DE/5AT, With about 83,000 miles.

The car suffers from a low end power loss after the engine is up to temp. It runs good cold and takes off as a rocket with pedal to the floor.

Description,
Say that i'm driving on the highway doing about 70 mph in 5th gear and give it some gas to change lanes, The car will not go anywhere, the rpm will just stay between 1500 and 2500, the more you press the gas the more you hear a "humming" noise, till you give it a GOOD amount of gas then it will take off.

What i tried,
- Brand new valve covers and gasket ( had oil in coil packs ).
- Brand new OEM spark plugs.
- Brand new coil packs.
- Brand new engine coolant temp sensor.
- Brand new cam shaft position sensors.
- Brand new re-manufactured throttle body.
- swapped MAF sensors.
- Brand new fuel pump ( with the assembly and filter )
- swapped the injectors with very low miles set.
- Disconnected the knock sensor and plugged in a 560K ohm resistor.
- Changed some vacuum hoses.
- Checked vacuum at idle and it seemed steady at about 22 inhg .

After all these parts and the symptoms remain the same, Also no CEL or any ghost codes.

Any ideas will be greatly appreciated.

Chris Gregg

iTrader: (59)

Did you reconnect the knock sensor?

Any mods or changes before this power loss (ie: intake)?

Have you checked the throttle body to ensure it is moving properly given peddle input (remove intake piping with car off - key in on position)?

Still running stock exhaust/cats?

NmexMAX

iTrader: (22)

That's how all VQ's are.

Your description leaves me to think it's more of a TCM/ECU issue rather than a true mechanical disfunction/actual power loss.

Mine does the same thing every now and then. Stupid DBW. So does my Pathfinder.

Unbootable

Answered in bold .


I can understand that it's acceptable to lose some power in hot weather or high engine temps, But i'm suffering from a SEVERE power loss, lol i cannot even pass a car with a 1.6 liter engine on the highway .

Child_uv_KoRn

iTrader: (7)

The KS is different on the newer VQs. I don't know if the resistor trick applies or if it's even close to the correct resistance, but I would think that it should throw a ghost code.

Chris Gregg

iTrader: (59)

You are making mature use of forum features!

So still have stock exhaust manifolds and I assume the G has precats? Maybe need to be gutted.

Unbootable

Never threw a code, I keep checking for any codes, Maybe i can try with the resistor removed ( open circuit ) .

Any idea what controls the ignition timing other than the knock sensor ?, The reason i ask is because i can see the timing drops BADLY when the car stumbles while giving it some gas !!!

There's no catalytics on the headers ( pre cats ), But i have test pipes with no O2 sensors or even non foulers connected, And the car never threw any codes for the down stream sensors.

I bought the car used over three years ago, And cannot tell for sure if it has a tune and the O2 sensor CEL was disabled by an uprev tune.

Maybe i need to check the fuel trims with the cipher cable, It should give an idea whether it's running rich or lean, Since i have no codes to start with !!!

defiance

iTrader: (1)

I would check that Knock Sensor resistor you installed.Could be causing trouble now and making you lose power. What year is your G35 again ?

Unbootable

It's a 05,

I went back and checked the resistor, It's a 560K ohm, which is the right value of the no-knock area;

NmexMAX

iTrader: (22)

Do some timing runs. OBD/Consult II type of date would tell a lot.

defiance

iTrader: (1)

Also check your Cam and Crank Sensors

Unbootable

I did install brand new OEM camshaft sensors ( both banks ), And bought an OEM crankshaft position sensor which i will install very soon, when changing the engine oil.

Unbootable

Here's the cipher log, I highlighted some cells to indicate the problem, The problem happens in the green area, Where i will start to give the car some gas gradually and it will fall on its face, till it reaches about 3K rpm.

Hope someone finds something wrong !!!

SterlingMistMax

The car suffers from a low end power loss after the engine is up to temp. It runs good cold and takes off as a rocket with pedal to the floor.<----This sounds like what my G was doing when i had a bad knock sensor/harness and for the longest time there was no code but it did show a ghost code eventually . but you said you bypassed this where did you bypass it and could it be that its corroded and not making contact anymore ? have you cleaned your throttle body at all ? i was getting a weird idle for a while and a hesitation at low rpm and after cleaning throttle body it was fixed . have you tryed pedal relearn at all ?

Unbootable

Thanks for your input,

I used a resistor to bypass the sensor and checked the voltage with a DMM, and it was within spec ( about 2.5V as per the service manual ) .

I cleaned the throttle body, Then replaced it with a new re-manufactured one, But symptoms remained.

Tried the pedal reset many times, But no luck.

NmexMAX

iTrader: (22)

If you could get a WOT run from as low RPM as possible to as high as possible without killing any one/animal/yourself, etc. That would be cool.

defiance

iTrader: (1)

It can be anything honestly.

It could be the AWD system assuming yours is an X
It could be that Reman Throttle body you put on
It could be the drive by wire system
Might even be a slowly dying O2 sensor

But since the Knock sesnsor/resistor seems to check out, I would now look into that throttlebody you had replaced. Test it

How long has this problem been with the car ? Has it always been like this since you had it ?

Unbootable

Lol, I can do that, Will post the log soon.

- Car is RWD .

Throttle body !!!

The very same symptoms remained after replacing the TB, No change at all , Which leads me to believe that it's not the culprit .

Drive by wire system !!!

Good call, I noticed something odd, I do believe that the car drives way better when i use the cruise control , But when i logged with cipher, Both APPS and TPS were pretty much consistent . Here's a pic from Cipher;



- Might even be a slowly dying O2 sensor

I will be replacing them very soon. I'm running without the rear O2 sensors, even with no anti foulers.

I disconnected the primary O2s, The car is running in open loop now all the time but the symptoms remained ...

The problem has been there for many months now, And the odd thing is that there's no codes at all !!!

The car used to drive fine before, I don't always drive it hard, I drive daily to work for about 15 minutes, city driving with traffic, so there is no way to tell exactly or to tie it to any mods i have .

mikehawk

Definitely re-connect your primary o2's, and after they're connected you might want to use the cipher to clear the learned fuel trims and go for another highway cruise.

Unbootable

I took the primary sensors off to see if the car will react any different, But there was no change.

The secondary O2 sensors have been disconnected for about 5 years ...

I tried clearing the fuel trims before with no luck .

Aviation005

I think you may have a bad ground. Check your negative battery terminal and wire, check the factory ground point. Clean off any corrosion, make sure your battery is not dying.

You could have lack of power to the coils due to bad ground. My car use to have this similar problem, then i did some insane ground mods and it pulls again

oh!! check that your PCV valve has a rubber 0-ring on it. Nissan stopped selling them for some time and this creates a vacuum leak and burns oil!

TunerMaxima3000

iTrader: (4)

I see this thread getting extremely complicated. Can I verify one thing first, the actual complaint.

You say you are doing 1500-2000 RPM on the highway, in 5th gear, and the car won't pull. That is normal.

Now, if you are saying that when you step on the throttle, the car doesn't downshift into 3rd or 4th like it SHOULD to give you gearing to put power down, that is a problem with the Transmission or it's sensors.

Unbootable

Battery is about 11 months old. And i checked, cleaned & tightened all ground points i could find. But i noticed that the charging voltage drops after the car is up to temp.

It starts charging at about 14.2V then drops to about 13.5V, Is that normal ?!!!

I changed both my valve covers about a month ago, It came with a new PCV valve, And i replaced the PCV hose to a new one.

That is perfectly true, Car also responds well at WOT, But i do believe that even when you are cruising in 5th gear & low RPM, The car should respond when you give it some gas, But in my case, Nothing happens, I start to push the pedal & i can see the APPS voltage increasing while the rpm stays the same, This continues to happen till i give it MORE gas, then it accelerates fine.

This is much noticeable after the car is at normal running temps.

TunerMaxima3000

iTrader: (4)

it really sounds more like a transmission issue (if there is an issue) more than anything else

Shift_A32B

iTrader: (14)

^ was going to say the same thing. Sounds like a transmission problem...like a slipping transmission.

Unbootable

Any procedures to test and tell for sure if it's the auto box ?!!!

TunerMaxima3000

iTrader: (4)

You can do a diagnostic check of the transmission for codes, but if there are no codes you will have to take it in to have the pressures checked.
There are 2 cheap routes I can think of to try and combat this issue, but they might both do nothing.

1. Drop the transmission pan and change the fluid out and see if it makes a difference.
2. Disconnect the battery for a day to reset the computers in the transmission and engine

I'm unsure which year your car is, but there may be some information here that will help you in your diagnosis

http://www.nicoclub.com/FSM/G35/Coupe/2004/at.pdf