200km for full tank of gas! help!

[krown]

Hey everyone, Im new to the boards and would just like to say that this is an amazing place...its sooo useful and has helped my out with past problems.

Now to the issue, I got a r32 gtr (bone stock) and Im getting poor mileage as was expected when buying the car, but the is alot worse than most stories iv read so far. Right now If im lucky ill get around 200km to a full tank and I'm driving like a granny light on the pedal and shift a lil under 3k. I know the car is running insanely rich ( you can smell it ) but why? I checked my ecu and everythings good and changed my spark plugs. some ppl were saying that the problem was my fuel injectors or my O2 sensors, others were saying i have to get my ecu mapped, ( i forgot to chek but i think its been chipped)

Any advice would be really helpful as this is just breaking the bank for me, you know you got problems when it costs more money to get to work, then what you make there.

thnx in advance

[EtienneGignac]

My first guess would be vacuum leak. Second guess the O2 sensors and 3rd guess the ECU map.

O2 sensors are easy to check. Vacuum leak not so much...

[mcfly]

how many liters/100 km are you getting.

[krown]

its terrible , around like 9-10mpg

and thnx etiene gona go chek my 02 sensors soon.

[GTR-Dad]

There are many causes of way rich mixtures. Check/change MAFS, check fuel pressure and fpr, check/change injectors (for size and leaks) for known good ones. If it's rich off boost it's not caused by a boost leak as a leak would add air and run lean.
My bet is leaky injectors.
GL
Dan

[rak123]

it never hurts to take a look at your gas tank also and see if it has any runs of gas on it. that would rule out one other thing it could be pretty easily.

[Skym]

Faulty O2 sensors can cause bad fuel economy. Disconnecting and driving without them can eliminate 02 sensors as a cause of bad fuel economy. My cars engine ran rich (flames from exhaust) when o2 sensor was faulty.

Another cause could be a larger fuelpump with stock injectors, which makes engine run rich. Checking fuelpressure, should give you an idea if the fuelpump is stock or not.

[EtienneGignac]

That's dabatable and really depends if you're spending more time on boost or vacuum.

Extra air makes it lean and causes the ECU to add more fuel. It really depends how the ECU handles the discrepancy between the MAFs and the O2 sensors.

There are many causes of way rich mixtures. Check/change MAFS, check fuel pressure and fpr, check/change injectors (for size and leaks) for known good ones. If it's rich off boost it's not caused by a boost leak as a leak would add air and run lean.
My bet is leaky injectors.
GL
Dan

[Coolstop]

I had bad gas milage when a coupler was loose on my intercooler... check your intercooler piping and see if you have any vacume leaks.

[GTR-Dad]

That's dabatable and really depends if you're spending more time on boost or vacuum.

Extra air makes it lean and causes the ECU to add more fuel. It really depends how the ECU handles the discrepancy between the MAFs and the O2 sensors.

If you've got an intake manifold leak... when you're on boost, air comes out the hole. When you're on vacuum air comes in. All the time, every time. Thus the reference to 'if' you're running rich off boost, it's not because of a leak...

As you point out, unmetered air makes the engine run lean, O2 sensors will tell the ECU about it, and if closed loop fuel trim is enabled and has the authority to add enough fuel it'll bring it back to stoich, but not rich - unless O2 sensors are goofed. Typically a closed loop fuel trim system can only add or remove a limited amount of fuel so its highly unlikely to see extreme (200 km/60-70 litres = 30-35 l/100km) rich conditions resulting from bad O2 sensors.

Cheers,
Dan

[Skym]

Please don't quote me on this. It helps to understand how the stock ECU o2 sensor feedback setup works.

From what I unerstand, when engine goes too lean, o2 sensor has a high voltage that it sends to ECU and if it hits the run rich voltage limit, ECU runs engine richer.

When engine goes too rich, o2 sensor has a low voltage that it sends to ECU and if it hits the run lean voltage limit, ECU runs engine leaner.

From what I have seen, when o2 sensor fails (gets build up of soot on sensor due to alot of non motorway trips, etc), voltage from o2 sensor slowly fluctuates. My car (R32 GTS-T) got to the point, where the idle rpm on engine would slowly fluctuate up and down (which I forgot to mention) and popped flames from exhaust. Nissan mechanic said when they tested, o2 sensor was making engine switch from lean to rich very slowly.

When there's a airleak, I've noticed the o2 sensor voltage fluctuates more at idle and engine misses, stumbles, as I presume because of unstable vacuum and idle rpm, it hits the lean, rich voltage triggers quicker.

When you disconnect o2 sensor or turn o2 feedback off, the missing, stumbling stops at idle and get a smooth idle.

I think with stock GTR ECU that has 2 x o2 sensors, like with 2x MAF"s, Stock GTR ECU looks at the middle ground between the 2x voltages from 2x o2 sensors. If one o2 sensor is faulty, the other o2 sensor is not, the lean then rich or just staying rich problems could be worse.

[krown]

thnx, guys for all your help gonna check out everything you guys said this weekend when i get some time off work. I have a feeling its a faulty O2 sensor.

ty

[1BADGTR]

I had the same problem last fall. sounds like a boost leak. Mine was a blown gasket on the back turbo to charge piping flange. I was getting about 250kms to a tank, the girlfriend complained everytime I drove it because I would smell like gas, and it wouldn't boost over 8psi. I replaced the gasket last winter and now it boosts to 14psi and I'm getting close to 500kms to a tank on the highway if I try to get good mileage.