Terrible Gas Mileage
 

My G20 has been doing terribly and I am wondering if anybody here has one that maybe has some experience with it. Should I replace my O2 sensor?

Bad gas mileage usually is related to:

1) Fuel injection problem - too much fuel being delivered or leaking injector
2) Vacuum leak
3) Sensor error - throttle position, intake air, manifold air pressure, etc.

Good luck trying to find which of the three it is. Sometimes it's a combination of them. Since your G20 is a 2002, it has OBDII. With the lousy mpg you've been getting, you should have had the CEL come on. The diagnostics of OBDII are pretty good at narrowing down the area where the problem is. If you have a CEL, go to Autozone. They will run their code scanner on it for you for free.

Too bad about your mpg issue. A car as new as yours should not be exhibiting this.

I have a Gas 1981 G20 = 18mpg avg

Gas 1993 G10 = 10mpg no matter what

Diesel 1995 G30 20 mpg no matter what

Diesel 1997 Ford e-350 26 mpg no matter what


...So trade it in for a diesel. :)

He's talking about an Infiniti G20, not a chevy van G20. though european and japanese markets did have an optional 2l diesel in low and mid trim levels.

Ah, my favorite FWD and second favorite car in general. Have you checked into www.g20.net yet? there's a wealth of information there. IIRC the things to check on the SR20DE are cleaning the IACV, cleaning the throttle body, check/replace the O2 sensor, and check if the EGR is stuck open. After those, do the usual things like broken vacuum hoses, general tune up (filters, plugs, wires, cap, roter), check that the cat converter isn't clogged. you should be getting mid-20s in town and over 30 mpg highway doing 80+ mph

Is that car an automatic? If the miles are around 100k the o2 sensor would help maybe 1-3mpg. Do NOT use a bosch sensor. Use an NTK or oem sensor. What hurts the G20 is weight. I'm familiar with the obd-1 SR20 but not the late model like yours. There is an extensive idle and part throttle stumble "fix list" on SR20forum.com. The best mileage mod for our old SER was a JDM intake swap. It did away with the problematic IAC and EGR systems.

You should still be able to hit 30-34 mpg highway and mid 20s around town.

I suggest checking the free stuff first. Jack each wheel up and check for dragging brakes or bearing issue. Then have the alignment checked(usually a check is free at national tire and battery).

Check the MAF wire filament if its dirty clean it with denatured alcohol and a swab.(research the cleaning process I'm not certain. Be gentle)

Read the spark plugs.

Run some seafoam through the gas or chevron techron. I prefer the seafoam. Then seafoam the intake manifold or run some type of cleaner through to get the gunk out the PCV system causes(my SR powered cars were prone to this).

Then take it to a nissan dealer and tell them you want the codes pulled. Complain that its getting terrible mileage. It should cost around $70 to hook it to the consult system.

I forgot to mention. The HAI is a waste of time IMO. My brother tested the HAI extensively in a 98 altima. The ECU adjusted over time to negate its effects. However if you wanted to reset the computer every 15 minutes it might help. Best mileage was running an HAI around 120-130f and moving the IAT sensor to ambient air. He called me after doing this and declared there was a major powerloss. To which I responded "perfect".

DO NOT pay to get codes pulled. Codes can be pulled for free from most parts stores. alignment, brake, and bearing issues could also be causing the problem like mentioned above and are often free to get checked.

SR20 O2 sensors are Bosche from the factory. I've got 2 engines in my garage both have the OEM plugs with both the nissan hamburger and bosche logos.

MAF can be easily cleaned with spray stuff...make sure you use MAF cleaner, not any other kind or they will leave residues. CRC MAF cleaner and one of the electrical parts cleaners will not leave residues

Yes its true any parts store can pull the "stored" codes. However the nissan consult system can identify a sensor that is dying or slightly out of range. They also have the ability to log and view the engine parameters while its running. A good tech will be able to discern a partial problem.

As for bosch sensors, I'm not a fan. I was advised to get the NTK's.

An aerosol based maf cleaner is a good idea. Much better than using a swab.

Winter mileage Ok I know it is cold out and all but I just got 12mpg to drive 1.5 miles. This tank average is going to be really low.