Hmm ill try to reset the fuel map. Bu how do i that. Just pull the battery?

 

Correct me if I'm wrong. But I think you can just disconnect the negative terminal. Apply the brake pedal for like 5 seconds to completely drain out the car of power.
Then reconnect!

The other method is to do a crazy pedal dance:

1. Confirm that accelerator pedal is fully released, turn ignition switch “ON” and wait 3 seconds.
2. Repeat the following steps (2a and 2b) procedures quickly five times within 5 seconds.
2a. Fully depress the accelerator pedal (HARD).
2b. Fully release the accelerator pedal.
3. Wait 7 seconds, fully depress the accelerator pedal and keep it for approx. 10 seconds until the CEL starts blinking.
4. Fully release the accelerator pedal (while the CEL is still blinking)
5. Wait about 10 second.
6. Fully depress the accelerator pedal and keep it for more than 10 seconds.
7. Fully release the accelerator pedal (The CEL light will continue to blink).
8. Turn ignition switch to “OFF” position and now you can start the car. The CEL light should be gone.
If the CEL light continues to remain ON, repeat the above steps. Timing is EXTREMELY critical to resetting the ECU.

 

Ok i just refill after 235 miles and used 15 gals. So that 15.6mpgs. But its been super cold so i understand that. However when i drove home 24 miles (about 90% hwy) i only fot 17.9mpg. Now thats not good.

 

16mpg hwy? That would be abysmal. I hope that's city which would be really close to what I am getting in my 2006 5at sedan.

Where are you buying gas? Are you sure they sell enough premium monthly to keep it from sucking up minister or being stale ?

 

Im apparently getting 17.9 mpg 90% hwy. Idk whats going on. I know this car is not the best on gas, but i would expect to get 21mpg mixed based on the way i drive. I put premium gas in, but im not sure about the premium sales there. I do however know that gas stations that usually dont sell alot premium gas is way more expensive than regular.

 

Ouch. I'd need to be driving 4k rpm on the hwy to get that mileage. I am afraid were down to things like compression tests, maf sensor being bad but not throwing codes, bad o2 sendig units and the like.

might be time to visit the actual dealershit.. erm stealership ... no that's not right ... dealership for a extended diagnosis.

you need to find out what your flow rates are and what the sensors are reading while driving.

 

Lol good call on the dealership...I mean stealership. When i do cold start the car it was stuttering or completely dying, but after doing the ECU reset like you suggested, It starts up alot better. I check my mpg after resetting the ECU and i got around 17mpg doing 60city/40hwy driving and that included 2 5 min cold start ups.

What flow readinf should i be getting. I have a bluetooth odb scanner that shows and logs my MAF, MAP, fuel trims, and o2 voltage. I doesnt show AFR however.

 

That I will need to defer to greater experts than I for the readings... I do not have any example data .. sorry. but I do know some tuners hang out here still and also in the MY350z forums...

 

MPG UPDATE

I took Max's advice on the ecu reset and checked my mpgs after a fillup. I went 300 miles on 16 gallons. So i got a MPG avg of 18.7mpg. This was with 40 hwy/60 city. Im more satisfied with these number and its more to build from.

 

I have a *bizzare* update for this thread.

Took my rig into the dealer to change out he idle tensioner's (squeaked on start up) and a oil change.

the put in the requisite amount of oil, but a flat 30 weight which struck me as odd for winter oil.

The effect on my millage was astounding. took a road trip to coos-bay (oregon) which is a long haul of 60-65mph traffic and avg'ed 24mpg which blew my mind, also noted a dramatic loss of in city millage as well.

with a huge fear ... I did a compression test on #1 and #2 and came up aces-ish with 168 \ 173 for 115k miles so I called that good enough given the horrible oem rings our second gen g35s are blessed with.

all I could think about was the aweful choice in oil wieght.

so, I popped the cork and drained out about 2.5 quarts and dropped in the same amount (5\20) of penzoils lpg based synthentic.

i will br god damned the milage went back up. not to the same point, but a (i5) portland trip yielded 28mpg..

so yeah... oil ... weird. way more impact that I expected. gotta be a 2nd-g-vq35 thing ...

will write back when I can do another Washington trip and really get longer term measure.

 

That's an all cars thing. If the crank is fighting to get thru cold dark honey its gonna take a lot more energy. I used to use 20/50 conventional, cuz in high heat, you just need that extra protection.

 

Hmm i didnt think about oil viscosity. The oil was just change when i bought my car, but its 300 miles away from a oil change and idk what kind of oil he was using so I am going to change it soon.

I just filled up my car and got 17mpg (255 miles off 15 gallons). This was with 60 city/40 hwy. Also had to do a 30 min idle and rev to bleed the cooling system. I still feel like it could do better. Oh i drove the car until it was right on E, and I only used 15 gallons

 

30 min idle will kill the hell out of gas mileage. These cars guzzle fuel when idling. Just crank the car, walk to behind it, and you can smell raw fuel pumping out the exhaust. Trust me, mpg drops like a rock when standing still/idling.

Have you cleaned the throttle body? MAF? Intake plenum? When I pulled the intake to add a MD Spacer, cleaned the **** out of it. Throttle body was all gummed up on the back side of the blade, so got that too. Not sure if it helped, but I can get 24 mpg with 90% highway driving and no idling. I crank the car and roll down hill out of my driveway and let it warm up driving through my neighborhood at 25 mph.

I also run Seafaom through it all the time, and do the Seafoam spray into the brake booster line before every oil change. Car never misses a beat/stutters. Gas mileage has gone down with winter gas, I've gotten 27 mpg before. Rain hurts mpg as well, and snow, something about the car pushing it's way through, takes more energy.

 

Good to know that! I thought it was something wrong with the car because it burns so much gas idling.

I want to clean the TB but i heard bad experiences about opening the butterfly and cleaning it.

 

Yeah were port injected... so Idling is not stratified. Idling is kinda costly.. but I am not thing 1 gallon of gas costly as the numbers would suggest.

i am still thinking poor winter gas, thicker oil, bad fuel map that sort of thing and or combination thereof.

i would steer clear of seafoam, but that's by opinion based on the number of horror threads in the Maxima forums (same vq35de)

also never ever use engine restore ..