Very Low Gas Mileage - Practically New

[Duster_360]

I bought an '07 Maxima 3.5 SL in Apr, the V6 engine with the CVT, it has 4200mi. I bought it to replace my '02 Maz DS PU which had a std trans and was only getting 15-18 in city stop-n-go traffic. The car can use regular - the other cars I considered were prem only, this prem recommended, but can run regular (CR is 10.3).

I ran prem for the 1st 1000mi and making a trip to Atlanta, saw mileage from 21.7 to 25.5mpg running reg. The car seemed not to care one way or the other. My 1st tank back to Houston after the trip in mixed hiway/in city netted 21.7.

Then something changed - mileage has done nothing but go downhill - 18.4, 16.5, 15.3, back to prem! - 15.8, 15.6, 13.9, 15.2, and 13.1 for the last fill. Window sticker said 21 in city, 28 Highway for mileage estimate. I've not had it back on the hiway, prob need to do that though.

I spent a sad day Fri at the dealership and was not really surprised when the only thing they did was run a diagnostic and try and tell me everything was alright - all parameters were within specs. The service mgr told me everything was alright and they expected mileage to slip due to ethanol content - 10-15% sold here in Houston. I went around to the rear of my car and stuck my finger in the exhaust - it came out black and sooty. The car has to be running very rich to leave any kind of residue in the tailpipe at all with unleaded gas. When my truck was traded at 48k, you couldn't wipe anything out of the tailpipe - it was completely clean.

So these guys are telling me I'm stuck with a car that gets 40% less gas mileage than it was sold/claimed to get and since there are no codes reported by the ecu, there's nothing they can or will do. I guess its too much to expect them to pull a spark plug and see if its rich like I think and then start back tracking to see what's causing this "self aware" auto to get it totally wrong?

Anyone by chance bump into something similar? If I took it to a chassis dyno used for state inspections here, would it fail sniffer test at speed running so rich?? Maybe that would force them to realize there is a prob?? Any ideas??

I'm an engineer and have raced cars and motorcycles, worked as a mechanic an keep pretty meticulous records. It really bothers me that such an obvious change has taken place and it seems to be no big deal to the dealer. Weather permitting, I'm planning a 150-200 mile trip tomorrow west on I-10 and will be filling up with some real (not the stuff they sell in Houston) gasoline - well as real as it gets these days. If mileage jumps, then I have to admit service mgr may be more right than wrong. If the mileage does not get close to the rated hiway, then they need to step up and admit something's wrong and get busy with Nissan USA and figure out why I have a problem. I also have a hard time believing mine is the only '07 Maxima in the US that's ever had this prob.

Thanks for any suggestions!

[MinisterofDOOM]

Well there's no reason a car with nothing wrong should be getting fuel mileage that poor. Are there any other Nissan dealers or trusted techs in the area who could offer a second opinion?

You might also consider contacting NissanUSA yourself. Always nice to let them know when you have a bad experience with a dealer.

[Duster_360]

Thanks for your reply!

Yes, there is one other Nissan dealership in Houston. The other Maximas at work were bought there. Its a good distance away for me, but if thats what I need to do, I'll be headed that way.

I was waiting until after tomorrows test trip - I'm driving far enough away from Houston to get away from the special crap fuel thats sold in Houston and will also try a different brand of gas. I'll be paying special attention to mileage in both directions. The dealership drove mine on the highway and proudly announced they had gotten 18.5 - car is rated for 28 and I've personally seen a tank average 25.5 when car had ~ 2200miles on it. I pointed that out and it did not seem to have much impact.

If I am still seeing low mileage, I'll be ready to be more aggressive about getting someones attention. I'm real unhappy right now, needless to say.

[PBfrEAk]

This may work and this may not but its free so it can't hurt.

Take your battery off overnight. In case you did some bad gas your ECU might have tried to compensate for the bad gas and screwed something up. Leaving your battery off overnight will reset anything changed.

It worked on a 95 Neon...maybe you too??

lol good luck though. and whatever you do I would go to that dealer and contact NissanUSA both. Thats a shame your dealer wasn't more helpful.