Will replacing the computer chip in my car solve the problem? (05 Altima)?

Question

It's a 2005 Altima with 38,000 miles on it. Took it for it's scheduled tune-up 3 months ago at the Nissan dealership and about a month later i noticed the gas was going a lot quicker than usual. Now i get around 270 miles on one tank of gas (I used to get around 400). Its a 20 gallon gas tank. Also around the same time the gas gauge started fluctuating back and forth. Ex: When i fill up the tank it would go to the top line and now when i fill it up it goes way past the top line all the way to the "F". The first 10 miles i drive it drops about 2-3 lines. I now get around 170 miles when driving from a fuel tank of gas to the middle line. Then from the middle line to when the car says i need gas i only get 100 miles. How is this possible? The tires are fine and i just did an oil change and put in a new air filter. If the problems were the Oxygen sensor or engine filter- the engine light would come on.

I took it to a mechanic today and he recommended me to get an engine analysis. He also said the computer chip can be sending the wrong message saying it needs more fuel than it actually does.

Would the engine analysis help solve my problem? Should i buy a new computer chip? I think this is a question for the professionals.

Please help

Answer 1

You are correct, the PCM should illuminate the CEL, when it has detected a failure. While it is possible that the PCM is faulty, it is not likely. More likely that the engine temperature is not reaching full hot operating range, or an O2 sensor is lazy,

Have a qualified tech look at the PCM data, and verify that all sensors are working and "in range." They can determine if the PCM has added or taken fuel away from the base line. This is the PCM adaptive control, usually around +/-15%.

As for the fuel level issue, the sending unit for level may just be inaccurate, record mileage manually, to be sure that your fuel economy is suffering, and not just off due to never running it to the actual low level. ( you may be refueling at 1/4 tank instead of empty, or at the reserve level)

Answer 2

Gauge fluctuation is not uncommon - the damper mechanism gets worn and the gauge moves over farther and faster - minor issue.

Unless a specific computer fault code is indicated, it is not the "Chip".  

The loss of fuel economy may be engine control related but do not overlook the much more likely causes, you indicated the tires are properly inflated - good, also have all 4 wheels checked for dragging brakes, a sticking caliper piston on only one brake can easily cause that kind of fuel economy loss, also consider having a 4 wheel alignment performed - misalignment can have a serious negative effect on fuel economy - long before the obvious signs of tire wear show up.

Interrogate the dealership and find out if they installed factory original spark plugs - if they used anything else have factory original plugs installed - accept no substitutes!  This is a major issue on modern cars - the supposed cross referenced alternate plugs are NOT actually identical to the factory plugs!

Go ahead and have the DRB scan performed (after installing the correct spark plugs if necessary) and ask the technician to perform a "Reset All" on the system which will clear the adaptive learning memory - after that has been done, drive like a little old lady (not the one from Pasadena!) for the next 50 miles to force the adaptive memory to learn a very lean economical curve - that can make a big difference.

Answer 3

the car should be under warranty. There is definetly something that is way out of specs. The nissan guys have a scanner that will read all the components in your car with live data. It's called consult 2. It will take them about an hour of going threw the data to show something that is out of range. To me sounds like something is unplugged, or not adjusted right.  example, I have seen on that car the mass air flow sensor installed backwards. I think the idle of the car also will give clue to your problem.  have it checked out at nissan

Answer 4

Try replacing th o2 sensor and do scan for trouble codes.