Guest comeandzpa Posted January 2, 2003 Share Posted January 2, 2003 My Z is in desperate need of some good gas milage...well,.more specifically my WALLET needs better gas milage. When I took a trip to one of my local Nissan dealers, I ended the trip with approx. 14 MPG. This is on two lane highways, mostly 55-65 MPH. Never punched the throttle. Very little city driving. Therefore, I have a few questions: 1) I recently got my Z inspected and they found a leaky exhaust gasket. Would this influence my milage, and if so by how much? 2) When I do hit the throttle hard, I get a large plume of black smoke out of the exhaust. I assume this to mean that I am running rich. If so, what are the easiest ways of fixing this? New AFM and/or O2 sensor? Also, might this just be a result of the leaky gasket? 3) My milage seems to be worse in the winter weather than it is in the summer; any quick fixes, or am I just imagining this? Thanks for any advice you can give! Quote Link to comment Share on other sites More sharing options...
denny411 Posted January 2, 2003 Share Posted January 2, 2003 Fuel economy usually does drop in colder weather. One way to offset this is to install a hotter thermostat. A fouled O2 sensor WILL cause the ecm to get a false lean reading, and in turn it will richen the air fuel mixture. Before running the engine after replacing the O2 sensor, I would recomend checking and possibly changing your plugs and wires. Fouled plugs and faulty wires will cause the exhaust gas to be rich and could foul your new sensors. The cost of replacing these prematurely could swallow up any fuel savings in a big hurry. Also the leaky exhaust gasket could be artificially leaning the reading that the O2 sensor recieves. Quote Link to comment Share on other sites More sharing options...
fl327 Posted January 2, 2003 Share Posted January 2, 2003 check the voltage at the 02, and maybe adjust the tps, most of the time when your mpg gets crappy on a efi z cars its tps, or the o2 also check voltage at the coil, it may be getting crappy, check resistance through the wires, check the condition of your plugs, i would try the tps adjustment, cause its free. Quote Link to comment Share on other sites More sharing options...
Mudge Posted January 2, 2003 Share Posted January 2, 2003 With an exaust leak, the O2 will sense more oxygen and therefore richen the mixture, yes this can explain to some degree 1) power loss (especially at higher RPM) 2) poor MPG Quote Link to comment Share on other sites More sharing options...
Guest comeandzpa Posted January 3, 2003 Share Posted January 3, 2003 One other question: My car is currently at the shop waiting for some new brakes. While I have it there, would it be cost efficient to get a tune-up for the engine, or would that be a waste of money?? Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted January 3, 2003 Share Posted January 3, 2003 I want to second what Mr. LEN168 had to say about the throttle position sensor. When I had a straight 6, I experienced the same bad mileage and rich exhaust. The TPS was malfunctioning, and telling the computer that it was at WOT during cruise. Test it very carefully using the procedure in the Haynes manual. Quote Link to comment Share on other sites More sharing options...
Mudge Posted January 3, 2003 Share Posted January 3, 2003 A tune-up just means basic things like, new plugs, new fuel filter, etc, nothing you can't do on your own and save a ton of dough. Quote Link to comment Share on other sites More sharing options...
Guest 240hybrid Posted January 4, 2003 Share Posted January 4, 2003 A fuel injection cleaning might help some. As far as the exhaust leak....I believe that can attribute to some mileage loss, but not sure if very noticeable/costly loss. Like everyone else said plugs and reg. tune up of car will help. Good idea/recommendation on throttle position switch too. Good luck on getting that extra mile. Quote Link to comment Share on other sites More sharing options...
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