Buck Wild Posted November 24, 2012 Share Posted November 24, 2012 I have a '81 280ZX that runs pretty good until yesterday that is. She runs but on a 100 mile trip she drank just over 6 gallons of gas...WTH could be the cause here? Any help would be appreciated. Quote Link to comment Share on other sites More sharing options...
Kurbycar32 Posted November 24, 2012 Share Posted November 24, 2012 Your getting 16-17 mpg which seems a bit low (or even normal depending on the car) but not "OMG what happened". What was your average fuel economy before? Start with the basics like tire pressure, air filter, spark plugs. If those check out inspect the fuel lines attached to the tank, they seem to get neglected and mine actually leaked a bit. Beyond those simple things you start looking at the fuel injection system Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 25, 2012 Share Posted November 25, 2012 Unless he took less than an hour on a highway, that's crap mileage.below 85mph, that car should get mid 20's easily. If this was in-town driving I might agree its nothing to get upset over. But for a highway trip that's a considerable drop. If you were 55-65mph average I'd expect 25-27mpg. Check the basics, including what it took on similar journeys... But generally a quick drop like this on the highway is a sign the O2 sensor has gone bye bye... When mine went away, I retrofitted a self-heating unit from a Z31 tied into the Fuel Pump Relay Circuit. Car gets into, and stays in Closed Loop MUCH longer with a heated sensor netting fuel mileage gains, primarily in-town where it may never get hot enough between stop lights to go into closed loop, and you stay on the preprogrammed fuel map (full power safe-rich) all the time. Quote Link to comment Share on other sites More sharing options...
B. Whisky Posted November 26, 2012 Share Posted November 26, 2012 That explains the random open loop hunting I would experience before unplugging the thing and tuning around it. Quote Link to comment Share on other sites More sharing options...
Buck Wild Posted November 26, 2012 Author Share Posted November 26, 2012 Was getting 27-29 mpg then all of a sudden a drastic change. Ordered an O2 sensor and will see. Check the timeing and have it set at 10 BTDC. Plugs look fine. Most everything that comes to mind is newly replaced parts in the last year. Quote Link to comment Share on other sites More sharing options...
NewZed Posted November 26, 2012 Share Posted November 26, 2012 Fuel pressure regulators have been known to get stuck/clogged. High pressure = low mileage. Quote Link to comment Share on other sites More sharing options...
Tony D Posted November 27, 2012 Share Posted November 27, 2012 High fuel pressure to kill mileage 10mpg would make the car a stumbling pig-rich black-smoke puffer at idle (if it idles at all).... Oh, and that will kill the O2 sensor! Quote Link to comment Share on other sites More sharing options...
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