RCWD21 Posted February 14, 2015 Share Posted February 14, 2015 1990 Nissan pathfinder. Vg30e. Recent major tune up and rebuilt transmission with aftermarket cooler. I get great gas mileage around town in pretty moderate stop and go traffic with a speedlimit between 25 and 45mph. But when I drive 45 miles over to Jacksonville and back (90mile round trip) I burn almost a half a tank. I only went over 3k rpm shifting a few times when there was a lot if traffic behind me. Other then me and my 2 friends there wasn't that much weight in the vehicle. Everytgingnis set to spec according the the FSM. Does anyone have any idea what's going on? I've never experienced this and I've owned several Nissans. PLEASE HELP! Link to comment Share on other sites More sharing options...
Kingman Posted February 14, 2015 Share Posted February 14, 2015 Possible faulty O2 sensor reading lean. They are used the most when cruising. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 14, 2015 Author Share Posted February 14, 2015 Thats literally the only thing I haven't replaced yet. Mainly because it looks like if I remove it its going to destroy the threads in the bung. I checked my ecm and I get code 55. I'll try the other mode where it monitors the sensor but is there also a way for mW to check it with a multimeter while its running? I can make a harness adapter for it no problem. Link to comment Share on other sites More sharing options...
5523Pathfinder Posted February 14, 2015 Share Posted February 14, 2015 Have you actually done the fuel mileage calculations? Reason I ask is that its well known our fuel guages are not exactly accurate all the time. What kind of mileage are you expecting? What kind of tires do you run? What pressures? Are you lifted or stock? Alignment ok? Air filter and box clean and clear of obstructions? When is the last time you changed the oil? Too much oil can cause issues. Have you recently changed where you fill up with fuel? What kind of fuel. Sorry for all the questions but there are lots of things as a possibility. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 14, 2015 Author Share Posted February 14, 2015 I'd like atleast 14 to 17mpg. I run Goodyear wrangler radials 235 75 15 I think, at 26psi. Air filter is new and every inch of the intake system is clean and free of obstructions. Oil is fresh and still golden stock ride height. Alignment is correct. I get my fuel from the shell station. 87 octane. No vacuum leaks all new gaskets and seals exept for the head gaskets. Everything engine wise is up to spec. All belts and fluids are new. I drove it from norfolk Virginia to Morehead city north carolina at an average speed of 75mph. I left with a full tank and had maybe an 1/8 once I got home. The gauge didn't work when I got it but I cleaned the contact on the sending unit and it works reliably now. I realize this being 4x4 and being as heavy as it is its not going to get fantastic mileage but ibwould like it to be as best as possible. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 14, 2015 Author Share Posted February 14, 2015 If you have any other questions feel free to ask. I'm really just hoping its just a faulty gauge. I have another sending unit out of a 96 hardbody that I was thinking about swapping in if the wiring is the same just to see if it made a difference Link to comment Share on other sites More sharing options...
Precise1 Posted February 14, 2015 Share Posted February 14, 2015 Are you certain the speedometer/odometer is accurate? A stock WD21 without issues should be able to achieve 13-14mpg town, 17-18highway at normal speeds/terrrain. B Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 Yes. I've gone 20 miles at 55mph with a GPS active from start to finish and its accurate with multiple GPS devices Link to comment Share on other sites More sharing options...
5523Pathfinder Posted February 15, 2015 Share Posted February 15, 2015 75mph might be your issue. Being aerodynamic as a brick, faster you go, more drag-less miles per gallon. Oh, try bumping your air pressure up to 30psi. More isn't always better, but a touch more might help things. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 I'll try bumping it up to 30psi. But it got better gas mileage BEFORE I did all this work. Why would this be? This is really wracking my brain. Link to comment Share on other sites More sharing options...
ebayfish Posted February 15, 2015 Share Posted February 15, 2015 Assuming its auto, are you sure overdrive is on? Make sure its not in "power" mode. I get 17-18 or so mpg running 33s, 75-80 mph....it should definitely be better than what your getting. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 Its not in power mode. Both modes work and I can achieve torque converter lock up but at slower constant speeds between 40/45 it fluctuates but I may try that lock up switch method to see if it will help resolve that issue. Link to comment Share on other sites More sharing options...
adamzan Posted February 15, 2015 Share Posted February 15, 2015 Heat up the o2 sensor and replace it. It will make your mileage terrible and not set a light when they go bad. Bad enough to affect things but not bad enough to set the light. You can just let the engine run for 10 minutes and get the pipe hot, I've never had a problem getting one out that way. Good luck. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 I'll spray it down with penetrating oil and get it hot and try and take it out again. If I break it off I have to replace everything from the Y pipe back because someone stupidly welded EVERYTHING from the cat back. They even put the muffler in with the weep hole on the top side. Not to mention the cat rubs against my crossmemeber and the rear hump by the axle is wrong and when I hit a bump it slams into the rear suspension so I have to baby it when I drive... Link to comment Share on other sites More sharing options...
ahardb0dy Posted February 15, 2015 Share Posted February 15, 2015 Don't think the O2 sensor would throw a code. If you haven't changed it probably a good idea to do so anyway. Link to comment Share on other sites More sharing options...
Slartibartfast Posted February 15, 2015 Share Posted February 15, 2015 I did my O2 recently. I didn't heat the pipe, and I had a hell of a time. The sensor came out in two pieces. Heat the pipe! Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 Ok thanks guys! I'm gonna look into getting a new sensor first then try to get the old one out. Hopefully it breaks free and screws out like it should Link to comment Share on other sites More sharing options...
SpecialWarr Posted February 15, 2015 Share Posted February 15, 2015 I warmed my 02 sensor with a propane torch after giving it a shot of PB Blaster and then smacked a pin punch on one of the flats with a hammer. More PB Blaster and then it unscrewed itself with a bit of elbow grease. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 (edited) I just don't want to snap it off or break the bung. Everything from the cat to the very end is welded together and I don't have the money to replace all the pieces like I'd want to. Let me put the rust thing into perspective if I can, there's so much rust that when I tried to remove it the first time the bung twisted the tubing so I left it alone. Plus its mounted on the upward side around 1 O'Clock and not closer to the side like its supposed to be. I'll try and post pics of this hack job that is currently my exhaust system later Edited February 15, 2015 by RCWD21 Link to comment Share on other sites More sharing options...
Nefarious Posted February 15, 2015 Share Posted February 15, 2015 Worst case scenario (if the sensor snaps or falls apart inside the hole) you can drill it out and re tap the threads or have a new bung welded on at a muffler shop for very little money if the hole is totally pooched. They won't have to pull the exhaust just to weld in a bung Link to comment Share on other sites More sharing options...
ebayfish Posted February 15, 2015 Share Posted February 15, 2015 You might want to unplug the O2 sensor at the harness before you replace. Mine drove much better when I did. I ordered an NGK sensor with harness off ebay for $16 shipped. Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 Would it matter if the sensor is further upstream? Or does it need to be close to the cat? Link to comment Share on other sites More sharing options...
Precise1 Posted February 15, 2015 Share Posted February 15, 2015 (edited) It needs to stay where it is, by Federal law to within a couple of inches. Before you randomly change the O2 sensor, check it. IIRC it will put out voltage between 0-1 volts during correct functioning, but if it is stuck or malfunctioning within this range, the ECU won't know that there is a problem. Test it cold, hot and while running... B Actually, the O2 sensor should read essentially 0 volts until it nears the ideal air/fuel ratio, at which point it should jump up to aprox 1 volt... Edited February 15, 2015 by Precise1 Link to comment Share on other sites More sharing options...
RCWD21 Posted February 15, 2015 Author Share Posted February 15, 2015 I'm in North Carolina, I don't have to pass emmisions. I'll test it tomorrow at the shop so I can also try to remove it if its bad. But on a different note what else could it be if the sensor is good and working correctly? I've double checked all wiring and it all checks out. I set ignition timing when I did the major servicing when it was on the stand. Could a bad TPS also cause symptoms like a bad o2 sensor? Link to comment Share on other sites More sharing options...
ebayfish Posted February 17, 2015 Share Posted February 17, 2015 I may be wrong, but I think a bad tps would cause bad read on tach, hesitation & cruise control would not work proper. Link to comment Share on other sites More sharing options...
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