subactive81 Posted December 10, 2011 Share Posted December 10, 2011 I'm new to this site and was wondering if anyone has any input on my problem. I have a 96 5 speed 4x4 pathy. For the 2 years I have owned it I can seem to get my mpg above 10, and thats hy and city. I tried keeping the Rpm around 2,000 when shifting same thing. If the tank is 21 gallons I have not cleared 210 miles per tank. I do have a bad knock sensor code and when cleared the idle rpm jumps up to about 2,000 rpm. Once the code reapears the idle drops. I am going to replace the knock sensor and the o2 sensor on monday. Is that the right direction. I read of others having good gas miliage then suddenly droping off to about where I am. The pathy also has a newer motor installed about 10,000 miles ago. I still had the same mpg with the old motor. This is driving my nuts as I want to put my 32s on her and give her lift. If I did it now Id run out of gas before making it to work! Thanks for any help. Link to comment Share on other sites More sharing options...
pathfounder Posted December 10, 2011 Share Posted December 10, 2011 (edited) I got 8-10mpg in my 97 automatic with a bad MAF and knock sensor. Replace the knock sensor, and forget about the whole "relocation" malarkey that you'll read about. Take the intake off, and replace the real one with the same part number, in the place where it belongs. Your front o2 sensors are probably shot by now from running in those conditions. Also, your cats might be done as well, but it won't affect mileage unless they've melted. The rear o2 sensors are not important for mileage. I myself have had back luck with MAFs. My first one made the engine underpowered but with occasional "burps" of torque such as right after a gear change. No codes ever thrown for it. My second one was mechanically damaged somehow, and the ECU would lose the signal from it, but it would just think the engine is turning off. It would stall at stops, and jerk hard at speed (basically stalling and bump-starting at speed). Consider replacing the MAF after all else fails. Or, if you can get one cheap, replace it FIRST because it's only two screws to swap it. If you're saying that this problem jumped from your old engine to the new one, then right away you can say that the problem is with a part that was NOT changed, again, maybe the MAF. If not, it's a pretty epic coincidence that two engines have the exact same issue. Edited December 10, 2011 by pathfounder Link to comment Share on other sites More sharing options...
1994SEV6 Posted December 10, 2011 Share Posted December 10, 2011 I'm new to this site and was wondering if anyone has any input on my problem. I have a 96 5 speed 4x4 pathy. For the 2 years I have owned it I can seem to get my mpg above 10, and thats hy and city. I tried keeping the Rpm around 2,000 when shifting same thing. If the tank is 21 gallons I have not cleared 210 miles per tank. I do have a bad knock sensor code and when cleared the idle rpm jumps up to about 2,000 rpm. Once the code reapears the idle drops. I am going to replace the knock sensor and the o2 sensor on monday. Is that the right direction. I read of others having good gas miliage then suddenly droping off to about where I am. The pathy also has a newer motor installed about 10,000 miles ago. I still had the same mpg with the old motor. This is driving my nuts as I want to put my 32s on her and give her lift. If I did it now Id run out of gas before making it to work! Thanks for any help. You hear people around here talking about terrible gas mileage, but 8-10 is the worst I've ever heard. I think this goes way beyond the typical "Do a tune-up and clean some parts" advice. You may need to do that, but I think there is something else tacked on too. I know the 1987-1995 Pathfinders have a 21 gal tank, but are you sure about the 96? Either way, nobody can seem to put more than 18 gallons on it. Is that how you're computing your mileage? the mileage divided by 21? or how many gallons you put in it? Anyway, I'm surprised it's taken you 2 years to do something about it. The knock sensor? You should go ahead and replace it, sure, but I'm not sure that knock sensors make a difference with MPG? You definitely need to replace your O2 sensor though. No doubt about it. Clean your MAF and do a tune up. Filters all around. Link to comment Share on other sites More sharing options...
sewebster Posted December 10, 2011 Share Posted December 10, 2011 Knock sensor could affect fuel economy... if it detects knock it retards the engine timing to prevent it. Link to comment Share on other sites More sharing options...
BowTied Posted December 10, 2011 Share Posted December 10, 2011 I don't have any first hand with the VGs but I am inclined to agree with the above post. One thing I will add - are you sure the engine is getting up to temperature in a reasonable time? If the temp stays low (or the computer thinks it is low) it will stay in open loop mode. This means the O2 sensors are bypassed and a rich fuel map is used (normally just for warm up). (It further prevents the torque convertor from locking up on the highway if it is an A/T but since no issue since you have a M/T). This will ruin fuel economy. The usual culprit of this is a stuck open tstat. It would seem unlikely that this would happen across two engines as I can't imagine how crazy it would be to put in a new engine with a used tstat. However, I could see the temp sender/sensor thingy being reused and/or a break in the wire to the sensor being present across two engines. Something to think about. What was reused on the old engine to the new one? Good chance of those is the trouble. Link to comment Share on other sites More sharing options...
5523Pathfinder Posted December 10, 2011 Share Posted December 10, 2011 Yeah thats some bad mileage! As to add to what everyone has stated, I think you should check the obvious tune up parts. Look for any loose vacuum lines or air leaks after the air flow meter. Remember, the knock sensor is there to detect knocking. I can only assume you are probably running rich and the fuel is not buring off correctly. This creates the knock code. Basicly, its telling to do some investigating. Now, the sensor itself could be bad. Harness could be bad(mice love it). I would throw a timing light on and see what your timing is. Now, this could go on and on on what to check. Make sure there is no misfires, your oil level is correct(overfilled can do some nasty things) and check all your basics. Oh, do you drive with a lead foot or take it pretty easy? Link to comment Share on other sites More sharing options...
Kingman Posted December 10, 2011 Share Posted December 10, 2011 Also might want to make sure the ECM Coolant Temp Sensor is behaving as it should. It directly controls how much fuel is being dumped in to the engine based on the temperature of the coolant. When those misbehave a lot of weird things happen including horrible gas mileage. I've been round and round with those things. Link to comment Share on other sites More sharing options...
Der_Vier Posted December 11, 2011 Share Posted December 11, 2011 R50's have a 21 gallon tank. 8-10, well damn. If i'm doing mostly highway at 70-75, I can get about 19.whatever. I have a 5 speed and the manual front hubs. With the hubs I saw an almost 2mpg increase on highway trips. Like others have said, check 02 and stuff. Also, might as well do a tune up. Do you still have power and oomphf? Maybe timing is off . . . Link to comment Share on other sites More sharing options...
pathfounder Posted December 12, 2011 Share Posted December 12, 2011 I know the 1987-1995 Pathfinders have a 21 gal tank, but are you sure about the 96? Either way, nobody can seem to put more than 18 gallons on it. Is that how you're computing your mileage? the mileage divided by 21? or how many gallons you put in it? The ONLY way to calculate average mileage accurately is to use the trip meter to measure how far you went since the last fill, and divide that number by how much fuel you put in to fill it back up. Tank capacity can't be used because no one runs it until it is empty, and the reported capacities are approximate. Link to comment Share on other sites More sharing options...
BowTied Posted December 14, 2011 Share Posted December 14, 2011 OP - any updates? Link to comment Share on other sites More sharing options...
1994SEV6 Posted December 15, 2011 Share Posted December 15, 2011 The ONLY way to calculate average mileage accurately is to use the trip meter to measure how far you went since the last fill, and divide that number by how much fuel you put in to fill it back up. Tank capacity can't be used because no one runs it until it is empty, and the reported capacities are approximate. Precisely why I'm making sure he's doing it the proper way Link to comment Share on other sites More sharing options...
pathfounder Posted December 15, 2011 Share Posted December 15, 2011 OP - any updates? Maybe he ran out of gas somewhere and can't get online to tell us. Link to comment Share on other sites More sharing options...
subactive81 Posted January 5, 2012 Author Share Posted January 5, 2012 sorry its took me so long to get back. I had to hold off on purchasing the o2 sensor and the knock sensor, because of the holidays. I got money now and am going to order them today and hopefuly get them on today. I did not run out of gas but that comment made me lol. Thanks for all the help. Link to comment Share on other sites More sharing options...
subactive81 Posted January 5, 2012 Author Share Posted January 5, 2012 also yes i filled the gas tank ran it out of gas and did the math. I have not gotten more than 200 miles on a full fill up, city or highway it stays the same. Link to comment Share on other sites More sharing options...
subactive81 Posted January 5, 2012 Author Share Posted January 5, 2012 also when I replaced the motor I had to change out the intake manifold because the motor was from a newer automatic pathfinder. I also replaced spark plugs wires ect. Link to comment Share on other sites More sharing options...
shift_love Posted January 7, 2012 Share Posted January 7, 2012 (edited) that really blows, but seriously, maintenance can go a long way, also, check your compression, timing and maf voltages if you can...those three things will tell you a ton about whats going on. if you have a timing light it makes reclocking that dizzy super easy, i just read your newest post...if you dont follow nissans insane 25 step torque sequence for the vg33 manifold it will cause gigantic vac leaks with gigantic problems, Edited January 7, 2012 by shift_love Link to comment Share on other sites More sharing options...
subactive81 Posted January 9, 2012 Author Share Posted January 9, 2012 [here is a update. I found I had a bad harmonic balancer and a bad tensioner pully. When I replaced there my engine rpm jumped up to 1200 rpm idle. Also I found a evap linw that is not hooked to anything. Im going to try to load a pix of it because i cant find where it goes for the life of me. Also what kind of readings should I be getting from the maf sensor and the o2 sensors?Thank you all again. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now