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Good gas mileage in town but horrible on freeway


RCWD21
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Just wanted to update. I haven't been able to test it et because for some reason either the starter or the relay has decided to go bad on me. I get a click but nothing more. I hope its just the relay

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I tried that already and nothing. I don't get anything from the starter. I have another relay here I'm going to try plus another battery justvto eliminate the variables

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I can't remove it without removing the transmission lines. I went through this when I rebuilt the transmission. The lines and the passenger side axle get in my way. But I'm going to try the relay and a booster battery and see if that fixes my problem first

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IIRC the little heat shield had to come off of mine to get it past those lines.

 

There's a fairly common issue with these where the contacts in the ignition column get worn out and can't pass enough amps to the solenoid. Some people have relayed that circuit (the relay that's there only breaks the circuit so you can't start in gear) so the solenoid gets full power.

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I removed the idler arm from the frame when I replaced the starter in my 94 the last time ( don't ask ! LOL), I would highly recommend a OEM Nissan starter ( rebuilt but good) or a aftermarket NEW ONLY starter ! I used one from Rockauto made by Pure Energy, only NEW one they had.

 

I was able to get the starter past the trans lines by rotating it, one time I pulled it out from the top.

 

Never had a problem removing the O2 sensor.

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Ok, well it starts and runs again. The fix? Threaten to replace the starter relay and magically it fixes itself. Hasn't given me one issue since I put the pare relay in the glove box lol as for the o2 sensor I'm still looking for a good price of an NGK brand. I looked at it today and sprayed some penetrating oil on it right after I drove it a little bit. Upon getting some more crud off of it I discovered its the original Nissan sensor and seeing as its 25 years old I'm just going to replace it to eliminate it as a variable. Also I drained the tank bone dry pulled the fuel pump fuse and left the key on and put in 5.25 gallons at a time and the fuel gauge is dead on accurate at each interval. That's about all I'm able to do for now because my work space is currently taken up by a 200sx that I'm servicing and installing a timing kit and brand new valves.

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I have an ntk sensor on its way, it should be here the 25th. I don't like cutting and splicing sensors in. This is the sensor to the plug. It tests good but I'm going to replace it since its the original sensor in there.the only code I'm getting is for a knock sensor so I'm oreding one of those today. And now I have a question about that. Can I mount the knock sensor somewhere else? Like on the intake plenum?

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Ok cool. I read on some of their stuff but wasn't 100% sure. I'm guessing as close to the original spot as possible would be best since it operates based on perceived frequency changes? Ill be replacing it once I get the oxygen sensor in and can test it. Would the knock sensor cause this bad of a drop in mileage? Everywhere I've read said it would only be a few mpg if that.

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You can relocate the knock sensor but you are slightly compromising it's effectiveness. On a daily driven naturally aspirated motor though, it's not a big deal. Just mount it central to the cylinder banks, just slightly off center biased towards the rear a bit. That pretty much where the stock one is, albeit a little lower from the factory. And you are correct. The Knock sensor is just a microphone. It transmits the noise of the engine running to the ecu, and built into the ecu is a specific filter that is looking for the frequency of 'pinging' that happens typically alongside detonation.

Edited by Nefarious
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Damn dude that sucks! Its in the high 20's here and raining/freezing and once this clears up or I can snag another bay I'll replace the sensor. It should be here tomorrow hopefully.

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Its so bad here that I've even checked the tank for holes lol when I cleaned the sending unit I had to remove chunks of what was probably 20 year old sugar that someone put in the tank. Surprisingly the tank had no rust/ scale and only 2 drops of water!

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How bad is yours?

Right now I am lucky to get 400km out of 70 something litres...

 

Also the one in mine was an ntk. That i put in in the fall. I am going to get a bosch one this time. That's what was oem.

Edited by adamzan
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I figured some things out with mileage. I'm getting 9.57 miles per gallon so that's right at 200 miles a tank. Which is obviously way off from the normal. I don't expect amazing mileage out of this thing but I'd like at least what was advertised or maybe a little better if that's possible. Everything else is new and well within spec. Hopefully the sensor will arrive today

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