Gas mileage decrease
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Joined: Nov 2001
Posts: 174
Gas mileage decrease
I use to get excellent gas mileage, like 400 to 410 miles to a tank. I have 162,000 miles and engine power I notice has decreased also. What should I do to my max to regain power and gas mileage? I also use premium gas.
Originally Posted by nitroz
I use to get excellent gas mileage, like 400 to 410 miles to a tank. I have 162,000 miles and engine power I notice has decreased also. What should I do to my max to regain power and gas mileage? I also use premium gas.
check ur o2 sensors..
BTW how do u know if ur knock sensor is dead... besides by the cel... how much is for a new one..
cuz my gas mileage is like 360 for tank... it's bad.. really bad... how do i know my o2 sensors are bad too.. besides the cel again.. hehe thanx!
BTW how do u know if ur knock sensor is dead... besides by the cel... how much is for a new one..
cuz my gas mileage is like 360 for tank... it's bad.. really bad... how do i know my o2 sensors are bad too.. besides the cel again.. hehe thanx!
I had a situation somehow identical... There was no cel light on...but when I checked the codes it said that there is a code stored.And like a dumb a$$ I thought that is the knock sensor. Because I was doing this before taking a trip to Florida, I ran right away to the Nissan dealership and bought (and replaced the KS). It was a O2 heater code,and not the KS.
In your situation ,you can check if there are any stored codes before you do anything else.Go from that point on. I don t mind having a new KS on my car (136 k) but I hate to fix it if is not broken. If you don t know how do check for codes,there are many posts about it.
In your situation ,you can check if there are any stored codes before you do anything else.Go from that point on. I don t mind having a new KS on my car (136 k) but I hate to fix it if is not broken. If you don t know how do check for codes,there are many posts about it.
I had a heater problem with my O2 sensor,and no CEL light on...just a code. I unplugged the sensors and measured the heater resistance (2.5-4.7 ohm) all seemed Ok on both upstream sensors. I plugged and unplugged them a few times to make sure thgat is a good connection,and at this point, no code for almost 3 days. We ll see what s going to happen from now on. Honda tecs said that if the heater goes,the sensor needs replacement. We ll see what s next.
Member
Joined: Apr 2003
Posts: 67
Here is my standarde knock sensor reply complete with instructios for extracting codes from the ECU:
Once and for all: a bad knock sensor WILL NOT trip the check engine light, you must extract the codes from the ECU to determine if your sensor is (potentially) bad (code 0304). Some other hints as to a bad KS: poor acceleration below 3000 RPM (I was getting tired of being left behind at stoplights by Honda Civics).
If you don’t already own a Haynes or Chilton manual, get one. In addition to telling you how to extract the codes and locate the KS, there is a wealth of useful information for the do-it yourselfer. I am very cheap, but this an area well worth spending the $20 or so (I bought mine off of EBAY for $10 shipped).
The ECU is located behind the center console on the drivers side. It is accessible by removing the plastic cover panel right next to the gas pedal. The ECU is a metal box with a screw on the side covered by a piece of tape. Peal back the tape to get at the screw. With the ignition in the “On” position, turn the screw all the way clockwise, hold for at least 2 seconds, turn it all the way counterclockwise. Your CEL will now start flashing out any codes stored in the ECU. The codes are two digit numbers. The first number is signaled by long flashes, there will be a two second pause, and the second number will be indicated by a series of short flashes. Long-long-long-pause-short-short-short-short = 0304 (KS fault). There may be more than 1 code in the ECU, they will be flashed out sequentially and the whole sequence will repeat. To clear the codes from the ECU, follow this sequence: clockwise, hold, counterclockwise, hold, clockwise, hold, counterclockwise.
A good KS will measure ~550 k-Ohm resistance between the left pin of the KS and ground. You can check the resistance without removing the KS by following the harness to the connector. The connector has two pins, only one of them hooks up to the KS, so try them both. The act of whacking on the KS with your wrench can (temporarily) start it working again, so checking the KS once you removed it may not give you the bad reading you suspect. Hint: the connector is not the green one closest to the KS (1995-1996 models – most likely 1994-1999), it is a few inches closer to the front of the car. A heat shielded wire leads into the bottom of it and there are two wires coming out the top, one clear and one black.
Low cost knock sensor sources: The dealer will charge you $160 or so for the sensor. I purcahsed a Nissan OEM sensor off of EBAY for $90 shipped. I have seen them for as little as $80 and routinely for $100-$110. Search for both “Maxima knock” and “Nissan knock” to make sure you get all the possible matches. You can get a Bosch sensors for $115 shipped from http://www.nissanpartstore.com/nissan_knock_sensor.html I prefer OEM parts when possible and have no information on the Bosch.
Two good article on KS replacement:
http://www.skippynet.com/maxima/knocksensor.htm
http://www.motorvate.ca/mvp.php/507
Modifications to the Skippynet method
The article suggest using a 14” (or longer) ¼” socket extension to reach the KS retaining bolt. I found that using a 9” extension made it much easier to get the u-joint onto the KS bolt. To save money, I used two 3/8” drive extensions with a 3/8 to ¼ adapter, a ¼” drive u-joint and a ¼” 12mm socket (most of which I already had). Skippynet suggest using a 12mm flex socket, but being cheap I used a separate socket and u-joint so that I would have a more useful general purpose tool left over than the 12mm flex socket (better yet, I borrowed the u-joint and saved another $8). A 3/8” u-joint is a slightly bigger animal and in my opinion would make it hard to get the socket onto the bolt. It was not at all difficult to loosen the bolt using this setup. I had also borrowed a 16” extension and found it very difficult to get the socket onto the bolt head (I gave up after about 2 minutes, so it probably could have been done).
Once the bolt was out, I used a magnetic pickup to retrieve it (and eliminate the possibility of dropping it into the engine cavity where as you will find out soon, is not a very friendly place). With the bolt removed, you can pull the knock sensor out of the cavity by the harness and replace it. Next, I put the bolt into the new KS and used a small piece of tape to hold it in place while I stuffed it back into the engine cavity (again to eliminate the chance of dropping it in there).
Now the difficult part: I don’t see how you can locate the bolt into the hole and get it started without stuffing your hand under the manifold (others have done it using a claw type pickup to position the bolt). If you have very large hands, you might try enlisting a girlfriend or your mom as others have done. I was able to get my hand in there and get the bolt hand tight, then it was just a matter of using the 9” extension/u-joint setup again to do the final tightening. Your hands will get cut up a little doing this, but no worse than I am used to with other auto repairs.
I was able to replace the KS in both cars in less than 1 hour including test drives using this method. The real key is using the skippynet socket extension method to crack the bolt loose. Once you have jammed your hand into the engine cavity you will realize how difficult it would have been to get a wrench on the bolt and loosen it.
Once and for all: a bad knock sensor WILL NOT trip the check engine light, you must extract the codes from the ECU to determine if your sensor is (potentially) bad (code 0304). Some other hints as to a bad KS: poor acceleration below 3000 RPM (I was getting tired of being left behind at stoplights by Honda Civics).
If you don’t already own a Haynes or Chilton manual, get one. In addition to telling you how to extract the codes and locate the KS, there is a wealth of useful information for the do-it yourselfer. I am very cheap, but this an area well worth spending the $20 or so (I bought mine off of EBAY for $10 shipped).
The ECU is located behind the center console on the drivers side. It is accessible by removing the plastic cover panel right next to the gas pedal. The ECU is a metal box with a screw on the side covered by a piece of tape. Peal back the tape to get at the screw. With the ignition in the “On” position, turn the screw all the way clockwise, hold for at least 2 seconds, turn it all the way counterclockwise. Your CEL will now start flashing out any codes stored in the ECU. The codes are two digit numbers. The first number is signaled by long flashes, there will be a two second pause, and the second number will be indicated by a series of short flashes. Long-long-long-pause-short-short-short-short = 0304 (KS fault). There may be more than 1 code in the ECU, they will be flashed out sequentially and the whole sequence will repeat. To clear the codes from the ECU, follow this sequence: clockwise, hold, counterclockwise, hold, clockwise, hold, counterclockwise.
A good KS will measure ~550 k-Ohm resistance between the left pin of the KS and ground. You can check the resistance without removing the KS by following the harness to the connector. The connector has two pins, only one of them hooks up to the KS, so try them both. The act of whacking on the KS with your wrench can (temporarily) start it working again, so checking the KS once you removed it may not give you the bad reading you suspect. Hint: the connector is not the green one closest to the KS (1995-1996 models – most likely 1994-1999), it is a few inches closer to the front of the car. A heat shielded wire leads into the bottom of it and there are two wires coming out the top, one clear and one black.
Low cost knock sensor sources: The dealer will charge you $160 or so for the sensor. I purcahsed a Nissan OEM sensor off of EBAY for $90 shipped. I have seen them for as little as $80 and routinely for $100-$110. Search for both “Maxima knock” and “Nissan knock” to make sure you get all the possible matches. You can get a Bosch sensors for $115 shipped from http://www.nissanpartstore.com/nissan_knock_sensor.html I prefer OEM parts when possible and have no information on the Bosch.
Two good article on KS replacement:
http://www.skippynet.com/maxima/knocksensor.htm
http://www.motorvate.ca/mvp.php/507
Modifications to the Skippynet method
The article suggest using a 14” (or longer) ¼” socket extension to reach the KS retaining bolt. I found that using a 9” extension made it much easier to get the u-joint onto the KS bolt. To save money, I used two 3/8” drive extensions with a 3/8 to ¼ adapter, a ¼” drive u-joint and a ¼” 12mm socket (most of which I already had). Skippynet suggest using a 12mm flex socket, but being cheap I used a separate socket and u-joint so that I would have a more useful general purpose tool left over than the 12mm flex socket (better yet, I borrowed the u-joint and saved another $8). A 3/8” u-joint is a slightly bigger animal and in my opinion would make it hard to get the socket onto the bolt. It was not at all difficult to loosen the bolt using this setup. I had also borrowed a 16” extension and found it very difficult to get the socket onto the bolt head (I gave up after about 2 minutes, so it probably could have been done).
Once the bolt was out, I used a magnetic pickup to retrieve it (and eliminate the possibility of dropping it into the engine cavity where as you will find out soon, is not a very friendly place). With the bolt removed, you can pull the knock sensor out of the cavity by the harness and replace it. Next, I put the bolt into the new KS and used a small piece of tape to hold it in place while I stuffed it back into the engine cavity (again to eliminate the chance of dropping it in there).
Now the difficult part: I don’t see how you can locate the bolt into the hole and get it started without stuffing your hand under the manifold (others have done it using a claw type pickup to position the bolt). If you have very large hands, you might try enlisting a girlfriend or your mom as others have done. I was able to get my hand in there and get the bolt hand tight, then it was just a matter of using the 9” extension/u-joint setup again to do the final tightening. Your hands will get cut up a little doing this, but no worse than I am used to with other auto repairs.
I was able to replace the KS in both cars in less than 1 hour including test drives using this method. The real key is using the skippynet socket extension method to crack the bolt loose. Once you have jammed your hand into the engine cavity you will realize how difficult it would have been to get a wrench on the bolt and loosen it.
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