bad mpg on a 2001 maxima
07-02-2012, 08:40 AM
#41
The knock sensor basically controls the timing of detonation in the cylinders. If the KS detects knock, it will retard the timing, if it is not working right and not giving the car the proper signals, the car will not run at its peak efficiency. Car not running at its peak efficiency=low gas mileage. Proper KS operation=peak efficiency=good gas mileage.
^^That's a giant OVERsimplicifcation of how it works, but the basic premise is right.
^^That's a giant OVERsimplicifcation of how it works, but the basic premise is right.
The Knock sensor is basically a microphone that listens to the engine. If it hears a Knock (detonation) in the engine, it retards timing.
One other thing it does that people don't really talk about is the adding of fuel.
Rich conditions are a 'failsafe' for engines. Extra fuel cools the intake charge which lowers combustion temperatures which removes the main ingredients for detonation.
Hence, retarded timing and more fuel = no more detonation
A failing or failed Knock Sensor can do 2 things:
1. Could be showing the engine a knock condition, which results in more fuel and retarded timing
2. Could be reading nothing at all, or 'shorted', which will result in a Default 'failsafe' timing Map. This is basically a much, much less noticable "limp mode" for the car.
You won't really notice a loss of power, especially if you never had it to start with. Most often the ONLY thing people notice is increased fuel mileage.
(When the Knock Sensor is working properly, it allows the engine to run near peak efficiancy because it can run close to the point where it Detonates. When working accurately, the knock sensor can tell exactly which cylinder is/was detonating and adjust ONLY that cylinder in millionths of a second. In short, it's seamless. Without intriquite datalogging you wouldn't even see it while monitoring the sensor.)
Last edited by TunerMaxima3000; 07-02-2012 at 08:44 AM.
07-02-2012, 08:47 AM
#42
Agree. OP, My vote is also to replace your MAFS with an OEM unit. I stress OEM unit.
07-02-2012, 06:29 PM
#44
I bought my 2001 MAFS from the local dealer close to my shop. With my shop discount, it was ~$85-$90. Without the discount, it should be around $110-120. The 2002-2003 MAFS's are pretty pricey. The only difference is the 2002-2003 have the IAT built in, in the form of a thermistor. The thermistor can be installed on the 2001 without much trouble.
-Nathan
-Nathan
07-02-2012, 06:47 PM
#45
I'd suggest buying a replacement thermistor separately, and buying a 2000/2001 MAFS suggested.
You should change that Thermistor for a new one though given your issues. They're not known for failing but they're super cheap. I forget where but someone found a replacement for it under $20.
You can also find MAFS's in the junkyard, go in and grab a couple. Ihave a couple in my basement.
Just remember this is rolling the dice REALLY BAD. if you don't get at least 2 or 3 don't bother. And try everyone of them. This is if you want to cheap out.
Personally with that crappy mileage, I'd spend the money on a new MAFS that is OEM, just find a good deal on it.
You should change that Thermistor for a new one though given your issues. They're not known for failing but they're super cheap. I forget where but someone found a replacement for it under $20.
You can also find MAFS's in the junkyard, go in and grab a couple. Ihave a couple in my basement.
Just remember this is rolling the dice REALLY BAD. if you don't get at least 2 or 3 don't bother. And try everyone of them. This is if you want to cheap out.
Personally with that crappy mileage, I'd spend the money on a new MAFS that is OEM, just find a good deal on it.
Last edited by TunerMaxima3000; 07-02-2012 at 06:49 PM.
07-02-2012, 07:49 PM
#47
I'd suggest buying a replacement thermistor separately, and buying a 2000/2001 MAFS suggested.
You should change that Thermistor for a new one though given your issues. They're not known for failing but they're super cheap. I forget where but someone found a replacement for it under $20.
You can also find MAFS's in the junkyard, go in and grab a couple. Ihave a couple in my basement.
Just remember this is rolling the dice REALLY BAD. if you don't get at least 2 or 3 don't bother. And try everyone of them. This is if you want to cheap out.
Personally with that crappy mileage, I'd spend the money on a new MAFS that is OEM, just find a good deal on it.
You should change that Thermistor for a new one though given your issues. They're not known for failing but they're super cheap. I forget where but someone found a replacement for it under $20.
You can also find MAFS's in the junkyard, go in and grab a couple. Ihave a couple in my basement.
Just remember this is rolling the dice REALLY BAD. if you don't get at least 2 or 3 don't bother. And try everyone of them. This is if you want to cheap out.
Personally with that crappy mileage, I'd spend the money on a new MAFS that is OEM, just find a good deal on it.
And Tuner's right, I would spend the money on a new one. Even if you buy 3 at the salvage yard, there's no guarantee they will work, and you can't take them back for a replacement if they don't. Definitely buy OEM new.
-Nathan
-Nathan
07-03-2012, 10:33 AM
#48
Member
Join Date: May 2011
Location: Culiacan, Sinaloa, Mexico
Posts: 263
I got a question about this thread.
I have read the important parts about the different kind of sensors (KS, MAF, O2, etc) and I want to know if exists the possibility of got a bad sensor but without a "Check Engine" light or that my scanner doesn't show it. Also I got a crappy gas mileage of 12 MPG (city) with temperatures above 100 Fahrenheit but in Highway I got a gas mileage of 24 Mpg with almost the same temperatures!
Also I changed the fuel filter, IACV, spark plugs and I'm using mineral oil (15w-40) with a High flow Air filter, BPI flowstack and a short ram intake.
Can it be that something is wrong with my car or it's just the damn weather that it's killing my gas mileage?!
Thanks.
I have read the important parts about the different kind of sensors (KS, MAF, O2, etc) and I want to know if exists the possibility of got a bad sensor but without a "Check Engine" light or that my scanner doesn't show it. Also I got a crappy gas mileage of 12 MPG (city) with temperatures above 100 Fahrenheit but in Highway I got a gas mileage of 24 Mpg with almost the same temperatures!
Also I changed the fuel filter, IACV, spark plugs and I'm using mineral oil (15w-40) with a High flow Air filter, BPI flowstack and a short ram intake.
Can it be that something is wrong with my car or it's just the damn weather that it's killing my gas mileage?!
Thanks.
07-03-2012, 10:44 AM
#49
Sounds like a heavy foot more than anything to me.. Also, why are you using 15w-40? That some pretty heavy oil for a 3.0 gasoline engine. 10w-30 would be the heaviest I put in my car, but I normally go with 5w-20, or 5w-30.
To answer your question though, yes, it's possible for a sensor to be causing a problem and not illuminate the MIL. However, if you continue running the car then eventually the part is bound to fail to the point that the MIL lights up.
-Nathan
To answer your question though, yes, it's possible for a sensor to be causing a problem and not illuminate the MIL. However, if you continue running the car then eventually the part is bound to fail to the point that the MIL lights up.
-Nathan
07-03-2012, 10:52 AM
#50
07-03-2012, 11:03 AM
#51
Member
Join Date: May 2011
Location: Culiacan, Sinaloa, Mexico
Posts: 263
Sounds like a heavy foot more than anything to me.. Also, why are you using 15w-40? That some pretty heavy oil for a 3.0 gasoline engine. 10w-30 would be the heaviest I put in my car, but I normally go with 5w-20, or 5w-30.
To answer your question though, yes, it's possible for a sensor to be causing a problem and not illuminate the MIL. However, if you continue running the car then eventually the part is bound to fail to the point that the MIL lights up.
-Nathan
To answer your question though, yes, it's possible for a sensor to be causing a problem and not illuminate the MIL. However, if you continue running the car then eventually the part is bound to fail to the point that the MIL lights up.
-Nathan
I use 15w-40 oil because the summer weather in my city can kill your engine (when sometimes the temperatures can reach the 120 Fahrenheit degrees). I'm going to use 10W-30 Synthetic oil in the next change.
Also, I'll keep an eye over my engine and check if something is wrong with that sensors. Thanks Nathan.
07-03-2012, 12:43 PM
#52
07-03-2012, 12:54 PM
#53
I try to drive in a easy and relaxed way, and try to use some Hypermiler techniques but the sad part it's that the traffic lights in my city aren't synchronized and you do a lot of stop and go. Now that I think about it maybe that's the main cause of my poor gas mileage in city.
I use 15w-40 oil because the summer weather in my city can kill your engine (when sometimes the temperatures can reach the 120 Fahrenheit degrees). I'm going to use 10W-30 Synthetic oil in the next change.
Also, I'll keep an eye over my engine and check if something is wrong with that sensors. Thanks Nathan.
I use 15w-40 oil because the summer weather in my city can kill your engine (when sometimes the temperatures can reach the 120 Fahrenheit degrees). I'm going to use 10W-30 Synthetic oil in the next change.
Also, I'll keep an eye over my engine and check if something is wrong with that sensors. Thanks Nathan.
You are in Mexico. Maybe the gas sucks...just sayin... They need to get some good signal electricians like me down there to set up the signals properly.
07-03-2012, 01:30 PM
#54
Member
Join Date: May 2011
Location: Culiacan, Sinaloa, Mexico
Posts: 263
Even now exists a problem with the low cost gas (Magna Sin with 87 octanes) where the engines doesn't perform in a proper way, even some people are reporting failures due to the use of this gasoline.
We got the another kind of gasoline (Premium Sin with 92 octanes) that I use in my car. And yes, it's my only choice by the moment.
And the problem with the traffic lights it's that the Traffic Department of my city it's full of ******** that doesn't know HOW to fix this. We have been trying to teach them (I work in the State Government) the proper way to synchronize the traffic lights and correct procedures for management of traffic in peak hours and the design, without promising results.
07-03-2012, 02:41 PM
#55
Sounds like a heavy foot more than anything to me.. Also, why are you using 15w-40? That some pretty heavy oil for a 3.0 gasoline engine. 10w-30 would be the heaviest I put in my car, but I normally go with 5w-20, or 5w-30.
To answer your question though, yes, it's possible for a sensor to be causing a problem and not illuminate the MIL. However, if you continue running the car then eventually the part is bound to fail to the point that the MIL lights up.
-Nathan
To answer your question though, yes, it's possible for a sensor to be causing a problem and not illuminate the MIL. However, if you continue running the car then eventually the part is bound to fail to the point that the MIL lights up.
-Nathan
There's no climate on this planet that requires 15w40 in a gas engine. And heavier oil will create more friciton which = worse performance/mileage.
Not that it's your issue, but it's really foolish to run 15w40 in this engine.
07-05-2012, 08:04 PM
#56
Newbie - Just Registered
Thread Starter
Join Date: Aug 2008
Posts: 15
sorry guys ive been very busy, but have been steadily watching my mileage go up..after changing my fuel filter, and fixing the problem that the bec filter gave me,,my miles went up from 13 mpg to 20 mpg. no im not imagining this. i tested this out the last couple days and its what im calculating. but id still like to get back some more of my mileage. is it still worth replacing the knock sensor??
07-05-2012, 09:23 PM
#57
20 mpg average should be just about right depending on driving mixture, weather, traffic, right foot, etc. I don't think changing a knock sensor will net you much of anything in the way of mpg.
-Nathan
-Nathan
07-05-2012, 10:11 PM
#58
Junior Member
Join Date: May 2011
Location: Santa Barbara, CA
Posts: 52
Not too sure about my city mileage, id say high teens. I get about 25-26 going to see my family which is about a 710 mile round trip. There are some hills here and there, 75 mph, traffic sometimes...
...and I try not to call bs but 37 mpg? How is that possible. Its still a 3300+ pound car, 227 hp v6. Uppers 30s are what modern sub compacts are getting.
...and I try not to call bs but 37 mpg? How is that possible. Its still a 3300+ pound car, 227 hp v6. Uppers 30s are what modern sub compacts are getting.
07-05-2012, 10:39 PM
#59
20 mpg is about average for this engine if you drive it.
22-26 is possible but you'll have to put some work in, KS is a good start. Fuel injector flush (professional one, not the 'in a bottle' stuff), etc.
After that you're looking at breathing mods>> exhaust. Y pipe will net gains in power and fuel economy. So will a good mandrel bent catback.
And a tune would be ideal to reap full benefit and put you over 25 mpg, WITH more power
But we're talking some coin now, right/
22-26 is possible but you'll have to put some work in, KS is a good start. Fuel injector flush (professional one, not the 'in a bottle' stuff), etc.
After that you're looking at breathing mods>> exhaust. Y pipe will net gains in power and fuel economy. So will a good mandrel bent catback.
And a tune would be ideal to reap full benefit and put you over 25 mpg, WITH more power
But we're talking some coin now, right/
07-05-2012, 11:46 PM
#60
Not too sure about my city mileage, id say high teens. I get about 25-26 going to see my family which is about a 710 mile round trip. There are some hills here and there, 75 mph, traffic sometimes...
...and I try not to call bs but 37 mpg? How is that possible. Its still a 3300+ pound car, 227 hp v6. Uppers 30s are what modern sub compacts are getting.
...and I try not to call bs but 37 mpg? How is that possible. Its still a 3300+ pound car, 227 hp v6. Uppers 30s are what modern sub compacts are getting.
In any case, I think your estimates here are spot on as far as what to expect from a Maxima that is running properly. Definitely do not use my 5.5 gen freak of nature as a guide for an average.
-Nathan
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