I do have an auto tranny. I used to have a bad rear 02, 0902 code, and the 0304 KS code was also lit up. I replaced the rear 02 and reset the ECU, no codes visibly but i know that KS doesn' make the ECU light up. I should check it again.

 

And later generations operate exactly the same way. However, there is only one timing map.

Also, since timing is also adjusted based on injector operation, so any adjustment the ECM makes to the fuel injection & mixture ratio control will affect the timing. And remember the knock sensor is monitored by that system as well.

In addition, the ECM also makes adjustments to the timing based on other ECM data during certain conditions like acceleration.

 

I maintain there must be 2.

we agree there's a default map with timing set points optimized for premium fuel. but if that were the only map then how do you explain ECU operation when the KS is faulty? The ECU can no longer rely on the KS to prevent knock, so it would have to use a second set of timing set points programmed to be safe with low octane fuel -- a "safe" map. and that's exactly what my observations confirm. with a faulty KS and no safe map, ignition retard would be arbitrary, and we know that's not the case.

now it could very well be that with a bad KS the ECU is simply programmed to retard timing by a fixed Xdeg less than default, under certain conditions. but that Xdeg delta would be applied to a matrix of operating parameters (A/F, RPM, etc) corresponding to said conditions, again forming a "safe" map.

I think I agree with most of this. but like I said before, injector operation is only one input, and the link between those inputs and timing is defined by the programmed map, and that link does not change through learning. so while injector pulse itself is adjusted through learning (so as to optimize A/F), the corresponding timing set point is simply assigned as a matter of course.

yes, that was my point when I said timing is not "static", it is constantly changing in response to operating conditions. those changes are what the timing map is all about.

 

A different view:
In my area we have three "grades" 87 regular, 89 and 90-93 premium or super or ultimate grade. Depending on gas station the high grade will vary between 90 to 93 but the price difference between regular (87) and premium (90-93) is about 10% with prices at about $2 USD for regular or $2.10 mid with $2.20 primium or $2.30, $2.40 and $2.50... again about 10% diff in cost per gallon.

But my mileage difference is when using high grade is more than 10%.

Average mpg with regular ten mile one way trip to work is 14-17mpg on regular and 19-23 on premium. Rush hour traffic so speed varies greatly from near stop (10/20) to 60/70mph with rough 40% at higher speed.

Highway mpg jump from low 20's to high 20's low 30's with premium at 65/75 mph and drops to mid 20's at 80 mph on a 100 mile nonstop trip. This is with knock sensor not working properly!

With observed mileage I stick with premium 93 even if price climbs to $3 USD a gallon. Not counting the benefits of more additives on premium grades I figure that with the increase mpg I get a lower per mile cost.

Ofcourse your mileage may vary..............

 

I tried to do a test of premium vs regular gas mileage on the interstate highway. My result was different from yours. But the results were not (IMHO) conclusive. I did get better highway mileage burning regular, but not enough of a difference to be significant (about 1 to 2 mpg better). In addition, there were other factors that seemed to be more important than gasoline octane on determining highway mileage -- particularly wind speed and direction. (You always get better mileage when you have a tail wind than when you are pushing a headwind.)

So I won't maintain that I proved regular gives better highway mileage than premium. Don't think I proved that. I do believe that for my Max I proved that I can get about the same mileage burning regular compared to burning premium. So I will continue to burn regular in my Max.

I did not know that any oil company in the USA marketed a 90 octane premium (some Canadians on this site say there is 90 octane at some Canadian stations). Given that you are in a major refining area (Texas), its possible that some refiners do make that octane premium and ship it by truck to local stations.

Along almost all pipelines (most gasoline is moved to market in pipelines), the pipeline shippers agree on a single gasoline spec for each grade of gasoline -- and I don't know of any US pipeline that has a spec of 90 octane for premium. There is a single spec because all gasoline volume for that grade goes into one or more tanks -- this is called comingled gasoline. Then each company loads this common gasoline into a tank truck putting in their own additive package and ethanol (if needed).

For most stations the cost difference between grades is not set on percentages, but on a fixed cents/gallon difference -- usally 10 cents for each grade (or 20 cents between regular and premium). I've seen stations in Wisconsin where this price spread is smaller between regular and mid-grade and wider between mid-grade and premium.

 

I think the difficulty I have in all this is understanding the statement in the FSM regarding timing is:

"The basic ignition timing is programmed within the anti-knocking zone, if recommended fuel is used under dry conditions."

My question is how broad is that zone and how is it adjusted?

Also in terms of whether there are multiple timing maps, I can't find any reference to them. All that is described is a "retard system" that is invoked when knock is detected.

 

I ran premium for many years, and now use strictly regular. There is no need for premium, as the motor will compensate. Even the fuel door states regular is ok.

The mileage does not go down as octane has an effect on predetonation. The knock sensor will not be worn out by using 87. It's a shame this topic can't be put to rest because there will always be feelings based on opinions, not fact. To date, nobody has ever tested where the results were statistically valid. There's always a lack of a control in these personal tests.

It's not a question of price, it's whether something is needed or not. In my other car, the owner's manual does state that 89 is the minimum that can be used, and premium is recommended. So I just use 93 period. But in the Maxima, 87 is just fine.

 

Could not agree more.

It is good to have another supporter for this reasonable position.

 

Good reading...I"ve been using 91 or better in my 03. I think I will try 89.

 

Excuse me, but the elevation is over 6000 feet where you live. Of course 87 is fine for you.

 

Close, but not quite correct.

Yes, I do live where the elevation is 6 K feet or higher. But here, regular gasoline only has 85 octane -- not 87 octane. The mid-grade gasoline here has 87 octane -- and costs 10 cents more than 85 octane. But 85 octane at 6 K feet elevation performs in most vehicles (read those without turbo-chargers) like 91 octane performs at sea level.

When I go to lower elevations, I buy the cheapest gasoline per gallon (which in Iowa and parts of Nebraska is mid-grade with 10% ethanol). Right now I'm visiting in Illinois and burning 89 octane that I bought in Iowa on the way here. Gasoline in the Chicago area is more expensive because it is a special blend (but not as costly to make as California gasoline). I try not to buy this special gasoline and hope to get back to cheaper gasoline in Iowa (or even western Illinois) before I fill up again on my trip home.

 

So given what you have posted in this quote above, why is my statement about 87 being fine in an engine designed and tuned for 91 where you live incorrect?

The fact you sometimes use a lower octane fuel at lower elevations with no problems apparent to you is a credit to the engineers at Nissan that built an engine and control system that can compensate for non-recommended fuel.

 

sorry to bug in -- with a broken KS ( i got the 0304 code) i use 87 and everyting is fine, do i even need to replace it ? its expensive

 

You implied that I was using 87 octane at 6 K feet elevation, where I live. You were wrong on that because I use 85 octane at 6 K feet. Your statement implied that given my elevation, 87 octane regular should work well (which is true) -- but the regular here is only 85 octane.
If you read the owners' manual, you will see that 91 octane is recommended for maximum performance, but that 87 octane is acceptable fuel to use -- and that 85 octane gasoline is acceptable at elevations above 4 K feet. That is the way the engine was designed, and (at least my VQ) works well as it was designed to operate -- burning regular gasoline.

On the question of replacing a mal-functioning Knock Sensor:
- What kind of mileage are you getting -- in the city and on the highway?
- Do you ever hear knocking when burning regular with your failed sensor?

With what you have reproted so far, it appears that your sensor failed in the retarded spark mode (not hearing knocking burning regular will confirm this). There are others here who know more about KS than I do, but if you are getting acceptabel mileage (about 21 mpg in the city and about 28 mpg on the highway) then I would not bother to pay big bucks to replace it.

 

There is no such thing as "retarded spark mode" on a Nissan Maxima. When the sensor hears a knock, the ECM retards the timing only for a short period of time that is described as an emergency response in the manual.

 

There is no such thing as "retarded spark mode" on a Nissan Maxima, except when sensor hears a knock and the ECM retards the timing only for a fairly short period of time which is described as an emergency response in the manual.

 

haven't we been through this already? in this very thread?

to those who don't believe there is a "retard mode" (aka "safe" mode) I suggest 3 things:
1) explain how the ECU prevents knock when the KS is faulty.
2) go get an OBDII sensor scanner. watch the timing advance under hard accel. then unplug your KS and watch it again. explain your observations.
3) define the word "mode"

until you do these things you are not in a position to confirm/deny the presence/absence of a purported "safe mode".

 

well i dont calculate mpg per say, but i get a very consistent 550 KM or so to a tank of gas, and i fill up usually when the meter is about half way into the last quarter marker

i definitely drive more in the city then in the highway for sure, so i can assume that to be 60city/40hwy - no codes except for KS within the last 8000KM i replaced the rear o2 (had a code and cleared) spark plugs, fluel filter, air filter, PCV valve and put some injector cleaner in for good measure as well as oil and filter (castrol gtx) and atf flush among other things as well

 

Thanks Sky ! I consider myself an expert on gasoline octane (having worked for an oil company for 35 years with need to know about octane topics). But I certainly know that I am not an expert on KS -- even the one in the Max. But my experience with the KS in my Max leads me to believe you have the correct information. Thanks again.

 

sky jumper & SilverMax-04.........There is NOT a "safe mode". As someone else pointed out, the FSM clearly states that there is one basic ignition timing "map" or program designed by Nissan that should allow the engine to operate WITHOUT pinging if, "the recommended fuel is used". The recommended fuel is "premium" with an AKI rating of 91. The basic ignition timing map does have revised data that is used for some operating conditions such as starting, warmup, idle and ACCELERATION. The knock sensor is nothing more that a vibration sensor that generates a voltage when it senses vibration caused by the pinging, and when the ECM sees that voltage it then retards the timing to eliminate the pinging. It's a "backup", knock prevention system, it was not designed as part of the normal ignition timing control system.

 

samson - you clearly haven't observed how the ECU reacts when the KS code is present. and you don't know the definition of the word "mode", or don't like how I'm using it. and you are missing the entire point.

your quote from the FSM is out of context -- in that section, the FSM is not talking about what happens when the KS is faulty - it is describing how the KS system works under normal conditions.

furthermore, the FSM does not describe what happens to timing when the KS fails. you seem to think nothing happens, and if so you'd be wrong. I know this because I have personally seen the results. but even logic should tell you this -- how else would the ECU prevent knock? the default timing map is optimized for premium fuel -- and it will likely knock if regular is in the tank. but we know that does not happen even with a bad KS. how can this be if there is no safe mode?

I invite you to complete the three steps I outlined above. then we can have a legitimate discussion on the topic.

EDIT: let's clear this up once and for all....

here's the text from the FSM.
note:
1) there's no mention of what happens when the KS fails.
2) there's no mention of "only one map"
3) but there is mention of several "conditions" that affect ignition timing. hmmm - might those be considered "modes"?? Webster's dictionary defines a mode to be "a particular functioning condition". so that fits.
4) when the KS fails, the ECU prevents knock by reverting to a conservative timing mode designed to be safe with regular fuel -- a "safe" mode. so that fits.
5) timing is decided once injector pulse is already determined, not the other way around. the example map shown dictates a single/unique timing set point for a given RPM/injector pulse --- but we know when the KS is faulty the timing is different over a select range of conditions, so it can't be based on the same map. and the ECU is not responding to knock in this case, so how does it know to retard the timing? and by how much? answer: a "safe" mode, and a "safe" map - just like the default map, but programmed to be safe with low octane fuel.
6) as I stated before, this "safe" map could just be a simple numerical modification to the default map - but the result is still a different map.
7) in this context, the term "map" is quite generic - much like the term "spreadsheet". people use the term "spreadsheet" to describe an Excel workbook, or a worksheet, or even a different array of data within the same worksheet. so is "the map" a map, or a sub-map, or a sub-sub-map? really, isn't it beyond the scope of this forum to debate such semantics.
8) again - the FSM doesn't talk about what happens to timing when the KS fails. but my own live testing confirms the presence of a "safe" ignition timing mode. and logic dictates the presence of a "safe" ignition timing "map".

 

^^^ Okay, here goes.

1. There is only one map defined in the FSM, therefore one can assume there's only one map.

2. The FSM clearly states the retard system is used ONLY FOR EMERGENCIES.

3. Although the following sentence looks different in the picture shown, this is how it copies and pastes from the PDF version:

"The basic ignition timing is programmed within the anti-knocking zone, if recommended fuel is used under dry conditions."

4. The FSM goes on to say:

"The retard system does not operate under normal driving conditions."

and it further states that it retards the spark ONLY WHEN A KNOCK IS DETECTED, which means that DETONATION is occurring, hence AN EMERGENCY CONDITION exits.

5. Nowhere in the FSM does it say that, or describes how, the ECM adjusts for non-recommended fuel.

6. When a knock is detected or the sensor has a certain fault, the SES light will not come on and the timing is retarded for what Nissan defines as "one trip."

7. One thing is almost correct about what was stated in the previous post. If the knock sensor circuit is faulty, the timing will stay in emergency retard mode until the condition is fixed.

http://www.courtesyparts.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=CP&Product_Cod e=22060-A32

 

kenshi, 95% of what you just posted is just a regurgitation of what I have been saying for the past 6 months (and earlier in this very thread) - with the exception of your "single map" theory.

but you *still* haven't explained how in the world - with only one map to work from, that was designed for premium fuel - how the ECU knows where to set the timing when the KS is bad (or even when it senses knock).

that the FSM does not explicitly define a second map does not mean it doesn't exist. the FSM also makes no mention of timing control while the KS code is present -- does that mean there is no difference in timing? of course not!

expand your thinking beyond a Japanese document that was translated to English, contains a myriad of grammatical ambiguities, and is intended for shop mechanics who don't know a computer data array from a solar ray. If the one and only map was programmed "...in the anti-knocking zone, so long as [premium] fuel is used..." then how do you explain the different timing profile when the KS is faulty? and what tells the ECU to keep it in the single digits at high RPM and heavy load?? surely not the same 2-dimensional map that tells it to set 26deg BTDC under the same conditions with a good KS!

I call that a second, "safe" map. you can call it the timing hotdog with a twist of lemon for all I care, but until you get an OBDII scanner and do some testing yourself, and explain the other holes in your theory, you are not qualified to reject the idea of a safe map. and I'm not going to argue the semantics of maps vs. sub-maps vs. secondary data arrays. I don't have the time or patience, and I've done enough computer programming in my day to know that what you call it doesn't even matter. which is why I'm getting sick of people saying there is no safe map, like they know something I don't.

 

Skyjumper.....So how did you simulate a failed KS, and when you mapped the ignition timing advance curve with a failed KS or circuit how did that compare with the advance curve with a non-failed KS or circuit? You could supply us with a chart/graph plotting the ignition timing against a couple of basic parameters for a failed and non failed KS. I hope you're not suggesting people disconnect their KS to be able to run on regular. I've read the manual, I know what's in it. The premise here is that the system is operating normally. Kenshi.......go back and read up again on "one trip" DTCs. You've carried the logic too far, re the KS and the retarding of the timing.

 

my testing results are summarized earlier in this thread. I didn't simulate a failed KS - my KS broke and I took measurements. then I fixed it and took more measurements. I didn't notice a big change, so I put the bad one back in and took more measurements - then I saw where the difference was -- under heavy acceleration at RPM. then I put the good one back in and confirmed the difference. for good measure I then unplugged the new KS and noted the same "bad KS" results.

and no, I'm not suggesting you need to unplug the KS to run regular -- people can run regular on either a good or bad KS - it doesn't matter. with a bad one the ECU has to compensate timing to eliminate the risk of detonation with regular fuel -- b/c it has no way of knowing if the engine is detonating, so it just plays it safe.

consider also, if there was a risk of detonation on regular fuel w/ bad KS, surely that would be cause to set the CEL -- but that does not happen.

 

Sky, the emergency retard is simply a fixed differential from the standard timing map. Do you really think that is would be anything more complicated than that?

Again, the only time the SES light is set is if there's high or low voltage in KS circuit, which indicates a circuit fault. IT DOESN"T LIGHT WHEN THERE"S A KNOCK.

THERE IS NO WAY THE ECM CAN DETECT AND ADJUST FOR THE USE OF NON-RECOMMENDED FUEL.

 

first - why do you keep restating what I have already said? read my earlier posts. especially this one, earlier in this thread....
but the simple fact is -- on the default timing map you are more likely to get momentary knock with 87 octane b/c the map is optimized for premium. on the safe map you will not (unless you have serious internal engine problems). why is this so hard to understand? why do you challenge it?

second - how in the world would you know if the emergency retard is fixed? you have not obeserved this, and the FSM doesn't say this -- but I'm the one who suggested it in the first place, based on my live testing results (read the posts). to be clear, I don't know if it is indeed fixed, but it looks like it could be, and I still maintain that it would constitute a different mode and a different map. why is that so hard to understand?

third -- the CEL *NEVER* illuminates for a faulty KS (you are wrong there), or knock, or anything KS related - I've been clear on this. where did I ever say the CEL lights up for knock?? please show me. this is one area where the FSM is clear, and anyone who has ever had a bad KS knows this. and so does the EPA.... http://www.gatewaycleanair.com/mechanic/air6_3/dtr.htm

 

I don't understand why you can't grasp the concept of an emergency, but regardless if the emergency retard is fixed or not, it is triggered by DETONATION, (knock) which is a destructive event.

The best way to avoid DETONATION (knock) is by using the recommended fuel, period.

Do you know why?

 

have you completely lost it? what did I say in my earlier posts, in this very thread...
have you forgotten how to read? I am the one who has been preaching the emergency line since early in this thread, not you.

and do you not understand that a faulty KS is also causes the ECU to go into "emergency" mode?? (aka "safe" mode). woops, there's that word again....

 

perhaps you read item 7 in post 62 in this thread before you accuse others of not being able to read.

 

I'll accuse you all night long. you are talking in circles about things that have already been discussed to death, and you don't seem to understand what you said in item 7 of post 62 (b/c you later claimed that it would throw a CEL! - wrong). your posts have turned into a waste of the resources of this board, and you need to learn when to stop. I am here to help you learn.

 

Where did I later state later that it would the SES would light?

Stated on page EC-388 of 2001-2002, EC-323 of the Maxima FSM, and page EC-249 of the 2001 Altima FSM:

"The MIL will not light for knock sensor malfunction."
__________

It lights for a circuit problem.

I hope that everyone else is enjoying this...

 

uhhh, you said it right here, about an hour ago...

the only KS code there is is P0325. it is trigger by voltage out of spec (which could be a wiring problem or a faulty KS), and it does not set the CEL. you are wrong again.

now please stop with this nonsense before you destroy what little bit of credibility you have left.

 

ok guys chill out, lets meditate or something -- hehe-- basically i am not going to change my KS (i have the ghost code) and here is why:

I cant justify purchasing premium at the prices that are happening right now so even if i do replace it i will use 87 and it will retard things again (or not, if there is not knocking at 87 which i dont think there is now anyway)so there is no point.

yes its there to protect the engine but i cant run 91 and that will never change

 

well andrei, I tried giving him an out several times, but he just kept coming with his misinformed posts. normally I would just ignore these things, but when a post contains false information it needs to be corrected, otherwise other people go to the last post, read it, and cling to those misconceptions. and that creates many of the problems we see here.

 

Jeez! I think we've come full circle here. The FSM explains what happens with a failure of KS and/or the circuit.......it sets the code immediately and that's it. If it did anything else the FSM would have stated it. I"ll go by the basic statement in the FSM "the ECM retards the timing to eliminate the knocking condition". The real caveat here should be, that the kind of pinging that comes up somewhat regularly in the forum, seems to be the off idle, part throttle, low power kind, that in fact is not going to damage the engine (I'm not talking about detonation caused by preignition here). Nissan addresses that in the Owner's Manual. AND by the way........the KS/ECM circuitry doesn't prevent THAT pinging don't forget. The problem is that the severe, engine damaging kind of detonation occuring under high loads and at high power may not be heard by the driver because of regular engine noises, road noises, other traffic and such. I suspect that"s when the KS really may have to do it's job. Vibration sensors like the KS are "tuned or calibrated" to sense or "pickup" only certain frequencies, and I gotta believe that the frequencies of vibration resulting from any detonation may be influenced by the firing impulses of the engine, so RPM may be part of this. We know detonation "control" during acceleration is catered for by the system "program". Because we know that the engine was designed to operate "out of the detonation zone" (yes, I turned it around) when using the recommended fuel, I personally think that if you drive at all aggressively, then stick with the recommended "premium" fuel. If you drive "sedately", in the cooler climes, then you maybe can get away with the regular.

 

no worries man, its a good thing. i understand that ur patience must run out sooner or later, i like this site for the information, directions, and pictures of peoples cars,mods and maintenance items. but sometimes people here complain too much.

if i dont like a post i skip it i dont comment and say something like " this thread is stupid go search or read the stickies" ect...

but correcting posts that missinform people must be annoying over and over but its a good thing non the less

 

so are you saying that a faulty KS has no impact on ignition timing? just because the FSM doesn't explicitly say so? if so, you are mistaken. I've addressed this at least 5 times in this thread. and it has been documented many times, by many other people. there's even a sticky about it in the 4th gen forum that I just found -- http://forums.maxima.org/showthread.php?threadid=233739 -- and to my knowledge 5th gens are no different.

again, I invite you to get an OBDII scanner and run the tests yourself. then you will have an informed opinion.

and again, you might explain how, in your view of things, the ECU prevents detonation when the KS is faulty. I mean, you don't really think nissan engineers would leave the engine vulnerable to knock and then choose not to set the CEL do you?

good grief I feel like a broken record. how many times can this be repeated in one day?

 

I stand corrected. I found the reference in the troubleshooting chart under "hesitation/surging/flatspot and the KS circuit is No. 2 on the hit parade of possible causes, which indicates to me that when code 0325 is set that the ignition advance curve is modified (at least retarded to some degree). BUT.............because it's not a perfect world, which includes engine variables and other variables affecting octane ratings and octane rating requirements, and because of the info out of the FSM and the Owner's Manual I'm still sticking with AKI 91 octane fuel. You and anybody else who uses regular, don't complain when you fail the KS. I'm suggesting that if you are causing it to be used as the retard "driver" you may just cause yourself more grief.

 

finally a sane response from someone.

well, I know you're not referring to me, b/c I have already covered this, earlier in this thread...
side note -- I spent the early years of my career designing piezoelctronic circuitry for cell phone RF filters. this is the same basic technology the KS uses. my opinions about the durability of the KS, and the root causes of failure, are based on my engineering experiences and my own KS breaking after a single tank of regular fuel when I had always run premium. I was not surprised when it happened.

now, I read through stevetec's sticky a bit more, and his comments and conclusions are very similar to mine (especially about "safe" mode and "safe" map). he actually thinks there are multiple maps for the various conditions -- and he might be right. his timing results are a bit different than mine - I saw more advance at cruising speed, and less advance under hard accel. he used a data logger and was able to print out his results. I had to read them in real time from a scanner (with some help from my fiancee), and they jump around a lot so the best I could do is note general ranges. so I'd say his results are more accurate than mine, but they generally confirm the same phenomenon. and I don't agree with him that it makes a big difference in power -- I personally didn't notice it, even though I could visually see the difference in timing. but he has a 5sp, and I have an auto. and I don't race my car at all, so I probably wouldn't notice a 10% power difference anyway.