Sounds like you are experiencing what is called "run on." You have turned off the engine but it keeps running without any spark. What happens in "run on" is that deposits in you engine are hot enough to ignite fuel. There are a number of solutions to correct "run on" -- in the order I would try them:

- Use premium gasoline to reduce the tendency of the gasoline to ignite from the heat of the deposits.

- Use a fuel injector cleaner such as Techron to try and clean the deposits from your engine. Techron now has a more expensive but more extensive cleaner for more than the injectors, so try that.

- Reduce the engine's idle speed to reduce the amount of fuel that is being fed to the engine when you turn it off.

- Take the head off of your engine and clean the deposts with a solvent -- or have the dealer or a mechanic do this.

 

How loud is this banging? Does it sound like its still trying to run, or is it just light metal pinging sounds? If it is light, its just the metal in the engine cooling.

And just put it in park. I couldn't even imagine why you would need to hold the brake to shut off you car.

 

it sound like metal pinging doesnt sound like an engine .......alright so i guess everything is ok....hmm does the brand of gas you get matter......say BP, EXXON, SUNCO, HESS ETC.......and what would you people perfer if there is a differences........in addition say when you fill up ur tank first 89 then fill it up with 91 .....does the octane mixes? or the 91 stays on top of the 89....my dad is a punk, he alway be filling mah thing up with 89 octance.......when would u recommend using the techron too? every wut mileages? thanks a lot guys

 

The gasoline you pump into your tank mixes fairly well, so would not worry about it.

I would not worry so much about gasoline brand (there are small differences) but go for the 93 octane to reduce any run-on.

I put Techron in my tank about 500 miles before I'm due for each oil change. In your case, you propably should do the first treatment as soon as you find that 93 octane does not fix the problem. After you get the run-on problem fixed, I would go to the plan of using Techron just before each oil change.

 

I beg to differ....
1999 I-30 two years ago wife took on trip to Texas...first fill up used 87 octane and "only" put 370 miles on the tank...second tank only got 290 miles and was on empty...and so on. Got home (1,500 miles) and told me the car got lousy mileage, and she rarely drives over 65...all on the interstate and one jaunt up US 75 between Topeka and home on 2 lane...trip average 21.2 mpg
I asked her what kind of fuel she used, and all she could say was-the cheapest I could find. I took the Infiniti away from her...
Last summer she took it to Tulsa and used higher octane fuel, returned consistent 28-29 mpg per tank and overall 27.55 mpg over 1,200 miles. If you even think using lower octane fuel is saving you money, think again.
The difference in costs (@2.35/gallon vs 2.10/gallon) is $4.00 when using the "good" stuff. (16 gallons). The improved mileage is saving about 6 mpg, so take 6 miles time 16 gallons and you get 96 FEWER miles per tank...now divide by 22 (benifit of the doubt) and you get 4.36 additional gallons needed to travel the same distance. Now for the proof...4.26 gallons times $2.10 per gallon is...$8.96 ADDITIONAL FUEL COST, resulting in additional expediture of $4.96 just because you didn't want to buy higher priced fuel. Do the math...

 

Respectfully, you've been reading too much of Consumer Reports. . . These statements are correct, only if your car is designed to run primarily on regular gas. Many engines, however, are designed to run OK on regular, but deliver improved performance with the use of higher octane fuel. The owner's manuals in cars with these engines will have language something like, "use of 87 octane fuel is permitted, but use of 91 octane or higher is recommended for improved performance". In these cars, the knock sensors and the ECU team up to keep the ignition timing as far advanced as the chosen fuel will allow. With premium in the tank, spark timing will be significantly advanced, resulting in higher hp an torque available. When regular is used, the ECU will retard timing to suppress knock, which will reduce output and efficiency. The current VQ35DE engines (as well as the current crop of V-6s from Toyota too) are set to run this way. But in the end, it's a matter of choice -- if the performance difference doesn't matter to you, go ahead and use 87. Personally, I can't stand how my VQ35 feels when fed 87, so of course, I use premium. By contrast, the 2UZ V-8 in my wife's Toyota Sequoia is not programmed to run this way -- it does fine on regular gas, and no better on premium, so in cases like that, premium is a waste.

 

Silver:

I'm hoping he's talking about just the sounds of hot metal cooling and contracting, as opposed to true "run on". True, old fashioned run on should only be an issue in carbureted engines. With FI, the supply of fuel is cut when the engine is turned off. Decades ago, my Mom drove a 73 Dodge Dart with a carbureted 225 cid slant-6 engine. It was actually a decent car, except it would have awful run on (a/k/a "dieseling"). After turning the key off, the engine, still turning but trying to slow to a stop, would continue to suck air through the carb. This was all that was required to draw fuel through the jets in the venturi, thus creating more burnable mixture, even though the key (and ignition system) were now off. Once this got drawn into the combustion chamber, hot deposits and compression were enough to fire it off, despite the spark plugs being inactive. This of course, kept the engine turning, and the cycle repeating. This was an ugly, stinky, smoky, noisy, and scary phenomenon. We had owned a 68 Dart before, and it was a stick (3 on the tree, no less...) so you could force an end to run on by putting it in gear and dropping the clutch. The 73 was an auto though, so much harder to stop. Flooring it in neutral and then turning the key off would often do it (my retro theory: massive air/fuel flow was enough to cool the deposits sufficiently to break the "diesel" cycle, but who really knows). Ooops, this is getting long. In short, if his fuel injected car is truly "running on", he's got issues far more involved than fuel choice.

 

Tork: I believe you are correct about the "run-on" that I thought might be happening. I forgot that the injectors and fuel delivery system cut off when the ignition is turned off in the Max.

Now to your post on Premium vs Regular: I did not know anyone here was arguing that you do not get better performance from your Max burning premium. Even a confirmed regular gasoline burner, like me, acknowledges that the performance from the VQ on premium will be better. The Owners Manual also says this is the case.

As far as getting "significantly advanced" spark timing burning premium -- I guess that depends on your definition of "significantly." There is no doubt that the spark timing will be advanced burning premium, but only up to the limits of the system. There is no doubt that this greater spark advance will increase both the Torque and HP output of the VQ engine vs burning regular.

You then say: "When regular is used, the ECU will retard timing to suppress knock, which will reduce output and efficiency." I'm not convinced that the VQ engine's efficiency is substantially reduced burning regular. There is no doubt that it is reduced somewhat, but how much is the question. I will be doing a highway test over Christmas and New Years on a drive back and forth to Chicago that will answer the question of how much the efficiency is reduced for my Max's VQ engine.

 

Silver:

I was responding particularly to Bones who had unequivocally stated that there was no performance or efficiency gain with premium.

Truth be told, I think the performance aspect is much more pronounced and noticeable than the efficiency part. On those occasions when I've experimented with regular (most recently in the aftermath of Katrina when you were lucky to find any gas and almost all of it was 87), I definitely notice the performance aspect, but have not noticed any significant change in mileage. FWIW, I noticed the same effect with the V-6 Camry I owned previously (uh-oh, does that admission set me up for a permaban... ). In both the Camry and the VQ-powered G, the engine feels sluggish to me on 87 (my car is also a 5AT, which may magnify the effect). I also freely admit I'm quite sensitive, picky, and particular about power. Many drivers may not notice the difference or care, and that's fine. That's what having a choice is all about anyway. Hey, we're all happy members of the VQ-power club -- we could feed this engine tanks full of weasel pi$$ and still be miles ahead of the typical driver in smoothness and performance!!!

 

I agree. 85 (at altitiude) and 87 work for me. If I get enough better mileage using premium in my test, I will be using it whenever I'm on the highway, otherwise it is the cheapest (89 in Iowa with ethanol is cheaper than 87).

 

"How bad is 87 for our cars?"

I wouldnt recommend it cuz it will cause instant engine detonation and explosion......
unless thats ur thing, then why the hell not....
I save myself the explosions and lives lost by putting in some high quality 93 octane.

 

Guess my Max must be toast by now. You should tell it to the VQ powering it that continues to hum along burning 85 octane gasoline here at 6 K feet elevation. I've also been successful burning 87 octane at sea level without any of the following:

- Instant engine detonation
- Instant engine explosions
- Any lives lost !

Must be doing something right.

My Max has a 10.3 to 1 compression ratio and your 99 (I think) has a 9.5 to 1 ratio. But then you may have engine deposits that boost the octane requirements of your VQ.

 

On a practical note, two friends have 95 and a 96 maxima and it only has seen 87 octane. NOt a single drop of 91 went in.

95 max has 245 000km on it and 96 has 220 000 km and the car still runs fine. I mean, 9 - 10 years of service did not kill the car and I will bet that it will run on regular for another 2-3 years and by that time, most will get rid of the car anyways.

I would say that the members here that fill 91 octane only represent a very very small percentage. Most average maxima drivers will fill 87 octane and probalby drive a good 10 years without their engines dying on them.

 

Most average Maxima drivers do not use 87 octane; those that do are in the vast minority. I would estimate that at least 80% of all .orgers use in excess of 87 octane gasoline.

 

I started putting 93 in mine last night and I noticed the smallest addition to responsiveness also.

This is only my second tank of gas though, so I'll see if I get better mileage or not.