With the warmer weather coming around, I'm starting to drive around with the windows down just so that I can here the exhaust. Recently I've noticed detonation occuring in certain circumstances. While in 3rd or 4th gear with RPMs at about 1500, if I give it a little gas, I can slightly hear the engine knock a few times. If I give it moderate gas, I can definetly here it (louder and many more times). At first I thought it could have been bad gas (Shell), but switched to Chevron and I still can here it (93 octane from both vendors). The powertrain is completly stock (besides an K&N drop in). There is nothing else abnormal (no dumby light or excessive oil burning).

Before I get flamed, I know that some people don't cruise with an RPM as low as this, but realisitically, I don't think 1500 RPMs is too low to cause the engine to ping. Am I wrong?

Perhaps bad break-in procedures may have caused this? When I bought the car, there was about 100 miles on the odometer. The dealership had mentioned that the car was a dealer trade from another dealer about 100 miles away. I'm wondering if the driver could have done something to cause this (pushing engine hard or driving at constant RPMs on the freeway).

Besides knowing what may have caused the engine begin knocking, is the detonation a sign of things to come (shortened engine life)?

I'll be seeing the dealership within the next couple of weeks (on a different issue) and would like to be somewhat prepared for the conversation on this.

Any constructive critism/help is appriciated.

Thanks

 

Actually, octane rating is 91.

 

Engine knocking in IC engines were eliminated with the addition of electronic "Knock" Sensors that sense this condition and adjust the timing of the engine accordingly. Say you add a really low octane, the engine knocks, the sensors determine this, and automatically change the timing. Altitude and air density have something to do with knocking too, but not in WA and with a newer car. Unless the person who drove the car before you drove the car like crap, that shouldn't make a difference.

I'm thinking that the knocking you're hearing may be something else. Check to see if you ran over someone and they're stuck under the car and trying to get your attention.

David

 

you sure its not your injectors pulsing they are very audible at low rpms and could be mistaken for knocking

 

Thanks for the input PoWeRtRiP.

Don't think it's the injectors. If it were the injectors, I should be able to hear the knocking all the time (at all RPM/Load/gears) shouldn't I? I don't really know for sure what the injectors actually sound like, but I do know what engine knock sounds like when using bad gas. This definetly sounds like I was using bad gas.

I should also mention that the pinging is more pronounced when going up a slope, no matter how steep of a slope.

Do you hear your injectors?

 

I would have thought the "knock" sensor would prevent the knock as well. hmm...
Possibly a bad sensor? would have assumed the dumby light would come on..

Nope... Nobody under the car. Would have assumed this would cause the knocking to be more pronounced when the car is stopped.

 

The Nissan Knock sensors are only active above 2000 RPM.(straight from NNA's mouth...)
Loading the motor in 3rd or 4th at 1500 will create a detonation problem as the ignition tries to advance to increase power but the increase can not overcome the gear ratio of the drive train and the knock sensor is inactive.

 

P.S. This is very bad on rod bearings...

 

How on earth can you hear the injectors pulsing from inside the car - if you are hearing that, you must be Superman!

On a more serious note, bring the car to the dealer and have them look at it; it's your best bet. The car should not knock or detonate at all under ANY circumstances, even with significantly more mods than you have

Adam

 

LOL Oh man, good one.

If you're loading the engine down at higher gears at low RPM's like that you are putting a lot of stress on your crank and rods. Just so you know.

 

Shell gas is not bad, It's one of the best ones out there!!!!!

Just my .02 cents.

 

I noticed that the other day too - my car loves shell...does not seem to like Mobil.

 

My car does the same from time to time. If I accelerate at low rpm in 3rd or 4th, I get a metallic "ping" sound. It's hard to describe the sound. You know when you drive an older car on a hot day and you get out, you hear what sounds like a piece of metal "pinging" the exhaust pipe. I don't hear it consistently just when I slightly excelerate at low RPM in 3rd or 4th. It's very prominent when you're next to a wall or barrier to richochet the sound. I took it to the dealer and VOILA.....can't reduce the problem. My mods include AEM intake, Borla exhaust, and JWT flywheel.

 

Probably exactly the same issue I'm having. Of course you can't repro it for the dealer. Murphy's law.

 

The tech actually told me to switch to 91 octane instead of 93. Unfortunately the majority of stations here in Tampa only have 87,89, and 93 so that wasn't an option.

 

That's strange. From what I understand, above required octane ratings doesn't help performance, but doesn't hurt either. Not true?

 

Theoretically it doesn't "help". Whereas lowering has an adverse effect and it can damage. This is why I have always put the highest available octance in my area i.e 93. Lower octane gas has a higher burn rate which can cause detonation or "knocking" because it has smaller amounts of octane (87 Octane means that the gas is 87% pure octane and 13% heptane or n-heptane) whereas 93 octane has higher amounts of octane so it can withstand higher compression before ignition. If your car was designed to run on 87 or 93, putting 103 in it will do nothing. The higher octane gas like 103,112 is for engines with higher compression or FI.

 

Again, strange. Why would a tech recommend going to a fuel more prone to detonation to solve detonation?

strange...

Tech just saying things to get you off his back? Telling eager ears anything? Obviously, I don't trust Nissan or their techs (a different story...).

 

True

 

This could be valve train noise! Have the dealer check this out. One of your valves may be out of adjustment.