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Discussion Starter #1
After researching the 2* advance threads I don't remember this potential issue coming up.
Went to my dealership for some cosmetic warranty work and have been talking to my service manager about doing the advance. He told me that I was the first he knew of that had requested it for a Titan and had some reservations about it so he checked around and had his tech call the dealer tech line at Nissan.
Consensus being that Nissan said any engine damage or failure related to the advance would not be covered. I remember reading about the fed act that covers this issue and told my service manager about that particular issue coming up on the forum. Advance is within Nissans parameters and should not void any warranty. He said he was still willing to do it but wanted to warn me of nissan's position on the issue.
So the tech hooked it up and set the timing advance and then took Alpha (?) readings to see the difference. He told me to make sure to use 92 octane in the future. I told him many are running the advance on 87 oct. with no pinging. His concerns were for the cat converters. His opinion after looking at the alpha readings was that exhaust temps going through the cats were higher with the advance and would probably shorten the life of the cats. Possibly lead to a failure sending pieces into the intake and making the engine go kaput.
I have read about this very thing on other treads here BUT never tied to the 2* advance.
The tech told me the cats sucked on these to begin with and that he had a customer with a maxima get a 2* advance and gave him the same warning about using 92 octane. Customer did not head his advice and higher temps fried the cats which came apart sending pieces into the engine and killed the engine. Now I know the two vehicles have very different engines, but here was his point. The 92 octane burns more efficiently leading to lower exhaust temps into the cats.
The slip off the consult II shows
A/F Alpha-B1 @ 93% before 101% after advance
A/F Alpha-B2 @ 96% before 103% after advance

I am no mechanic, and have no idea what these mean, but I am planning on keeping this truck till death do us part and want to avoid anything that could result in long term issues. He used these readings as evidence that the temps at the cats was higher after the advance. He also said something interesting regarding the actual degree of advance. He said the Consult II when prompted to advance timing 2*, actually bumped it 5 degrees. Can anybody explain that in layman's terms?
Fearing the extra cost of 92 octane canceling any gain in mpg I was hoping to achieve, and his take on the cats being abused, I opted to not advance the timing and had him return it to factory settings for now while I researched this issue with the forum.
I would really appreciate the technical wizs here chiming in on his views. What do you think? The tech made it sound logical to me.
My utmost gratitude to everyone for reading a long post and extra thanks in advance for any responses.
Merry Christmas everyone!
 

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There's no way it was bumped five degrees. Hundreds of members have been running the advance for tens of thousands of miles with no ill effects on 87 octane. Personally, I run 89 with it because that octane performs well with my particular setup. Alpha AF adjustment is just that till the ECU learns the new parameters.
 

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That's an interesting read, however I'm not buying the relationship between 92 octane and lower EGTs and here's why...

First, 92 octane contains the same amount of energy and burns at the same speed as 87, the only difference is its ability to resist compression ignition and ignition from a secondary source (Hot carbon or other hot spots in the combustion chamber). It takes more heat to ignite, therefore it doesn't ignite at the same point as 87 would, which delays ignition just enough to not ping.

Second, the 2-degree advance is not a static setting. The ECU will retard the timing if it detects spark knock, effectively cancelling out any advance that was programmed in. Often times you won't hear the pinging so you may not even realize the timing has been retarded. Folks running 87 with the 2-degree advance likely aren't realizing any benefits of the tune as the ECU will learn and run in the most efficient timing and fuel maps. Think of it like a rat, food, and shock training. The ECU is the rat, at first it will push the red button (timing advance) and get a shock, over time the rat learns and presses the red button less and less until it has been trained to operate where it doesn't get hurt. You can't reset a rat, but you can reset the ECU if you make any drastic changes, such as 2-degree advance and switching from 87 to 92 octane. Switching to 92 octane alone won't give any immediate results since running with 87 has trained the ECU to not test the other maps as often and re-learn. This is why it's best to reset the ECU and why a lot of people experience an immediate difference after doing a reset.

Third, cats run hotter than the exhaust coming out of the engine. This is due to the chemical reaction that takes place and makes them work, however they will overheat if too much unburned fuel is fed to it. Since 87 burns easier than 91/92 you will generally see more unburned fuel when using 92 octane when it's not needed, meaning if an engine runs at max advance without pinging when using 87 octane gas then running 92 octane will have a negative effect and will potentially send more unburned fuel to the cats, raising their temperature.

I think what you'll find is that the folks with the blown cats are the ones that have done more than just the 2-degree advance and generally run their trucks hard to get the most enjoyment out of the truck. That being the case, it is impossible to conclude the 2-degree advance caused blown cats. There are too many variables (CAI, exhaust, TBS, timing advance, etc) to be able to single out one of them as the cause unless you did a controlled test.
 

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Yahooligan said:
That's an interesting read, however I'm not buying the relationship between 92 octane and lower EGTs and here's why...

First, 92 octane contains the same amount of energy and burns at the same speed as 87, the only difference is its ability to resist compression ignition and ignition from a secondary source (Hot carbon or other hot spots in the combustion chamber). It takes more heat to ignite, therefore it doesn't ignite at the same point as 87 would, which delays ignition just enough to not ping.

Second, the 2-degree advance is not a static setting. The ECU will retard the timing if it detects spark knock, effectively cancelling out any advance that was programmed in. Often times you won't hear the pinging so you may not even realize the timing has been retarded. Folks running 87 with the 2-degree advance likely aren't realizing any benefits of the tune as the ECU will learn and run in the most efficient timing and fuel maps. Think of it like a rat, food, and shock training. The ECU is the rat, at first it will push the red button (timing advance) and get a shock, over time the rat learns and presses the red button less and less until it has been trained to operate where it doesn't get hurt. You can't reset a rat, but you can reset the ECU if you make any drastic changes, such as 2-degree advance and switching from 87 to 92 octane. Switching to 92 octane alone won't give any immediate results since running with 87 has trained the ECU to not test the other maps as often and re-learn. This is why it's best to reset the ECU and why a lot of people experience an immediate difference after doing a reset.

Third, cats run hotter than the exhaust coming out of the engine. This is due to the chemical reaction that takes place and makes them work, however they will overheat if too much unburned fuel is fed to it. Since 87 burns easier than 91/92 you will generally see more unburned fuel when using 92 octane when it's not needed, meaning if an engine runs at max advance without pinging when using 87 octane gas then running 92 octane will have a negative effect and will potentially send more unburned fuel to the cats, raising their temperature.

I think what you'll find is that the folks with the blown cats are the ones that have done more than just the 2-degree advance and generally run their trucks hard to get the most enjoyment out of the truck. That being the case, it is impossible to conclude the 2-degree advance caused blown cats. There are too many variables (CAI, exhaust, TBS, timing advance, etc) to be able to single out one of them as the cause unless you did a controlled test.
92 octane fuel burns slower and cooler than 87. That's why it is more resistant to detonation. The fact that it burns slower is why too high of octane actually loses power. Which leds to the argument that unless your engine needs higher octane you might not make more power with it.

So I agree with the tech that higher octane will result in lower EGT's. But this reasoning is based on only doing the 2*advance.

With my Fram boost CAI (AEM) and 2* advance I get pinging/detonation at part throttle with 92 octane until the engine gets good and warmed up. So I agree that it is more than just the 2* advance and in my case is most likely the CAI.

When I got my truck dynoed the tech checked the A/F ratio because Fram boost/AEM's tend to run lean according to him. Which is most likely why I get some detonation when running cold/lean. Once warmed up I get 0 detonation and the truck runs like a beast.

Just my .02
 

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Wildmike said:
92 octane fuel burns slower and cooler than 87. That's why it is more resistant to detonation. The fact that it burns slower is why too high of octane actually loses power. Which leds to the argument that unless your engine needs higher octane you might not make more power with it.
Suggest you read up on octane ratings as higher octane fuels do not burn slower based on octane. The AKI affects the point at which the fuel ignites but it does not affect the rate at which it burns. The AFR *will* affect flame speed, AKI will not. It doesn't burn any cooler, as I said 87 and 92 contain the same amount of energy. If 92 burned cooler that would translate into less energy and less power and that is not the case.

I stand by my initial statement. :cheers:
 

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I was just told (thread in General Titan Discussion) that after five restarts of the engine any timing advance will default back to original. WTF - I wish there was a way to just go and get something done without a bunch of know-it-alls telling you their reasonings why it won't work.
 

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Discussion Starter #7
So how likely is it that the 2* advance and the resulting higher exhaust temps going into the cats could damage them?
 

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It is true that octane rating does not affect burn rate (deflagration). As far as whether or not there are energy differences between fuels of different octane ratings, that is an "it depends". Since different formulations that result in octane changes do affect the specific gravity, and therefore the specific energy of the fuel, you could say there is a difference. How much is pretty much negligible for the intents and purposes here.


As far as the 2* advance affecting the cats? I would say not enough to cause failure. I've ran my truck with an over-rich tune (cruise AFR's in the 10's) for thousands of miles without issue. Same with my Maxima when the thermostat stuck open. Didn't even get hot enough to blue the heat shields on the cats which would be the first sign of an overheating issue.
 
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