KR15DDT Recommended Octane Different in NA from EU/Asia

[Chris...]

What confuses me is that the user manuals for the KR15DDT in the US recommend "at least 87 AKI number (91 RON)", while the user manuals in Europe and Asia recommend at least 95 RON.

From what I can tell, all the engines for the entire world are made in the same plant in Japan.

So what's different?

[VStar650CL]

My guess would be the firmware. North American and Euro drivers prefer distinctly different characteristics. NA drivers generally want torque off the line and smooth operation, Euro drivers typically want an engine that will wind higher with better peak horsepower. So there may be major differences in the tuning, even though the engines are mechanically identical.

[Chris...]

I would think that the knock sensors are so sensitive these days, that if what I was hearing was knock it would richen the fuel and do other stuff to address the issue, but I do hear odd noises at times under moderate load at very low RPM. Its certainly an odd noise I've yet heard on any other engine, although not quite like the knock I'm familiar with from a vehicle from the 90s.

Just for giggles, I'm going to run a few tanks of 93 octane during this hot summer and report if the noise goes away or not.

If it does, I hope this isn't shenanigans where the marketing team overruled the engineering team, and they advertise 87 octane recommended purely because it sells more vehicles.

[V6er]

My guess would be the firmware. North American and Euro drivers prefer distinctly different characteristics. NA drivers generally want torque off the line and smooth operation, Euro drivers typically want an engine that will wind higher with better peak horsepower. So there may be major differences in the tuning, even though the engines are mechanically identical.

don't have any information on KR15DDT, but:
1) subaru tribeca had higher torque numbers on euro firmwares (I think it was 3.6 engine, not 3.0).
2) nissan t32 calibrations on qr25de seem to be worse(performance wise) on JDM/EUDM than USDM. at least when I compared acceleration 0..100kmh - our USDM one was running ~1sec faster than those from other side of word (and they had WAY less mileage - like 50-70kkm, when my USDM had 150-170kmiles).

[Chris...]

I hope so, but that's the weird thing too the listed peak power is the same.

Most of them are worded saying you CAN use 91 RON (87 octane), just that its not ideal:

"Use UNLEADED PREMIUM petrol with an octane rating of at least 95 (RON).

If unleaded premium petrol is not used, UNLEADED REGULAR petrol with an octane rating of at least 91 (RON) may be used at slightly reduced performance. However, for maximum vehicle performance and the best driveability, the use of unleaded premium petrol is recommended."

https://www.nissan.co.uk/owners/car-rep ... ne-1.shtml

I'll wait at least a couple of tanks full before I report back anything, and hopefully placebo effect isn't too strong. Texas summers can be very hot, which might be considered extreme conditions, particularly since I'm not convinced the KR15DDT in the Rogue has a super robust cooling system to handle stop&go traffic. I know people in death valley were complaining of rental Rogues that went into limp mode from overheating going up hills, although granted that's an even higher level of extreme.

I'm usually one to always say stick to the manufacturers recommendation on octane, but in this case they aren't consistent and with Nissan bleeding money, I pessimistic thinking the marketing team may have won on this.

[V6er]

remember to look at whatever data you can get via obd2 - ignition timing, fuel, fueltrims. that way you can compare and see differences.

actually - T32 had power and torque live data... though I don't it was via obd2 protocol, but via nissan ... don't know what/how to call them - pids, uds or whatever.

[Chris...]

I really wanted to wait longer, but I'm compelled to share.

Switch your 22+ Rogue to eco mode, turn the instrument cluster display to show boost gauge and compression ratio.

Accelerate lightly from a stop, ensuring that you are keeping the gauge maxed out on 14:1 compression ratio (maximum eco on the bottom), meaning you can't give it too much throttle.

If you can accelerate lightly while keeping compression ratio pegged at max eco, you will hear light knock like this: https://www.youtube.com/shorts/yXdRoxyA0DA (you'll have to turn volume up, but its the light rattling can sound)

Nissan will say this is normal because any vehicle on their lot will make this sound.

Here's the kicker, wait until your tank is almost empty and fill to the top with 93 and drive around a while to ensure you don't have anymore 87 in the lines. Now try and reproduce the test again... can't make the sound!

There's no way around it, 14:1 compression ratio is extremely high, even for a naturally aspirated engine to be running 87 octane. For comparison, the Nissan Kicks naturally aspirated engine runs 11.7:1, and turbos typically require lower compression ratios. You won't hear knock most of the time because watching the variable compression gauge, it only enters 14:1 max under very specific circumstances, and certainly not on normal to hard acceleration where it reduces compression ratio significantly and gets much closer to its 8:1 ratio on the gauge.

I'll keep watching, but I'm fairly confident Nissan lied about 87 octane for North America market to sell more Rogues at a time they were hurting for money, and that's why other markets show 93 recommended for the KR15DDT. Certainly 93 octane considerably increases fuel costs, being on average 25% more expensive. Effectively, it reduces Nissan's advertised 33mpg combined on FWD base trim to 25mpg equivalent, dollar for dollar!

[Chris...]

And to me this could also explain why so many people have zero problems with their turbo Rogues racking up miles without issue, because they drive in "normal" mode and accelerate briskly, while others say they had their engine replaced under warranty only to have the replacement also fail.

This could be explained if its just certain drivers like me that always drive in eco mode (its the first button I press every time I start up my car) and accelerate very gingerly and can brag about often showing over 40mpg on the built in trip calculator, are far more likely to enter a situation where there's knock. And when you have a variable compression setup that is really complicated with extra bearings and what not, that engine knock even though mild could cause some premature wear on sensitive components.

A problem that only shows up for certain driver behavior (at least quickly) would explain that discrepancy.

So lesson learned: don't drive in eco-mode accelerating like a grandma to maximize fuel economy, and the engine management system isn't likely to put you into a situation where there's knock, or just bite the bullet and pay more for 93 octane and be worry free.

[Chris...]

Update is that I can no longer reproduce the light knock sound on 93 octane, even with the weather being much hotter now. That said, proof in the pudding will be next tank, I'm going to run it near dry and refill with 87 octane, drive enough to clear the fuel lines, and see if I can make it knock again. Anyone else played with octane yet?

[Chris...]

Last update and I'll drop it, tank of 87 and could reproduce the knock again, back to 93 and can't, so that's conclusive enough for me and no longer going to experiment.

Furthermore, I've been informed that the KR15DDT is undergoing a major recall that could involve hundreds of thousands of affected units with many of the engines ending up being replaced due to bearing failure.

The bearing failure is apparently never catastrophic, but gradual. Symptoms of bearing failure can include engine knock, and I'm wondering if the 93 is just more resistant to that. Or if its the other way around and 87 octane is sometimes producing the knock that is damaging bearings.

What is interesting is that as part of the engine recall, they are not only going to check for metal particles in the oil but whether they decide it meets the threshhold for replacement yet or not during the recall check, they are going to retune the ECM.

Dealers will inspect the engine oil pan for the presence of specific metal debris. This inspection will be
performed free of charge for parts and labor and should take less than one (1.0) hour to complete.
• For customers with the 3-cylinder 1.5L VC-Turbo engine, if no debris is detected during the inspection,
dealers will replace the oil pan gasket, engine oil, and reprogram the vehicle’s Engine Control Module
(ECM). This repair will be performed free of charge for parts and labor and should take less than half of
one (0.5) hour to complete

What are they reprogramming on the ECM that would help slow or eliminate bearing failures? Could it be remapping to reduce the compression ratio and avoid detonation?

[VStar650CL]

Depends what you call a "catastrophe", we've seen two cases where practically the whole bottom end was spun.

Yes, I suspect the reprogram is some sort of remap, plus maybe paying more or better attention to any patterns in the sensor data which might give early indications.