Solved my bad MPG

That is interesting.

What was the gap, comparing old to new?

Possibly a dud set of Denso plugs, or may be just one dud?

 

I hope it stays that way, instead of reverting back to the bad MPG.

I've witnessed numerous fixed problems turn out to not really be fixed.

 

Heat range would be my guess. You cannot hear the engine knock (pre ignition) until it is really severe, but even a very mild knock robs serious power because it is trying to push one (or more) DOWN when it still wants to move UP.

I learned decades ago on High Performance 2-strokes which are VERY heat range sensitive, that "does fit", "will fit" and "equivalent" are not the same as being RIGHT for the application. Even minor changes in heat range (same application but different brand) can lead to serious and immediate engine failures.

 

They look to be the spec'd denso SK16R11:



Yeah maybe the gap?

FWIW, our previous Civic Hybrid had 2 plugs per cylinder, and when I pulled them, there was one NGK and one Denso per cylinder.

Strange.

 

0.043" is spec, replace at 0.047" or before, but no manufacturer recommends adjusting the gap on double platinum or iridium plugs as the electrodes are VERY easy to damage.

 

Considering it can take 100k plus to change 0.003", plenty

 

Those centre posts hardly wear. If it's off, probably because someone knew better.

 

Curious if you swapped the Denso back and milage dropped or you left the NGK in?

 

Well still improved from the Denso.

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Did you disconnect the battery and reset the computer when you did the plug swap?

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Interesting. You're thinking it forces a recalibration of sorts?

 

I'd like to add here that when I replaced my spark plugs at 200,000 km, Sparkplug replacement at 200,000 km (pictures). | PriusChat the OEM ones that I removed were the NGK IFR5T11 and the ones I replaced them with were Denso SK16R11.

There was no loss of performance or MPG, and at 320,000 km the Densos are still performing as they should.

 

It definitely changes things for a tank or two of gas before it's calibrated.

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Yes, it's still a bit of a mystery (well at least to me) of exactly how it does it, but the ecu that tracks fuel consumption somehow uses "historical data" to tweak the accuracy of the raw fuel consumption data taken from the fuel injector pulses.

The raw fuel consumption data essentially just counts up the pulse widths of all of the fuel injector pulses, and assumes that they all deliver some nominal amount of flow. In practice though, the open loop behavior of the fuel injector might be a little bit leaner or a little bit richer than the nominal value and this throws off the calculation. If the actual injector flow is a little more than it's nominal value, then more fuel is delivered than what the ECU counts, so you get an overly optimistic calculation (this one seems to be the most common). If the fuel injectors deliver a little less than the nominal amount then the ecu counts more fuel than is actually used and calculates an overly pessimistic consumption (my Prius actually does this one).

While I'm not exactly sure of what data or what feedbacks it uses, over time the ecu learns and adjusts for the fuel injector inaccuracies and gives a more refined calculation. It can take quite some time (several full tanks worth at least), but most people report that it usually settles to a calculation that is just a little bit optimistic, but still reasonably accurate.