fi tuning clarification

I was reading a review on the '14 yz450f in one of the magazines. What has me confused is that they had mentioned how the stock mapping was lean on a hot dry day and would therefore be ubber lean on a cold humid day. I understand how that statement would apply to a carbureted motor but with an fi motor the sensors should allow it to compensate for changes in environmental conditions. This should result in no change in how lean the bike runs in different weather correct?

The fuel injection system that the modern dirt bikes use is anything but modern.  I can speculate all day long on the reason for that but I believe the simplest reason is to keep it as simple as possible yet still run fuel injection.

 

In order for the engine control unit (ECU) to adjust for an air charge that is more or less dense, the system is missing a key sensor, an oxygen sensor. (o2 sensor) A mass air flow sensor would also help, but again, as you add sensors things start to get more complicated.  That's the last thing we need is our dirt bikes to be complicated, right?

 

These bikes do adjust for temperature changes and altitude changes but they do not adjust for density changes.  Such as humidity changes or porting, cam, exhaust, or intake changes.  Basically anything that can add more or less air to the intake charge that the already attached sensors can't account for doesn't get accounted for.

These bikes do adjust for temperature changes and altitude changes but they do not adjust for density changes. 

 

The statement above is an oxymoron. The system cannot compensate for altitude unless it is capable of sensing altitude as air density.  (EFI doesn't use GPS, so barometric pressure is the only way to find out)

 

The system has a barometric pressure sensor that compensates for altitude.  It also manages fuel based on intake air temperature.  When first started, the system checks these values and adjusts for any changes.  It will not readjust on the fly in real time, exactly, but will recheck the parameters at set intervals to see if there has been a change in the environmental factors significant enough to require an adjustment, and it will make those adjustments when rquired at that point.

 

Being lean on a hot day does NOT translate into being even leaner on a cold day, or richer at higher elevations.

 

Oxygen sensors and mass air flow sensors do not play a part in the environmental adaptation of more sophisticated systems, either.  They are used for fine fuel trim on the road under cruise situations, and at WOT, the oxygen sensor is taken out of play.

So then it is neccesary to re map for say summer/winter?

Generally not, no.

 

Bear in mind that applies only to AF ratio, not timing, optimum settings for which can be affected by ambient temperature.  The other wrinkle in winter riding for the EFI YZf's is that without a thermostat, they won't run the water temperature up far enough to get themselves out of the cold start/warm up mode, and can run excessively rich because of it.  The simplest cure has been to cover one radiator with cardboard, or tape, etc.

Generally not, no.

 

Bear in mind that applies only to AF ratio, not timing, optimum settings for which can be affected by ambient temperature.  The other wrinkle in winter riding for the EFI YZf's is that without a thermostat, they won't run the water temperature up far enough to get themselves out of the cold start/warm up mode, and can run excessively rich because of it.  The simplest cure has been to cover one radiator with cardboard, or tape, etc.

Yes, Yamaha sometimes covers part of   a radiator at a night supercross because of this.  Very good info Gray!

Yes, Yamaha sometimes covers part of   a radiator at a night supercross because of this.  Very good info Gray!

Nobody wants to use a thermostat in the event that it fails and will not open......

Edited by Greg Pennsiltucky Lykens

Nowbody wants to u

 

Nobody wants to use a thermostat in the event that it fails and will not open......

When did anyone say a single word about a thermostat?

When did anyone say a single word about a thermostat?

Gray did.   

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