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question about effects of altitude on FI

With modern FI engines, does altitude effect them as much as it does the old carbureted engines?

With the carbureted engines, there were two problem that I know of when going to high altitudes. One is that the air is thinner, so some power loss is inevitable without supercharging. The other is that with fixed ratio jets, the mixture became was more rich at higher altitudes.

FI fixes the mixture part of the problem (I think). But then, we're still left with thinner air. But, I think the engine will still run better with mixture control being constantly tailored to match the altitude. Is this right?

Reply to
RB
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No, because as you guessed, half the problem -- the mixture going rich -- is eliminated. In fact, more than half the problem is eliminated, since many engine management systems can increase the spark advance, giving back some of the power lost to thinner air.

However, there is still considerable power loss to thinner air, unless you're bringing thicker air with you in the form of a turbocharger or supercharger.

DS

Reply to
Daniel J. Stern

As far as fuel mixture, the system will automatically compensate for changes in barometric pressure - GM systems, at least, measure the MAP reading when the key is first turned on. I believe they also update the barometric pressure at wide-open throttle as well.

I've heard this can cause problems sometimes when the vehicle is driven through a large change in altitude without the engine being shut off at some point - it may run badly until the engine is restarted.

Reply to
Robert Hancock

Correct. Ford, Chrysler and most if not all of the imports do likewise.

More common to see if the vehicle is driven from high altitude to lower altitude since there is less likelyhood of going WOT to initiate a BARO update.

Reply to
Neil Nelson

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