Altitude? What the heck happened? (or is happening)

I've not been focused on tuning like I should be and the last thing I remember doing to the bin was upping the spark table a little bit.

My gas mileage seems to have dropped, but I can't be for sure and one thing is that I am frustrated as it seems like the more I look at the gas gauge, the faster it moves to the empty side.

In any case, I drove to a friends house to look at some old radio equipment and logged that drive to and from.

The altitude where I live is 2750 feet. His place is about 3300.

When I went to leave, I let the truck idle for a few minutes to show him the TBI system and laptop monitoring it.

Logs are attached.

Why was the truck idling at his place so lean?

to his house is the "to eds" and back home is the other.

600 foot elevation change is not that much. May find time to look at log later but your probably just observing something that is always happpening during a warm up?

As for fuel mileage... it's winter here and my mileage drops horribly. Warming up and idling makes it worse.

BLM of 139 is not really lean! Your still warming up, it may be the 600 elevation change if you could compare exact situation at lower elevation? But the O2 sensor is doing it's thing very well. Your very close to perfect... you can fine tune these things ever day and it will change with weather and tempreture.

Mark, I did not think the engine was that cold.

I started the log at 60 degrees, just as I have been doing every other time.

In the start of the log from his house, you can see my temps at 185 and the blm is at 139.

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Originally Posted by damanx

Mark, I did not think the engine was that cold.

I started the log at 60 degrees, just as I have been doing every other time.

In the start of the log from his house, you can see my temps at 185 and the blm is at 139.

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IIRC they started at 16x*f and were at 139 BLM too! Your really worried about nothing here, over analyzing again. I saw the temp climbing to the 180s as you said, but even then the intake is not fully warmed up either.

11 points off perfect 128 when cold and warming up? Not an issue! When you hit the limit of 172 then we will talk about lean...

Do you have a warm air tube from exhaust to Cold Air Intake? This also helps in warming up fuel, air, intake and helps MPG when winter temps set in.

theres no air temp correction with the 747, right?

Nope!

so maybe the drop in temp at the higher alt would cause some leaning? I live at ~2400 and my work is at ~3300ft but in the winter the temps vary by at least 10-15*F, more at night or early morning. Higher alt being cooler of course

tables max -min blms at key on , yours is set 138 that is where it goes till every thing is warm, I set mine 130max 126 min.

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Originally Posted by ony

tables max -min blms at key on , yours is set 138 that is where it goes till every thing is warm, I set mine 130max 126 min.

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I believe that is for "stay alive memory" and that saves the last average BLM value used in that cell after power down. So if that cell was 136 at shut down then it will use 136 until CL correction changes it iirc.