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TBI at altitude

84k5

84k5

1/2 ton status
Joined
May 13, 2000
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Location
Dublin, CA
How is it???

My truck is a disaster. Stock 84 305. Lots of surging, no power, runs hot. Could only manage about 15 mph @ 10,000ft on a steep grade. Not sure how steep, it was a small unmarked backroad. I understand it is going to lose a lot of power, but my dad's explorer did 45 on the same grade. I'm pretty sure I hit triple digits coming down though. :grin:

Just considering my options for when I throw this 305 in the ocean next year. :whistle:
 
TBI should be self-adjusting at altitude, unlike a carb...I would think anyway. could be wrong.
 
Any fuel injected vehicle will run the same at sea level or at 10,000 ft. elevation. Also doesn't matter if hot or cold outside temps. still runs the same. Got to love electronics. :thumb:

As far as gas mileage, i would be ecstatic to get 15mpg at anytime. Reality sets in though and considering my 4.56 gears and 8" of lift with 35's i am happy getting on avaerage of 10mpg.
 
Good. I wasn't sure how much these sytems are able to adjust. There is a big difference between sea level and 10k. I am going find a 350 TBI to swap in this sucka. That's about all I can get away with in smog nazi land anyhow. Regearing the axles should help significantly also I would think. :grin:
 
4X4HIGH said:
Any fuel injected vehicle will run the same at sea level or at 10,000 ft. elevation. Also doesn't matter if hot or cold outside temps. still runs the same. Got to love electronics. :thumb:

As far as gas mileage, i would be ecstatic to get 15mpg at anytime. Reality sets in though and considering my 4.56 gears and 8" of lift with 35's i am happy getting on avaerage of 10mpg.
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Not even close to true. At 10,000 ft, you are making half the power you are making at sea level, no matter if you are running fuel injection or a carb (theoretically). Carbs, however, do not recalibrate for the altitude change. This causes them to run very rich, and lose even more power and mileage. If two identical rigs, one with fuel injection, one with a properly set up carb, ran up I-70 here in CO (summit around 11,000), the fuel injected vehicle would be able to hold better speeds and get better mileage. Carbs have very little way of compensating for altitude (though less air pass the venturis draws less fuel, it comes no where near compensating). This certainly is one of the advantages to fuel injection, but I still have no plans to pay big $$$ and tons of time to change (and I don't mean just install, also the tuning which can be much harder than tuning a carb).
 
38377k5 said:
Not even close to true. At 10,000 ft, you are making half the power you are making at sea level, no matter if you are running fuel injection or a carb (theoretically). Carbs, however, do not recalibrate for the altitude change. This causes them to run very rich, and lose even more power and mileage. If two identical rigs, one with fuel injection, one with a properly set up carb, ran up I-70 here in CO (summit around 11,000), the fuel injected vehicle would be able to hold better speeds and get better mileage. Carbs have very little way of compensating for altitude (though less air pass the venturis draws less fuel, it comes no where near compensating). This certainly is one of the advantages to fuel injection, but I still have no plans to pay big $$$ and tons of time to change (and I don't mean just install, also the tuning which can be much harder than tuning a carb).
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Ok, so explain to me how you figure that you're making half the power. :ears:
 
You lose a lot due to the air pressure drop. I've heard 15 hp per 1000 ft, don't know how accurate that is? Someone from Denver will probably chime in.
 
I know that my TBI 350 has plenty of power at 11,000 feet. There is a small decline in power, but definitely NOT 1/2.
 
Well, I've heard of some percentage before. Something like 5% for every 1000ft. But like firefighter184 said, I've never really "felt" a difference. I suppose it may have to do with the total net change. We are going from 5000 to 10000, so maybe if you were going from 1000 or 2000 to 10000 you could feel more of a change.
 
Surging, no power, running hot are all problems that can be solved now. I wouldn't be calling any engine a POS or think about swapping to EFI if I had those problems.

Sounds to me like it needs to be gone through, get running right, then consider a course of action once it's running the way it should be in the first place.
 
hehe, sounds like our poor school bus that we took into the rockies... Has a 366 big block in it, he had the poor bus floored constantly, never once taking the gas off unless stopping or turning off the road, lol On big hills the old thing would slow down to like 10 - 15 mph, and on the downhill, get up to like 75 - 80 mph, lol
 
when i had my 91 s-10 we went to Colorado and we were going up a steep grade and i could only go 20-25mph and this happened several times while there-when i got back to Dallas i called a mechanic place and they told me it was my o2 sensor-not sure if it was i didnt replace it, but in dallas it never did it again -anybody know what it might have been ???
 
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