High altitude

[denver_dave]

My xj seems to be running a bit weaker now that I have brought it to denver, need I get it tuned for higher altitude? What needs to be done?
thanks

[kubtastic]

I don't think Electronic Fuel Injection needs altitude tuning... just my intuition. I also lived there for a while and got the best mileage ever with 85 octane at 7,000 ft after bringing the XJ from CA.

[drifto77]

Since higher altitude = thinner air. (less air to suck into the motor)
Can you say "supercharger"???

Mine was lacking a little power when I went up there also.
I have heard that you can run a jumper wire somewhere for high altitude's but I know nothing about it.

[old_man]

You will always lose power at altitude. It is because of the lower pressure. Jeeps sold locally come with a high altitude CPS, which advances the timing a few degrees and helps out.

[Wil Badger]

wouldn't anything newer than Renix be taken care of in the computer?i know it should be atleast in an OBDII computer .

[WB9YZU]

Yah, I don't get that either. Use a lower octane gas, and advance the timing? Huh?

Anyway, I would think that even the Renix system should be able to compensate within reason as it's all MAP and oxygen sensor loop.

Fact is that no matter what computer you run, you will have less power available, because there is less oxygen available to make a proper mixture.
Depending how high you go, the power reduction can be really annoying. Also figure into the mix that the "hills" are a little steeper and carry on a bit longer in the front range. With that in mind, my XJ with stock gears and 31's seems OK in Denver. It's going up into the tiny hills west of Denver that I really notice the power loss ;)

I'd be hard pressed to remember where but I remember hearing the figure of 30% power loss at 9K ft bantered around somewhere. Seems about right from a "seat of the pants" standpoint.

,Ron

[JJacobs]

I've heard it's 25% at 5000 feet. A few months ago I saw a density altitude reading of 14,500 feet on a 100 degree day, at 5000 feet physical altitude. That's not good for power to say the least.