Need help with High Altitude tune fix

[Pook]

Hi Guys, I'm at a rockcrawl competition in Northern California, at Donner Ski area. Car runs at idle and at slow speeds ok... but when I need to get on it and get a good hard launch its hesitating real bad.

I'm at around 7200' and the car was tuned for sea level.

I'm running a MAF and MAP sensor but no O2's.

Is there something I can do as a quick fix for the full throttle stuff? Sorry not super familar with EFI yet. The computer came tuned by Schwanke engines for me and I've just done minor idle issue tuning due to the cam. Its a slightly warmed up 5.3, cam'd and suppose to be around 425hp but feels like it has a 100hp right now.

Thanks

8269

[Pook]

If someone wants to pm me a phone number I'll call you if you can walk me through it real fast. Thanks.

[WeathermanShawn]

I can't do the phone number walk-through..but here is all you need to do.

Turn the car off. Let it sit for 15 seconds and turn back on. Your BARO will update (as it should at WOT also). If your car was properly tuned Open-loop, altitude will not make any difference. At worst, your BARO was off..which does effect Injector Flow (vacuum).

Your other option is to take it back to closed-loop..but you will need your narrowbands and a new tune.

Thats all I can think of..

[Pook]

I don't think its running in open loop. Shutting of restarting etc has no effect.

[WeathermanShawn]

I don't think its running in open loop. Shutting of restarting etc has no effect.

Well, just going by your statement that you do not have O2's. That would preclude closed-loop.

In any case, it is just a guess at this point. Remember, you lose ~ 3% HP for every 1000' change in elevation. 7000' is ~ a 21% loss. Since you are still running MAF, perhaps those lower frequencies were not tuned for WOT. It is hard to hit over 7000 Hz MAF Freq at those elevations.

There is really not much you can do at this point. You could contact the Engine Builder, but without a tuning log they would also be guessing. Unless you can talk a fellow Californian to help you, I say just enjoy the views and nice weather..:).

Sorry, I could not be of any further assistance. I always run closed-loop at high elevations (with O2's). Fueling and Trims always stay in sync. But, even my car feels like at slug at 10,000'.

Good luck..

[joecar]

Do you have any logs...?

See if there's any physical problems causing the hesitation (ignition components, fuel pump, etc...).

[picnic_george]

Remember that our altitude up here kills horsepower. I know it's a little late right now and the event is probably about over. If fuel trims aren't correcting(you'll need a wbo2) then you'll need to lean it out quite a bit. But either way with the thin air up in these mountains you can add quite a bit of timing and get away with it.

[kbracing96]

It's going lean. I have ran into this several times going from low to high elevation in open loop. I know that sounds backward, but trust me, it's like the PCM over compensates for the altitude. A quick fix it to just unplug the IAT. That defaults it to -18* or something like that and add fuel cuz it thinks its getting cold air. Or you can fatten up the VE and MAF tables a good bit. Anther way that is frowned upon by many, but works is to reduce the injector flow rate table a bit. It thinks it has smaller injectors so it keeps them open longer richening it up.