altitude correction map? issues
 

friend bought an fd; 10 psi with a 60 trim single turbo, 800/1000 injectors, large street port, supporting mods

tuned in denver by, i think nelson performance? cant remember now ~330hp

so anyway. he bought the car. drove it there. was great. drove it home, salt lake city. now runs like crap and hits a wall at 5000 rpm. i havent driven or seen it, just his description. sounds like its going rich and cutting out. no compression issues. does have and has had cold start issues but i think thats an unrelated problem.

i dont think there is a correction map but i thought id check. if you have any other advice/input or need more information from me, please please post it up. he is new to the rotary and fd world and id really like to make him happy and enjoy his car.

thanks guys.

Hello mate

There is a map sensor calibration/scale offset adjustment but doesn't make huge differences to the car unless of course your altitude change is massive.

It sounds more like it's developed a problem or shown up an existing problem on the drive home.

If it has a start problem aswell it could be a fuel filter or compression issue

The oxygen content or % is constant up till around 70,000 ft.
The only thing that changes is pressure or also called density.
10 psi boost at sea level is equivalent to 10 psi at 10,000 ft.
Same timing and same fuel required.
The only difference is at 10,000 feet the turbo has to work harder.

You people need to know science instead of guessing.

The only caveat to this is if you have a significant change in engine volumetric efficiency due to a change in exhaust back pressure. If this is the case then the fuel requirements will also change.

A quote from the Motec forums that doesn't really pertain to the PFC, but good info in general www.motec.com • View topic - TPS vs MAP tuning

Id look elsewhere for the problem mate,and a few more details may help you solve it.

I think the man was after advice and I was trying to inform him I didn't believe it to be an altitude problem.I can't tell through the forum if the "you people" comment was said with laughter behind it or frustration so please excuse me.

Beat me to it. Come down off the mountain and the EMAP changes which changes the pressure differential across the engine. When that happens, the tune goes to crap. Understanding that when you calibrate a fuel map, you're working with much more than just boost pressure in the intake really helps one understand these situations.

You people and your science that you don't fully understand.

Don't all OEM ecu's have barometric pressure sensors built in to have a reference for the map sensor to work from?

I know ford and EOBD Mazda do.

Any more news with this or is it a dead thread?

https://www.rx7club.com/canadian-for...e-fuel-853587/

Bad tune to begin with is the real cause.

This is wrong.

The % oxygen is correct, but the higher the altitude the less oxygen is present ber volume of cubic foot because the pressure is lower.

Our wastegates work off of pressure differentials.

so.

at sea level

14.7 PSI atmosphere, + boost pressure (10 PSI) = 24.7 PSI absolute manifold pressure

at 6300FT where I am at atmospheric pressure is 11.7 PSI

11.7PSI + 10PSI = 21.7PSI absolute manifold pressure.

I have less power and less fuel at 6300 ft compared to sea level. They are not the same.

If you tune to 12PSI at altitude and run 12PSI at sea level, one would need to re-tune the car, if one tuned at at sea level, idle and very low part throttle cells might need to be touched up.


If you tune your own car at higher altitudes, your boost gauge will read 10PSI, when you reference your PIM voltage on our powerFC or tuning software, it will read 7PSI.

You need mental help.

I am willing to bet he tuned the car at higher altitude, when you went to lower altitude your are probably hitting the boost cut in the powerfc. The car isn't tuned for the pressure you are trying to run at.

if you set a boost controller to say 20% gain, and you run the car at higher elevation, the pressure ratio is higher here.....so you run say 12PSI.

11.7 + 12 = 23.7 PSI absolute.

when you don't touch the boost controller and go down in elevation, the pressure ratio becomes more favorable, so the turbo will boost more at the same % gain, also, the wastegate pressure is a pressure diffierential over atmosphere. so let's say atmosphere went from 11.7 to 12.7, and your boost creeps to 13PSI.

12.7 + 13 = 25.7PSI absolute.

your engine is seeing 2 PSI higher pressure. Hence, depending on the tune, could be going off its map where it was tuned for.

This happened to speedjunkie when he went on a trip to sea level and tried boosting, he was hitting the boost control cut off on settings 1 tab. If you need help I am in CO and can help you out.

Tough to argue with the facts, so revert to name calling. nice try.

The AEM boost controller I just tuned is an absolute pressure boost controller (from sea level). My HKS unit is not, and neither is the greddy unit in another car I tune.

so pay attention to how the boost controller controls boost, because they vary.