ITB - Atmospheric pressure compensation

s300 and SManager software questions & answers
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shiroitenshi
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Joined: Sat May 19, 2007 9:24 pm

ITB - Atmospheric pressure compensation

Post by shiroitenshi »

Tuned my itb car at sea level with alpha - n, it runs fine, although since the car is street driven, i run very fine load index at 1 to 15% tps ranges for excellent streetability at very low throttle positions.

I am going to make a hill run at 400m sea level and the atmospheric compensation looks to be mighty useful, the question is, does it reference nternal ecu PA sensor or the MAP sensor? currently i run a map + tps secondary fo compensate a/c load and for stock idling characteristics.

If it references the MAP sensor, does this mean i can just disconnect the vacumm line to the map sensor and use it as a baro and run full tps indexing with compensation? i have managed to do full tps indexing even with a/c, idle is lightly affected but not an issue, so i don't really require the map sensor.

Ecu is JDM P30, with s300j. Thanks for any help or clarification offered.
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Hondata
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Re: ITB - Atmospheric pressure compensation

Post by Hondata »

It uses the PA sensor for compensation. Does the JDM P30 have a PA sensor?
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shiroitenshi
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Re: ITB - Atmospheric pressure compensation

Post by shiroitenshi »

No, it doesn't. I have tried enabling it in parameters->misc, all i got is a solid cell without codes.
No alternative way to use MAP sensor as compensation then?
the stock MAP sensor would be enough for the purpose at hand if i can use it. :(
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Re: ITB - Atmospheric pressure compensation

Post by Hondata »

No, the MAP sensor is still used to read manifold pressure.
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shiroitenshi
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Re: ITB - Atmospheric pressure compensation

Post by shiroitenshi »

Hmm, looks like I might have to source a hondata ecu with PA sensor. Any suggestions? Wish I could use my current ECU though, lots of memories with it.

BTW, I'd appreciate if you would explain how the MAP sensor functions in an hondata's alpha-n map tables? I am at the moment using it as a gauge of when the engine sees atmospheric vs tps index, but apart from that, does it serve any other purpose, apart from measuring load in MAP indexing?

I've heard of MAP + Alpha-N method of compensating for different atmospheric pressures, is this not possible on hondata?
Luke
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Re: ITB - Atmospheric pressure compensation

Post by Luke »

i'm not an ITB expert...

but: if you would drill holes in every runner behind the throttle body, but there a NPT plug in, put those plugs with a hose together and this to the MAP sensor, you should get the manifold pressure and be able to tune your car with the MAP calibration and not alpha-n.

or am I wrong?

this would get you a opportunity to drive wherever you want, without messing up the engine ;)

best regards Lukas
shiroitenshi
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Re: ITB - Atmospheric pressure compensation

Post by shiroitenshi »

Lukas, read first post again about what i am running currently. I can tune it with map, but I am trying to use alpha n for the response, and running map on huge itbs won't work well, since the low pressure reading aka vacuum would be wacky as even 2-3% throttle would make the MAP read atmospheric, aka what you call the high load portion of the MAP load index.

can it run on MAP? , sure it can... but it is a compromise.
Luke
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Re: ITB - Atmospheric pressure compensation

Post by Luke »

ahh, I see.

as I said: i'm not the biggest ITB expert, so that was just an idea, which could work, but doesn't as expected.

never mind.

best regards Lukas
shiroitenshi
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Re: ITB - Atmospheric pressure compensation

Post by shiroitenshi »

Lukas, i appreciate the suggestion, but i already have map based indexing, as mentioned in the first post. purpose is to try to get alpha n as a workable long term solution. but i guess i might have to manually compensate for the elevation then. still wish there was a way to use the map as a compensation factor.

Edit:
Finally worked out a stop gap solution till I can get system that can compensate, switching to secondary tables at 90Kpa should do it for now, if the atmospheric pressure is too low, it'll just switch to MAP sensor, so it'll work for now. Crossing my fingers on hoping it runs adequately. I'm hating to think that I might have to retune everything. Thankfully I did the a full load index MAP sensor tune before I switched to alpha-n, so I have fully tuned tables on primary and secondary.

Here's hoping SManager might one day allow compensation based on MAP, till then, I guess this stop gap measure will do.

Either that, or allow using an alternate method of compensation via external PA sensor, ECU with PA sensor isn't exactly plentiful.
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