How to tune for 4 psi?
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TECH Apprentice
Joined: Sep 2005
Posts: 344
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How to tune for 4 psi? I have a 3 psi spring in my TTI kit, just wondering how to tune for this low boost. Basically I retarded the timing down 4 degrees (to 24 degrees). Do I need to add more fuel or will the computer do enough with this low a boost level?
The pcm will do the best it can, based on the maf sensor, the map sensor, and the tps. TPS won't help it know more air is flowing. Maf probably still helps as long as it's not maxed out. Map sensor is already maxed out as soon as you get any positive boost. So the pcm probably can't get you right in the middle of that safe range, since it doesn't know all the factors. And even more so since the safe range for FI is richer than the safe range for NA.
Dyno with wideband, or logging on the street with wideband, is the only sure way to cover it.
You can see if you're off the trail by a lot, by logging the narrowband sensors, but you can't dial it in using them.
Those factors (in hptuners anyway) are a multiplier for the fuel. So 1.0 means stoich, and 1.2 is rich (stoich/1.2)
For example 14.7/1.2 = 12.25 and 14.7/1.3 = 11.3 as far as commanded afr.
(so a small change in the PE multiple makes a big difference in the a/f ratio)
But that commanded afr is still based on what the pcm thinks is going on with the air flow based on maf, map, and tps readings.
You could bump your PE factors by .05-.1 for some peace of mind.
Wideband to be sure of what's happening though.
Going from 3 psi to 4 psi is not a huge change, so it's just a judgement call on your part.
Dyno with wideband, or logging on the street with wideband, is the only sure way to cover it.
You can see if you're off the trail by a lot, by logging the narrowband sensors, but you can't dial it in using them.
Those factors (in hptuners anyway) are a multiplier for the fuel. So 1.0 means stoich, and 1.2 is rich (stoich/1.2)
For example 14.7/1.2 = 12.25 and 14.7/1.3 = 11.3 as far as commanded afr.
(so a small change in the PE multiple makes a big difference in the a/f ratio)
But that commanded afr is still based on what the pcm thinks is going on with the air flow based on maf, map, and tps readings.
You could bump your PE factors by .05-.1 for some peace of mind.
Wideband to be sure of what's happening though.
Going from 3 psi to 4 psi is not a huge change, so it's just a judgement call on your part.
