Therefore they aren't affected by boost leaks like other dsm's. yes, a boost leak will cause bad performance but only because the turbo will have to work harder to build the same amount of pressure. it has little to no affect on tuning, engine performance, idle, pushing in the clutch after boost, etc.
420a cars use a MAP, intake temp sensor and the front O2 sensor to determine the amount of air entering the engine and how to adjust the fuel curve accordingly. This process is called Speed Density. The unfortunate side of this is that the 420a MAP sensor is only a 1 BAR map sensor that reads vacuum only. This is why the missing link or other fuel cut defender are necessary so that the MAP sensor doesn't see any positive pressure and panic.
More detailed discussion from dsmlink forums to follow. ECMLink V3 is going to offer speed density in the future and IMO is a better/easier way to tune
QUOTE (twdorris;296586)
I agree. There's a LOT of paranoia and even more confusion going on in this thread.
Any pressure sensor you use for SD is going to have to measure absolute pressure. Which means, except for some obscure variations like those Dave mentioned, I can't see anything changing related to SD operation as you increase or decrease altitude. Unless, of course, you end up moving yourself around into areas of the VE table that you simply haven't calibrated properly yet... That's FAR more likely to be the reason behind any variation you might notice with altitude change and SD operation.
SD works and it works fine. Far too many cars are running just fine on SD straight from the factory for it to be "poor choice". My post above was simply pointing out the pros and cons on both sides.
Thomas Dorris
QUOTE (pwee05;297046)
420a is SD out of the box. Its OEM MAP is barely 1 BAR so I tossed a GM3BAR on the RS I built, increased base fuel pressure slightly and it always ran just fine. I never had any issues tuning it with only an AFC and an AEM WBO2. Though, I never made more than 400whp nor have I ever been a tuning genius either, which may be a credit to SD's ease of use
QUOTE (burnett03;297094)
I find this hard to believe. A non turbo ecu does NOT like boost at all. That's why you put in the missing link on the map sensor so it doesn't see any boost. Simply tossing in a gm 3-bar in place of the factory map is not going to work.
QUOTE (pwee05;297109)
True, that ECU doesn't like boost but thats only because the MAP sensor is overrun. Once it hits its peak 5v signal (which should never happen on a N/A engine) the ECU will panic and fuel cut. That is what the missing link is for. It's a check valve that remains open under vacuum and closes during positive pressures. Mine failed at 15psi so changed to the 3BAR
Since the GM 3BAR also uses 3 leads (0-5v signal, 12v supply, and ground wire) it splices in nicely. It fools the ECU into thinking there isn't any boost because it produces its 0-5v signal using a vacuum to pressure range of roughly 14.5mm/hg to 29psi. Therefore, takes alot more air to over run the 3 BAR and it never sends that peak 5v signal. Unless you are more than 29psi of course
The added fuel pressure was because the AFC couldn't correct within a resonable limit for the larger MAP. The 3 BAR sends about 1.6v at 0mm/hg or 0psi. This is roughly the same as the OEM MAP during a 20mm/hg idle.
420a Cars Use A Map Sensor And Speed Density, not a MAF
Jan 27 2009, 11:06 AM
