Quick MAP Sensor Question

[Ethan]

LS Swap car 376/525 purchased new, wiring harness and e38 ECM purchased from Swap Specialties

Question: Does anyone know why in the name of everything that is good, that the map sensor is reading in reverse; i.e. when i depress the accelerator, kPa goes from around 70-60 at idle to around 20-30 even as low as 15 and higher RPMs?

I have checked the wiring to the ECM and to the MAP, even replaced the MAP.

[mowton]

MAP is an indication of load and will drop in the cruise/unloaded rev scenario's.

Try Key On Engine Off and log the Map sensor. Should report current barometric pressure based on elevation with 101/103 kPa at sea level and about -3 kPa per 1000 ft of elevation. Try a wideopen blast on the road and she should peg at your ambient Barometric pressure minus a little pumping inefficiencies.

The ASA cam in that setup develops very little vacuum at idle which is why you are seeing 60-70 kPa there. You might be able to increase the vacuum a bit by messing with the idle advance. Tune for the lowest kPa (higher vacuum)

Ed M

[Ethan]

Thanks!

[Ethan]

Hey Mowton, you wouldnt happen to have any idea as to why the ECM is stays at 158 mph would you?

[mowton]

no Vss input?

Ed M

[Ethan]

Let me start at the beginning, the ECM when i first read it appears to have came from a 2013 Chevy Express 3500 with a 6.0 L. I had to change the throttle maps back to stock from what the person who flashed the ECM had put in, because it kept putting the throttle pedal in limited mode. The tune is crap. Ive compared the tune to another LS3 that ive previously worked on and there are lots of things that dont line up. Not things like the MAF, but stuff like the injector flow rate vs press is completely different from another engine that has the same injectors, fuel pump, etc, as well as the flow rate multipliers.. The engine is sitting in front of a Tremec TKO 5 spd from Silver Sport Trans, on which i have the VSS plugged in. The ECM appears to have came from a auto trans. I have changed the PPR with no luck. Im wondering if the ECM thinking the car is moving 158 mph is giving me problems in other areas. Thanks for your help!!!