how dose 2 bar map work and why cant you use one with a stock ecu to read boost

 

I'm not completely sure on this, but anyway. A normal MAP sensor only measures vacuum, but not pressure. The 2 bar MAP can measure pressure in addition to vacuum, so it will see boost. You can't use this with a stock SD ECM because its not configured to deal with situations involving boost. This is why people are swapping to the Sy/Ty ECM.

 

In a way, a MAP sensor actually sees engine vacuum as pressure as well.. this might be a hard concept to understand, but engine vacuum is only seen as vacuum because it is being compared to atmospheric pressure.. so it's less than atmospheric but higher than absolute zero (so there is always positive pressure in an engine as far as the MAP is concerned). A MAP sensor starts at absolute zero, and a one bar MAP can only understand pressure to 14.7psi (which I believe is equal to 100Kpa but don't quote me on that), which when maxed out means that the pressure outside of the engine and inside of the engine are equal (generally, anyway). Using a supercharger or turbocharger to increase pressure above atmospheric means that you're exceeding 14.7psi and the one bar MAP sensor can't interpret anything that high, and as the previous poster said, the stock F-body computers just don't have the capability to read anything higher.

 

It's not so much that the stock ECM's can't read boost, is that the TPI code is not written to recognize boost, ei not programmed to read a 2 bar MAP only a 1 bar MAP. Both the 1 bar MAP and the 2 bar MAP return a signal between 1 to 5 volts, however the 2 bar signal is 1/2 the voltage for the same Kpa. A 3 bar MAP returns 1/3 at the same Kpa. The 730 will work with boost provided there is a 2 bar MAP sensor and correct code. The Turbo Grand Prix uses a 727 ECM and $8F code. The SyTy and Sunbird both use the 749 ECM and $58 code, both ECM's are based off the same motherboard as the 730. The $8F code is distributorless, while $58 is dizzy based. BW

 

That makes a lot of sense, although that makes me wonder why it isn't possible to run the $58 type code on the 730 ECM if the only difference is the programming to make it able to interpret the signal from the MAP sensor.

Where could I download a copy of the $58 code to look at? Thanks..

 

It is possible to run the $58 code on a '730 ECM. Although there are a couple of items to take into account. If running the $58 Turbo Sunbird cal the '730 won't work correctly. The Sunbird cal uses both injector drivers of the '749, the '730 only has one.

The $58 Sy/Ty cal (the code is the same, only the cal parameters change) will work on the '730 as only one injector driver is in operation.

The other area is the pinouts. Now the I/O channels vs the pins are the same between the two ECMs. The '730 & '749 use the same PC board. What changes is which I/O channel used for what function. This is where the $8D mask will use channel X for the TCC, and the $58 mask will use channel Z for the TCC, and the $88 mask will use channel Y for the TCC.

This just means a couple of harness pins need to be swapped around. There are lists around (on the web) of which pins are required to be moved. In reality this has nothing to do with using a '730 vs a '749, only when using a harness from a '730 vehicle will the pin juggle be required.

See the diy-efi site for bins.

RBob.