I just read an item that got me thinking. In car craft magazine, they write that forced induction cars need an upgraded MAP(capable of reading pressure up to 30psi), compared to the stock piece. Have others upgraded, or is it a matter of simply reprogramming? Thanks.

 

Although they make MAP sensors that read positive pressure their output doesn't correspond correctly with the factory one. It would take more than just reprogramming it would take modifying the hard code in the programming. As far as I know no one has done this on the stock computer. Aftermarket computers usually accept positive pressure MAPs. Usually you have to tune in the 95/100 Kpa load area (0 psi) in the programming for your full throttle tuning even though the computer won't know if you are at 1 psi or 20 psi.

 

Speaking with my engine builder, i found that he applied a MAP from a turbo buick. Sounds fine to me. Thanks for your help.

 

You can physically bolt the turbo Buick MAP onto your manifold, BUT ...

When you turn the key to start your engine, the PCM looks at the MAP sensor while the ignition is on but before the engine actually fires to read atmospheric pressure. Substituting the Buick (or any other 2-bar or 3-bar) MAF will screw up that reading, which will screw up your tune. Basically, the PCM will think you're on top of Mount Everest.

It screws up the reading because all MAP sensors use the same output voltage scale regardless of whether they are a 1-, 2-, or 3-bar MAP. If I start my car at sea level on a nice day, the stock 1-bar sensor will send a full-scale signal to the PCM. If I swap in a 2-bar MAP, starting my car under the same conditions will send only a half-scale signal to the PCM. The PCM will see this half-scale reading and assume the atmospheric pressure is only 1/2 bar, which corresponds to some insanely high altitude.

Since there are fewer oxygen molecules per cubic foot of air inhaled by the engine at higher elevations, the PCM will command less fuel from the injectors and you will run lean. Really lean.

AFAIK no one has figured out how to twiddle the PCM code to adapt a 2- or 3-bar MAP because of this atmospheric pressure problem.

 

So, when adding a s'charger, what is the protocol? Leave the MAP and nevermind it? I read in carcraft that forced induction cars need a 2 or 3 bar MAP. That raised a flag in my mind. Thanks for your help, i appreciate your time.

 

What about the optional crane maps that you can buy with their box? I just installed the hi6r an noticed they have after market maps.

 

If you are staying with a stock PCM then you use a stock MAP. When the MAP maxes out, the tune goes to a power enrichment table and it is basically a certain degree of guessing and trial and error to get the tune perfect. LT1 Edit is a common program used to retune our PCM's. Ideally you have to go to a dyno to get a WB O2 reading and then make adjustments to your PE tables from there.

If you go with an aftermarket computer it can read a 2 bar map and of course you can also get built in WB O2 and tune on the fly. Its beauty.

 

Anyone have a part number for the 2 bar maps? or Which year turbo buick one to get?

 

I am running an MSD 2-bar with my DFI; I started to get one out of the GN but they had to be ordered. Do a search on Autozone.com for a 85-86 GN. Should put you in the ball park.