Just to see what would happen on my OBD1, I plugged in a 2BAR MAP. (It uses a different connector.) I replaced my stock 22lb injectors with 44lb injectors and then I drove it using the stock Ebrock chip and my Vortech charger. (Used a Ebrock MPFI) To my amazement it not only ran, it ran great even with the stock spark table. I changed absolutely nothing in the chip program. The only trouble was it wouldn't idle well. (Too lean). The GM Map and connector I got from Caspers.com. I think it was about $75. After that, I ditched my FMU and supplemental injectors setup.

 

I did this with my setup. You can get Mallory/MSD 2 bar maps from summit for about $43.

 

I am running a 2-Bar MAP sensor and 36# injectors with the factory First-Gen OBD-II PCM.

You are correct - MAP resolution is cut in half and MAP vlues are now displayed as 50% of their actual values.

All the values in the PCM that reference MAP need to be halved in order to work with the 2-BAR. Tables are not quite a simple, especially VE.

Do remap the VE table you need to take a copy/paste approach to the values, not half them. For example, into 15kPa copy 30's data. Into 20kPa copy 40's data. Into 25kPa copy 50's data, etc. until you get to 55kpa. At that point the best way to get close is to take the original data from 105kPa and copy it into all remaing cells 55-105kPa on the map. You'll need to them scale each 5kPa increment up by a factor, say 1.04 for example, until you reach 105.

This will not be perfect but it will get you close.
The first problem you will notice with your new fuel map is a stumble when hitting the accellerator fast, especially off idle. This is a problem I've had to overcome by artifically inflating the VE tables just off idle and also dropping Power Enrichment TPS for the lower RPMs.

Don't forget to copy your main VE values into the backup VE table, and don't forget the spark tables that reference MAP. Those need to be refilled the same as VE, but for 55-105 you can probably use 105's original values without too much tweaking unless you have detonation.

This is my current (and unconventional-looking) Main VE table:


You will notice what I've had to do in the low RPMs for good throttle response. It's revs up VERY fast like this. I wish there was a table for "accelleration enrichment" that worked similar to a carburetor accellerator pump in these PCMs. The aftermarket ones have it.


Good luck.

 

You say you are running aTBI setup,how are you able to run 8 injectors?Are your 72lb injectors high impedence?I run a 2bar SD setup from HPtuners,so the PCM can read the 2bar MAP sensor correctly and there's need to half any tables.Is 2bar tuning available for the later Vortec setups?Or are you left to improvise your own setup?

 

what is the part number for the 2 bar map that is a plug and play deal with our intake/wiring.

 

MNC5 said it perfect, the OUTPUT of the sensor to the computer is still 0-5V regardless of what the measurement range is ( 1 bar, 2 bar, etc ). I liked the thought of using the GTP sensor on the GM products if it truly is a plug and play, it keeps you from having to use a remote sensor and intercept/substitute the updated signal. The doubling formula is great if the sensor started at the same minimum value like -30psi ( or 30mm/Hg ). Make sure to check the old/new sensor range before arbitrarily halving the values of an aftermarket or upgraded sensor. It will be close but you might leave some power and fuel mileage on the table without fine tuning.

 

I think you are asking me. My truck was originally a TBI which has had a few transformations. The TBI was replaced with a Edelbrock MPFI, which is next going to a Victor; hence, 8 injectors. The PCM was changed to a FAST (now XFI) with wideband O2 using 72# low Z injectors. No more chip burning. OBD1 and ten years ago was like the stone age for EFI. It was mostly guys experimenting and double the MAP with double the injector crudely worked. You could also burn chips or use a Typhoon\Syclone set-up. All kinds of choices now.