How to make a 2 BAR MAP work with a GM 8D #1227727 ECM?

[Flame Red]

Hi Folks,

I tried searching and goggling for help on this but my extensive efforts were not fruitful.

I have a L98 350 TPI in a 90 Vette running the stock 8D ECM with a Procharger 600b. I am a novice tuner so please take that into consideration when you explain this to me.

I was advised that I could get a better tune if I used a 2 BAR MAP instead of the stock 1 BAR MAP. I purchased a 2 BAR MAP for a 87 Buick GNX, and cut the key ways so I could plug the MAP into the stock connector.

Some of the posts I found said others have switched to 2 BAR maps in "similar" GM ECM's by just halving the VE to MAP table. I tried cutting my current VE to MAP table by 1/2 but the car will not start or run when I install the 2 BAR MAP. So I assume there are more changes needed. It kind of stuttered. Reinstalling the stock 1 bar MAP and the car runs good.

I was hoping someone could guide me on how to get the #1227727 ECM to work with a 2 BAR MAP.

Or is it impossible?

Thank you in advance.

[Six_Shooter]

Not impossible, but you will not get ideal results, in fact, most people seem to "live with" issues that this causes, when using a 2 BAR MAP with a 1 BAR program.

I would normally suggest using $58 or $59, but I believe your car needs to see certain communication between the ECM and the BCM, which would cause issues changing to a different mask.

Another way to do it would be to learn hex and assembly language to be able to "patch" your bin, to be able to use a 2 BAR MAP sensor and have all corresponding values match.

[maticulus]

The way his statement reads he literally halved the values in his VE table when what should have been done would be referred to as scaling.

A 2 Bar MAP will limit a naturally aspirated VE table to use about half of the table (up to 50 kPa) 2.5 volts for natural aspiration instead of 5 volts, and 2.5 volts for the boosted range, so if my thinking is correct, the values from 0 to 50 kPa would need to be approximately doubled for proper compensation for the voltage cut caused by the 2 Bar Map that needs to see 15 psi before it will deliver the max voltage that the 1 Bar MAP sensor delivers at wide open throttle.

It stands to reason that every other MAP dependent table would need to be scaled in the same manner to function correctly. Sounds like a big headache given the challenge that can be faced with a system designed to use a 2 Bar MAP sensor.

[Flame Red]

The way his statement reads he literally halved the values in his VE table when what should have been done would be referred to as scaling.

A 2 Bar MAP will limit a naturally aspirated VE table to use about half of the table (up to 50 kPa) 2.5 volts for natural aspiration instead of 5 volts, and 2.5 volts for the boosted range, so if my thinking is correct, the values from 0 to 50 kPa would need to be approximately doubled for proper compensation for the voltage cut caused by the 2 Bar Map that needs to see 15 psi before it will deliver the max voltage that the 1 Bar MAP sensor delivers at wide open throttle.

Yes, I was told to just double the values in the VE table, which did not work. What you state makes perfect sense. Double the values in the VE table to 50kPa sounds logical. But now the questions is for the values from 50kPa to 100kPa, how should one scale those? Any advice?