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MAP Parameters


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Hi there,

I have a Lancia Montecarlo fitted with throttle body fuel injection. It’s an 8 valve twin cam, normally aspirated engine producing around 200 bhp. It has been running on an Emerald K6 ecu, but current changes have highlighted an issue that this old tech is unable to cope with and has proved impossible to map at low load and cruise. The reason is down to a very low vacuum reading (0.23 Bar). 

Each cylinder is ported for a 4mm tube, joined and baffled before running to a 3 Bar map sensor with links to fuel pressure regulator and brake servo. 

I am looking to upgrade to the Atom x and need to know if the software is able to read small changes in MAP?  I see there is an option for a 1.15 Bar sensor, which will reduce the range but will it be enough?


The engine itself is good, with 175 psi across the cylinders and no air leaks anywhere else. Cams are fast road type and do not have a large overlap - for some reason just low vacuum. 

Thanks in advance and look forward to any help you can give me. 

All the best, Darren 

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A speed-density (MAP based) fuel strategy will rarely work well with ITB's.  You will find with ITB's that MAP is no longer a good indication of engine load and the MAP can read the same at many different loads. 

So, nearly always for ITB's you are best to use an Alpha-N strategy (TPS for load), in cases where there is an idle valve or boost on top of the ITB's then we take MAP into consideration as well, but TPS is the main fuel table look-up.   

So you may still be able to get a decent tune into your Emerald if you can change to TPS based load.  Its been a long time since I tuned one so cant remember.  The G4X is certainly far more capable though and will you have many more advanced options as well as good logging etc.  From memory the Emerald analog inputs are only 8bit vs 12bit on the G4X - so 16 times finer resolution which is why we can get away with a 7 Bar MAP sensor.

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As I mentioned the G4X has higher resolution analog inputs so it will be able to "see" a much smaller change in MAP.  However, it is unlikely the small variance in pressure from idle to WOT that is causing your problem.  The problem is with ITB's is MAP is often not proportional to air flow - so calculating the amount of fuel to inject based on some parameter that doesnt closely relate to airflow is never going to give you a satisfactory result. 

I have seen ITB engines with the same MAP at 10% throttle cruising as it has at 60% throttle accelerating up a hill, obviously you dont want to inject the same amount of fuel for these two very different operating conditions.  You should be using Alpha-N no matter which ECU you use.        

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Hi again Adam, thanks again for your reply and I will look at alpha-n. It’s good to know that the atom has the additional capacity and I think I will upgrade from Emerald anyway and use it or other Link ECUs on future builds. 

can anyone recommend a UK supplier of wired in units?

Thanks again,


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