355 355 ECU

The engine management system in the 355 uses MAF sensors (Mass Air Flow) to measure the amount of air going into the engine. It’s a hot-wire system with Wheatstone bridge that measures varying electrical resistance caused by the cooling effect of the intake air to deduce the density of the air going into the engine & adjust fuelling accordingly. Air is less dense at higher temperatures and/or higher altitudes and MAF can detect this and relay the information to the ECU which uses a pre-programmed table (called a “fuel map”) to adjust the fuelling. The whole process, when running in “closed loop” is measured in milliseconds.

As an interesting aside, most cars now infer or calculate the air mass using data from the MAP (manifold absolute pressure), TPS (throttle position sensor) and air intake temperature. This has become possible as processing power has become cheaper and ECUs more powerful. The MAP system is more robust and slightly cheaper than using a MAF. Again, the whole process measured in milliseconds.

My “internet guess” would be that the car you’re referring to is running in open loop (fixed fuelling) and for some reason the CEL isn’t on.

 

When running properly this does not happen
Could be a lot of things
People who do not understand these cars tend to unplug lights, oxygen sensors, etc.
This kind of thing then happens and others start to create myths about poor running cars etc.

 

MAP-TPS-IAT (no AFM or MAF) is a rather old concept. I had exactly that on my 1986 Daimler Double Six (5.3 Lit V12) with a vacuum hose running all the way from the inlet manifold to the ECU (Lucas) in the trunk, connected to a hose adapter on the ECU itself. It was considered, in those days, not as accurate as systems with AFM; perhaps the modern ECU-s have made it more accurate.

 

There are differences between MAF and MAP both have good and bad quality’s
one being a MAF system will not see vacuum leaks down stream of the sensor which will cause a lot of performance issues and a MAP only sees the incoming air as a pressure difference to atmosphere “aka vacuum” and not volume——- yes there’s more to it but this is the easy way to look at——

all cars with ECM’s will have some type of a baro sensor input —-cars with a MAP us the reading straight from the sensor before start up
MAF systems usually have built in to the ECM and you will notice that’s there’s a vent cap on most of those ECM’s or have a externally mounted sensor

Either way a good scan tool will have PID info and you can see baro pressure as well as MAF and or MAP readings —- depending on your system—-

Do note the ECM will only reads baro at start up no matter how the reading Obtained and calculated
so if you are driving from sea level the high Mountain just turning off the car at the new elevation should recalculate the new baro reading

I would think you have more then that going on
If possible check your plugs and see if at higher elevation if you are running richer or leaner ? Does the engine temp run hotter ? Is there long lagging acceleration when changing gears ?

Before paying for a new or reman ECM I would go through the engine and all sub systems drive with a scan tool at both elevations and compare your readings see what is really going on a little time spent on checking right will save you money in the long run



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