Where Do I Take A Map Sensor Reading From?

[JayCaz]

Hi Guys

I'm really hoping you can help me...

In South Africa we don't get front clips, we can only buy the engine itself and so this hardly ever comes with the original ECU. So it goes without saying that we almost always use an aftermarket management system. My engine didn't even come with an airbox, and so, didn't have the AFM sensor either. (I later realised that it was an AFM 4AGZE) Not that is matters because the aftermarket ecu uses a map sensor anyway.

But now the problem I'm having is... were must I take the map sensor reading from? Before the supercharger or after the charger (in the inlet manifold)

I would obviously assume that it must come off from between the supercharger and the engine, so as to get a boost reading.

Now at wide-open-throttle this all works well. The computer senses the boost and increases the fuel accordingly. But the moment you tap of the accelerator the ecu dumps in so much fuel that the engine struggles to keep running. This is because when you decelerate you should have a 'vacuum' in the inlet manifold, and so the ecu must tell the injectors to squirt in less fuel, because the throttle butterfly is closing or closed. But whats actually happening is that as I tap off after boosting, the charger is still spinning, and so the map sensor is not actually reading a vacuum, but rather a slight high pressure, and so the ecu thinks the engine still needs fuel, and so it dumps fuel (while the throttle is actually closed) and so floods the engine.

So my question is: How do I counter act this? I thought of putting the map sensor before the s/c, but then obviously it wouldn't be able to read any boost, and so run the engine too lean.

So on a standard 4AGZE what do you do? Where is the map sensor placed? And how does it work?

Your help would be appreciated guys.

Thanks

p.s Is what I'm saying making sense, or have I got the wrong idea of how a standard 4AGZE map sensor actually works?

[dawesy]

MAP sensor should be plumbed into the plenum on the inlet manifold between the throttle and the cylinder head. make sure that nothing else shares the same pipe as the MAP sensor. failing that sounds like a mapping problem with the ECU