Map sensor loom help..

[L18M]

After having problem after problem..
james is now in a situation of everything wired in but when the ign is on, the commander on the ap eng pfc is reading -200 boost pressure.
Now the car wont start due to lack of fuel in the -ive so this should read 0.

This has been narrowed down to either:
a) 2 faulty gm  3 bar map sensors, one new, one used.
b) wireing between map sensor and ecu (though was running fine before car went to james)
c) faulty pfc

when james followed the wore for the map sensor it lead towards the water housing wires which he said is not right as it seems someone rewired it, which is a bit strange as it was a stock car bar induction and exhaust.

can someone follow their wires from the map sensor and see where they lead to pls.
Just trying to narrow down the problem.

Would it be a problem with the engine?

if anyone has any ideas why this might be reading -200 please step forward

cheers in advance and enjoy the weekend.

[Prof]

Probably the easiest thing to do is put a multimeter on the centre lead of the map sensor plug if you can get it on there.  The MAP sensor get\'s 5V from the ECU - so the 2 outside wires should have 5V on them when the ignition is on - check that first.
 
Then, Check the voltage on the centre wire - red multimeter probe on the centre pin, black multimeter probe on ground.  You should have a voltage between 0 and 5 Volts, and closer to 0 (probably about 1 volt in free air).  
 
Pull off the hose from the MAP sensor and apply a vacuum or some pressure to it - check the voltage on the centre pin of the MAP sensor goes down / up respectively - if it doesn\'t the MAP sensor is faulty.  If it does - your problem lies elsewhere.
 
The MAP sensor I sold you was definitely working when wired to the emanage in my car - If I can find it, I have a graph of pressure / versus voltage for the GM 3 BAR sensor.

[Prof]

Here you go
 
http://hhscott.com/93tmv/3-bar_map.htm
 
3 BAR sensor should have about 1.8V on the centre pin in free air

[L18M]

cheers dave, will forward the message on and get him to test it out

[L18M]

ok, the map sensor is working fine :Thumbs-up
the banzai one i got new, is not.

The AP pfc is working / reading fine as its pretty much the same boost reading when another pfc is plugged in.

so this leaves the wiring. will try a crude wire from pfc to map sensor to see if this fixes the problem. fingers crossed it will.

IF not then anywhere else i should be looking?

[a.tapos]

Yeah thats a real quick test splice wires from map to pfc and that will make it certain if still no good its gotta be pfc,if you can get a mityvac that does boost and vac that would be conclusive ive had a map that only fails under boost