MAP sensor issues - wiring experts needed
 

Last hurdle I have to tackle is this crazy MAP sensor reading, then i'm up and running.

He's the situation. I installed a harness from www.fasttrackperformance.com that splices in the Speed Pro computer to the factory wiring harness. This harness, for those who are new, splices in to the factory harness and uses the factory sensors and connectors. Basically, it simply takes the readings from the sensors by splicing into the wires near the stock computer.

Anyway, I installed a new 3-bar MAP sensor today and the sensor is giving funny readings. It says i'm at 39 kPa, which of course is wrong. Should be near 101 kPa, which is atm. pressure

The voltage in the wires, with the connector plugged in, are screwy. They should be, as far as I can tell, 0 volts in the ground, 1.67 volts in the signal return wire, and 5.0 volts in the 5 volt reference wire.

I have ~0 volts in the ground, 0.6 volts in the signal return wire, and 1.7 volts in the 5 volt reference wire.

Now, as Fred mentioned earlier, you cannot have two computers supplying 5 volts to the same sensor and expect them both to get a reading that's anywhere right. But that isn't the case here. Both computers are simply reading the same sensor (many other sensors as well).

Another thing I noticed has to do with the wiring diagram. The same 5 volt referense wire used in the circuit above also supplys the A/C refrigerant pressure sensor and the A/C evaporator temp sensor with their proper voltages. With this in mind, my A/C system is not charged. Thoughts?





anybody have any ideas?

well if its a 3-bar MAP sensor then doesnt that mean it can measure 3x that of a 1-bar sensor or 3x atm pressure? if so then maybe the 39 is almost correct b/c 100 kpa is 1 atm so 1/3 of that is 33 kpa which you are close to. but i suppose the 3-bar could also mean it will read up to 300 kpa in which case id be completely wrong.

the 3-bar MAP sensor is used in cases where people need measure higb-boost pressures. Meaning, it will measure up to 3 times atm. pressure or 303 kPa = 3 bar

Have you measured the 5 volt reference at any of the other sensors that it supplies?

Just to clarify - we seem to be having a "failure to communicate" here - I NEVER said you can't parallel (all) sensors into two computers. I very specifically said resistors (thremistors) like temperature sensors. When you have a device like a MAP or TPS, that is effectively a rheostat producing a varying output signal, across a fixed (+5V) signal, no problem at all using them with two devices in parallel. Where you get into trouble - IMHO, and I know your "expert" doesnt' agree - is when you use a simple two wire circuit with a resistor/thermistor in it, like the inlet air or coolant temp.

And I am not "challenging" your expert here.... simply trying to explain exactly what I said, so you don't incorrectly extrapolate it to ALL sensors.

Fred,

NOW were getting some where. I also failed to mentioned (it slipped my mind until now) that there is a resistor module that is included in the harness. Basically, it connects to the IAT circuit and the water temp circuit (I think) and gives a reading to the stock PCM to make it think every thing is peachy keen.

I thought the MAP sensor issue was similar, but it is of course not. Since it has a supplied voltage it's a completely different issue. It seemed to slip my mind when we were discussing the MAP and IAT circuits... i lumped them together and that's of course my problem.

Basically, as I understand it, there is only one computer reading the IAT and water temp sensor. The PCM is getting "fake" readings from the resistor module. Does that make sense?

Jesse