Map sensor issue, wiring?

dudemaaan · 05-05-2008, 05:58 PM

I was having a problem with my idle showing up in a higher airflow area then it should have on my PFC.

Anyways i tested the map sensor which checks out fine at the map sensor, but the voltage at my PFC is wrong. So i think my wiring somewhere is messed up but its really confusing. The problem is my PFC shows 2.48 volts, which is correct with the engine off(atmospheric) . But when i hook a mityvac up or let the car idle (vacuum range) at the MAP sensor the voltage is something like 1.5v or less which is correct, BUT my power FC still shows the voltage at 2.48.

I could understand if the wire became disconnected then the power fc would either always show 5 v or 0 v depending how it works, it would also highlight it in the sensor check. So somehow this wire is getting voltage... but it is not changing the voltage according to what the map sensor says it is.

I will add this, if i test the A/B terminals (black and green wires) on the MAP sensor harness, with the map sensor completely removed i will get the same 2.48 volts.

Does anyone know which wires do what at the map sensor there are 3 wires green, black, and brown. And where do each of these wires go?
__________________

dudemaaan · 05-05-2008, 08:54 PM

got it figured out and fixed

scotty305 · 05-05-2008, 09:23 PM

It sounds like something may be shorted to one of your MAP sensor wires. What is the history of the car and wiring harness? When was the last time everything worked correctly, and what have you changed since then? It could be something as simple as a pinched or pulled harness from working in the engine bay.

The MAP sensor voltage is pin 1O on the ECU (should read about 2.38-2.78V at atmospheric pressure when the engine is not running, and about 1.2-1.5V when idling), ground for the MAP sensor is pin 4D on the ECU, and the +5V reference power is pin 3I on the ECU. Try measuring these pins on the ECU (poke the back of the ECU connector with a paper clip to get a reading) and see if the ECU matches the MAP sensor when they are both plugged in.

edit: congrats! What was the problem?

dudemaaan · 05-05-2008, 11:10 PM

something between the emanage system and the PFC i honestly am not entirely sure how i fixed it. i just got under there with a flashlight and pulled some wires apart and hooked it up the way i knew to be correct and it worked. I had noticed that the emanage was displaying the correct map sensor voltage as well so i knew the wiring had to be correct at least somewhere close to the ECU. I studied a few different wire diagrams and wrote down what color wires were input and output and then it was rather simple. Thanks for the reply

cewrx7r1 · 05-06-2008, 06:47 PM

Some people have experienced ecu harness pins that had backed out.

05-05-2008, 05:58 PM	#1
dudemaaan Rotary Fanatic Join Date: Mar 2008 Location: Brenham, TX Posts: 335 Rep Power: 17	Map sensor issue, wiring? I was having a problem with my idle showing up in a higher airflow area then it should have on my PFC. Anyways i tested the map sensor which checks out fine at the map sensor, but the voltage at my PFC is wrong. So i think my wiring somewhere is messed up but its really confusing. The problem is my PFC shows 2.48 volts, which is correct with the engine off(atmospheric) . But when i hook a mityvac up or let the car idle (vacuum range) at the MAP sensor the voltage is something like 1.5v or less which is correct, BUT my power FC still shows the voltage at 2.48. I could understand if the wire became disconnected then the power fc would either always show 5 v or 0 v depending how it works, it would also highlight it in the sensor check. So somehow this wire is getting voltage... but it is not changing the voltage according to what the map sensor says it is. I will add this, if i test the A/B terminals (black and green wires) on the MAP sensor harness, with the map sensor completely removed i will get the same 2.48 volts. Does anyone know which wires do what at the map sensor there are 3 wires green, black, and brown. And where do each of these wires go? __________________ __________________ 500+ HP thanks to: Fast reacting IAT sensor thread! Mechanical Pre-turbo Water Injection Thread Dual Stock fuel pumps Thread T2 differential swap!

05-05-2008, 08:54 PM	#2
dudemaaan Rotary Fanatic Join Date: Mar 2008 Location: Brenham, TX Posts: 335 Rep Power: 17	got it figured out and fixed __________________ 500+ HP thanks to: Fast reacting IAT sensor thread! Mechanical Pre-turbo Water Injection Thread Dual Stock fuel pumps Thread T2 differential swap!

05-05-2008, 11:10 PM	#4
dudemaaan Rotary Fanatic Join Date: Mar 2008 Location: Brenham, TX Posts: 335 Rep Power: 17	something between the emanage system and the PFC i honestly am not entirely sure how i fixed it. i just got under there with a flashlight and pulled some wires apart and hooked it up the way i knew to be correct and it worked. I had noticed that the emanage was displaying the correct map sensor voltage as well so i knew the wiring had to be correct at least somewhere close to the ECU. I studied a few different wire diagrams and wrote down what color wires were input and output and then it was rather simple. Thanks for the reply __________________ 500+ HP thanks to: Fast reacting IAT sensor thread! Mechanical Pre-turbo Water Injection Thread Dual Stock fuel pumps Thread T2 differential swap!

05-05-2008, 09:23 PM	#3
scotty305 Rotary Fan in Training Join Date: Mar 2008 Location: Culver City, CA Posts: 84 Rep Power: 18	It sounds like something may be shorted to one of your MAP sensor wires. What is the history of the car and wiring harness? When was the last time everything worked correctly, and what have you changed since then? It could be something as simple as a pinched or pulled harness from working in the engine bay. The MAP sensor voltage is pin 1O on the ECU (should read about 2.38-2.78V at atmospheric pressure when the engine is not running, and about 1.2-1.5V when idling), ground for the MAP sensor is pin 4D on the ECU, and the +5V reference power is pin 3I on the ECU. Try measuring these pins on the ECU (poke the back of the ECU connector with a paper clip to get a reading) and see if the ECU matches the MAP sensor when they are both plugged in. edit: congrats! What was the problem?

05-06-2008, 06:47 PM	#5
cewrx7r1 The Judge Join Date: Feb 2008 Posts: 196 Rep Power: 18	Some people have experienced ecu harness pins that had backed out.