ohioredrx7

iTrader: (13)

Hey guys, I could use some advice. Long story short, I purchased a car that had been tinkered with by a serious amateur. There are short cuts galore on this car. For example, fender liner is stapled in place? Anyways..enough ranting about how some people shouldn't touch their vehicles and on to the problem.

The previous owner had some large wheels on the car with some serious lowering springs and no fender liners so the tire rubbed through a few wires in the harness in the driver's side wheel well. I repaired the wires that were broken and tucked the harness out of the way so this won't happen again.

I have never driven the car because it runs pig rich at idle to the point where it spews black/brown smoke. Eventually it stalls.

I've rechecked all of the connections on the EM harness and confirmed that all of the connectors go to the correct sensor (i.e. confirmed fuel thermistor vs water temp, crank sensor vs TDC sensor, etc) and it's not anything related to that.

Today I checked the MAP sensor voltage per the FSM by reading the voltage between pins "A" and "B" as shown below.

With IG ON, engine not running, the voltage between the two pins read 4.90-4.98V which should be out of spec and above a WOT condition which would help explain the pig rich idle.

So before I purchase a new MAP sensor I have a couple of questions:

1. Do I check the voltage between the pin closest to the front of the vehicle (Brown/White wire I believe) and the center pin?

2. Is there way to confirm that it's the MAP sensor and not a wiring problem? The reason I ask is because of the harness damage in the driver's side wheel well. None of the MAP sensor wires (or at least what I believe to be the MAP sensor wires based on color) appeared to be damaged.

If there was a short in the wiring would I still get ~5.00V when I back probe the MAP sensor?

3. Finally, when I unplug the MAP sensor and check the voltage again on the harness side I get exactly 5.00V which makes me believe that the MAP sensor is bad?

Any insight would be greatly appreciated!!

scotty305

iTrader: (2)

The center pin (Black/LightGreen wire) should connect to pin 4D on the ECU, you can check this with a multimeter in resistance mode (should be less than 1.0 ohms resistance between the MAP connector and the ECU connector), or in continuity mode if you have that sort of multimeter. You will probably need to add a long length of jumper wire unless you have very long probe leads on your meter. This pin is sensor ground, it should measure about 0.0V-0.1V compared to battery ground. Let me know if you need more help with this concept.


The other two pins are going to be sensor 5V power (Brown/White wire, connects to ECU pin 3I) and MAP signal (Green/Yellow wire, connects to ECU pin 1D). It's not always easy to tell which pin is which just by looking at the diagram, if you are the wrong two pins you will always measure 5.0V.

With the MAP sensor disconnected, the stock ECU may have a 'pull-up resistor' circuit that will cause the voltage to be about 5.0V in order to allow the ECU to detect a broken wire or disconnected sensor. Try using a paperclip to 'back-probe' the pin with the sensor connected.


If you suspect there may be a short in the harness, disconnect the sensor, turn all the power off, and measure resistance between PinA - PinB, PinA - PinC, and PinB - PinC.



Hope this helps, trying to troubleshoot electrical problems via the internet isn't an easy process...

arghx

iTrader: (3)

You could have a loose pin in the connector.

ohioredrx7

iTrader: (13)

Thank you for the insight! I will have to check the continuity this weekend as that may take more time. But I did unplug the sensor (everything powered off) and measured the resistance between the pins on the harness and got the following:

PinA-PinB = 239 ohms
PinA-PinC = 129 k ohms
PinB-PinC = 129 k ohms

The PinA-PinB is quite a bit lower than the other two readings but I would have expected significantly less resistance if there was a short present. Does the PinA-PinB resistance seem correct?

dgeesaman

iTrader: (7)

FYI I think the stock fender liners actually have some stainless staples.

linnadawg

iTrader: (14)

Another FYI: The G/Y wire for the map signal is terminal 1O on the ecu, not 1D. Very hard to read the electrical manual, I know.

JM1FD

iTrader: (1)

If you're measuring pins at the MAP sensor connector, and only that connector, you're measuring resistance of the parts inside the ECU which is a meaningless test.

You need to probe one pin at the MAP sensor connector, and its corresponding pin at the ECU connector to test the resistance of the harness itself.

RotaryEvolution

iTrader: (30)

not if you're checking for cross continuity which is what happens when the LF harness rubs through. but yes, disconnecting the plug from the ECU will give more of an idea if it is a problem or not.

other issue is that it may not be crossing onto another map sensor circuit wire, there are at least 40-50 different wires in that bundle where it gets munched. if one of them happens to be a full ground or 12V feed, kiss your ECU goodbye.