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I have a 93 eg hatch with a 1996 GSR motor. I recently had a leaking radiator hose. I changed the hose and oil. I drove the car after the oil change and it ran well. Typical small sputter randomly but nothing abnormal. On my way to work a couple hours after that the CEL came on and the car is running super rich. I checked the CEL and it was for the MAP sensor. I have tried four MAP sensors, three different connectors, four ECUs and nothing. I ran new wires directly to the ECU and still get the same code. I am seeing 133mV on the signal wire no matter what I do, engine on or off. One ECU showed 2.9v but once I started it it came back after revving the motor a little. I checked the grounds and nothing is extraordinary. A23 has about 4 ohms of resistance but the others have 0.4-0.5 ohms of resistance from the ECU pins to the body. Has anyone ever had this issue? What else can I check?

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The MAP voltage is 4.96V at the sensor and ECU.

Caoboy

@RonJ

@NotARaCist


Help is on its way!

Former User

Code 3 or 5?

Where and how are you taking this measurement? What is the wire color?

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Code 3. I am taking the measurement at the ECU pin d17 and the wire to the right on the map sensor I get the same voltage. I don't recall the color at this time. I'm not with the car at the moment. I am back probing the connectors and putting the red lead to it and the black to the body ground. And the measurement is the same if I put it to the sensor ground.

Former User

Unplug the MAP sensor connector. Turn key to ON(II). Measure voltage to body ground at the two outer MAP sensor connector pins that run to ECU pins D17 and D19. Do you measure approximately 5V?

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The two MAP pins on the outside are d17 sensor signal on the right and d19 sensor power on the left correct? The middle pin is sensor ground and runs to d21 right?

Former User

below top pin is D19, middle pin is D17, and bottom pin is D21

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So I just tested my brothers car with his DMM. He is getting 2.9V at the exact pin I was getting 133mV on his car. I'm going to change my batteries later tonight and retest. I think this could be where such an odd voltage is coming from. I don't get off until 1130 so I will probably update in the morning. Thanks for the quick replies.

Former User

Seriously, why do members like you create a thread asking for help but then ignore advice given? I don't get it. Post the voltage readings I requested or move on and stop wasting time here.

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Also I am going to double check that it is wired correctly. I've had this car in this motor for almost 2 years and its just now giving me these issues.

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I'm not ignoring anything said. I am not with the car at the moment so I can not check the voltage as you stated. I'm doing what I can with what I have on hand at the moment. If the DMM has been reading wrong this whole time it could be the reason my voltage readings I am getting are making no sense. I've been testing wires for the past three days. I'm sure I've done that reading I just don't recall the numbers I got.

Former User

How you should proceed from here entirely depends on knowing the two voltage readings I requested. Post again when you have those readings.

tony_2018

So just respond when you followed through with the questions that are put to you, its that simple.

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Its also possible that my DMM is bad. So there could be wrong voltages and my reading may not be correct. That might pose an issue in diagnosing an electrical issue. My brain is still intact although I can not seem to figure out this issue.

Now, for the white wire I got 4.96V and for the yel/red wire I got 12mV with the connector disconnected and the key in the on position.

I was questioning the wires you posted because everything I have read shows the grn/wht wire to d21 not d17, yel/red to d19 not d21, and the wht wire to d17 not d19 as your diagram shows. I have the sensor wired just as the diagram RonJ posted as of now.

According to the FSM and the flow chart wht goes to d17, grn/wht goes to d21, and the yel/red goes to d19. Pages 245-246 in adobe or 11-55-11-56.

Former User

This^ is the problem if the three MAP sensor wires are properly pinned to the ECU.

You are correct. I mixed up the ECU pins in my post. Repin the wires properly to the ECU as shown in diagram below. I'll edit my original post to avoid confusion for people reading this thread.

However, if you did the voltage tests on the two outer pins of the MAP sensor connector with the wires properly pinned to the ECU, then you found the problem. The Wht wire and Yel/Red wire both should read 5V.

below: top pin is D19; middle pin is D17; and bottom pin is D21

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So all four ECUs are bad? As this is possible it also seems highly unlikely. Can you explain how this sensor works? I thought the 5V goes in travels along a resistor that changes based on vacuum pressure to ground. The signal wire is before ground and just sends the ECU what the voltage is at a specific point on that resistor. The ECU makes fuel and timing adjustments based on that sensor wire. Or am I wrong and it send 5V on the signal wire which gets adjusted on the wire at the sensor which changes the whole wire reading?

Former User

What brings you to this conclusion?

Let's start simple. The ECU supplies a reference 5V on the Wht wire and the Yel/Red wire, and the Grn/Wht wire supplies ground for these reference voltages. If you don't have 5V on the Yel/Red wire and it's properly pinned to the ECU, then you found the problem, right?

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All four ECU's get the same value. 12mV on the signal wire.

I did forget to update that with the wires repinned correctly I am seeing 4.96 on the yel/red and 12mV on the white. I know the problem is low voltage on the signal wire. But I am trying to figure out why. I have changed everything in the circuit and get the same readings.

Former User

Same difference. This^ is the problem.

FYI - You are taking the voltage measurement from the MAP sensor connector, though the voltage source is the ECU. So, what are possible causes for the low voltage reading on the Wht wire in the MAP sensor connector and what test(s) might you do to provide additional diagnostic information that could pinpoint the problem?

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The only things that cause a low voltage in a wire are an open/resistance or a short. I have tested the voltages at the ECU with D connector unplugged. The readings are the same. I have an old ECU plug harness that I can depin and disconnected the plug with the key in the on position and slid just the terminals on the ECU pins and I have continuity to ground on d21, 4.96V at d19, and 0.9mV at d17 now.

Resistance on the yel/red 0.3 ohms, grn/wht is 0.7 ohms, and wht is 0.9 ohms.

Are there any tests I am missing?

Former User

Did you test the Wht wire for a short to ground?

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Yes. There is not a short to ground. I have just recently ran all three wires directly to the ECU in my attempt to diagnose the issue. And tested it again when I did the resistance tests.

Former User

What are you using for ground in your voltage tests?

For example, what is the voltage reading to body ground versus to ECU pin D21 on the Wht wire if you leave all ECU connectors plugged in and then back probe ECU connector D at Wht wire pin D17?

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It is the same. 0.9mV whether I use the body ground or pin d21 to ground. I have done just about all voltage checks both ways.