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Old 09-05-2019, 12:09 PM   #1
Mitsu940
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Default Idle problems Running rich

Hello all..

i think i have a problem with my 92, 940 b230ft..
After cleaning the throttlebody and replacing the engine temp sensor, its now running really rich in idle until its warmed up. it smells really bad of gas from the exhaust.
I have a AEM AFR meter installed.
starting it up cold my AFR says around 10.6, half warm around 12-13 and fully warm 14.3--14,9 when the car is idling around 750-800rpm. Sometimes when its at operating tempeture it also runs around 12.6 when cruising.
Before replacing the engine temp sensor i had the 123 code from socket2, and AFR was around 14 when starting the engine cold.
Throttle position sensor is adjusted all the way clockwise and back until the click is coming.
I cant find any vaccum leaks, most are replaced with new silecone hoses.
New spark plug wires, and plugs are installed and after 50miles they show no sign of getting to much fuel..
I get no fault codes. i runs great, but im pretty sure something is wrong?
It also runs lean +18 when cruising and releasing the throttle completly, but im pretty sure thats normal because it cut off the injectors, right?

Any suggestions on what could be the problem?
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Old 09-05-2019, 12:32 PM   #2
dl242gt
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I would get out your ohm meter and check the engine coolant sensor resistance at three test points. Cold engine, warm engine, and fully up to temp. Measure those resistances at the connector on the computers. You will have to test both at the fuel ecu and ezk. There is a resistance test chart in the manuals and on posts here.

If the engine coolant sensor is open circuit then your engine never goes into closed loop and runs very rich as if you are in the middle of winter above the arctic circle. I've had sensors that are bad and out of spec brand new and also experienced sensors that fail and go open circuit when hot. It may also be the connector or wiring so that is why you test at the computer. That way you check the wiring and the sensor.
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Old 09-05-2019, 12:56 PM   #3
DET17
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Exactly. Your new ECT has likely created this mess. With no input data, the ECU goes into a "safe mode" and many times will run pig rich.
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Old 09-05-2019, 03:23 PM   #4
Mitsu940
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Will have to try at the ECU tomorrow when i have more time, tried measure with cold engine, connectors says 4.17 and 4.21k , started the engine and turned it of half way up and got 1.6 and 1.8k and when the AFR goes back to normal it says 0.5 and 0.7k.. Without the sensor connected it starts at AFR around 14.3-14.7 with cold engine, dont know if that tells anything.
the pins i need to meassure on the ECU is between pin 13 and ground? and for the EZK its pin 2 and ground?
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Old 09-05-2019, 03:40 PM   #5
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Quote:
Originally Posted by Mitsu940 View Post
...
the pins i need to meassure on the ECU is between pin 13 and ground? and for the EZK its pin 2 and ground?
Yes, those are the pins, but when you measure resistance, the car needs to be shut off and the plug you're probing disconnected from its ECU.
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Old 09-05-2019, 04:01 PM   #6
Mitsu940
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#5 thanks, ill remember that.. But isnt it enough to meassure between the connectors pins to the engine temp sensor and pin 2 and 13 to see if there are connection?
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Old 09-06-2019, 05:38 AM   #7
cleanflametrap
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Quote:
Originally Posted by Mitsu940 View Post
#5 thanks, ill remember that.. But isnt it enough to meassure between the connectors pins to the engine temp sensor and pin 2 and 13 to see if there are connection?
You're right, that's one of the tests you could make. I just can't envision you snaking DMM test leads both under the manifold and at the ECU at the same time.

The object of testing the ECT by measuring resistance to ground at the ECU connector is to leave as much of the circuit in place as it is normally when you drive the car. When you pull things apart to test them you assume the connectors make sufficient contact in a stable way. Checking from inside the car is easier and cleaner.

Even better is learning to leave the entire circuit intact, measuring the voltage that results as the resistance changes, because now you could watch your AFR meter simultaneously as you watch the warmup bring the ECT sensor resistance down. You don't have to guess when to stop the car and take another resistance reading. And, if the sensor or its connection is thermally or mechanically intermittent, you'll probably catch it in the act as you take the motor from stone cold to thermostat temp. Use this chart to match voltage to temperature.

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Old 09-06-2019, 11:57 AM   #8
Mitsu940
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#7 You talked about not having the engine running, and have the connector to the ECU disconnected, thats only when im meassuring resistance?
So i have to understand this correctly, I can meassure the voltage between pin 13 and ground with the car running and see how it goes down in voltage as the resistance drop on the ECT?
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Old 09-06-2019, 02:10 PM   #9
dl242gt
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Yes, you can back probe the connector while connected and car running to watch the voltage change as warmup proceeds. I have had sensors go open circuit when hot but are in spec when cold or warm. The voltage is a better mechod to watch the entire process. You would see the voltage jump back up to the applied voltage if the sensor goes open circuit.
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Old 09-06-2019, 10:06 PM   #10
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At 68 degrees you should get a good idea of what it tests between engine ground to each of the 2 sensor terminals. the sensor may not give an accurate reading if the probe is not immersed in liquid.
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