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Old 01-13-2013, 09:50 AM   #1 (permalink)
DP
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Stuck in an open loop

The reading on the X11 pins 2 and 3 stays at 2.90V (VOM set to DC, scope showing a steady pulse that doesn't widen or narrows as I try to change the duty cycle) and steady no matter where I adjust the tower 3mm screw.
I have adjusted the air flow meter potentiometer
I have replace the O2 sensor (New unit)
I have replace the EHA (New unit)

Could it be a temp sensor?
I am going back to the garage to check how the O2 sensor is reacting on its own. In the mean time, tell me what you think.
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Old 01-13-2013, 12:26 PM   #2 (permalink)
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Okay, here is my update.
I unplugged the CIS temp sensor and the reading between pins 2 and 3 jumped to a steady 9.8V. The pulse wave widened on scope accordingly. This tell me that without the temp sensor in circuit the CIS goes to the other extreme.
Basically one extreme resembles the wave with the ignition on and engine off even if the engine is warm, that is the DC reading is 2.9V. The other extreme is when the temp sensor is out which brings the reading to 9.8V.
The happy medium should be something in between with fluctuations due to the O2 sensor.

Having observed that I measured the resistance of the temp sensor while the car was warm. I got about 800 to 900 Ohms between the poles and 400 Ohms via ground.
Reading the CIS troubleshooting guide, I should have between 290 and 370 Kilo Ohms to ground.

I think the sensor is shot!
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Old 01-13-2013, 12:29 PM   #3 (permalink)
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This guy

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Old 01-13-2013, 12:36 PM   #4 (permalink)
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I am reading conflicting stuff on the net and in the CIS manual itself. In some places it says at 80C the resistance should be between 290 and 370 Kilo Ohms and in others the range value is ONE THOUSAND times less, like 290 and 370 Ohms.
Which one is correct?
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Old 01-13-2013, 12:38 PM   #5 (permalink)
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This graph


Shows the range as 290 to 370 Ohms at 80 C. I am guessing there is a mistake in the CIS manual and some posts on the Internet are dead wrong as well.
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Old 01-13-2013, 02:37 PM   #6 (permalink)
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I just measured the resistance after the car cooled down. it's at 3.7 Kilo Ohms.
It's definitely shot!
Time to order a new one
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Old 01-13-2013, 03:54 PM   #7 (permalink)
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Originally Posted by DP View Post
I just measured the resistance after the car cooled down. it's at 3.7 Kilo Ohms.
It's definitely shot!
Time to order a new one
But at what Temp? 3.7K is fine if near 10C ( 50F, sounds like a cooled down motor to me )
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Old 01-13-2013, 04:10 PM   #8 (permalink)
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You are right but I ordered it anyway. Let's see if it fixes the open loop.
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Old 01-13-2013, 05:46 PM   #9 (permalink)
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that was the culprit of my 2.6...
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Old 01-13-2013, 07:49 PM   #10 (permalink)
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This is all great information! My one question (for anyone): How does the CIS computer know that the temp sensor is shot when it is based on ohms?

The CIS computer takes information from the many little sensors within our systems, works its magic, then sends the correct signals to wherever, right? So, if the engine is running on the "limp-home-mode," then one of those incoming signals is way off. It sounds like your temperature sensor isn't too far off....but would that slight deviation from what the CIS computer expects force it into "limp-home-mode?"

I personally think you have a bad electrical connection somewhere. Maybe a bad fuse or relay somewhere? In my experience, 95-98% of the issues on my '92 2.3 have been due to:
1. Electrical connections (sand the connections to fix it)
2. or those damn ceramic/plastic fuses...and their connections in the fuse box.
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