93 starts won't Idle

[shorod]

Just a guess here on the code 412. Sounds like maybe the idle air control is not working. Do you happen to have a signal generator that can generate a 5-volt PWM signal? If so, I think you could probably bench test the IAC.

As for a spot that's prone to abrasion, I'm not that familiar with any particular spot, but then again I'm a hobbyist automotive tech, not a professional who sees a lot of Taurii on a daily basis. I owned a couple of Taurus SHO's, but never a "normal" Taurus.

-Rod

[ss#4]

Well I was thinking the same with the IAC but I had a new one and it didn't seem to act any different. I just took it back to the parts store today.. I am only a hobbiest also so I know what you mean. I got it to idle by adjusting the set screw but I know this is not the fix. Is there a good way to check with a DMM the lead from the harness on the O2 sensor to check for a break???

DonSor: it will not start unless I apply the gas, it will start right up then but it will not idle, dies right out.

[shorod]

According to the service manual, the items that can cause the code 412 are:
-Open or shorted circuit
-Throttle linkage binding
-Improper idle airflow set
-Throttle body/ISC solenoid contamination
-Items external to Idle Speed Control system that could affect engine rpm.
-Damaged ISC solenoid
-Damaged processor.

Have you removed the processor from the car before, or are you comfortable removing it? If so, you could remove the processor and check for continuity between the processor and the O2 sensors. One check you could try before doing that is to disconnect one at a time and see how that affects the readings you get. For one, that will help you determine which sensor is in bank 1, and two, if a code would be set if the sensor wiring is open.

The wiring connector to the PCM unbolts from the upper firewall under the hood on the passenger side. The PCM will be removed from the inside after you open the glove box door completely and remove the one mounting bracket. The service manual shows that pin 94 is for the #2 O2 sensor, and it's labeled "Front." The wire color should be Red/black. Pin 74 is for the #1 O2 sensor, and that wire color should be gray/black. Pin 46 is the signal return for the O1 sensors, and it is a gray/red wire. Of the two remaining wires for the O2 sensors (heated), one is power with the key in "Run" and the other is ground.

-Rod

[ss#4]

I did the check to see which O2 sensor gives me a problem and I have determined it is the Bank against the firewall (go figure). It is interesting that it does not throw a code with both sensors (or either one) unplugged completely. it acts exactly the same. I have the PCM disconnected now (funny you should recommend that) and will check for continuity to the pins. Should I assume a new harness if I find a bad wire? (thinking like as a repair shop). I will post back in an hour or so.

thanks Again.
Rod if you don't mind PM me your phone number.

[ss#4]

Okay here is what I have so far. I pulled the main connector off the firewall retained with a 8mm bolt. Removing the shroud shows me the wire colors and the numbers. However this is only a 60 pin connector. Does the manual show some sort of offset/coorelation on the Pin numbering scheme?? Just so I can verify the pin location.

I did however find the wire colors you mentioned and on the front sensor #2 the red/black wire has connection to the sensor connector. What is the wire color for the signal on #2.

Sensor #1 the gray/black has no connection = BAD The Gray/red (signal) is Good.

Can I assume I could run a wire directly from the connector at the sensor up to the PCM connector and effectively Jump the bad wire? Or do I need to locate the bad spot in the wire? Is there anything inbetween the 2 connectors or just wire?
Thanks we are getting closer.

[ss#4]

BTW do you think there could still be a problem with the IAC? If still have a couple hours to pick one up before the part store closes for the weekend. thanks

[shorod]

Originally Posted by ss#4

Okay here is what I have so far. I pulled the main connector off the firewall retained with a 8mm bolt. Removing the shroud shows me the wire colors and the numbers. However this is only a 60 pin connector. Does the manual show some sort of offset/coorelation on the Pin numbering scheme?? Just so I can verify the pin location.

I did however find the wire colors you mentioned and on the front sensor #2 the red/black wire has connection to the sensor connector. What is the wire color for the signal on #2.

Sensor #1 the gray/black has no connection = BAD The Gray/red (signal) is Good.

Can I assume I could run a wire directly from the connector at the sensor up to the PCM connector and effectively Jump the bad wire? Or do I need to locate the bad spot in the wire? Is there anything inbetween the 2 connectors or just wire?
Thanks we are getting closer.

Oops, I gave you the number from the wrong column in the wiring table. O2 #2 (front) signal wire is pin 43 (red/black), pin 44 (gray/light blue) is the signal wire for O2 #1 (rear). I guess I was tired when I typed the last message. Gray/black as I typed last message is the wrong wire color for this. The gray/black wire is for the transmission speed sensor, and should be in pin location 5. The sensor return is pin 46 (Gray/red).

If you do find a bad wire, ask me to double check the wire color and pinout again (although I did get a good night's sleep last night). If everything still matches up, then you should be able to run a jumper wire to see if that changes the idle. However, I would suggest following the original wire and trying to determine when the problem is. If something happened to cause this low current wire to open, chances are pretty good there are other wires in the harness that are or are about to open as well.

Sorry for the passing on some wrong info in my last post.

As for the ISC/IAC, you should probably hold off on that until you get the O2 sensor issue resolved.

-Rod

[ss#4]

Can you tell me again what are the 2 Pins and colors for the #1 Sensor (Rear)?

[ss#4]

Corrections: here is what I have.
Looking at the wires from the harness connector at the O2 sensor to the PCM connector.

Sensor #2 Front:
red/black wire continuity to #43
gray/red wire continuity to #5, #28, #46

Sensor #1 Rear:
gray/light blue wire continuity to #44
gray/red wire continuity to #5, #28, #46

I assume the gray/red wires are T'd in the harness some place. Are these a power or ground by chance?

It appears to me these maybe connected correctly in that case the PCM is questionable correct??

[shorod]

Pin 5 is for the Transmission Speed sensor (gray/black) and Pin 28 is for the Power Steering Pressure switch. Pin 46 is the return for the oxygen sensors (ground) and yes, the return line is common between the two O2 sensors. I'm not sure though why they would have continuity to the PSP though. The transmission speed sensor is probably essentially a DC motor/generator, and therefore that makes some sense as your "continuity" is probably small DC resistance through the coil of the motor. The PSP continuity makes sense after reading the description for the PSP, "With no power steering pressure applied the reference voltage is shunted to ground along the SIG RTN circuit."

Have you verified the remaining two wires to the O2 sensors for the heater? You should do that prior to condemning the PCM. Ford PCMs have a pretty high reliability. If your O2 sensor heater is not working, your O2 sensor will not work properly until it's up to temperature.

-Rod

[ss#4]

argh!!
Both of the O2 have 12.46 volts across the other 2 wires and they physically get warmer with the key on. Assume this says the PCM is doing its job?? But still why no #1 O2 reading on the scanner. It seems a complete 0.00 reading should throw a code.

[ss#4]

Help!!! I can't figure this crazy thing out!!!!

[shorod]

There a few options here that I can think of:

1) You can try to find someone with a known good loaner PCM for your car and see if that makes a difference.

2) You can backprobe the O2 sensor wires for the signal and return lines either at the sensor or at the PCM (preferably at the PCM) and see if the voltages reported on the scan tool agree with the voltages one from the sensor. You'll obviously need to have the PCM installed for this step.

3) You can remove the O2 sensor from the car and test it on the bench with a vice, a DMM, and a propane torch.

Since you've replaced the sensors recently and still no change in the readings of the O2 from the PCM, I'd suggest starting at the second option. Finding someone to help out with option 1 could be pretty tricky. If you find that the O2 sensor is reporting accurate voltages to the PCM, then your PCM seems like a likely suspect.

-Rod

[ss#4]

What input voltage is the output voltage based on?? 5 volts? With just the key on and engine cold both sensors only have a 12volt supply. Seems as though one of the sensor pins should have a lower supply voltage.

What is the other pin# at the PCM for the #1 O2 sensor (Rear)??

[ss#4]

Here is what I know today.

I back checked the o2 sensor outputs at both the sensor and the PCM. The front sensor (red/black wire) fluctuates like the scan tool reports, .25 to .8 volts. the rear sensor (gray/light blue) reads .9 to .8 with the voltmeter, scan tool still says 0.00. Since the rear is sending info to the PCM does it make sense that PCM is not getting it. The power is getting to the pin and the pins on the PCM look fine. Does the lack of fluctation in the output, .1 volts relative to the front, that the PCM is not adjusting fuel to this set of cylinders?

I will also try pinching the pin on the connector side to make sure the connection is being made to the PCM.

Just to cover another base I pulled the EGR and flushed with cleaner and pulled a vacuum on the diaphragm and it all looks okay and moves freely.

Lastly, what are your thoughts on a yard PCM vs a reman from Carquest??

Thanks for your continued support on this I will owe you a twelver when this is finally fixed.