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oh yeah good catch, that was the ground wire for the O2 sensor from the EECM pin 49... See post #6.....
Still surprised at the .7v reading you were getting.
Was the ECT Code O, CM or R ?
Check the wiring to it as well, disconnected you should get voltage on one side of the connector LT G/Y, ground on the other, Black.
Last edited by vjsimone; Sep 21, 2018 at 01:47 PM.
Reason: Modify/adding text
The ECT was during the KOER test. It didn't show up in the CM or KOEO. But the truck was warmed up and at operating temp. I had driven about 10 miles just to make sure it was in fact warmed up. It seems like things just keep breaking on this truck. Now I don't have spark. Truck fired up fine but I got about 200 yards down the road and it just quit and wouldn't restart. Put my spark tester on it. No spark. I swapped out coils no change. That was all the testing I could do at the time. I need to check the TFI and if I'm getting power to the coil pack. I'll also unplug the PCM and see if it will spark. I love my truck but half the time it seems like there's something wrong with it.
Ok I found the problem... The Autozone distributor sheared off the roll pin on the gear. Exactly why I quit using their parts about a year and a half ago. Rebuilt my original Motorcraft dist and in a new Motorcraft PIP. All is good now. Thanks to everyone who helped. BTW... you know an aftermarket dist is bad if the gear just slides up and down on the shaft. I had to use my shop press to remove the gear on the Motorcraft distributor.
Anybody has a wiring diagram for that o2 sensor and the orange wire on intake side? Im trying to track down my o2 wiring as well. Getting 0.6 v ildling on the sensor wire, which is pretty good. Still keep getting 41 code. Engine runs smooth, no prob. Just that code. My old snapon scanner says it even could be trans throwing the code. Also it could be the old ECM which has to be updated to newer calibration, according to snapon. See pics. Thanks!
Here is a 1991 drawing.
Where are you measuring the 0.6 v ? Pin 29 on the EECM ?
Thank you for the diagram.
So far I only measured directly from the sensor wire (disconnected from vehicle harness). Whats the best way to get to the terminal? There is a big round connection under steering wheel or do I go to ecu directly behind firewall?
Also, snapon scanner says its terminal or pin 49. How to tell which one it is? Is the wire at the terminal going to be the same collor? (Orange)?
The output from the O2 is on pin 29 I believe, Pin 49 would have the source voltage for all those devices tied to pin 49, 5volts dc most likely.
With the O2 output to the EECM, you want to measure it at the EECM pin 29 with the engine running.
Measuring it anywhere else may not show the voltage that the EECM is reading.
Depending on the condition of the connectors and wire along the path, you can get some resistance that will affect the voltage reading before it gets to the EECM.
If a 1990 is the same as a 91, looks like it is a Gray / Light Blue striped wire at the EECM pin 29.
While you are at it, measure the voltage at the O2 connector for the O2 Heater, looks like a Purple / Orange striped wire.
Last edited by vjsimone; May 10, 2022 at 08:18 AM.
Reason: Adding text
Got it. Can it be measured at under steering wheel terminal? Or i gotta go to where heater core is where ECU is located? If so, can inside area be easily accessed? Thanks!
Got it. Can it be measured at under steering wheel terminal? Or i gotta go to where heater core is where ECU is located? If so, can inside area be easily accessed? Thanks!
It's best to measure that small voltage at the wire in the connector to the EECM. The connector needs to be connected to the EECM for testing.
You may be able to get to the pin 29 via the back of the connector, you can sometimes secure a pin or paperclip in the back of the connector, shoved down next to the connector the wire is attached to.
Less popular, but I’m not opposed to, is to skim off some insulation to get to the wire, you can slap some liquid tape on that spot once the fix is completed.
You can run a sharp pin through the insulation, to the wire as well.
In my old age I take the easiest route, and liquid tape it after. But I have an EECM breakout box for the EECM that makes the measurement at the EECM easier for me.
What model Voltmeter do you have?
Alligator clips for the meter leads are always handy
It's best to measure that small voltage at the wire in the connector to the EECM. The connector needs to be connected to the EECM for testing.
You may be able to get to the pin 29 via the back of the connector, you can sometimes secure a pin or paperclip in the back of the connector, shoved down next to the connector the wire is attached to.
Less popular, but I’m not opposed to, is to skim off some insulation to get to the wire, you can slap some liquid tape on that spot once the fix is completed.
You can run a sharp pin through the insulation, to the wire as well.
In my old age I take the easiest route, and liquid tape it after. But I have an EECM breakout box for the EECM that makes the measurement at the EECM easier for me.
What model Voltmeter do you have?
Alligator clips for the meter leads are always handy
Ive got a regular walmart voltmeter for 20$. I guess millivolts DC would be good right?
also, what color of wire is it? Do you happen to have a diagram of the ECU terminal? Thanks!
