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I've done wiring wiggling a thousand times. I think there may be a wire run to the wrong place. As an example, I have three wires running to my IAC, 2 of them hot. If I disconnect one of the hot wire, it still runs. If I switch one hot wire with the other, it still runs. They are still connected that way because there's NO place for the other hot wire to go. Very confusing.
Originally Posted by vjsimone
Maybe some wire wiggling testing..........
Brand new Relay right?
I’m working on an 85’, built in July, and yes, I get plenty of codes. I can report that yesterday she passed KOEO self-test (code 11 !!) and just the O2 sensor code left on KOER test.
I went through something similar on a 1993 Taurus (still OBD1 but lots more advanced by then) and it was the fuel system, the sensors were doing their jobs. Might consider that but I know nothing of your project.
Originally Posted by vjsimone
Others have stated, and from what I have read, there were a lot of programming changes to these computers by the 86 model year. Could these programing changes effect the newer version computers enough to effect the self-test if installed in an older vehicle?
I can't see how that could be possible.
There is *one* OBD1 self-test connector used the entire lifetime across the entire Ford product line. IOW any Ford self-test connector should be able to talk to any Ford computer in any vehicle, that wiring stayed the same.
If I disconnect one of the hot wire, it still runs. If I switch one hot wire with the other, it still runs.
OMGosh you're doing stuff like that? This can be very dangerous to do to a computer, applying a large amount of incoming voltage to any pin that isn't designed to accept it, you can damage the computer doing that.
The vehicle is shut off when I switch the wires. And, I'm doing so with an extra IAC that I have (I suppose that still doesn't matter since it all flows back to he ECM.) I don't know.
I can't see what the use is to have two power sources coming into the IAC unless it's getting two different messages from two different places pending on the running conditions.
Originally Posted by ctubutis
OMGosh you're doing stuff like that? This can be very dangerous to do to a computer, applying a large amount of incoming voltage to any pin that isn't designed to accept it, you can damage the computer doing that.
I got it with the two wires wired together and didn't change it because I can't see where the extra one would go. But I can't see what the use is to have two power sources coming into the IAC unless it's getting two different messages from two different places pending on the running conditions.
The IAC (throttle air bypass valve solenoid) has two wires that feed it, but one of those wires contains a splice and branches off to a diode.
Specifically:
The red wire (Circuit 361) supplies power from the EEC power relay (it's two pages in the book so two images, follow the red wire)
The gray/white-stripe wire feeds Pin 21 on the computer, but that wire also splices into a connection to a diode blocking power coming directly from that same EEC-relay circuit.
I'm missing the diode. I have two wires coming from the harness (red - no striped) coming into a red wire on the IAC connector. I have one white wire on the connector connecting to the grey/white stripe wire in the harness. There is no diode. What sort of problems might that cause? Where can I purchase the diode if I must have one?
I take it that second red wire connects to the diode? I'm sorry but schematics are hard for me to follow. It's not that I'm stupid; I have some brain trauma going on due to a disease and it's hard for me to follow along sometimes.
Originally Posted by ctubutis
The IAC (throttle air bypass valve solenoid) has two wires that feed it, but one of those wires contains a splice and branches off to a diode.
Specifically:
The red wire (Circuit 36) supplies power from the EEC power relay (it's two pages in the book so two images, follow the red wire)
The gray/white-stripe wire feeds Pin 21 on the computer, but that wire also splices into a connection to a diode blocking power coming directly from that same EEC-relay circuit.
OK...I see it now. So, do I need the diode AND do you know where I can get one?
Originally Posted by ctubutis
The IAC (throttle air bypass valve solenoid) has two wires that feed it, but one of those wires contains a splice and branches off to a diode.
Specifically:
The red wire (Circuit 36) supplies power from the EEC power relay (it's two pages in the book so two images, follow the red wire)
The gray/white-stripe wire feeds Pin 21 on the computer, but that wire also splices into a connection to a diode blocking power coming directly from that same EEC-relay circuit.
Appears from what you wrote and from the diagrams that a diode is absolutely necessary and could be the cause of my inability to have the computer send codes. I've read some post where ht elater model IAC's actually have a diode built into the connector, but in looking at my IAC, that doesn't appear to be the case.
I am unable to find what type of diode to use (high voltage, low voltage, etc.) If you (ctubutis) or anyone else reading this thread can offer assistance, I thank you!
Originally Posted by ctubutis
The IAC (throttle air bypass valve solenoid) has two wires that feed it, but one of those wires contains a splice and branches off to a diode.
Specifically:
The red wire (Circuit 36) supplies power from the EEC power relay (it's two pages in the book so two images, follow the red wire)
The gray/white-stripe wire feeds Pin 21 on the computer, but that wire also splices into a connection to a diode blocking power coming directly from that same EEC-relay circuit.
Yeah, you guys are a riot. We made better beer too before globalization.
Anyways, just a thought on your lack of self test codes. Are you using a reader or a test light? If I recall correctly, 85/86 did not have a check engine light in the dash. The STO from pin 17 of the computer does not supply a positive voltage, rather it is a switched ground. That means you hook the other end of the test light to the +12V terminal! I don't know if the computer has an internal pull up resistor, but without a check engine light and depending on the circuitry of the code reader, you may not be getting any codes because of the lack of any reference to battery +. There is a minor difference in wire color between 85/86 and later models. The STO wire is tan/red stripe instead of pink/lt green stripe. Maybe this was already covered, but thought it was worth mentioning.
The other issue is your damp weather fuel pump problem. Have you ever determined if the fuel pump relay is in fact activated when this happens? It would be easy enough to measure the voltage at the self test connector on the tan/lt green stripe wire. Should be +12V pump not running and 0V with the pump running. Measuring this voltage with the fault present will be an important clue.
Oh, wow, a 1985 diode... I have a picture of a 90's-gen version around here somewhere but can't say right now it looks anything at all like what they used in 1985... boy I miss Ralph.
You could possibly detect if that diode is there by unplugging the IAC and the ECM and using the diode check function on your multimeter across the red and grey/white wires at the IAC. Should be able to read that diode across there without any interference from other circuitry.
Like Chris says, probably have not unwrapped the harness enough to find it. Very unlikely it's not there. If it does have to be replaced, something simple like a 1N4005 would work. Anything 1A and over 50 PIV should work.
