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Vic - Please repot back on the results when you cut one diode out. I ask because I cannot figure out how two diodes could cause a problem. Whichever diode switches on fastest will conduct the back EMF from the solenoid. The other one may switch on and help, but we are talking about such small differences in current that just a different diode would make bigger changes.
Given that, I don't think you will see a difference. But, I'm here to learn so please let us know.
Will do, Gary.
My electronic technician & computer tech skills get rustier every day, so electronically, I don't know why 2 parallel diodes would cause an issue.
But Ford put out a TSB on the issue because it was causing idle issues; TSB 89-24-04 IAC Diode.
There would be a voltage drop across each diode, so slightly less voltage would show up at the ECM (if I got my directions right). When the computer activates the FET to ground the IAC it should still work the same way, I would think.
Yes, Vincent. Clarification for you. I do not intend to use the second diode. In fact, I have already removed it. But, the second red wire was originally connected to the side with the white wire. Still disregard it? I will do what you recommend.
I am suggesting that it is now a spare wire, for now I would tape it over. Let's see what happens moving forward.
Last edited by vjsimone; Jul 21, 2016 at 09:47 AM.
Reason: Modify text
There would be a voltage drop across each diode, so slightly less voltage would show up at the ECM (if I got my directions right). When the computer activates the FET to ground the IAC it should still work the same way, I would think.
Yes and no. Whichever diode is fastest will come on first and start conducting current. And at the end of the cycle whichever diode has the lowest voltage drop, and we are talking .7v ish, will be the last to conduct with the other having stopped conducting.
Let's take two scenarios:
Diode 1 is fastest and has the least drop: In this case Diode 1 will start conducting first, Diode 2 will kick in and help but drop out at the end. So, the effect is that it is basically as if Diode 2 isn't there.
Diode 1 is fastest but Diode 2 has the least drop: Diode 1 will kick in and start conducting first, then Diode 2 will start and will take it to the end. In this case the overall timeframe will be shortened slightly over just having Diode 2.
Bottom Line: The differences between having one diode and having multiple should be very small, and probably are within the tolerances of the spec's on production line diodes.
Yes and no. Whichever diode is fastest will come on first and start conducting current. And at the end of the cycle whichever diode has the lowest voltage drop, and we are talking .7v ish, will be the last to conduct with the other having stopped conducting.
Let's take two scenarios:
Diode 1 is fastest and has the least drop: In this case Diode 1 will start conducting first, Diode 2 will kick in and help but drop out at the end. So, the effect is that it is basically as if Diode 2 isn't there.
Diode 1 is fastest but Diode 2 has the least drop: Diode 1 will kick in and start conducting first, then Diode 2 will start and will take it to the end. In this case the overall timeframe will be shortened slightly over just having Diode 2.
Bottom Line: The differences between having one diode and having multiple should be very small, and probably are within the tolerances of the spec's on production line diodes.
There would be a voltage drop across each diode, so slightly less voltage would show up at the ECM (if I got my directions right). When the computer activates the FET to ground the IAC it should still work the same way, I would think.
The EEC (ECM as you call it) grounds the wire in a varying pulse width so the EEC can adjust the air being bypassed during deceleration (for emission) and at idle for RPM.
To try and alleviate your concerns about a stray red wire and what to do with it...
That red wire is part of Circuit 361 and powers all sorts of engine-control devices.
In the Ford diagram, they are thick, black lines (with "361" and "R").
Notice how they all converge together at Splice 172 (near the blue ZZ triangle):
Point being, having a stray red wire that is no longer connected to anything isn't going to hurt anything, it's a good idea to "cap it off" and isolate it from everything else. Do NOT connect it to a different-colored wire!!!!
The EEC (ECM as you call it) grounds the wire in a varying pulse width so the EEC can adjust the air being bypassed during deceleration (for emission) and at idle for RPM.
Thanks, kinda like the injector banks....
I kinda stick with the Ford documentation for the 85'. They call it an ECA - Electronic Control Assembly.
I have a fold out wiring diagram, dated 4-2-84, on the 5.0/5.8, 1985, this labels the computer as an; "Engine Electronic Control Processor”
In my Jeep, they call it a “PCM”, all synonymous for the main computer. But on the Jeep forum, you have to be careful, for there are 3 different computers in my 2008 Jeep.
Oh, for EEC I have seen; Electronic Engine Control - Electronic Emission Control
Your schematic post have been great for understanding what is going on inside the computer, first time I have seen any. Hieroglyphics to Steve, but I understand them. Thanks for posting them.
Last edited by vjsimone; Jul 21, 2016 at 10:59 AM.
Reason: Adding text
I did not pick up a vacuum gauge yet. I did spray some WD40 around hoses, intake, throttle housing, IAC connection to the throttle housing, PCV valve, you get the idea. No increase in idle to report.
I suppose I need to go out a get a gauge. Not exactly sure what to do with it from there. I'm guessing I disconnect a hose at a time and test it. What reading should I look for?
Originally Posted by vjsimone
Consistancy is good.
Did you pick up a vacuum gage to help troubleshoot your Code 34?
Thanks!! - That's what I've done. And I am beginning to understand the schematics. Learning the symbols helps. I learned them a long time ago when I took my test for my Ham Operator's License. But I forgot most of them.
Originally Posted by ctubutis
Steve,
To try and alleviate your concerns about a stray red wire and what to do with it...
That red wire is part of Circuit 361 and powers all sorts of engine-control devices.
In the Ford diagram, they are thick, black lines (with "361" and "R").
Notice how they all converge together at Splice 172 (near the blue ZZ triangle):
Point being, having a stray red wire that is no longer connected to anything isn't going to hurt anything, it's a good idea to "cap it off" and isolate it from everything else. Do NOT connect it to a different-colored wire!!!!
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