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Topic: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil (Read 533 times) previous topic - next topic

22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

helped a guy out who watched my several parts series on youtube relating to bench testing your TFI's & PIP's off the car to verify your spares are actually good.

he was going through distributors a lot,, meaning over a few months bad again.  he's a fox stang 85 cfi.
we talked on the phone a lot and bounced around ideas then it appeared after he dragged his dad into all of it,, his dad being a dealer wrench (retired i guess) , started to focus on this good ole 22k ohm resistor.

my suggestions were not so helpful because to be honest ,, not many of us here ever talk about that red headed step child and i admitted i just dont have the subject matter experience to speak to where its at,, what it does or anything.  I fixed all that and i clearly understand now its purpose.  the fella got his 22kohm resistor installed and i suggested a 5watt min and also to paint on some liquid electrical tap all over the soldered areas and then get it in the wire loom.

to to my thougths,,,
in my EVTM,, for the 87 version,, the 22k ohm resistor shows up in the wiring diagrams on one of the DG/Y branches.
the CFI 3.8L shows this particular branch does not go back to the EEC pin 4 like the 5.0 and 2.3L does.  Now im confussed.
To  my best examination of the EVTM,, i do not see this resistor mentioned anywhere else except for the diagrams pertaining to ignition on the 5.0 & 2.3L only.  there is no reference as to its location as well.   the fella that i was helping told me he found his just a couple feet up the coil harness headed towards the firewall.  His was 100% open.
So those of you with knowledge about this resistor,, share your thoughts..  I get what it does now and its malfunction perfectly explains why many of us or you out there keep having to replace distributors,, and yes there are poor quality parts out there today but would'nt you like to eliminate this easy to repair part just for the sake of knowing you "know" its good and perhaps maybe the next dizzy you get might actually work correctly.

here is a great snipit from TMOSS that really explained it in better detail.
the short version is once the primary of your coil transfers energy out to the secondary,,, and then once that event is over,, the secondary will discharge some residual energy back onto the primary (which is not what we want),, ford "knew" that one branch of wire would lead up to pin 4 off the EEC.  That being said,, they installed what i would technically be able to refer to as a "strike absorber" like in a SPD or TVSS in the world of AC Power.  it basically absorbs the massive amount of energy headed towards pin 4 of the EEC and absorbs the hit and disipates the vast majority in the form of heat.. while the 22k ohm resistor will allow some safe level to reach pin 4 and do its job of monitoring spark triggers.

***my issue is,, what the heck is going on with the 3.8L??????  it seems to have no such animal and i just dont understand why.
furthermore why would the 2.3L and 5.0L have this in common being such different platforms...?

anyway,, here is some high level TMOS ramblings of the topic of the 22kohm resistor... Enjoy and reply if you have knowlege or thoughts on this,, i find it very interesting.



Re: dark green / yellow wire from the ign coil

Reply #1 –
looks like there is  a 5000 character limit to each post so i put it here.....
===========================================
tmoss
11497 posts · Joined 2001

#6 · Aug 29, 2005
I don't know about auto and manual differences, but here is some info on the two different TFIs I'm aware of...........

The early TFI system, which Ford calls the "Push Start" TFI system, uses a gray TFI module. Originally, the module was mounted on the distributor. In the late '80s, Ford began to relocate it away from the distributor on some vehicles to provide better protection from the effects of engine heat, but system operation remained the same. It uses a Hall effect pickup (stator) in the distributor, which generates a battery voltage, 50% duty cycle square wave, called the PIP signal, to the EEC-IV PCM and the TFI module. The PCM processes this signal and sends out another battery voltage, 50% duty cycle square wave, called the SPOUT signal, to the TFI module. As long as the TFI module is receiving a SPOUT signal, it will fire the coil at the rising edge of that signal (except during engine cranking, when SPOUT is ignored) and the vehicle will run with the amount of timing advance commanded by the computer. If the TFI module does not receive the SPOUT signal, it will fire the coil at the rising edge of the PIP signal, and the vehicle will run at base timing. This is true on all TFI systems.

Ignition dwell with the Push Start (gray module) system is controlled by the TFI module alone, and increases with engine rpm. The Ignition Diagnostic Monitor (IDM) signal on a Push Start TFI system comes from the coil negative circuit and is filtered through a 22k ohm resistor to pin #4 on the EEC-IV computer. The computer monitors this circuit to verify a coil firing for each PIP signal, and sets codes if it sees missing or erratic signals. Another feature that is unique to the Push Start TFI system is the start input on pin #4 of the module connector. This is wired into the starter relay trigger circuit, and signals the TFI module that the engine is cranking. When the module sees battery voltage on this circuit, the SPOUT signal is ignored.

In the early '90s, Ford began using a different TFI system on certain vehicles -- the Computer Controlled Dwell (CCD) TFI system. The TFI module on CCD TFI is always black in color. There are a few major differences between the two systems. As the name implies, with the CCD system, the computer controls primary dwell. The CCD TFI module still ungrounds (fires) the coil at the rising edge of the SPOUT signal, but now the falling edge of the SPOUT signal (which had no meaning to the Push Start TFI module) is used by the CCD TFI module to ground the coil. The PIP signal remains the same 50% duty cycle square wave, but SPOUT signal duty cycle varies according to how much dwell is desired by the computer.

Another major difference between the two systems is the IDM circuit. Pin #4 on the CCD TFI module, which was the start circuit input on the Push Start TFI module, is now the IDM signal, sent directly from the TFI module to pin #4 on the EEC-IV computer. This signal is still a filtered (low voltage) version of the ignition primary waveform, but is filtered internally in the TFI module rather than through an external resistor. There isn't any start circuit input to the CCD TFI module; the module infers engine cranking from a low rpm input from the PIP signal.
Since these two TFI systems are so significantly different, yet so similar in appearance, parts application problems will inevitably occur. A gray Push Start TFI module will plug right into a CCD system, and vice versa. To make matters worse, parts books are often incorrect on TFI module applications! With the incorrect TFI module installed, the vehicle will run, but drivability and MIL (malfunction indicator lamp) problems will result. For instance, if a gray Push Start TFI module is installed in a CCD system, the computer will not be able to control ignition dwell, and the MIL will illuminate with memory codes for the IDM circuit set, as the gray TFI module is incapable of generating an IDM signal to the computer. If a black CCD TFI module is installed in a Push Start system, dwell will remain fixed, since the SPOUT signal duty cycle never changes. If in doubt about which TFI module belongs on a particular vehicle, consult the ignition system-wiring diagram for the vehicle. If the wire going to pin #4 on the EEC-IV computer comes directly from pin #4 of the TFI module, it is a CCD system. If not, it is a Push Start system.

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #2 –
Some information from the 1993 Ford Shop Manual.
Looks to me like Its only the PCM (EEC) that needs the "Ignition Suppression Resister" for protection from the coil "flyback voltage".

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #3 –
I agree... what is odd is that its not shown as used on the 3.8L within the 87 evtm.
i am going to dig into the 87 shop manuals for clarifications but i bet the shop manuals agree with the evtm in this instance.

the 2.3 has more in common with the 3.8 as both only use 2 pins on the eec to fire injectors... while the 5.0 is 8 pins.

oddly enough seems there is no (and i like your description "flyback") protection on the 3.8L eec cause its not wired for such.  seems like this is some sort of lenz law or something ford was engineering around.

just what the heck is so different about the 3.8L that the 2.3 and the 5.0 needs this protecton but the 3.8 does not,,,? :dunno:

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #4 –
The 3.8 does not have IDM so no code 18. EEC pin 4 is not used.

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #5 –
i found this tid bit of illustrated knowlege at the below link as it starts of pertaining to "how easy" it is to convert older points system vehicles to ford TFI push start (gray) ignition systems.  It even speak to this day that this is the only stand alone spark system in the automotive industry to this day not requiring any computer system to manage it.

https://www.49ccscoot.com/manuals/FORD%20TFI%20electronic%20ignition.pdf


I am still really confused about your reply softtouch ,, i cant get my head around what makes the 3.8L (which uses a push start TFI) does not need a IDM signal.  

the 2.3 fires injectors off two eec pins,, and so does the 3.8L.  the 5.0SEFI uses 8 injectors fired off 8 pins.... yet the 5.0 sefi and 2.3 are so different.
maybe the answer is simple and just as you say it so a follow up questions...
are you saying its as simple as .......  the 3.8L "could" have had Ignition Diagnotsic Monitoring but ford did not include that table/firmware/software onto the 3.8L eec so therefore its non-existent?
~if yes,, i have to wonder why they did this

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #6 –
Let me start by saying that the IDM has nothing to do with how the engine runs.
It is one of the things that the Continuous Self Test can look at to see if there is a problem with the pulses between the TFI and the coil. The Continuous Self Test runs while driving the car. If it detects a problem with the IDM, it sets a memory code 18. These are typically intermittent things that the KOEO and KOER tests don't find.
Why the program coders did not include this in the 3.8 continuous self test ? I have no idea.
The 1988 T-Bird EVTM shows the 3.8 has the IDM. I guess they redid the program when they got rid of the CFI and changed the EGR senser and the idle speed control.

If your Mustang guys IDM resister was open, then he probably didn't really have an ignition problem. He had a false code 18 because the monitor circuit was open.
Are you saying IDM is needed for push starting to work?

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #7 –
no,,
and not to say i knew much of any of the pin 4 function until recently....  but i am on the same page as you that pin for takes in a signal used by the computer to deliver a code.  its not really needed perse'.   the mustang guy will get back to me but from what i can tell, he maybe was under the impression that it may have been a reason his dizzy's went bad.  Now i am in doubt.

this has been a decent rabbit hole adventure btw, finally i understand why there are black and gray TFI's as to "why".

thanks softtouch

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #8 –
Car is good now that I’ve fixed the 22k resistor.

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #9 –
oh,, you posted your pic,, i was gonna.  very nice mint pony

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #10 –
Quote from: jcassity – on
y.  there is no reference as to its location as well.   the fella that i was helping told me he found his just a couple feet up the coil harness headed towards the firewall.  His was 100% open.
And there you have it!!! CROSSTALK
The IDM wire and the other TFI wires are bundled together for a couple of feet in the harness before you get to the resistor.
The broke resistor is no longer doing its ignition suppression job.
The high voltage flyback voltage spike is being picked up by the other wires in the harness by what is called crosstalk.
This would explain the erratic PIP pulse error code.

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #11 –
so lets settle this... from a forensic perspective............

the 22kR blew open.  (lets call this resistor a srike absorber or MOV of sorts).
The primary of the coil has sent 18kva there abouts onto each plug.
the tfi manages to switch the coil ground to open,, and the magnetic field in the coil secondary now reverses back onto the primary.
due to proximity, the harness containing this DG/Y branch headed to eec pin4, the other tfi related wires picked up the HV due to inductive coupling / antenna sorts of an effect.
the 22kR being a high ohm value its going to perform by taking on the majority of the voltage drop of this flyback voltage.
see pg43 87evtm splice 320 (unprotected), the remaing DG/Y wires would be a much lower voltage level safe for TFI use if the resistor is proper and working, the opposite if the resistor is open.
this hv would obviously effect the tfi's ability to operate and sense pip signals and overheat or burn up.


i bring this up to discussion because although the IDM DG/y wire going to pin 4 according to TMOS has said its only a monitoring lead and the 22kR is there to protect the eec,,, if the 22k goes bad,, what we are trying to say is that if its open,, then there **IS** a possibility of the TFI being burnt up??
Second, there are a lot of people out there having aftermarket relacement parts issues with Dizzy's,, and maybe due to age we should start checking the resistance of this branch circuit to eliminate a probable fault.  my son was going through dizzy'z and troubleshot it across two years then finally stumbled on intermittant issues at the TFI connector so an LMR kit fixed that.

not sure anyone else has covered this aspect before on any ford forum

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #12 –
If I am wrong about how the TFI to EEC cable harness is constructed, then forget everything I said.
Are the 4 wires on  EVTM page 57 coming into the bottom of the EEC, not in the same harness?

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #13 –
yes they are,,
all these tfi wires travel from the coil, travel along the upper intake, go left along the engine bay firewall and penetrate the pass side firewall to the eec.

im confused because of your earlier take on post 6 that the open resistor is likely "not" the problem... sorry i just dont understand what your getting at.  i get what your saying and agree with your thoughts on the cross talk part.

Re: 22k ohm resistor Ignition wiring dark green / yellow wire from the ign coil

Reply #14 –
The TFI doesn't need any external resistor to protect it from voltage spikes generated by the coil windings. It is designed to deal with them.

Posted: Some points ignition systems. The negative ends of both windings are tied together internally, the same as the TFI coils.
I believe this was design change from the original Charles Kettering/Delco version. It makes the spark last longer for a cleaner burn.
I believe the original had the high winding grounded to the metal coil casing.
The TFI replaces the points and capacitor.
Posted: Scope pics of the negative side of the coil in a points ignition system.

The voltage developed  by the high voltage winding depends on gap width. When the voltage gets high enough to ionize the air in the gap it arcs across the gap. The ionizing of the air gap causes the gap "resistance" to drop and the voltage to drop.
Posted: 84 Shop Manual pics of spark plug voltage.