I think the 18 code is a little misleading. I think what it is trying to say is that it ask the ICM to change the timing and the timing did not change.
Some have fixed this one by replacing the Computer. I do not think changing the ICM will help any on this one. I do not know how it checks on this but it may use the IDM input. If it looks for a change in idle speed the hole you drilled may be the cause of it.

I do not know how drilling a hole would help alleviate a code 12.

 

The aftermarket 70mm throttle body didn't have any air bypass hole in it when purchased and the IAC was fully open and unable to bump the idle above 1500RPM during its self tests.

It was suggested on a foxbody forum that drilling the hole would alieviate the 12, and it did so immediately.

The lean backfire existed well before the car styled intake and TB was on the truck.

As soon as the truck kicks over to Closed loop, I get the back fire...and if I unplug the O2 sensor and try to force "limp mode" I still get the lean backfire.

Maybe I am being a little thick and I just don't understand what you're saying...I am not sure how changing the ECM again would fix anything. I have a re-man unit in the truck now and it behaves identically to how the original ECM behaved, which I havent taken back as a core just yet.

Thanks again for the help, though, Subford. Your responses to this and other posts have helped tremendously as far as my understanding of exactly what the ECM looks for and how and why codes and drivability problems crop up.

 

OK...I changed the ignition module (BWD part) and put the Motorcraft one back in. Problem persists but 12 and 18 go away. Now I get either a 44 or a 41. Depending on when I check it. And still the backfire persists.

 

And now the 18 is back...good grief it seems to show up when the truck hits closed loop. troublecodes.net/ford lists the 18 as being a timing check and advance functions. fault. So the advance function is faulty (most likely through the Ignition Diagnostic Module).

But that begs the question: where is the IDM? Does this suggest the distributor is acting up or is it part of the ECM?

 

The code 44 shouldn't be a big deal, the code 41 indicates pass. o2 indicating lean. Either the O2 is bad, something in the harness is bad, or it is actually running lean. An easy way to test this is to trade O2 sensors sides. If the code 41 persists, then it is actually running lean. If code 44 goes away and switches to whatever code is for the driver side, then the O2 is probably bad. If it is actually running lean you either have a plugged injector or one cylinder running lean due to something like a vacuum leak. In either case, you might be able to pull a spark plug and compare colors to see if one is obviously leaner than the others. Your attempt to clean the injectors by soaking them in cleaner does not mean they are clean, the only way to verify their operation is to pull them out and do a volume test on them.
The code 18 could be more of your problem than anything else, if the spout is disconnected then the computer won't be able to advance the timing and you will be stuck at the base setting. This would account for poor mileage, lack of power, but not likely the code 44 you are getting. Make sure the spout is plugged in and that there aren't any problems in the wiring harness. Also, if you have a timing light, you can watch the timing change while you change RPMs. If it is stuck as the base setting with the spout connected, the computer isn't able to advance the timing, and this would indicate a problem somewhere in the wiring harness.

 

There is no shut thing as a Ignition Diagnostic Module. There is a Ignition Diagnostic Monitor (IDM).
The IDM is just a wire and a resister going back to the computer from the Ignition Coil.
This is how the computer checks on timing and so on.

 

Forgive me for the misnomer. With the power of Google I have discovered what and where it is, I'm just now at work for 8 hours...working shift/on call maintenance on a Holiday shut down is boring.

Subford, would the resistor go bad (I know thats a dumb question, I guess they can)? The lean backfire has progressively gotten worse over the last 8 months or so. Now I can't drive the truck without a lean backfire on anything but flat ground.

 

Well a lean backfire is from low fuel pressure most of the time.
You need to put a fuel pressure gauge on it and put it where you can see it and see what the fuel pressure is doing.

 

I realize this, and I drove the truck with a fuel pressure gague rigged where I could see it in January and found adequate fuel pressure. And, again this is a problem that crops up only after the truck switches to closed loop opperation and only when the vehicle is being driven where there would be extra load on the truck (uphill or after skipping a gear (2 to 4)) around 1500 RPM. I thought perhaps it would be a low pressure fuel pump problem (I.E. lack of volume) but it does it with both tanks.

Is there a filter in the dual function resiviour that could be clogged? I replaced the resiviour two years ago, but I guess that could cause a problem.

Also, the 18 code comes and goes as something is unplugged or re-plugged. I switched out the ECM this morning and it showed up...then I changed the ICM for the Motorcraft unit and it went away, then it came back when I unplugged the MAP as I had become suspiscious that maybe it was plugging and unplugging things causing the 18 to come and go.

 

My fiance says that the truck is mad at me because just before Christmas I sold my '69 Mustang, which she claims was the truck's boyfriend.....

 

Disconnect the computer plug, and check the resistance using a multimeter between Pin 47, and the green pin on the TPS connector. A computer not receiving a proper TPS signal will have lean tip-in issues.

Another test you can do is try disconnecting the MAP sensor and giving it throttle. If it falls flat on its face, I'd suspect it's not receiving a good TPS signal.

 

I found in an old post Subford recommended testing resistance on 200K scale of wiring between pin 4 on ECM connector and negative side of coil. Looking for 20-24,000 ohms.

Just a note for myself in the morning.

The gentleman in that post had similar problems to what I, now, seem to be having. I think that guy found his spout wire was actually grounding out to something.

 

The wires leading between the PCM to the Ignition Control Module are in a shielded bundle. The previous thread you were referring to the SPOUT signal was grounding out to the shield. This was a common problem back in the day.

Here is an excellent diagram of the ignition circuit:

courtesy of oldfuelinjection.com

The IDM resistor is on the bottom of the diagram, labeled Ignition Suppression Resistor.

 

22.4 ohms through the IDM circuit from coil to ECM, .3 ohms on spuot circuit...No wiring problems there.

 

AND,for those of you playing along at home...according to the Actron fuel pressure tester, rigged cleverly with a stick and a twisty tie so the driver could monitor the fuel pressure while driving, the backfire occurs with roughly 38-40lbs of fuel pressure. Go figure.

I figured I best check.

SO, it seems to me, in light of the evidence provided here to for...it seems very much to be an ignition problem....