TFI replacement cleans up ignition
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Tuned
Joined: Aug 2009
Posts: 402
Likes: 16
TFI replacement cleans up ignition
Aero 3.0L with distributor mounted TFI module.
*********
About six weeks ago my aero went dead as I was cruising up to a left-hand turn on an expressway.
I rolled it back onto the center strip and got my *** towed.
A quick check revealed a blow fuse in my new box which had been uneventful for about a year and perhaps 1K miles.
(Note: this is a different incident than the cabin light circuit blowing fuse #8).
To have a fuse blow was not entirely unexpected since I was guessing at the conversion factor from slow-fry fuse-link to honest fuse technology.
On this circuit (aka 37Y12) the yellow wire size is 12ga and the link size was 16, so I was running it through a 30 amp fuse.
This incident then motivated me to open the schematic and track down all the loads.
Downstream of the main, there were fuses totalling 100amps, but no individual one of the downstream fuses was larger than the main fuse.
Therefore two or more of these loads would have to conspire in order to blow the main fuse. It's possible.
However there is also another fuse-link on this circuit that leads to the ignition system consisting of the the coil and the TFI module.
Since the fuse-link could by its self momentarily flow enough amps to kill the main fuse, this ignition system load was place on the list of prime suspects.
We also designated the 37Y12 circuit as mission critical, because if the main fuse blows then the ignition dies for sure, perhaps at a bad time in your life.
Therefore, it was decided to...
- upsize the main fuse from 30amps up to 40 amps
- Offload some of the loads from 37Y12, and
- Nuke the ignition system--> new coil, new TFI module.
***** Result of TFI replacement *****
I cant say whether the TFI was the source of the fuse problem but it sure did resolve a year-long hunt for rough idle, misfires and knocking.
The TFI module had been replaced about 10 years ago, but at that time it failed dramatically and I eventually received a refund against the Ford TFI recall. Google "Ford TFI recall".
After looking thru old blogs I see that there can also be a gradual degradation in addition to an abrupt failure.
There are numerous symptoms and it is not silly to swap it out as driveability problems surface.
Modules were mounted on the distributor till '91, then remoted later.
Servicing the TFI module requires a deep thin-wall 7/32-inch socket.
Old/failed was an "A2A". An "A1A" version has a different resistance and suspected more advanced timing. There is a blog about this.
*********
About six weeks ago my aero went dead as I was cruising up to a left-hand turn on an expressway.
I rolled it back onto the center strip and got my *** towed.
A quick check revealed a blow fuse in my new box which had been uneventful for about a year and perhaps 1K miles.
(Note: this is a different incident than the cabin light circuit blowing fuse #8).
To have a fuse blow was not entirely unexpected since I was guessing at the conversion factor from slow-fry fuse-link to honest fuse technology.
On this circuit (aka 37Y12) the yellow wire size is 12ga and the link size was 16, so I was running it through a 30 amp fuse.
This incident then motivated me to open the schematic and track down all the loads.
Downstream of the main, there were fuses totalling 100amps, but no individual one of the downstream fuses was larger than the main fuse.
Therefore two or more of these loads would have to conspire in order to blow the main fuse. It's possible.
However there is also another fuse-link on this circuit that leads to the ignition system consisting of the the coil and the TFI module.
Since the fuse-link could by its self momentarily flow enough amps to kill the main fuse, this ignition system load was place on the list of prime suspects.
We also designated the 37Y12 circuit as mission critical, because if the main fuse blows then the ignition dies for sure, perhaps at a bad time in your life.
Therefore, it was decided to...
- upsize the main fuse from 30amps up to 40 amps
- Offload some of the loads from 37Y12, and
- Nuke the ignition system--> new coil, new TFI module.
***** Result of TFI replacement *****
I cant say whether the TFI was the source of the fuse problem but it sure did resolve a year-long hunt for rough idle, misfires and knocking.
The TFI module had been replaced about 10 years ago, but at that time it failed dramatically and I eventually received a refund against the Ford TFI recall. Google "Ford TFI recall".
After looking thru old blogs I see that there can also be a gradual degradation in addition to an abrupt failure.
There are numerous symptoms and it is not silly to swap it out as driveability problems surface.
Modules were mounted on the distributor till '91, then remoted later.
Servicing the TFI module requires a deep thin-wall 7/32-inch socket.
Old/failed was an "A2A". An "A1A" version has a different resistance and suspected more advanced timing. There is a blog about this.
Lead Driver
Joined: Sep 2003
Posts: 7,014
Likes: 206
From: SoCal
I would relocate the TFI module to a cooler place, since you've now had 2 failures. I did this on my Mustang, even though I've never had a problem, just to avoid potential problems:
https://plus.google.com/photos/11555...45868659142833
I rounded up parts from either Explorers or other Aerostars in the scrap yard to make my mods.
https://plus.google.com/photos/11555...45868659142833
I rounded up parts from either Explorers or other Aerostars in the scrap yard to make my mods.
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