89 strange no spark, tfi question?

chriscash96

Member
Mar 6, 2022
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Ive been dealing with a loss of spark on a 89 152,000 miles this began after I parked the car for a month to replace the intake gaskets due to a coolant leak. I lose spark at random anywhere between 20 seconds to about 5 mins, the car just shuts off no sputtering or coughing and all lights, radio, heater everything still works the engine just quits. Whats really weird is if I cycle the ignition key on/off or disconnect the tfi harness (more specifically ive narrowed it down to just disconnecting the power run wire to the tfi which still has 12 volts when it dies ) it restores spark and instantly starts. So far I have tested codes and none were found, I cleaned the ecm ground and secondary ground off the backside of the engine to firewall and any other ground I could find. Ive tried 4 known good tfis (two were brand new a standard, 2 napa and one motorcraft units and i apply a light layer of thermal grease) I checked voltages on the tfi plug and everthing checks out according to a tfi troubleshooting flowchart I found on this forum. I went on to also try two coils, a spare ecm from my friends running 89 mustang and new napa distributor which I made sure to check that i have a good pip signal going to the module. My latest attempts have been to replace the igniton switch and I used two working fuel and ecm relays off my friends running car. I have also taken the wire harness off the engine and gone through looking at wire integrity and continuity to the best of my knowledge and it appears fine. The problem is also unaffected by having the spout in or out it dies either way and only starts after the key is cycled or disconnecting and reconnecting the tfi. I was just wondering if anyone would have any insight or new direction to go in troubleshooting? Ive also been through numerous troubleshooting guides for the tfi with my dvom and all signs point to a tfi issue i just cant fathom how disconnecting and reconnecting power fixes it let alone 4 other tfi modules having the exact same issue. From my understanding the tfi has power, is getting a pip signal, i can even trigger the module on the pip wire and hear the fuel pump and relays click but it doesnt ground the coil, it seems as if the module just stops grounding the coil but the minute I cycle the key or unplug and reconnect the tfi it works flawlessly for a few seconds to minutes. I am at a loss and was hoping maybe someone has had a similar issue and could give some insight or new direction for troubleshooting? Thanks again.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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Check the plug at the coil, these cars are old and connections get loose and/or burnt.
There is also a fused link, I think it's in that gob of wires under the solenoid, if you look for the 'cranks but no start checklist' in the technical how to threads pinned to the top of the tech forum it's in there.
 

jrichker

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Correct the actual switch, I also replaced the key switch because I accidentally purchased it as well and just held onto the part, the plug looked fine and no loose wires.
How the TFI ignition works in 86-93 model Mustangs:

Revised 15 Feb 2022 to add need for thermal conductive paste on the TFI module.

Tools needed: DVM, noid light, safety pin.

Theory of operation:
The TFI ignition in 86-93 Mustangs has 4 main components: the ignition switch, the coil, the TFI module and the PIP sensor inside the distributor.

The ignition switch gets power from the two yellow wires that are supplied power by a fuse link located in the wiring harness that connects to the starter solenoid.

Diagram courtesy of Tmoss & Stang&2birds
IgnitionSwitchWiring.gif


Excess heat is the primary reason for intermittent TFI problems. When working with the TFI module, make sure that there is plenty of thermal conductive paste on the distributor mounting pad for the TFI module or the mounting pad of the TFI module itself.

I.) The coil is mounted on the driver’s side strut tower on most EFI Mustangs. It gets power from a red/green wire and a brown/pink wire from the ignition switch. That wire from the ignition switch feeds a 20 gauge blue fuse link that connects to the red/green wire. The fuse link protects the wiring and the ignition switch, since the fuse link for the two yellow power supply wires has a much higher current rating. Without the smaller fuse link protecting the smaller wiring used in the ignition circuit, a short there would cause the red/green wire to overheat and burn up.

A bad TFI module or a bad PIP sensor have similar problem symptoms - a high speed miss on a warm engine. It can be difficult to tell which one may be the problem cause of the high speed miss on a warm engine.

II.) The TFI module is mounted on the side of the distributor and supplies the ground for the coil. Every automotive power supply circuit uses the ground as the return path to carry power back to the negative side of the battery. The TFI switches the tan/yellow wire coming from the coil to ground. It gets power from the red/green wire when the ignition switch is in the Run position. The red/lt blue wire supplies a signal to turn on more power (dwell time) when the engine is cranking. The increased dwell can cause excessive current draw if the red/blue wire remains energized when the ignition switch is in the Run position. The trigger signal comes from the PIP sensor when cranking and the computer when the engine is running. The SPOUT jumper plug enables computer controlled spark advance. When the SPOUT is removed, spark advance is locked at the setting determined by the mechanical position of the distributor.

III.) The PIP sensor is in the bottom of the distributor under the shutter wheel. It is a Hall effect magnetic sensor that senses a change in the magnetic field when one of the slots in the shutter wheel uncovers the sensor. Then it supplies a pulse that triggers the TFI module to provide a ground to the ignition coil and tells the computer to trigger the fuel injectors. A bad PIP will often set code 14 in the computer and cause hot start problems. The fuel pump control looks for the PIP pulse to keep the fuel pump control circuit turned on and keep the fuel pump running. Replacing the PIP sensor requires removal of the distributor and pressing the gear off the distributor shaft to expose the sensor. For most people, a remanufactured distributor ($55-$75) is the solution, since they may not have access to a press.

IV.) Troubleshooting the ignition system – no spark or weak spark. All the tests are done with the ignition switch in the Run position unless specified otherwise. A safety pin may be used to probe the wiring connectors from the backside.
1.) Check for 12 volts at the yellow wires on the ignition switch. No 12 volts and the fuse link near the starter solenoid has open circuited.
2.) Check for 12 volts on the red/green and brown/pink wires coming out of the ignition switch. No 12 volts, replace the ignition switch.
3.) Check for 12 volts at the ignition coil. No 12 volts and the blue 20 gauge fuse link has open circuited.
IV.) Troubleshooting the ignition system – no spark or weak spark. All the tests are done with the ignition switch in the Run position unless specified otherwise. A safety pin may be used to probe the wiring connectors from the back side.
1.) Check for 12 volts at the yellow wires on the ignition switch. No 12 volts and the fuse link near the starter solenoid has open circuited.
2.) Check for 12 volts on the red/green and brown/pink wires coming out of the ignition switch. No 12 volts, replace the ignition switch.
3.) Check for 12 volts at the ignition coil. No 12 volts and the blue 20 gauge fuse link has open circuited.
4.) Check for 12 volts at the red/green wire on the TFI module. No 12 volts and you have wiring problems.
5.) Remove the small red/blue wire from the starter solenoid (looks like it is stuck on a screw). This is a safety measure to keep the engine from turning while you are making measurements. Have a helper turn the ignition switch to Start and look for 12 volts on the red/lt blue wire on the TFI module. No 12 volts and you will have starting problems, but push starting the car will work OK. No 12 volts, replace the ignition switch. Be sure to reconnect the red/blue wire to the starter when you finish.
6.) Check the red/blue wire to make sure that it has less than 8 volts when the ignition switch is in the Run position.
7.) A noid light available from any auto parts store, is one way to test the PIP pulse. The computer uses the PIP signal to trigger the fuel injectors. The noid light plugs into the fuel injector harness in place of any easily accessible injector. Plug it in and it will flash if the PIP is working. No flash from the noid light and the PIP is suspect. To confirm the PIP is being the source of the non flashing noid light, look for 12 volts on the red injector wiring. Good 12 volts and no flashing noid light means the PIP has failed.
8.) Remove the SPOUT plug from the harness and try to start the engine. If it starts, replace the PIP. This is a common no start condition when the engine is hot.
9.) The TFI module is a go/no go item when you have a no spark/weak spark condition on a cold engine. It either works or it doesn’t.
The TFI failure mode on a running car is usually a high speed miss on a warm engine. Many auto parts stores will test your TFI module for free. Bring along a hair dryer to get it hot while testing it and run several test cycles, since it often gets weak when it heats up.
Spraying the TFI module with “canned air” used to dust computer keyboards while the engine is hot and misfiring is one way to check the TFI. Turn the can upside down and spray away; this will cool the TFI of quickly. If it stops missing, the TFI is the likely suspect.

The coil is somewhat more difficult to pinpoint as a problem. A good coil will make a nice fat blue spark 3/8”-1/2” long. The problem is that one person’s perception of a fat blue spark looks like may not be accurate enough to spot a weak coil. The coil is cheap enough ($13-$16) that having a known good working spare might be a good idea.

Excess heat is the primary reason for intermittent TFI problems. When working with the TFI module, make sure that there is plenty of thermal paste on the distributor mounting pad for the TFI module or the mounting pad for the TFI module.

diagram courtesy of Tmoss & Stang&2Birds
fuel-alt-links-ign-ac.gif


TFI_5.0_comparison.gif


tfi-module-troubleshooting-gif.585284


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

Vacuum diagram 89-93 Mustangs

HVAC vacuum diagram

TFI module differences & pinout
 
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chriscash96

Member
Mar 6, 2022
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Hey thanks again for the advice, I ended up replacing the pigtail for the tfi and coil and was going through that guide. Im still stuck with it dying basically the tfi module checks out fine but after it dies and loses spark the module stops grounding the coil until the key is cycled. The only thing I came across that seemed out of place was on the coil wire from the tfi to the coil, while the engine was running using my power probe i saw voltage spikes. I dont know if it was by chance but im gonna look into that tomorrow. I dont know if it could be because of the power probes speed at showing voltage but out of curiosity do you know what could cause voltage irregularity on TFI to Coil wire pin #2 wire?
 

chriscash96

Member
Mar 6, 2022
6
1
13
Hey thanks for reading, it runs longer with the spout removed but still ultimately dies then there is no ground signal from the module to the coil present. After it has lost spark (before cycling the key or disconnecting the tfi) I have gone as far as to disconnect the ecm and even that doesnt make a change. As far as the pickup and cap and rotor I replaced the whole distributor with a new distributor from napa, but I am quickly wondering if I could even have replaced a bad part with a bad new out of the box part and chasing my tail because of it. I have determined where the problem is I am just taken aback how the ignition system is fine and it runs smooth and then the tfi just stops grounding the coil but a quick cycle of the key and it works fine for a short while again. I have a strong pip signal, the coil tests fine and is not the only one ive tried, ive tried running wires to bypass the factory harness to no avail, ive tried 3 tfi modules of various brands, new distributor, ignition switch, Im stumped.
 

manicmechanic007

5 Year Member
Sep 26, 2017
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There are two tests I do in your situation
You need a spark tester plugged into the coil high tension post to coil wire
You need to have a test light on the coil to watch the blinking light on the negative side
As it is blinking wait for it to die while watching the blinking light (drives technicians to drink)
If it quits flashing then dies your stator is no good
If it is still flashing when the spark quits your TFI module or coil is at fault
Run only Motorcraft parts
Damn straight all of your new parts may be NFG