Missfire And Stalling

BOBCAT TECH · Jul 5, 2016

89 MUSTANG 5.0.... It would die or stall at random times. Thought maybe the tps or iac was causing this so replaced them and set the tps at idle at .97 volts. found some cracked and dameaged vacuum lines. replaced them. replaced the distributor. Now I notice when I have a test light connected to the pos. side of the battery and the other end on the ground of the coil the light will blink when the engine starts missing and hunting around. Also if I'm not mistaken pin number 4 on the ecu should be seeing this ground as well as the tack (green/black wire. only codes I am getting is for smog stuff and that is no longer there. checked all my grounds and they are all below 1.5 ohm does the ecu need to see the pulse signal on pin 4?

Mustang5L5 · Jul 5, 2016

After replacing the IAC...did you perform the idle reset procedure?

BOBCAT TECH · Jul 5, 2016

yes. disconnected iac. set idle and made sure the tps was under 1v

BOBCAT TECH · Jul 5, 2016

let me add this problem was intermittent until I charged my ac and now it is all the time ac on or off

jrichker · Jul 5, 2016

Pin #4 on the computer is the IDM (Ignition Diagnostic Monitor) signal that is used to drive the tach and computer. It expects to see an IDM pulse for every SPOUT pulse. It uses this information to determine if the ignition coil and other ignition components are working properly. This signal is low current and will only drive test equipment with a high input resistance - that means no test lamps or other low resistance devices.

Diagrams courtesy of Tmoss & Stang&2birds

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

BOBCAT TECH · Jul 5, 2016

you are correct jrichker. but if I check the wire from the ign module (green) to pin 4 I show ol on my meter. the print that I have shows the number 4 pin through a ignition suppression resistor to connection s102 to were it goes to the tach tfi module and to c191 ground of the coil guess what I am asking is how this works. does the signal start from the ecu and go out or is this supply info to the ecu

jrichker · Jul 5, 2016

The IDM signal originates with the TFI module. The 22K ohm resistor drops the voltage down to somewhere between 9-15 volts for the Tach and the computer.

How the TFI ignition works in 86-93 model Mustangs:

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

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.

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. A bad PIP will often set code 14 in the computer and cause hot start problems. 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 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.

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.

diagram courtesy of Tmoss & Stang&2Birds

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
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

BOBCAT TECH · Jul 5, 2016

BOBCAT TECH · Jul 5, 2016

sorry didn't see your reply. very good information thank you. will do some testing when I get home

BOBCAT TECH · Jul 5, 2016

ok after digging through some other posts I decided to change out my tfi even though its a new distributor (advance auto) idle came back like it should and so on. still misses a bit and doesn't have the power it should but with a 2 year old helping doesn't work to well.... I'm going to put the tfi on my old distributor and try it tomorrow and will let you know

BOBCAT TECH · Jul 8, 2016

WELL ITS A SAD DAY. AFTER 2 DAYS OF RUNNING GREAT I LOST SPARK. SWAPPED OUT THE COIL AND DISTRIBUTOR AND NOTHING. CHECKED FOR 12V AT COIL, GOOD WITH TEST LIGHT ON POSITIVE AND OTHER END TO THE GROUND OF COIL NO LIGHT TILL I START TRYING TO START IT. ON THE TFI THE START HAS 12V WHEN TURNING OVER, RUN HAS POWER WITH KEY ON, AND IGNITION GROUND IS GOOD.... THIS THING IS GOING TO GIVE ME A HEAD ACHE. ALSO THE RED WIRES GOING TO THE INJECTORS ALL HAVE 12V. IM GOING TO TRY TO LOCATE A NOID LIGHT THIS EVENING TO SEE IF THE INJECTORS ARE FIRING. AND I CAN SMELL GAS WHEN CRANKING FROM THE EXHAUST

Missfire And Stalling

BOBCAT TECH

New Member

Mustang5L5

That is…until I whipped out my Bissell

BOBCAT TECH

New Member

BOBCAT TECH

New Member

jrichker

StangNet's favorite TOOL

BOBCAT TECH

New Member

jrichker

StangNet's favorite TOOL

BOBCAT TECH

New Member

BOBCAT TECH

New Member

BOBCAT TECH

New Member

BOBCAT TECH

New Member

Similar threads

Missfire And Stalling

New Member

That is…until I whipped out my Bissell

New Member

New Member

StangNet's favorite TOOL

New Member

StangNet's favorite TOOL

New Member

New Member

New Member

New Member

Similar threads

Privacy & Transparency

Privacy & Transparency