Engine Drove fine, stopped, then ran poorly, stopped, then wouldn't start.

Driver460sz

Active Member
Jan 14, 2019
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Last night I took my 86 (302, 5 speed)to the store. It is about a 8-9 minute drive, on a nice cool (60 degrees) evening. It ran fine, all was good. I shut off the car while daughter listened to the radio for about 6 or so minutes. I started the car, started right up. Took off, went around the turn and when I hit the gas and the car went over 3500 it sputtered and backfired, but still ran fine below 3500. Drove home, another 8-9 minutes and parked. Next morning, I went out to start the car and NOTHING. Lights go on, bells go off, fuel pump makes noise for the 2 seconds or so (Always does), but nothing at the key. My started click, nothing. I put a jumper on the battery just to see what would happen, same thing. Radio, bells, lights all go on, but nothing at the starter........

So yeah.....Where to start? Ignition but why was it running funny last night? Was it running rich/lean for some reason, maybe something with the fuel pump, but why was it totally fine up until I left the store? TFI slowly let go.... maybe. Plugs are all new (Less than 200 miles, proper gaps), no burnt wires. Recent TB/EGR gaskets but that problem has been fine for the past 500 miles. Dist, O2 sensor, gournds?

Still a SD car, not MAF.

What to do....what to do.....what to do.

Thanks for the help eveyone.

Scott


Update: Just ran a screwdriver across the starter relay and she started right up. Idle was great, was able to WOT and then after about 2-3 mins of idle, when warmer (Maybe) the 3500 rpm stumble came back.

No idea what to do next. Two problems affecting one thing or one problem affecting two things??????
 
Last edited:
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Start with the basics, voltage drop test the battery/cables from the battery to the solenoid then on to the starter, I would clean all the cables first then test.
The 'no acceleration after warm up' may be a symptom of a bad charging system and/or bad connections. Start with the cable cleaning and test first.
 

Driver460sz

Active Member
Jan 14, 2019
76
36
28
41
New Hampshire
Last night I took my 86 (302, 5 speed)to the store. It is about a 8-9 minute drive, on a nice cool (60 degrees) evening. It ran fine, all was good. I shut off the car while daughter listened to the radio for about 6 or so minutes. I started the car, started right up. Took off, went around the turn and when I hit the gas and the car went over 3500 it sputtered and backfired, but still ran fine below 3500. Drove home, another 8-9 minutes and parked. Next morning, I went out to start the car and NOTHING. Lights go on, bells go off, fuel pump makes noise for the 2 seconds or so (Always does), but nothing at the key. My started click, nothing. I put a jumper on the battery just to see what would happen, same thing. Radio, bells, lights all go on, but nothing at the starter........

So yeah.....Where to start? Ignition but why was it running funny last night? Was it running rich/lean for some reason, maybe something with the fuel pump, but why was it totally fine up until I left the store? TFI slowly let go.... maybe. Plugs are all new (Less than 200 miles, proper gaps), no burnt wires. Recent TB/EGR gaskets but that problem has been fine for the past 500 miles. Dist, O2 sensor, gournds?

Still a SD car, not MAF.

What to do....what to do.....what to do.

Thanks for the help eveyone.

Scott
Start with the basics, voltage drop test the battery/cables from the battery to the solenoid then on to the starter, I would clean all the cables first then test.
The 'no acceleration after warm up' may be a symptom of a bad charging system and/or bad connections. Start with the cable cleaning and test first.
Put in a new battery and the green wire started melting. Radio no longer works, car still doesn't start with the igtion key. Thats the update so far. The green wire goes into a rubber piece and comes out as two wires. Can these simply be splices together or is there an unseen fuse in there?
 

mikestang63

SN Certified Technician
Aug 27, 2012
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sounds like you have a short in a fuseable link wire. i would like at the igniition switch under the column and trace back that melted wire. Check for bad or missing grounds
 

Driver460sz

Active Member
Jan 14, 2019
76
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41
New Hampshire
Holy christ. After swapping put a new battery, starter solenoid, and fixing the burnt wire off the solenoid she started up just fine. Did a few short drives, 15 mins or so each. No stumble and happy.....but get this.

Radio, hazards, left headlight no longer work. Left blinker works with lights off but not on. Fuses are all good in the panel.

Something done did get effed up. Going to be a long few days running wires.

Thanks for the help and guidance.
 

Driver460sz

Active Member
Jan 14, 2019
76
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41
New Hampshire
Car started this morning and after work. Went to the store on the way home and it wouldn't start. Got a jump and came home. Swapped out the alt for a new 3G one that is was going to put in it when I swap motors, so it was a free try. Started right up after a jump from the truck as the battery wasn't charged from before. Charged up and starts fine currently. But now NOOOOOO exterior lights or the radio work and the wire that was smoking the other day is smoking again.

I am going to have to start at the starter solenoid and start tracing wires I guess. But the electrical is all f-ed up, so it seems.

I'll take a peek at the ignition switch to see if it checks out. But man this is a TERRIBLE time for it as I was going to do the motor swap eaerly Oct.... not sure if I should wait until I fuigure all this out first or what.

Again, thanks for all the suggestions and input.

Scott
 

jrichker

StangNet's favorite TOOL
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The wire that is heating up is the one that is attached to the orange/black alt wires and voltage regulator.
That's the voltage sense wire....

Alternator troubleshooting for 86-93 5.0 Mustangs:

Never, never disconnect an alternator from the battery with the engine running. The resulting voltage spike can damage the car's electronics including the alternator.



Revised 28-Nov-2018 to add warning that the instrument cluster must be in place and working for the alternator to charge

Red color text applies to cars with a 3G alternator.

Do all of these tests in sequence. Do not skip around. The results of each test depend on the results of the previous tests for correct interpretation.

Simple first step: Remove the alternator and take it to your local auto parts store. They can bench test it for free.


Use a safety pin to pierce and probe the insulated connectors from the rear when doing tests with the connector plugged into its' mating connector.

Engine off, ignition off, battery fully charged.
1.) Look for 12 volts at the alternator output. No 12 volts and the dark green fuse link between the orange/black wires and the battery side of the starter solenoid has open circuited.
3G alternator: Look for 12 volts at the stud on the back of the alternator where the 4 gauge power feed wire is bolted.
No voltage and the fuse for the 4 gauge power feed wire is open or there are some loose connections.

2.) Look for 12 volts on the yellow/white wire that is the power feed to the regulator. No 12 volts, and the fuse link for the yellow/white wire has open circuited.

The alternator MUST have the instrument cluster in place and working properly. The alternator warning light is a part of the charging circuit. No cluster, then no working alternator.

Engine off, ignition on, battery fully charged
1.) The alternator warning light should glow. No glow, bulb has burned out or there is a break or bad connection in the wiring between the regulator plug and the instrument cluster. The warning light supplies an exciter voltage that tells the regulator to turn on. There is a 500 Ω resistor in parallel with the warning light so that if the bulb burns out, the regulator still gets the exciter voltage.
Disconnect the D connector with the 3 wires (yellow/white, white/black and green/red) from the voltage regulator.
Measure the voltage on the Lt green/red wire. It should be 12 volts. No 12 volts and the wire is broken, or the 500 ohm resistor and dash indicator lamp are bad. If the 12 volts is missing, replace the warning lamp. If after replacing the warning lamp, the test fails again, the wiring between the warning lamp and the alternator is faulty. The warning lamp circuit is part of the instrument panel and contains some connectors that may cause problems.

2.) Reconnect the D plug to the alternator
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see 2.4-2.6 volts. No voltage and the previous tests passed, you have a failed voltage regulator. This is an actual measurement taken from a car with a working electrical system. If you see full or almost full12 volts, the regulator has failed.

Engine on, Ignition on, battery fully charged:
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see battery voltage minus .25 to 1.0 volt. If the battery measured across the battery is 15.25 volts, you should see 14.50 volts

Familiarize yourself with the following application note from Fluke: See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .



You will need to do some voltage drop testing of several of the wires.

Start looking for these things:
1.) Bad diode(s) in the alternator - one or more diodes have open circuited and are causing the voltage to drop off as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.

2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Do the voltage drop test as shown in the Fluke tech note link. Measure the voltage drop between the alternator frame and the battery negative post. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.

3.) Bad regulator that does not increase field current as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.

4.) Bad sense wire - open circuit in sense wiring or high resistance. The yellow/white wire is the voltage sense and power for the field. There is a fuse link embedded in the wiring where it connects to the black/orange wiring that can open up and cause problems. Disconnect the battery negative cable from the battery: this will keep you from making sparks when you do the next step. Then disconnect the yellow/white wire at the alternator and the green fuse link at the starter solenoid/starter relay. Measure the resistance between the alternator end of the yellow/white wire and the green fuse link: you should see less than 1 ohm. Reconnect all the wires when you have completed this step.

5.) Bad power feed wiring from the alternator. Use caution in the next step, since you will need to do it with everything powered up and the engine running. You are going to do the Fluke voltage drop tests on the power feed wiring, fuse links and associated parts. Connect one DMM lead to the battery side of the starter solenoid/starter relay. Carefully probe the backside of the black/orange wire connector where it plugs into the alternator. With the engine off, you should see very little voltage. Start the engine and increase the load on the electrical system. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.


Alternator wiring diagram for 87-93 Mustangs.



The following are diagrams courtesy of Tmoss & Stang&2birds

Alternator wiring diagram for 94-95 Mustangs.


Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections
0.0V bolt together connections

Alternator wiring circuit
Notice the green wire connects to a switched power source. The circuit contains a 500 ohm resistor in series between the switched power and the alternator. Connecting it to switched power keeps the regulator from drawing current when the engine is not running. The resistor limits the current flowing through the wire so that a fuse isn't needed if the wire shorts to ground.

Also notice the sense wire connects to the starter solenoid and it is fused. It connects to the starter solenoid so that it can "sense" the voltage drop across the output wiring from the alternator.


Fuse link for 86-93 Mustangs
Replacement parts:
14 gauge fuse link for stock alternator.

Bussman BP/FL14 Fusible link
AutoZone

Dorman - Conduct-Tite 14 Gauge Fusible Link Wire Part No. 85620
Advance auto parts #85620
Pep Boys - SKU #8637594



Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.

The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.

Correct way to install a 3G alternator
Alternator wiring.






If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

Starter solenoid wiring 86-91 model cars.

Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.


Starter solenoid wiring 92-93 model cars.




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.

94-95 Mustang wiring diagrams
http://www.veryuseful.com/mustang/tech/engine/#95-95Diagrams

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.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

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

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.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 & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
https://www.stangnet.com/mustang-forums/attachments\21328

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-Alt.gif
 

Driver460sz

Active Member
Jan 14, 2019
76
36
28
41
New Hampshire
Hey folks. Great information being shared here. New battery, new starter relay and a new 3g Alt and she starts right up, some surging at idle (Always has) and no more lagging. I think along the way, perhaps when the alt failed, it did some damage to some wiring......if thats a real thing. Blinkers work fine with the lights off and don't work when they are one. The left side (High and low) light do not work up front but do in the back and the radio is still out. Fuel pump works, as does the ignition, hence it starts with the key no problem or delay. Perhaps something got goofed in the fuse panel which I will check tomorrow. As some of the components work off the yellow but not all.....hummmmm. I did order a hazzard multi switch and an ignition switch.....because why not, it's only $55 and the components are 34 years old. So the hunt continues for the electrical gremlin now. Can't imagine it is the ECU as the blinkers work with the light off but not when on (Socket problem or ground I bet). So my guess is a bad relay and the radio could just be a dead wire for whatever reason.....that seems to be how electrical things work....or don't from time to time.

Any other clues let me know.

Thanks again, motorheads!!!!
 

Driver460sz

Active Member
Jan 14, 2019
76
36
28
41
New Hampshire
Well. Like most wiring I have ever done. Changed the starter solenoid, new battery and new 3G alt. I was going to do those things for the new motor anyways. Changed out the melted wire from the solenoid (It was green), ran the new 3G alt wire then moved inside the car. The radio fuse and all four amplifier fuses were blown as was the radio fuse in the panel. Blinkers work fine but the hazards are dead and two headlights (Driver side) burnt out. Some type of surge hit me some how and seems to have blown every fuse on the dedicated line from the solenoid to the panel and out. New hazard switch and headlights and all is well now.

May have been over kill but it all works fine now.

Again, thanks for the helpful tips and suggestions.

Now I can move on the to engine swap!