Intermittent Starting (Video)

Xkuzme1

Member
Sep 21, 2019
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Kansas City, MO
Here are two videos.
One, my car is starting, the other is not. This just started today. I have an in-line spark tester in line between the distributor and the coil. The first video shows nothing but cranking, and no spark. The next video was taken 2 mins later. No changes were made to the car at all. You can tell that the spark is just enough to get the car going but once it is running, it does ok.

I carry an extra TFI. I’ve tried both of them, and the situation doesn’t change with either TFI.

New plug wires. I have substitutes the old coil wire and it made no difference either.

Almost seems to me like a bad ground, but I’ve checked and agitated all my grounding straps.

thoughts?





Not starting

Starting
 
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jrichker

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You could have a 1950 stove bolt Chevy straight 6 for all we know. The absolutely no useful information about your car year, model, engine: carb or EFI or modifications to the stock engine or electrical system.

Making the dangerous assumption about this mystery car that you seem reluctant to tell us about, I will guess that it is a fox body Mustang.
Fox body mustangs changed radically in terms engine and electrical systems during the 79-93 time period.
 
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Xkuzme1

Member
Sep 21, 2019
47
15
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Kansas City, MO
LOL. My bad.

It’s a factory five AC cobra but it’s donor motor, tranny, harness, and computer are a 1993 Fox Body GT, with upgraded cobra intake, Edelbrock heads, x303 cam, fly cut pistons.
 

90sickfox

I didn't really have an issue with the stink...
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It could be the coil. A weak coil will do that sometimes.
 

Xkuzme1

Member
Sep 21, 2019
47
15
18
44
Kansas City, MO
Update:

My car was built with two switches below the dash and a start button.

I noticed that if I held down the start button before I flipped the switches It would occasionally fire off. If I could get it to fire off just right, the car would start. I started thinking about it, and it sounded like a lack of voltage or a bad ground.

So I left the switches flipped and started poking around. I noticed that when I wiggles the wiring loom that was close to the ignition coil, the fuel pump would prime (like it would when the ignition switch was flipped just prior to start). So I cut open the loom and started wiggling each wire individually. When I wiggled a black wire with a secondary color (white I think), it primed again... and every time I time I touched it it primed. I chased it down to a small plug and beyond the plug was a ground. I took apart the plug and cleaned it. Plugged it back in and taped it back together and it solved all my issues. As a matter of fact, the car runs better, idles better, and drives better.

If it gives me any more trouble, I’ll just remove the plug and wire it straight to ground.

I hope that this helps someone in the future.

Cheers

T
30E351A7-9EC3-46B6-AB9C-83D5AA2CBE95.jpeg
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
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Dublin GA
lowendmac.com
Update:

My car was built with two switches below the dash and a start button.

I noticed that if I held down the start button before I flipped the switches It would occasionally fire off. If I could get it to fire off just right, the car would start. I started thinking about it, and it sounded like a lack of voltage or a bad ground.

So I left the switches flipped and started poking around. I noticed that when I wiggles the wiring loom that was close to the ignition coil, the fuel pump would prime (like it would when the ignition switch was flipped just prior to start). So I cut open the loom and started wiggling each wire individually. When I wiggled a black wire with a secondary color (white I think), it primed again... and every time I time I touched it it primed. I chased it down to a small plug and beyond the plug was a ground. I took apart the plug and cleaned it. Plugged it back in and taped it back together and it solved all my issues. As a matter of fact, the car runs better, idles better, and drives better.

If it gives me any more trouble, I’ll just remove the plug and wire it straight to ground.

I hope that this helps someone in the future.

Cheers

T
30E351A7-9EC3-46B6-AB9C-83D5AA2CBE95.jpeg
Here's a bunch of diagrams you'll need...

The black/white wire in the computer/body harness is probably the computer power ground. It is the second most important ground in the entire car.

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

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 /img]

Engine mounted fuel injector harness


5.0 wiring diagram for Fuel Injectors, Sensors, and Actuators
[img]http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Grounds

This checklist applies to all Mustangs , not just the EFI equipped cars. Some of the wiring will be different on carb cars and carb conversions

Revised 26 –Oct -2016 to add fuel pump ground to the list.

Grounds are important to any electrical system, and especially to computer controlled engines. In an automobile, the ground is the return path for power to get back to the alternator and battery.

Make sure that all the ground places are clean and shiny bare metal: no paint, no corrosion.

1.) The main power ground is from engine block down by the oil filter to battery: it is the power ground for the starter & alternator.


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. The clue to a bad ground here is that the temp gauge goes up as you add electrical load such as heater, lights and A/C.

Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just as much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above in paragraph 2. A screwdriver points to the bolt that is the common ground point.

The battery common ground is a 10 gauge pigtail with the computer ground attached to it.
Picture courtesy timewarped1972
ground.jpg


Correct negative battery ground cable.


3.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally: it comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

All the grounds listed in items 1,2 & 3 need to bolt to clean, shiny bare metal. A wire brush or some fine sandpaper is the best thing to use to clean the ground connections.


4.) All the sensors have a common separate signal ground. This includes the TPS, ACT, EGR, BAP, & VSS sensors. This ground is inside the computer and connects pin 46 to pins 40 & 60, which are the main computer grounds. If this internal computer ground gets damaged, you won't be able to dump codes and the car will have idle/stall/ performance problems

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself. The TFI module ground terminates inside the computer.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) Fuel pump ground the fuel pump has a ground pigtail the connects to the body under the gas tank. You have to drop the gas tank to see where it bolts to the body.

49675.gif


See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help troubleshooting voltage drops across connections and components. Be sure to have the maximum load on a circuit when testing voltage drops across connections. As current across a defective or weak connection, increases so does the voltage drop. A circuit or connection may check out good with no load or minimal load, but show up bad under maximum load conditions. .

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

64167.gif


Extra grounds are like the reserve parachute for a sky diver. If the main one fails, there is always your reserve.

The best plan is to have all the grounds meet at one central spot and connect together there. That eliminates any voltage drops from grounds connected at different places. A voltage drop between the computer ground and the alternator power ground will effectively reduce the voltage available to the computer by the amount of the drop.




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.[/b]

TFI module wiring for 94-95 Mustang GT
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-IgnitionControlModule.gif

Complete computer, actuator & sensor wiring diagram for 94-95 Mustangs

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

Complete computer, actuator & sensor wiring diagram for 88-90 Mass Air Mustangs

5.0 wiring diagram for Fuel Injectors, Sensors, and Actuators

Main body EFI wiring harness

Ignition switch wiring

O2 sensor wiring harness

Vacuum diagram 89-93 Mustangs

HVAC vacuum diagram

TFI module differences & pin out

Fuse box layout

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

93 power window wiring

T5 Cutaway showing T5 internal parts

Visual comparison of the Ford Fuel Injectors, picture by TMoss:

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

Engine mounted fuel injector harness

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:

Starter circuit

Alternator diagram for 94-95 Mustangs.
 
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