Electrical 1990 LX 5.0 Not starting

Olivethefet

Slap me as well as point and laugh
May 17, 2018
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Enterprise AL
HI, I recently picked up a 90 5.0 LX as a project car. When I bought the car the owner said it needed a fuel pump, but really couldn't say why other than it quit running and that's what he thought the issue was. In short its a basket case. There is a pressure gauge on the inlet fuel line in the engine bay. When the car is turned on it pumps up to 40-45psi. I don't think anything is wrong with the fuel pump, but you guys can let me know what you think. At first when I tried to start it, it had not spark at the plugs. Simply pulled one of the plugs and turned it over, nothing. moved to the coil, nothing. The car had a MSD 6AL in it, but it wasn't hooked up. Did some research and figured out how to wire up the 6AL to the coil to test it. Got a great spark at the coil, but still nothing when hooked to the distributor. Long story short, it has a MSD Pro Billet, MSD 8.5mm wires, and a Street Fire Performance TFI coil. I narrowed things down to the distributor. I removed it and replaced the pickup. While doing this the position of the distributor was marked on the intake and distributor, and the location of the button was noted so that I could put it back in and keep it in time. (picks were taken to, hopefully it isn't out of time). All that done and I have spark at the plugs. Went a head and replaced the plugs with new Bosh ones. I have checked the injectors with a noid light. It flashes but almost looks like it just stays on. The car turns over strong and occasionally it will sputter a little. I've been reading through looking for ideas of what to check next, but though I would go ahead and ask as well. This is an old custom build 347. BBK intake, BBK long tubes, BBK 75mm throttle body, ignition upgrades, cant verify what's in the block. I pumped all the old gas out and put 5 gallons of fresh 91 octane ethanol free gas in it. Look forward to the comments. I'll get some pics up later.
 
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jrichker

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Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995


A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work your way down. Jumping around will possibly cause you to miss just what you need to see to find and fix the problem. Don’t skip any steps because the next step depends on the last step working correctly.



Revised 26-Jul-2017 to add fuse link diagram.


All text applies to all models unless stated otherwise.


Note: 94-95 specific changes are in red


1.) Remove push on connector (small red/blue wire) from starter solenoid and turn ignition switch to the Run position. Place car in neutral or Park and set the parking brake. Remove the coil wire from distributor & and hold it 3/8” away from the engine block. Jumper the screw to the big bolt on the starter solenoid that has the battery wire connected to it. You should get a nice fat blue spark.

Most of the items are electrical in nature, so a test light, or even better, a voltmeter, is helpful to be sure they have power to them.


No spark, possible failed items in order of their probability:

A.) MSD, Crane, or other ignition box if present - Bypass it and return to stock configuration if possible. Do this as a temporary measure to eliminate it as a possible problem source.

B.) PIP sensor in distributor. The PIP sensor supplies the timing pulse to trigger the TFI and injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed. See paragraph 5A – Using a noid light will tell if the PIP is working by flashing when the engine is cranking.

C.) TFI module: use a test light to check the TFI module. Place one lead of the test light on the red/green wire on the ignition coil connector and the other lead on the dark green/yellow wire on the ignition coil connector. If the TFI is working properly, the test light will flash when the engine is cranked using the ignition switch.

D.) Coil

E.) No EEC or computer power - EEC or computer relay failure

86-93 models only: EEC relay next to computer - look for 12 volts at the fuel injector red wires.

94-95 models only: EEC or PCM power relay in the constant control relay module. Look for 12 volts at the fuel injector red wires.

Both 86-93 and 94-95 models: No 12 volts with the ignition switch in the run position on the fuel injector red wires. The relay has failed or there is no power coming from the ignition switch. Make sure that there is 12 volts on the red/green wire on the coil before replacing the relay.

F.) No EEC or computer power - fuse or fuse link failure

86-93 models only: Fuse links in wiring harness - look for 12 volts at the fuel injector red wires. All the fuse links live in a bundle up near the starter solenoid. Look for a 20 gauge blue fuse link connected to 2 black/orange 14 gauge wires.

94-95 models only: 20 amp EEC fuse in the engine compartment fuse box. Look for 12 volts at the fuel injector red wires.

G.) Ignition switch - look for 12 volts at the ignition coil red/lt green wire. No 12 volts, blown fuse link or faulty ignition switch. Remove the plastic from around the ignition switch and look for 12 volts on the red/green wire on the ignition switch with it in the Run position. No 12 volts and the ignition switch is faulty. If 12 volts is present in the Run position at the ignition switch but not at the coil, then the fuse or fuse link is blown.

Note: fuses or fuse links blow for a reason. Don’t replace either a fuse or fuse link with one with a larger rating than stock. Doing so invites an electrical fire.

Ignition fuse links may be replaced with an inline fuse holder and 5 amp fuse for troubleshooting purposes.

94-95 models only: Check inside fuse panel for fuse #18 blown – 20 amp [fuse

H.) Missing or loose computer power ground. The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's 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

I.) Computer. Don’t replace the computer just because you don’t understand how it works. Computers seldom fail, it usually is a sensor or wiring problem that causes the problems.

J.) Bad or missing secondary power ground. It is located between the back of the intake manifold and the driver's side firewall. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges.

K.) Engine fires briefly, but dies immediately when the key is released to the Run position. Crank the engine & when it fires off, pull the small push on connector (red/blue wire) off the starter relay (Looks like it is stuck on a screw). Hold the switch in the crank position: if it continues to run there is a problem with either the ignition switch or TFI module. Check for 12 volts at the red/green wire on the coil with the switch in the Run position. Good 12 volts, then replace the TFI.
See the Ignition switch wiring diagram for more information on the ignition wiring fuse link because it is the next thing to be tested. You will need a Multimeter or DVM and know how to use the Ohms function to check continuity between the red/green wire on the ignition coil and the red/green wire on the ignition switch. Make sure that the ignition switch is in the off position when you do the check. You should see less than 1 Ω (Ohm) between the red/green wire on the coil and the red/green wire on the ignition switch. More than 1 Ω means that the fuse link may have blown open and needs to be replaced. If you get 1 Ω or less means the fuse link is OK and the ignition switch is bad.



Wiring Diagrams:



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information 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



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 94-95 Mass Air Mustangs

http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif





AutoZone wiring diagrams: You can navigate to the diagrams yourself via Repair Info | AutoZone.com and select the car year, make, model and engine. That will enable you to bring up the wiring diagram for your particular car.



2.) Spark at coil wire, pull #1 plug wire off at the spark plug and check to see spark. No spark, possible failed items in order of their probability: [/b]

A.) Moisture inside distributor – remove cap, dry off & spray with WD40

B.) Distributor cap

C.) Rotor

D.) Spark Plug wires

E.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil



3.) Spark at spark plug, but no start.

Next, get a can of starting fluid (ether) from your local auto parts store: costs a $1.30 or so. Then pull the air duct off at the throttle body elbow, open the throttle, and spray the ether in it. Reconnect the air duct and try to start the car. Do not try to start the car without reconnecting the air duct.



Two reasons:

1.) If it backfires, the chance for a serious fire is increased.

2.) On Mass Air cars, the computer needs to measure the MAF flow once the engine starts.

If it starts then, you have a fuel management issue. Continue the checklist with emphasis of fuel related items that follow. If it doesn’t, then it is a computer or timing issue: see Step 4.



Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 2-4 seconds and shut off. To trick the fuel pump into running, find the EEC test connector and jump the connector in the Upper RH corner to ground. The EEC connector is near the wiper motor and LH hood hinge.







If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the Schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. Beware of fire hazard when you do this. In a pinch, you can use a tire pressure gauge to measure the fuel pressure. It may not be completely accurate, but you will have some clue as to how much pressure you have. If you have any doubts about having sufficient fuel flow/pressure, rent a fuel pressure test gauge from the auto parts store. That will tell you for sure if you have adequate fuel pressure.





4.) No fuel pressure, possible failed items in order of their probability:

A.) Tripped inertia switch – Coupe & hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch

B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter. Look for 12 volts at the Pink/Black wire on the fuel pump relay.

C.) Clogged fuel filter

D.) Failed fuel pump

E.) 86-90 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay.

91-93 models only Blown fuse link in wiring harness. Look for 12 volts at the Pink/Black wire on the fuel pump relay.

The fuse links for all model years 86-93 live in the wiring harness near the starter solenoid.







94-95 models only: 20 amp fuel pump fuse in the engine compartment fuse box. Look for 12 volts at the Dark green/yellow wire on the constant control relay module.

F.) Engine seem to load up on fuel and may have black smoke at the tailpipe. Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect for fuel escaping while the pump is running. If fuel is coming out the vacuum port, the regulator has failed. Check the regulator vacuum line for fuel too. Disconnect it from the engine and blow air though it. If you find gas, the regulator has failed.



5.) Fuel pressure OK, the injectors are not firing.

A.) The PIP sensor in the distributor tells the computer when to fire the injectors. A failing PIP sensor will sometimes let the engine start if the SPOUT is removed.

A noid light available from any auto parts store, is one way to test the injector circuit to see if the injectors are firing. The noid light plugs into the fuel injector harness in place of any easily accessible injector. Plug it in and try to start the engine: it will flash if the injector is firing.



I like to use an old injector with compressed air applied to the injector where the fuel rail would normally connect. I hook the whole thing up, apply compressed air to the injector and stick it in a paper cup of soapy water. When the engine cranks with the ignition switch on, if the injector fires, it makes bubbles. Cheap if you have the stuff laying around, and works good too.

B.) Pull an injector wire connector off and look for 12 volts on the red wire when the ignition switch is on.

C.) No power, then look for problems with the 10 pin connecter (salt & pepper shakers at the rear of the upper manifold).



See the graphic for the 10 pin connector circuit layout.

?temp_hash=3ef2497fff29a7a9daee955cf93e5805.jpg


The injector power pin is the VPWR pin in the black 10 pin connector.




D.) No power and the 10 pin connections are good: look for broken wiring between the orange/black wire on the EEC relay and the red wire for the 10 pin connectors.

E.) TPS voltage exceeds 3.7 volts with the throttle closed. This will shut off the injectors, since the computer uses this strategy to clear a flooded engine. Use a DVM, a pair of safety pins, and probe the black/white and green wires to measure the TPS voltage.

On a 94-95 Mustang, probe the black/white and grey/white wires to measure the TPS voltage.

It should be .5-.1.0 volts with the key on, engine not running. Note that if the black/white wire (signal ground) has a bad connection, you will get some strange readings. Make a second measurement using the battery post as the ground to eliminate any ground problems. If the readings are different by more than 5%, you may have a high resistance condition in the black/white signal ground circuit.



6.) Spark & fuel pressure OK.

A.) Failed IAB or improperly set base idle (no airflow to start engine). Press the throttle ¼ way down and try to start the car. See the "Surging Idle Checklist for help with all your idle/stall problems.

B.) Failed computer (not very likely)

C.) Engine ignition or cam timing off: only likely if the engine has been worked on recently. If you removed the distributor, there is a good probability that you installed it 180 degrees out of time.

D.) Firing order off: HO & 351 use a different firing order from the non HO engines.

HO & 351W 1-3-7-2-6-5-4-8

Non HO 1-5-4-2-6-3-7-8

E.) No start when hot - Press the throttle to the floor & try starting it, if you get this far. If it starts, replace the ECT.

F. ) Engine that has had the heads off or valves adjusted. Do a compression test to make sure the valves are not adjusted too tight. You should have a minimum of 90 PSI on a cold engine.




Putting the distributor back in and setting the timing.

Revised 15-Apr-2016 to add fix for TFI hitting the thermostat housing while trying to set the base timing at 14°.

You can forget about anything beyond this point if you don't have access to a timing light. You will never get the timing set right without one.


Note: If you don't have access to a timing light, most of the larger auto parts stores will rent or loan one if you have a credit card or leave a cash deposit.


Putting the distributor back in is fairly simple. Pull #1 sparkplug, put your finger in the sparkplug hole, crank the engine until you feel compression. Then line up the TDC mark on the balancer with the pointer on the engine block.


The distributor starts out with the #1 plug wire lined up at about 12:00 with you facing it. Align the rotor to about 11:00, since it will turn clockwise as it slides into place.


Align the distributor rotor up with the #1 position marked on the cap, slide the distributor down into the block, (you may have to wiggle the rotor slightly to get the gear to engage) and then note where the rotor is pointing.

If it still lines up with #1 position on the cap, install the clamp and bolt. If not, pull it out and turn 1 tooth forwards or backwards and try again. Put the #1 spark plug back in and tighten it down, put the clamp on the distributor, but don't tighten it too much, as you will have to move the distributor to set the timing. Note that there is no such thing as one tooth off on a 5.0 Mustang if you follow the spark plug wire order on the distributor cap. If it doesn't align perfectly with #1 position, you can turn the distributor until it does. The only problem is that if you are too far one way or the other, you can't turn the distributor enough to get the 10-14 degree optimum timing range. If the TFI prevents the distributor from being turned enough to get 14°, there is a simple fix. Pull the distributor out and turn the rotor 1 tooth counterclockwise Don't move the wires from the positions shown on the cap on fuel injected engines!!!! The #1 position cast into the cap MUST have the spark plug wire for #1 cylinder in it. Do it differently and the timing for the fuel injectors will be off. The computer uses the PIP sensor to time injector operation by sensing the wide slot in the PIP sensor shutter wheel. If the injector timing of #1 and the firing of #1 do not occur at the right time, the injector timing for all other cylinders will be affected.


Setting the timing:

Paint the mark on the harmonic balancer with paint -choose 10 degrees BTC or 14 degrees BTC or something else if you have NO2 or other power adder. I try to paint TDC red, 10 degrees BTC white and 14 degrees BTC blue.


10 degrees BTC is towards the drivers side marks.



Note: setting the timing beyond the 10 degree mark will give you a little more low speed acceleration. BUT you will need to run 93 octane to avoid pinging and engine damage. Pinging is very hard to hear at full throttle, so it could be present and you would not hear it.



Simplified diagram of what it looks like. Not all the marks are shown for ease of viewing.



ATC ' ' ' ' ' ' ' ' ' '!' ' ' ' ' ' ' ' ' ' BTC

---------------- > Direction of Rotation as viewed standing in front of the engine.



The ' is 2 degrees.

The ! is TDC

The ' is 10 degrees BTC

Set the timing 5 marks BTC. Or if you prefer, 5 marks towards the driver's side to get 10 degrees.



To get 14 degrees, set it 7 marks BTC. Or if you prefer, 7 marks towards the driver's side to get 14 degrees.



The paint marks you make are your friends if you do it correctly. They are much easier to see than the marks machined into the harmonic balancer hub.



At this point hook up all the wires, get out the timing light. Connect timing light up to battery & #1 spark plug. Then start the engine.



Remove the SPOUT connector (do a search if you want a picture of the SPOUT connector) It is the 2 pin rectangular plug on the distributor wiring harness. Only the EFI Mustang engines have a SPOUT. If yours is not EFI, check for a SPOUT: if you don’t find one, skip any instructions regarding the SPOUT

Warning: there are only two places the SPOUT should be when you time the engine. The first place is in your pocket while you are setting the timing and the second is back in the harness when you finish. The little bugger is too easy to lose and too hard to find a replacement.



Start engine, loosen distributor hold down with a 1/2" universal socket. Shine the timing light on the marks and turn the distributor until the mark lines up with the edge of the timing pointer. Tighten down the distributor hold down bolt, Replace the SPOUT connector and you are done.



The HO firing order is 1-3-7-2-6-5-4-8.

Non HO firing order is 1-5-4-2-6-3-7-8



 
Last edited:

Olivethefet

Slap me as well as point and laugh
May 17, 2018
673
396
73
39
Enterprise AL
Thanks for the guide.
A) MSD box is working fine, but removed it from the equation just to be safe.

B) Had to install a new pickup in the distributor.

C) New TFI installed on the distributor. Coil is sparking.

D) Coil is throwing a strong spark.

E) Getting 12 volts at the red wires. Also checked with a noid light and it is flashing when the engine is turned over.

F) Again getting 12 volts.

G) 12 volts at the red green wire with the key on. 12 volts at the positive side of the coil with the key on.

H) Computer ground is there and appears to be in good shape.

I) Havent done anything to the computer.

J) Cant easily get to this with the aftermarket intake, but all gauges seem to be functioning fine.

K) Only sputters doesn't run.

SO. I decided to check that I am on TDC. I started pulling plugs so that I can turn the motor over easier by hand. #1 and #5 plugs are black sooty and smell like gas. I was checking number 5 through this whole adventure for spark and gas smell. Plugs 2,3,4,6,7,and 8 are all shiny and new looking with no smell. I checked #5 and 6 injectors with the noid light. They are both flashing but only one appears to be firing. I've attached pick of the plugs and one general of the engine bay. At this point I'm thinking that I have fuel injector issues. Obviously if I'm not getting fuel in the mix then I won't get the car to run. The fuel system primes up to over 40# when the power is turned on. I have been jumping the starter solenoid to start the car. The key is in the on position when doing this. I don't think its a factor but thought I would mention it.
I checked the TPS and got 0.9 volts.
2) Good spartk all around. New MSD cap and rotor.
3) Not a fan of starting fluid
4) Good fuel pressure. Need to check the vac line mentioned in part F.
5) PIP is new. I have power on the red wire at the injector. TPS is 0.9 volts.
6) Haven't checked the IAB yet. Didtributor was removed checking TDC now. Double checked the firing order. Getting 120# compression on test.

Thanks for all the help.
Engine Bay.jpg
Plug #1.jpgPlug #2.jpg
 
Last edited:

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
I would follow the pistons, as you turn the engine over verify that your timing sequence matches the compression stroke, 1 compression 3 compression 7 compression. 3 is the second number in the timing sequence so if you have compression on 3 and the rotor is approaching #3 on the distributor you have an ho, there likely is an easier way but that is how I'd do it (the hard way).
 

Olivethefet

Slap me as well as point and laugh
May 17, 2018
673
396
73
39
Enterprise AL
New issue. I had the fuel injector/accesorry wiring harness off cleaning the connectors and just put it back on today. I also sent the injectors out to have them cleaned and tested. I also just put them back on.

Needing to prime the fuel system I was connecting the ground to the battery and disconnecting it while watching my fuel pressure gauge. I got up to about 25.punds and realized that when I reconnected the ground nothing was happening. It's like I lost all power. I checked the battery and it's good. I tried to make a window go up it started to creep up extremely slowly.

My battery ground goes to a bolt where the block( it's on the cover plate where a mechanical fuel pump would go on an older model. I removed this and cleaned all surfaces. Once reconnected I tried the ground again with nothing. I can't even jumper the starter.

The injector harness ground and battery to firewall ground are both connected to the driver's side cylinder head.

My next steps are to start checking other grounds and dues but thought I would check to see if anyone had a better spot to start with


Thanks for the help.
 

jrichker

StangNet's favorite TOOL
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Mar 10, 2000
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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.



No Crank checklist for 5.0 Mustangs

Revised 24 May 2018 to add check for backup lights harness as a no crank problem.

No crank, slow crank and stuck starter solenoid problems have the same root causes – low battery voltage and poor connections. For that reason, they are grouped together.
Use the same initial group of tests to find the root cause of slow crank, no crank and stuck solenoid problems.

Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…


1.) Will the car start if it is jumped? Then clean battery terminals and check battery for low charge and dead cells. A good battery will measure 12-13 volts at full charge with the ignition switch in the Run position but without the engine running.
A voltmeter placed across the battery terminals should show a minimum of 9.5-10 volts when the ignition switch is turned to the Start position and the starter engages or tries to engage. Less than this will result in a clicking solenoid, or slow cranking (if it cranks at all) or a starter solenoid that sticks and welds the contacts together.

Most auto parts stores will check your battery for free. It does not have to be installed in the car to have it checked; you can carry it with you to the auto parts store.

The battery posts and inside of the battery post terminals should be scraped clean with a knife or battery post cleaner tool. This little trick will fix a surprising number of no start problems.

The clamp on with 2 bolts battery terminal ends are a known problem causer. Any place you see green on a copper wire is corrosion. Corrosion gets in the clamped joint and works its way up the wire under the insulation. Corroded connections do not conduct electricity well. Avoid them like the plague...

If the starter solenoid welds the contacts, then the starter will attempt to run anytime there is power in the battery. The cables and solenoid will get very hot, and may even start smoking. The temporary fix for a welded starter solenoid is to disconnect the battery and smack the back of the solenoid housing a sharp blow with a hammer. This may cause the contacts to unstick and work normally for a while.

A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection while trying to start the car: more than .25 volts across a connection indicates a problem. The voltage drop tests need to be done while cranking the engine. It's the current flowing through a connection or wire that causes the voltage drop.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .



Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch or solenoid
100 mV Ground
0.0V Connections
A voltage drop lower that spec is always acceptable.

2.) Check the battery to engine block ground down near the oil filter, and the ground behind the engine to the firewall. All grounds should be clean and shiny. Use some sandpaper to clean them up.

3.) Jump the big terminals on the starter solenoid next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

The rest of the tech note only concerns no crank problems. If your problem was a stuck solenoid, go back to step 1.

4.) Then pull the small push on connector (small red/blue wire) off the starter solenoid (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it cranks, the relay is good and your problem is in the rest of the circuit.

5.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then you have wiring problems.

Typical start circuit...
Diagram courtesy of Tmoss & Stang&2birds



6.) Pull the starter and take it to AutoZone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.


Starter solenoid wiring for 86-91 Mustang




Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.



Electrical checks for the switches and starter solenoid
Remove the small red/blue wire from the starter solenoid. Use a screwdriver to bridge the connection from the battery positive connection on the starter solenoid to the small screw where the red/blue wire was connected. The starter should crank the engine. If it does not, the starter solenoid is defective or the battery lacks sufficient charge to crank the engine.

If the starter does crank the engine, the problem is in the clutch safety circuit (5 speed) or Neutral Sense Switch (auto trans) or ignition switch.

See the Typical start circuit diagram above for wiring information for troubleshooting.

You will need a voltmeter or test lamp for the rest of the checks. Connect one lead of the voltmeter or test lamp to ground. The other lead will connect to the item under test.
Look for 12 volts on the white/pink wire when the ignition switch is turned to the Start position. Check the ignition switch first.
No 12 volts, replace the ignition switch.

The next step will require you to push the clutch pedal to the floor (5 speed) or put the transmission in neutral (auto trans) while the ignition switch is turned to the Start position.
Good 12 volts, check the clutch safety switch (5 speed) or Neutral Sense Switch (auto trans) for good 12 volts on both sides of the switches. No 12 volts on both sides of the switch and the switches are defective or out of adjustment. Check the wiring for bad connections while you are at it.

The next check is courtesy of Killing Hours.
For manual shift transmissions only: check to see that the backup light switch harness is intact and in good condition. There is a wire in the harness that loops 2 pins coming from the body side of the harness. This is the bypass for the auto transmission Neutral Safety Switch. If the connector is damaged, oil soaked or missing you will have a no crank condition.

Backup lights harness for 5 Speed transmission showing the bypass loop for the Auto Trans NSS
Courtesy of Killing Hours
 
Last edited:

Olivethefet

Slap me as well as point and laugh
May 17, 2018
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Enterprise AL
Finally got it running. Thanks for the help. Turns out I had a few things wrong; bad injector, corroded connections, bad pickup in the distributor, battery issues, distributor 90° out of time.
In the process of redoing the interior and addressing other issues. This isn't the place for all that, but I'll put something up in the appropriate section when I get time. Thanks again for the help!
 
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