Cranks OK, but No Start Checklist for Fuel Injected Mustangs

rbrown777

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Jul 22, 2017
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Riverview, FL
Probably a good thing to explore. I've looked into the easy to access grounding locations already, but it's going to be at least another week before I have time to go after the rest. This is a project car, and I only have a few hours on the weekends to work on it.

One thing I hate to confess, is that a week or so before this issue started, I cleaned the engine bay with the de-greaser and a light hosing. Nothing high pressure. I covered all of the obvious electrical components, but it's possible I got something wet that is causing the issue. I just don't know what, and now I'm kicking myself for it.

Thanks for the input.
 
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rbrown777

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Jul 22, 2017
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Thanks Karthief, It's helpful getting feedback.

What I'm having trouble getting my head around, is that the only symptom I know for sure is when the negative signal to the coil stops from the ICM (#5 Pin) as the car is running, and the car dies immediately with no spark, even at higher RPMs (verified by timing light on coil wire).

When I try to restart with the key still in the run position (without cycling key off first):
- The PIP signal remains okay, based on the LED flashing signal on the #1 Pin,
- I still have 12v to the coil on #4 pin,
- I still have 12v ground on the #6 Pin,
- There is no #5 Pin signal, and the car won't restart (cranks fine, just no spark).

However, when I cycle the key from run to off, and then back on again to the start position, the #5 Pin negative signal works again, and the car immediately starts.

Like I said, I'm not great with electrical issues, but I can't seem to get around the reality that the negative #5 Pin signal fails from the ICM, and won't reset without the ignition key cycling off-on again. This is 100% repeatable.

With constant 12v and ground connections to the distributor, what does cycling the key actually reset to get spark again?

Sorry for rambling, but I'm running my mind in circles, and won't have time to finish the negative ground testing for the next week or two.

Thanks again.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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I started a new thread for ya in the tech section, I tagged ya so you can get some more feedback, I still say you need to check that switch, I don't know anything that would 'reset' by turning the ignition switch off then on.
Question: do you hear the fuel pump when you try to restart before cycling the key?
 

rbrown777

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Jul 22, 2017
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Riverview, FL
Once the fuel pump starts, I can't hear it, and haven't checked. I hear it start when I cycle the key, and everything else electrical seems to stay on when the #5 Pin stops. I guess it's something else I'll check.

Thanks.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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When you first turn the key on the pump will run for a few seconds, if you crank the engine for 5 seconds or more when you stop but leave the key on it should run for a few seconds again.
Have you tried using a quick shot of starting fluid?
 

rbrown777

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Jul 22, 2017
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Riverview, FL
I've never noticed the fuel pump run again after cranking, and I've never tried starting fluid.

This seems like a spark issue, so I never went down a fuel path, but I'm gathering a list of all your suggestions to check. Thanks.
 

rbrown777

Member
Jul 22, 2017
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Riverview, FL
I've checked grounds, and everything is good. I also pulled codes today and got the following: KOEO 85 (no emissions) and 96 (Fuel pump relay or battery power feed was open). KOER 11.

I've had the 96 code since I bought the vehicle about a year ago, so I'm not sure it relates to the intermittent 'no spark' issue I started having a couple weeks ago. I'll look into it though, and I haven't yet verified that at the same time I have no spark, that maybe I also have no fuel.

Tomorrow, I'm going to put the original TFI back on that I replaced because of bad spark at high RPM. It's never died on me with that module. If it doesn't die with the original module back in place, that may signify that I've had 3 bad replacement TFI modules. If it does die with the original module, that will lead me to believe that the problem is not due to the replacement modules, and I'll need to keep troubleshooting.

I've also got a new ignition switch arriving next week, so I'll replace that next weekend. Since the 'no spark' condition clears for a while after cycling the ignition key, I'm hopeful.
 

rbrown777

Member
Jul 22, 2017
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1
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Riverview, FL
Well, I put the original Motorcraft DY1074 TFI module back in, and everything runs fine (except for the spark breaking up at high RPM, which is why I replaced it in the first place). Plenty of spark, didn't die at all.

This is leading me to believe that I've had 3 bad replacement TFI modules (all Motorcraft DY1284, which I understand is the replacement for DY1074). I have another new DY1284 I just exchanged, but I'm going to run with this original DY1074 for a while to make sure of my findings, before I install the 4th replacement module.

Thinking out loud...What was the reason for the module change? What was wrong with the DY1074? If you can still find one, the DY1074 is almost twice the price of the DY1284. Was it a better (and more expensive to manufacture) module? Anyone have any personal experience or knowledge whether the more expensive DY1074 is a better module?
 

rbrown777

Member
Jul 22, 2017
13
1
13
Riverview, FL
Final update...It turned out to be the ignition switch, and possibly one of two bad ICMs along the way (seemed like multiple issues). The problem was intermittent, so after changing the last ICM, the problem seemed to go away after a test drive. However, it came back.

I pulled the ignition switch, opened it up, and found burned contacts.

After replacing the ignition switch, and then driving occasionally for the past month, there have been no more incidents.

(Thanks kartheif!!! I should have just followed your first suggestion. It would have saved me a lot of grief).

Life is good again...
 
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ztomlee

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If you're looking for the fusible link between the ignition switch and coil. It is located in the engine bay near the fire wall, under the brake master cylinder. I found it in the image linked labeled as "fuse link N". It is a blue 20ga link.

Fusible link location.jpg
 

347pipedream

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Mar 24, 2020
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With regards to number 4 about no fuel pressure and cranks fine with spark. I assumed it was the fuel pump and replaced it and it did not fix the issue. I already tried another fuel relay sensor from my brothers car and it did not work. I checked for 12 volts at the relay sensor and it does have 12 volts at the pink/black wire and I'm assuming 6 volts at the red wire with this 6v/12v tester that makes a high pitch on the pink wire and low pitch on red wire. I do not get any voltage at the inertia switch unless I take a paper clip and stick it into the green/yellow wire and pink/black wire in the fuel relay. When I do that I get 12v at the inertia switch and the fuel pump begins to wine and I have 40 psi in the fuel lines under the engine bay. So is it the fuel pump relay connector that needs to be replaced? Or is there something else not happening that allows the fuel pump relay to work then the inertia switch and so on
 

347pipedream

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Mar 24, 2020
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Side note: I used a different multi meter digital one and it shows 11.2 volts at the pink/black wire and 5.2 volts at the red wire in the fuel pump relay.
 
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jrichker

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Side note: I used a different multi meter digital one and it shows 11.2 volts at the pink/black wire and 5.2 volts at the red wire in the fuel pump relay.
What year car? The fuel pump wiring changed several times between 86 and 95.

I have 3 separate fuel pump test paths designed to speed up and simplify testing and repairing the fuel pump circuitry. Post the year of you car and any known changes to the wiring and I will post the test path for your car.
 

347pipedream

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Mar 24, 2020
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What year car? The fuel pump wiring changed several times between 86 and 95.

I have 3 separate fuel pump test paths designed to speed up and simplify testing and repairing the fuel pump circuitry. Post the year of you car and any known changes to the wiring and I will post the test path for your car.
1991 gt mustang. So I by passed the inertia switch. The pink/black wire has 11 volts and the red wire has 5ish. The green wire goes from the fuel relay to the inertia and onto the fuel pump. I noticed with a paper clip applied to the pink/black wire thats always hot and the greem wire that goes to the back does supply the power needed to turn on the fuel pump because then it turns on and the fuel line has 40psi near the fuel rail. But only when I direct that power from the pink to the green line. Otherwise a new fuel relay switch doesn't make a difference
 

jrichker

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1991 gt mustang. So I by passed the inertia switch. The pink/black wire has 11 volts and the red wire has 5ish. The green wire goes from the fuel relay to the inertia and onto the fuel pump. I noticed with a paper clip applied to the pink/black wire thats always hot and the greem wire that goes to the back does supply the power needed to turn on the fuel pump because then it turns on and the fuel line has 40psi near the fuel rail. But only when I direct that power from the pink to the green line. Otherwise a new fuel relay switch doesn't make a difference
Fuel Pump Troubleshooting for 91-93 Mustangs

Revised 6-Feb-2016 to add fuse link diagram

Ignition switch in the Run position, engine not running tests.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 2-5 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the upper RH corner to ground.

Foxbody Diagnostic connector
foxbody-mustang-diagnostic-connector-jpg.586766


Foxbody Diagnostic connector close up view
foxbody-diagnostic-connetor-closeup-view-jpg.586765


attachments\68357



If the fuse links 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. A tire pressure gauge can also be used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.


No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The 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 Relay:
On 91 cars, it is located under the driver's seat.
On 92 and 93 cars it is located under the MAF. Be careful not to confuse it with the A/C WOT cutoff relay which is in the same area. See the diagram to help identify the fuel pump relay wiring colors.
Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect
for fuel escaping while pump is running.

Theory of operation:
Read this section through several times. If you understand the theory of operation, this will be much easier to troubleshoot. Refer to the diagram below frequently.

Diagram of the fuel pump wiring for 91-93 cars.
attachments\57323


The electrical circuit for the fuel pump has two paths, a control path and a power
path.

Remember that the computer does not source any power to actuators, relays or injectors, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

Control Path
The control path consists of the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the relay coil and then from the relay coil to the computer (light blue\orange wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.

Computer power path
The computer power relay must properly function to provide power for the fuel pump relay. That means you must check the operation of the computer power relay (PCM Power Relay) before chasing any problems with the fuel pump circuit. The computer power relay is located above the computer under the passenger side kick plate cover. . It is not easy to get to, you must have small hands or pull the passenger side dash speaker out to access it.
With the Ignition switch in the Off position, check the resistance between the black/white wire and a clean bare spot on the car body metal. You should see less that 1 Ohm. More than 1 Ohm is a broken wire, or bad connection of the black/white wire and the car body metal.
Check for 12 volts at the yellow wire. Good 12 volts and the fuse link is OK. No voltage or low voltage, bad fuse link, bad wiring, or connections.
With the Ignition switch in the Run position, look for good 12 volts on the red/green wire. No voltage or low voltage, bad fuse link, bad wiring, or connections.
Good 12 volts on the red/green wire, look for good 12 volts on the red wire or any of the red fuel injector wires. No 12 volts or low voltage and the relay isn’t closing, or relay socket contacts are dirty/corroded. Water has been known to run down the radio antenna wire or leak from the windshield and get into the relay and relay contacts.

Fuel pump power path
The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (pink/black wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the pink/black wire to the contacts and through the dark green\yellow wire to the inertia switch. The other side of the inertia switch with the brown\pink wire joins the pink/black wire that connects to the fuel pump. The fuel pump has a black wire that supplies the ground to complete the circuit.

Fuse links at starter solenoid
64326.gif


Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect.

Fuse link material is available at most good auto parts stores. There may even be a fuse link already made up specifically for your car. Just be sure to solder the connection and cover it with heat shrink tubing.

Heat shrink tubing is available at Radio Shack or other electronics supply stores.

See the video below for help on soldering and heat shrinking wiring. There is a lot of useful help and hints if you don’t do automotive electrical work all the time.

View: http://youtu.be/uaYdCRjDr4A

Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay).
No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92 or later models the fuel pump relay is located under the Mass Air meter. Watch out for the WOT A/C control relay on these cars, as it is located in the same place and can easily be mistaken for the fuel pump relay.

Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed, or there is a broken wire in the relay control circuit.

Inertia switch:
The location for the inertia switch is under the plastic for the driver's side taillight.
There should be a round plastic pop out cover over it, remove it to access the switch button.
With the test connection jumpered and ignition switch in The Run position as described above, check the brown/pink wire. It should have 12 volts. No 12 volts there, either the inertia switch is open or has no power to it. Check both sides of the inertia switch: there should be power on the dark green\yellow (inertia switch input) and brown/pink wire (inertia switch output). Power on the dark green\yellow wire and not on the brown/pink wire means the inertia switch is open.
Press on the red plunger to reset it to the closed position. Sometimes the inertia switch will be intermittent or will not pass full power. Be sure that there is 12 volts on both sides of the switch with the pump running and that the voltage drop measured across the switch is less than .75 volts.

Pump wiring: Anytime the ignition switch is in the Run position and the test point is jumpered to ground, there should be at least 12 volts present on the black/pink wire. With power off, check the pump ground: you should see less than 1 ohm between the black wire and chassis ground.

Make sure that the power is off the circuit before making any resistance checks.
If the circuit is powered up, your resistance measurements will be inaccurate.



49675.gif


Control path:
Relay: The light blue/orange wire provides a ground path for the relay power. With the test connector jumpered according to the previous instructions, there should be less than .75 volts.
Use a test lamp with one side connected to battery power and the other side to the light blue/orange wire on the fuel pump relay. The test light should glow brightly. No glow and you have a broken wire or bad connection between the test connector and the relay. To test the wiring from the computer, remove the passenger side kick panel and disconnect the computer connector. It has a 10 MM bolt that holds it in place. Remove the test jumper from the ECC test connector.
With the test lamp connected to power, jumper pin 22 to ground and the test lamp should glow.
No glow and the wiring between the computer and the fuel pump relay is bad.

Computer: If you got this far and everything else checked out good, the computer is suspect.
Remove the test jumper from the ECC test connector located under the hood. Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer and everything else is connected. Turn the ignition switch to the Run position and observe the fuel pressure. The pump should run at full pressure.
If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad.
If it does run at full pressure, the computer may have failed.

Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn the key to the Run position. This can sometimes fool you into thinking the computer has died.
Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin.
With the ignition switch Off, jumper the computer into self test mode like you are going to dump the codes. Turn the ignition switch to the Run position. The light will flicker when the computer does the self test routine. A flickering light is a good computer. No flickering light is a bad computer. Remove the test jumper from the ECC test connector located under the hood.

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

Fuel pump runs continuously:
The fuel pump relay contacts are stuck together or the light blue/orange wire (pin 22) has shorted to ground. Remove the fuel pump relay from its socket. Then disconnect the computer and use an ohmmeter to check out the resistance between the light blue/orange wire and ground. You should see more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t jumpered to ground.
If the wiring checks out good, then the computer is the likely culprit.


a9x-series-computer-connector-wire-side-view-gif.gif



Prior to replacing the computer, check the 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. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

The picture shows the common ground point for the battery , computer, & extra 3G alternator ground wire as described above. 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.jpg
 

347pipedream

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Mar 24, 2020
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Found the issue ECC relay above the computer was corroded and not working. Replaced the switch cleaned the wiring up and that fixed the issue. Thank you!
 
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daffyduck

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Hello All,

First I would like to thank everyone on this forum. You guys rock! It definitely made my diagnosis easier.

My mustang would crank but not start. I went through the check list posted here and it helped a lot.

Just making a note to possibly help anyone else out in the future.

I won't go through my entire diagnostic list here as all the steps won't be relevant.

2 major indicators for me was the fact that I only got spark WITHOUT either the computer plugged in, or the SPOUT plug on the distributor unplugged.

It was the EEC relay (behind the passenger side kick panel) that was shot. Replaced it and started right up.

Stay safe everyone.
 
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Cabernet88GT

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Jan 15, 2021
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I am at step "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."

The vehicle cranks when I jumper the screw to the big bolt on the starter solenoid but I am not seeing a "fat blue spark". Should I be seeing the "fat blue spark" between the coil wire and the block or at the jumper on the starter solenoid? Or am I just trying to see if the engine cranks with this test and moving on to step 2? Thank you in advance.