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ASEMaster35yrs, Master Auto Tech
Category: Ford
Satisfied Customers: 2095
Experience:  ASE Certified since 1972,Master Auto tech,Heavy Truck,worked on all makes and models
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Have a 1987 Ford Mustang. V8. It has spark, but there is no

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Have a 1987 Ford Mustang. V8. It has spark, but there is no pulse on negative side on injectors. Need to troubleshoot.
Hello and Welcome to Justanswer, My name is XXXXX XXXXX I am here to try and assist your with your question.

Do the injectors have power on both wires with the key on ad cranking?

Do you have a nice blue spark out of the coil while cranking?
Customer: replied 4 years ago.
12 v at the red wire on injectors. No voltage on the negative side with key on. There's good spark at the plug wires.

The injector are fired by ground switching from the PCM (computer) by the signal from the distributor pick up and the ignition module which cause the coil to fire the spark plugs as well as ground switch the injectors. If you have good spark as well as key and cranking power on the red power supply wire to the injector but no pulse then this means the PCM has failed. The drivers in the PCM are bad and the fix is going to be to replace the PCM. The PCM is located in the RH side kick panel under the glove box. See the location HERE
Customer: replied 4 years ago.
the spark I'm getting from coil pack is orange but strong and steady.
That simply means the distributor pick up coil is sending the crank signal to the PCM and the ignition module to fire the coil. Another thing I didn't mention, is that the injectors should have power on both wires with the key on and only lose power on the ground switching side while cranking. You have a failed PCM.
Customer: replied 4 years ago.
Ok.I'm ordering a pcm. Let you know a soon as I replace it.
Im here if you need me.
Let me know how it goes, im here all day.
Customer: replied 4 years ago.
Installed a new pcm, still no juice to injectors
Do you now have power on both wires at the injector with just the key on?
Customer: replied 4 years ago.
So does the red power wire on each injector have power as stated yesterday with the key on?
Customer: replied 4 years ago.
Both wire need battery voltage at each injectors until the engine cranks, take your ohm meter and ohm the pins #13, #12 , #58, #58 ,#14 and #15 from the injectors to the pin on the PCM to see if you have an open in the harness. Also check and see if you have a good ground at the PCM on Pins #40 and #60. See the diagram here For reference.
Customer: replied 4 years ago.
Will do. Let you know
Okay , im here all day.
Customer: replied 4 years ago.
All of that checks out ok

One last thing to check is to make sure you have battery voltage at the PCM on Pins #37 and #57 at the PCM with key on.

Customer: replied 4 years ago.
I have power there fine
If you have power and ground at the PCM along with good spark and no injector pulse and all the wires check okay then are you sure the new PCM isn't defective?
Customer: replied 4 years ago.
Its a reman unit by cardone
Something is sure being overlooked here, If it where me, I would go back and double check every thing we have discussed.
Customer: replied 4 years ago.
You don't think that there could be a faulty module on the distributor because we have spark signal?
If you have spark the module should be fine, you did say you have spark correct?
Customer: replied 4 years ago.
Yes. We re definitely missing something then.
From what your saying you have No injector pulse , you have power to them but no ground switching, every time I have ran into this it was caused by a bad PCM.

One other time I ran to a Stuck open TP sensor which shut off injector pulse in cases of flooding. Have you tried unplugging it and see if the injectors then pulse?
Customer: replied 4 years ago.
Just tried it. Still no juice or pulse on the negative side

With everything you have checked and verified its still pointing to a bad PCM.

Customer: replied 4 years ago.
Ok, will order another one.
There really isn't much else if it can be if all your other testing is correct.
Hello again Ron here.

I noticed we have not yet resolved your concern you asked about. I would sure appreciate it if you would reply so I can offer my skills and knowledge and repair guide access to help as best I can.

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Thanks Ron
Customer: replied 4 years ago.
I have now tried 2 new computers, still no reaction at the injectors. Can you redirect the question to somebody else that may have other ideas?
Sure thing Steve, I will relist it right now. Hopefully some else can come up with a solution for you.

Glad to be of help. OHM check each and every fuel injector. From your description, you have a shorted injector. A shorted injector will cause your PCM to shut down injector pulse to protect itself. Also check your PIP & TFI module connections. See video:

Injector specs: Injector Resistance Specifications

Customer: replied 4 years ago.
Haven't tried that yet. Will check in morning, let you know.

That's what it sounds like to me. Let me know what you find out. Don't forget to check your connections at distributor. See these forum links:

Customer: replied 4 years ago.
I've unplugged all the injectors and probed the connectors. With key on I get no voltage at the negative wire. So that rules out a short in the injectors. I've checked ground coming from the distributor module, plus I have spark. I assume that means the module is fine.
Customer: replied 4 years ago.
Have replaced tfi and pcm. All power feed to pcm and feed to injectors are good. With the noid light I'm getting a continuous glow that's real dim at the injectors connector.

Did you ohm the injectors themself? Did you watch the video?

What were the readings?

Checking at injector connector does not rule out a shorted injector. You need to ohm the injector, not the connector. All readings must be within 2 ohms of one another and be within specs. Let me know your readings.


Here's a link to test your TFI circuit:

Follow the instructions at this link:



There may be a wiring problem or bad connection so you need to check continuity and check coil pick-up. This is what gives the injector pulse signal to computer.

Customer: replied 4 years ago.
this pcm connector does not have a pin 24.
Customer: replied 4 years ago.
This one has it on pin 56 and circuit is closed. I was under the impression that pick up up coil is good since we have spark.
Customer: replied 4 years ago.
All connections on that circuit check out.

Ok, I'm going to ask again, what are the ohm readings of your injectors? Did you ohm the injectors themself with connector removed as in video?

Typically the injectors will be 12-14 ohms.

The specs for your vehicle are:

Injector Resistance:

11-18 Ω

Customer: replied 4 years ago.
Reading is 16 on all injectors
Ok, now we have verified that the injectors are good. Is there a security light on that I should be aware of? Have you checked your EFI relay?
Customer: replied 4 years ago.
No warning lights. Please explain about the efi relay. Where is it located and what is its function?

Before we do that check your TPS sensor.

If 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.



If this checks out it may be a problem with PIP sensor or connections.

The PIP is a Hall Effect magnetic sensor that triggers the TFI and injectors. There is a shutter wheel alternately covers and uncovers a fixed magnet as it rotates. The change in the magnetic field triggers the sensor. A failing PIP sensor will often set code 14 in the computer. They are often heat sensitive, increasing the failure rate as the temperature increases.

Spark with the SPOUT out, but not with the SPOUT in suggests a PIP problem. The PIP signal level needs to be above 6.5 volts to trigger the computer, but only needs to be 5.75 volts to trigger the TFI module. Hence with a weak PIP signal, you could get spark but no injector pulse. You will need an oscilloscope or graphing DVM to measure the output voltage since it is not a straight DC voltage.

See and for verification of this little detail from Wells, a manufacturer of TFI modules and ignition system products.

Have you checked all your fuses inside and underhood?
Customer: replied 4 years ago.
Ok. Will read the article. So if I swap in a known good distributor which contains the pip I shoud be able to determine id that's the issue
Spark with the SPOUT out, but not with the SPOUT in suggests a PIP problem.
Customer: replied 4 years ago.
Spout wire is good and circuit is closed to pcm. So I'm going to try swapping in a good known distributor to rule out the pip deal.
Great! Try that. That will rule the PIP out or find your problem.

Here's a TFI wiring diagram:


Make sure you have the correct TFI module.

Here are the comparisons:


Customer: replied 4 years ago.
this is the way this one is wired. All these connections are verified to be good. So its got to be a bad pip. I'm going to try cranking without the spout connected to see if I still have spark.

Ok, let me know. Here's an excellent forum link with a lot of information:

Customer: replied 4 years ago.
I'm seeing the same results with a known good distributor. There's still good spark, but the noid light shows a dim glow that seems to be flickering a little bit
Customer: replied 4 years ago.
I get same results with the spout wire unplugged
Customer: replied 4 years ago.
I'm turning the distributor by hand and it fires all 8 injectors at the same time.

There is probably a relay somewhere in the system that has failed. Get your manuals out and start tracing wires until you locate them in the drawings. I feel like its a relay going to the computer, mainly the ECC main relay (EFI relay). Check the EEC and fuel pump relays mounted inside the pass side kick panel for activation. Locate the fuel pump relay (for 86-90 Mustangs, its location is under the driver seat). Check the 12V trigger wire to the EEC relay from the ignition switch. Also check the fusible links at the starter solenoid on the d/s inner fender. When you find the one component that
is not sending the power through as it should, there is your problem.

Start tracing the systems and check for voltage at all of the proper places leading to the ignition and fuel controls. recheck for injectors pulse....if test light doesn't blink = test the injector pulse signal wire for continuity between the injector connector to the ECM connector. The resistance reading should be less/equal to 5 ohms? OK = ECM is kaput, needs to be replaced? NOK = trace and repair wiring harness.

See this Forum link,588.0.html

Relay wiring diagram


ECC relay location


Customer: replied 4 years ago.
eec relay must be good, since pins 37 and 57 at pcm are live with 12 vdc. Also fuel pump is working so that relay is good too

Test the injector pulse signal wire for continuity between the injector connector to the ECM connector. The resistance reading should be less/equal to 5 ohms? OK = ECM is kaput and needs to be replaced? Not OK = trace and repair wiring harness. The TFI module sends the signal to the computer. If you are getting the signal from TFI module, the problem is either in the wiring harness or computer. If you are not getting the signal from TFI module, the problem is either PIP sensor or TFI module.

When the engine is being to be turned by the starter (~200 RPM or less), the PCM has no idea where the crank is in its rotation and must wait to get a signal from the distributor before it can synchronize the fuel delivery to the crank position. During that very short time, it fires all injectors together.
When you turn the distributor manually, you are simulating this pre-sync "Crank
Mode" condition and they will all fire together. If all fire together when the engine is actually running, then it is in limp mode.

Chase the codes, check your harness grounds. Verify your computer code matches the engine. The PCM is not getting an important input that it needs. More like
something isn't plugged in or the wiring harness has become damaged.

Customer: replied 4 years ago.
Ok, so if the pcm is on limp mode, there is a faulty sensor or circuit that's causing that. If I unplug every sensor in the harness I might be able to wake up the pcm.
No, moving the distributor by hand only simulates what happens in limp mode when engine is running. Unplugging the sensors will not do anything to help you. You are either not getting the signal from TFI to computer or you are not getting the signal from computer to injectors. You need to first verify that the signal is comming from TFI, and if not, replace your TFI module. If it is, you need to trace the wiring to computer to find where signal is lost. If there is signal going into compter but not going out, replace computer.
Customer: replied 4 years ago.
I'M in a bind because I've verified connection from tfi to pcm, from pcm to injectors with 3 different computers

There are only four possibilities. The PIP sensor is bad, The TFI module is bad, The computer is bad or there is an open or short in wiring harness. I'm going to take an educated guess and say your TFI module is defective since you swear all connections are good and you have tried a known good distributor and replaced the computer three times. Keep in mind a bad coil can damage a TFI module.

Customer: replied 4 years ago.
I've also replaced the tfi

Did you verify you have power to ICM at #3 and verify you have on-off pulse at ICM #2 and pulse at IDM pin 4 at computer & have ground at ICM #1? See diagram:

Customer: replied 4 years ago.
There is power at icm at 3,I'm assuming there's pulse to coil at #2 since there is spark. there is ground at #1 from distributor. I'll look for pulsing from #4 to pcm

I learned one thing, you can't assume anything, it needs to be physically checked and check PIP & computer grounds. Check ignition switch to make sure there is power to coil+ in run & crank position. Power goes through starter relay in crank position.

Customer: replied 4 years ago.
There is power to pcm in run position. Will check power to coil in run.
You did of course check all your in vehicle and underhood fuses, didn't you. I assumed you did.
Customer: replied 4 years ago.
No I haven't. There is no fuse box under hood. Will check cabin fuse box just in case
I'm out of ideas. If the Noid does not flash and the injector 12 volts is good, the computer or PIP is at fault. That's all it can be but you say all connections are good and both PIP and computer is good and you checked everything. If you are getting pulse from the computer, you should get pulse to injectors.
ASEMaster35yrs, Master Auto Tech
Category: Ford
Satisfied Customers: 2095
Experience: ASE Certified since 1972,Master Auto tech,Heavy Truck,worked on all makes and models
ASEMaster35yrs and other Ford Specialists are ready to help you
Customer: replied 4 years ago.
Is the signal from the pip to the pcm a negative or positive? And what's the voltage
Customer: replied 4 years ago.
I will accept defeat on this one. You did great though. Thanks for your expertize.
Thank you for your excellent feedback. If your components check out, it has to be in the connections. Corroded connectors between the Hall Effect PIP unit in the distributor and the TFI module on the distributor housing are common. Thank you for using just answer.