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Technical => Engine Tech => Topic started by: jcassity on April 15, 2020, 11:24:25 AM

Title: spark loss while driving - SOLVED
Post by: jcassity on April 15, 2020, 11:24:25 AM
hello all!!!!!!!

87 20th anny Coug 345k miles all stock

symptom.
- while driving engine will shut down.
-no loss of power to the IP, clock, warning indicators or speedo or elsewhere during the event of engine stop.  There is no warning of hesitation,, not bucking prior to the event,, no odd "feels" to speak of.  Its like someone just unplugged the car from the outllet,, it simply goes quiet in the cabin except for any accessory i may have on.   My tach does got to zero though (the 87 20th is the full digi cluster for those who dont know.
-I can not while coasting simply go to N and restart.
-I must coast over to the side, put car in P,,, turn Ign sw off then restart which it does each time.
-I do need to confirm if my fuel pump relay is loosing its trigger sig from the EEC or its high current contact power delivery,,, but i dont think so.  The fuel rail does not seem to "sound" like its repriming when i turn the key from off to forward again,, trust me i know what that sounds like.

troubleshooting....
-yesterday i confirmed something.  I coasted to the side of the road, put car in P, kept the ign sw in the run pos, popped the hood and removed the coil spark plug wire.  I reached into the car and rotated the Key Sw from run to start and as the motor is turning over , the coil is not sparking to the car or anywhere.   If i rotate the ign sw to the off pos then crank, sparks fly everywhere.  So.... i put the coil plug wire back on and start up and go about my day.  This is hapening without regard to engine temp, moisture outside, outside temp or anything,,, its just random and seems as though it only happens once or twice during a driving period of time.
**Simply put,,,, engine spark will remain absent until i rotate the key sw back to the OFF pos!!!!!!!!!!!!!!!!!!!
-while driving i have beat the hell out of the steering col , inst cluster as well as wiggle tested harnesses within reach and no results.

Comments.............
A few months back i noticed that when i first start the car up, i can not tune into any AM stations for my regular Glenn Beck,, Rush L or Hanity shows.   The signal is totally washed out by engine noise ,, not static or anything ,, just a constant whine high pitch.   Eventually over the course of 15 or so min, the signal is  clear enough to listen to but ,,,, its like only 70% there with 30% engine noise.
Normally when i have an intermittent what appears to be electrical issues, i tune into an AM station with KeyON Eng OFF or KeyON Eng Running and perform wiggle tests on various connections while listening for voltage / current static induced by my interrupting any possible bad connections.  This helps me quickly narrow down particular circuits that otherwise an EVTM may not as quickly reveal.

So.. the reason i bring this up..............
Yesterday when i started my short trip,, my radio was acting up as it normally does but soon the AM band cleared up for the most part.  When i had my loss of spark,,,,, and did my prior mentioned test...... when i got restarted instantly,, the radio AM station was back to 100% washed out by engine whine or noise.  It soon cleared up again.


Final thought...........................
My son's 88 5.0L bird is doing the exact same thing.

Conclusion.....
Although i have not pulled codes yet,,, what i am starting to think is that perhaps my computer has reached the end of its life or is getting there. ,, or Maybe that diode that appears near the coil is faulty and is over clocking an EEC chip or over charging one of the 3 electrolytic caps on the EEC PCB,, or ...... nevermind.


SO,,,
thoughts on this very odd problem which simply fixes itself ??????????????
Title: Re: spark loss while driving
Post by: Mikey97D on April 15, 2020, 02:03:55 PM
I am way too under knowledge in electronics to really be of any help.

This sounds to me like a capacitor bleeding off almost that isn't used 100% of the time.  Or the diode like you were saying feeding a cap.  Have you popped open on the computer to check?

Just stuff from the TV shop I use to work at decades ago.
Title: Re: spark loss while driving
Post by: jcassity on April 15, 2020, 03:58:57 PM
i did replace all three caps a couple years ago because one of the electrolytics was leaky.

sorry in advance of posting such an odd issue,, / problem but i am skeptical of moving forward till i get some more advanced opinions on or if this issue has ever been seen before.

short and sweet,,, i loose spark during drive and the car will not regain spark until i fully rotate the key to the off position and restart.
Title: Re: spark loss while driving
Post by: Haystack on April 15, 2020, 06:34:14 PM
Bad spark plug wires cause interference on am radio.

I had an 88xr7. Tach never worked. It ran okay but needed a tune up and had a bad head gasket.  When I removed the coil wire while I was doing some in related work, I put it back on and tach started working intermittently. When the tach died, it would start to stumble and miss. I figured it was caused by the bad head gasket.

Threw new spark plugs and wires at it after the headgasket repair and it worked fine.

Title: Re: spark loss while driving
Post by: softtouch on April 16, 2020, 01:11:34 PM
Try unplugging the SPOUT jumper. this will allow the TFI to generate the spark without any EEC involvement.
Title: Re: spark loss while driving
Post by: jcassity on April 16, 2020, 03:27:34 PM
will do,,

then i should drive?????????????????????????????????
Title: Re: spark loss while driving
Post by: softtouch on April 16, 2020, 04:55:11 PM
will do,,

then i should drive?????????????????????????????????
You can. It shouldn't hurt anything. You would be running at the base timing.
I was thinking if when you have to coast to a stop, you unplug the SPOUT, and it starts without turning the key off, that eliminates the TFI as the problem.
Title: Re: spark loss while driving
Post by: softtouch on April 16, 2020, 08:35:21 PM
1. Car stalls
2. Pull SPOUT jumper
3. Still wont start
4. Check spark
5. Got spark
6. Check voltage between the O/W and BK/W wires at the TPS. Should be 4-6 Volts

This is the output of the EEC's 5v power supply. The computer hardware runs on this voltage.
If it is less than 4v it could be on the "hairy edge" of being good/bad.
Title: Re: spark loss while driving
Post by: jcassity on April 17, 2020, 02:19:55 PM
thank you ,,, that clears things up.
as i mentioned my son has almost the identical  issue ,,, too bad i had him test bassakwards.
i had him test with spout out before starting..... but i am going to follow what you said,, that actually makes better sense and i can see where your going with it now. 

i'll report back.
Title: Re: spark loss while driving
Post by: jcassity on April 17, 2020, 02:23:46 PM
by the way,,,
when i coast to the side of the road with the key "KEPT" in the run positioin,, i know for a fact 100% that i WILL NOT have spark.

the only way i will have spark is if i rotate the key switch all the way to the off pos then rotate back around again to START.

stay tuned though,,,,
Title: Re: spark loss while driving
Post by: jcassity on April 17, 2020, 02:45:27 PM
i do have a question though.....
the TFI ign system is independant from the computer,, meaning,,,
even without a computer installed,,,, i can crank and still have spark.  the green wire the leaves the coil is controlled by the tfi.

the green wire sources from the TFI and goes to the coil,, ,, then from teh coil to the cluster tach and another run to teh eec through a 20 or 10k ohm resistor.

so ,,,,, i am not understanding how the 5v power sup in the eec can have any jurisdiction over spark?
Title: Re: spark loss while driving
Post by: jcassity on April 17, 2020, 05:55:03 PM
nothing went wrong,,, i will re-attempt tomorrow
Title: Re: spark loss while driving
Post by: softtouch on April 18, 2020, 01:07:12 AM
I haven't forgot that switching the key  off and back on makes the problem  go away.
All of the checks I suggested should be done without switching the key off.
The TFI only operates independent from the EEC if the SPOUT is disconnected.
When the SPOUT is connected, the EEC controls when the spark fires. This is how it controls the timing.
If you are getting spark with the SPOUT disconnected and it still won't start:
1. It says the TFI is working.
2. There are other things the EEC is not doing besides not triggering the SPOUT, maybe like also not triggering the injectors.
The EEC  5v power supply being out of specs may explain why it's behaving erratically.
Title: Re: spark loss while driving
Post by: jcassity on April 18, 2020, 09:00:34 AM
hummm,, i think your learning me sumthin there,,,,,,!!!

the eec is in the game of spark control only if the spout is connected.

now there is a few youtubes out there and one specifically i can think of where a fox body guy has the EEC unplugged.

he cranks the engine and he has spark regardless of spout or not being undone. 
Title: Re: spark loss while driving
Post by: jcassity on April 18, 2020, 09:01:43 AM
going out to test again,, this time if i stop somewhere i will not shut the car off,, i will let it idle while i go do what i need to do.

Title: Re: spark loss while driving
Post by: jcassity on April 18, 2020, 11:34:27 AM
well the problem did not happen again,,, its like it knows i am watching and tooled up to find it to!

will try again tomorrow.
Title: Re: spark loss while driving
Post by: softtouch on April 18, 2020, 02:24:51 PM
hummm,, i think your learning me sumthin there,,,,,,!!!

the eec is in the game of spark control only if the spout is connected.

now there is a few youtubes out there and one specifically i can think of where a fox body guy has the EEC unplugged.

he cranks the engine and he has spark regardless of spout or not being undone. 
Come on now. Pulling the Spout jumper and unplugging the EEC does the same thing. Opens the SPOUT circuit between the TFI and the EEC.
Spoke too soon . EEC pin 16 is the ignition ground for the TFI. I am surprised you could spark with EEC unplugged.
Title: Re: spark loss while driving
Post by: softtouch on April 21, 2020, 07:26:18 PM
Are you running the stock '87 EEC?
What color TFI. gray or black?
Title: Re: spark loss while driving
Post by: mr glee on April 22, 2020, 12:19:39 AM
Sorry but not familiar with this car but familiar with this problem mine would cut out without any symptoms and would not restart until I had turn the key off the cause bad pip in the distributor.
Title: Re: spark loss while driving
Post by: jcassity on April 26, 2020, 05:27:11 PM
im back

TFI is Gray
the PIP might be bad as well or going out.  we will see.

so....after several days of this problem not showing up ,, it did today.

so with key still i the RUN pos i tested the following..............
-TPS org to blk= 5v
=unplug spout and recrank but no spark.
-poked at the shrader valve and fuel went everywhere.
-confirmed no spark at coil
-the red wire at coil had 12v
-****i am 80% sure the green wire had zero volt but  this confused me because after my tests,,, i went to key off then key back on to retake coil voltage readings.  the red had 12v,, the green had 12v.  when it breaks again,, i will double down on the green coil trigger wire to see if it actually did hold a zero volt condition

sorry for late updates but i decided to wait till the car failed again...  evidently it took a few days.
Title: Re: spark loss while driving
Post by: softtouch on April 27, 2020, 03:33:42 PM
Gray is the correct TFI.
I don't have anymore more trouble shooting suggestions.
Sounds like you are down to PIP or TFI.
Stopping with 0v on the coil green wire is not good. It means you have full power on the coil.
The coil and TFI will overheat.
In the old days they used a ballast resister to lower the voltage on the coil.
The TFI controls the dwell time to limit how long the coil has voltage applied.
In even older days, dwell time was how long the points were closed.
Title: Re: spark loss while driving
Post by: jcassity on April 28, 2020, 10:58:30 AM
the issue happened again yesterday.

I confirmed the green wire potential and yes the green did have source 12 with the key kept in the on pos.

this is normal so,, i have to conclude as well that since its the job of the TFI and PIP to switch on and off the ground potential to the coil (green wire) then the dizzy pieces parts must be the issue.

I will try to find a complete dizzy with "STANDARD" branded tfi and pip..  meaning i want the highest quality / rated as such dizzy money can buy.
Title: Re: spark loss while driving
Post by: jcassity on April 28, 2020, 02:16:22 PM
just got back and the car did just fine.  researching a reliable complete dizzy.

thanks everyone!
Title: Re: spark loss while driving
Post by: jcassity on June 28, 2020, 06:41:01 AM
this issue was solved by a new TFI.  Confirmed now after several weeks.
Title: Re: spark loss while driving - SOLVED
Post by: mcb82gt on June 29, 2020, 08:42:14 AM
this issue was solved by a new TFI.  Confirmed now after several weeks.

Was it STANDARD brand?
Title: Re: spark loss while driving - SOLVED
Post by: jcassity on November 09, 2020, 06:21:13 PM
yes it was