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Topic: spark loss while driving - SOLVED (Read 4612 times) previous topic - next topic

spark loss while driving - SOLVED

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 ??????????????

Re: spark loss while driving

Reply #1
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.
1988 Thunderbird TC, 5spd
Stinger 3" single exhaust, Cone Filter, Adjustable Cam Pulley, Schneider roller cam, Walbro 255 lph, AEM Wideband O2
'93 Mustang Cobra replica wheels on 235/50R17

'21 F150 Powerboost
'17 Husqvarna TX300

Re: spark loss while driving

Reply #2
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.

Re: spark loss while driving

Reply #3
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.

Quote from: jcassity
I honestly dont think you could exceed the cost of a new car buy installing new *stock* parts everywhere in your coug our tbird. Its just plain impossible. You could revamp the entire drivetrain/engine/suspenstion and still come out ahead.
Hooligans! 
1988 Crown Vic wagon. 120K California car. Wifes grocery getter. (junked)
1987 Ford Thunderbird LX. 5.0. s.o., sn-95 t-5 and an f-150 clutch. Driven daily and going strong.
1986 cougar.
lilsammywasapunkrocker@yahoo.com

Re: spark loss while driving

Reply #4
Try unplugging the SPOUT jumper. this will allow the TFI to generate the spark without any EEC involvement.

Re: spark loss while driving

Reply #5
will do,,

then i should drive?????????????????????????????????

Re: spark loss while driving

Reply #6
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.

Re: spark loss while driving

Reply #7
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.

Re: spark loss while driving

Reply #8
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.

Re: spark loss while driving

Reply #9
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,,,,

Re: spark loss while driving

Reply #10
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?


Re: spark loss while driving

Reply #12
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.

Re: spark loss while driving

Reply #13
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. 

Re: spark loss while driving

Reply #14
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.