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  1. #1

    Question Symptoms of faulty EEC Relay????

    Hi guys,

    86 GT 5sp

    I just noticed it the other day driving - for a half a second or less, the car quit, gauge needles flickered down to zero, and then it came back.

    Driving last night, car doesn't want to stay running, runs perfectly fine, then boom, like I shut off the ignition, dies, then comes back to life. Luckily, I was close to home so I let it cool down for 2 mins and limped it home. Letting it idle in my driveway, it would intermittently act like there was no power...it stayed "idling" but it kept shutting off for a split second, then come back to life. I heard my Fuel Pump relay clicking, and then opened the hood and heard my WOT Cutoff relay clicking as well when the car would "miss".

    TFI is recently bought, same with coil, wires, blah blah blah, all the normal stuff that usually craps out was replaced when I did my heads/cam build. I've never had an EEC relay problem, so I don't know if these symptoms are normal. All I know is that for my tach to go to zero for the split second - means my coil is temporarily not getting power, and with my WOT A/C Relay clicking, and fuel pump relay clicking, something tells me that a relay or connection further up in the circuit that provides power is intermittently breaking the circuit. Oddly, though, when it would finally die and not idle anymore, the fuel pump was still running as I could hear it (Walbro 255, very audible when car is off), and the A/C WOT Relay would intermittently click every couple seconds, along with the fuel pump relay (and when this clicked, I could hear fuel pump momentarily shut off for the click). Voltage at the AC and Fuel Pump relay is good, I'm not home right now or I'd check the EEC relay.

    Aside from EEC relay, what could cause this odd situation?
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  2. #2

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    Check the ignition switch lately?
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  3. #3

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    If that's good, then I'd suspect the pick up in the distributor.
    '88 Mustang GT convertible, T5, 3.08:1 gears. 5.0 Explobra Jet: A9L Mass Air conversion, Fenderwell Mac cold air intake, 70mm MAF meter = 4.6 T-Bird/Cougar housing + '95 Mustang F2VF-12B579-A1A sensor, aftermarket 70mm throttle body and spacer, Explorer intakes, GT40P heads with Alex's Parts springs and drilled for thermactor, Crane F3ZE-6529-AB 1.7 "Cobra" roller rockers, Ford Racing P50 headers, Mac H-pipe, Magnaflow catback, Walbro 190 LPH fuel pump, UPR firewall adjuster and quadrant with Ford OEM cable, 3G conversion ('95 Mustang V6), Taurus fan, rolled on Rustoleum gloss white paint...
    Past Four Eyes: Red well optioned '82 GT 5.0, Black T-top '81 Capri Black Magic 3.3L 4 speed, Black T-top '84 Capri RS 5.0 5 speed.Over 200,000 miles driven in Four Eyes, and over 350,000 in Fox Body cars.

  4. #4

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    Swapped in new EEC relay, let it warm up for 20 mins, took it for a 10 minute drive, no problems. It's idling where it "was" again, too. When I was experiencing problems, when it would stay running, it idled around like 700, which sounds awesome with my cam, but not where it should be. New relay and it's idling at 850-900 and drove around perfect.

    Would dizzy pickup affect all of my relays clicking on and off? I'm 99% sure my relay replacement fixed it, relay I took out was the original brown one, so it's had 123k miles on it and 30 years on the car.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  5. #5

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    PIP sensor would not cause the EEC relay to cycle, but it would cause the fuel pump relay to cycle.
    After the initial prime, the ECU only runs the fuel pump when it sees pulses from PIP. Dunno if that's
    also true for the compressor clutch relay.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  6. #6
    FEP Power Member Ray Dog's Avatar
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    I would check to see if the voltage to the EEC is not dropping out.
    If you can set up a volt meter to monitor battery volts as you drive,like at the cigarette lighter or a point that is easy to connect to.
    A loose/bad connection can drive you crazy.
    Ray
    86 Mustang LX 3.8 Convertible (bought new}
    65 Galaxie 500 XL 390 auto
    2A

  7. #7

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    Monitoring is always a good tip, but it's not as simple as hanging off the cigarette lighter socket. Our cars
    don't have a single power feed, other than the battery itself. So it's necessary to identify which feed we
    need to monitor, and connect the meter there.

    In the case of the ECU and fuel pump, those are each on their own dedicated power feed, with the ECU
    relay controlled by the ignition switch, which is on yet another power feed. None of these are shared with
    the feed for the always-on accessories, such as the cigarette lighter.

    I think it's a moot point now, but being as I try to never replace parts that I haven't proven are failing, I
    definitely would have hung a meter on the output side of the EEC relay, and worked back from there.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  8. #8

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    Quote Originally Posted by JACook View Post
    I try to never replace parts that I haven't proven are failing
    What an unusual strategy!

    I'm following this thread with interest. I had an incident a few weeks ago where my car (1990 SEFI w/A9P) got me almost all the way home, and then quit on me on the offramp for home. And it didn't want to restart. It would just crank and crank. Seeing as how I was on the side of the road, (as well as swimming through high humidity and heat... not to mention pissed off) I couldn't really do much diagnosis. The thing eventually restarted, and I was able to drive it the rest of the way home. I told a friend about what had happened and he recommended checking the EEC relay and the fuel pump relay. Here's what he said "if the engine just shuts off, its usually the brown (EEC) relay, if it chugs a bit then stops, it's usually the green (fuel pump) relay". The next day, having been pretty disenchanted with the car I was willing to throw a hail mary and spend a little money to just fix the thing. I went to The Zone and they had a fuel pump relay on the shelf, but did not have the EEC relay in their system for some reason. I figured my choice was made for me, so I swapped in the new fuel pump relay, and haven't had a problem since. That said, I haven't encountered the exact conditions from that day, those being high heat and humidity and having been on a long drive. I intend to still buy an EEC relay and put it in, but haven't gotten around to it.

    Rock, what about your starting and charging systems? If your scenario happened to me, the first thing I would check is the static battery voltage, and then check it again with the engine running to see if the battery and alternator are any good. I've had dying batteries do some pretty weird things. One time I had a battery pass an Auto Zone load test and STILL crap out on me!
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  9. #9

    Default Symptoms of faulty EEC Relay????

    Problem persists.

    Though it was fixed, drove it to a town about 30 mins away, got back, cruising around my home town and it intermittently cut out again and would come right back to life just like last time. I know the fact that the fuel pump stays on when it finally "dies" is a sign, even though I can hear it intermittently cut out for a split second several times after the car isn't running anymore.

    I'm out of town now so won't be able to mess with it until tomorrow, but I'm going to monitor the EEC's voltage for a while until the problem comes back so I know where to look. I have to do some more reading before I know if the dizzy is a potential culprit. I have a perfectly good Motorcraft from a running car setting in the garage if so.

    Battery voltage is good, and the fact that the AC WOT relay is "clicking" at the same time as my fuel pump relay tells me it's not specific to the fuel pump relay.


    Sean
    Last edited by rock4451; 08-09-2015 at 07:46 AM.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  10. #10

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    The fuel pump should not keep running for more than a couple seconds when the engine dies. So it
    sounds like the ECU is continually going through it's prime cycle. This could be an ECU failure, but
    you definitely need to check that it's always getting the volts it needs. And while you're checking the
    power feed to the ECU, don't forget to also check the ground, which is the single-wire pigtail at the
    negative battery cable. That connection is crucial, because the black/light green wire that plugs into
    that pigtail is -the- ECU ground.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  11. #11

    Default

    It's not like the fuel pump is predictably going through the prime cycle if that's what you meant. It will run after the car dies, and sporadically it will click off for a fraction of a second and then click back on. The time between the click-offs isn't predictable or in a pattern, it's sporadic. I have found, though, that the problem happens when the car is warm. I get off work here in 40 mins and I'll hook up a volt meter to the computer power, install my Motorcraft dizzy, and see what happens.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  12. #12

    Default Symptoms of faulty EEC Relay????

    Computer voltage from pins 37 and 57 is good, replaced dizzy with Motorcraft unit with newer TFI it had on it. Ran it for about a half hour to 45 mins, beat the heck out of it several times to 6300, let it idle, get up to operating temp for a while, it ran good. Also checked computer ground by the EEC as well as one by battery, made sure they were making good contact with bare metal, and made sure the quick disconnect plug was making good contact within. Time will tell if it's fixed!


    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  13. #13

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    Quote Originally Posted by rock4451 View Post
    It's not like the fuel pump is predictably going through the prime cycle if that's what you meant...
    No, not exactly. If the ECU is not getting enough power, it can sporadically reset, and each time it does,
    it will begin a prime cycle, which may or may not complete before the next reset. Lather, rinse, repeat.
    Just a theory, but such a scenario would not tend to have any sort of regularity to it.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  14. #14

    Default

    With the car running and driving, the voltage at pin 37 and 57 was right at 14. I know 37 and 57 provide power for other things, but the computer has to be getting enough power to give the correct voltages there, right?
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  15. #15

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    Problem persists. Putting the battery on a 6 amp charge overnight to make sure a low battery isn't causing this.

    Today, the problem came back. Drove to the gym for ball, car sat 2 hours while I played, came back out, started my car up, drove off the lot, and it sputtered and died, not like a stalling, like some connector is grounding out or something. I'd give it gas and it'd fire here and there, but wouldn't maintain RPM. Tach would bounce between the RPM it was trying to maintain and zero, like instantaneously twitching between 2k RPM and 0 as if someone unplugged my tach intermittently. All the while I'm hearing my fuel pump and WOT relay clicking.

    Finally got it to start and drive right, bam - drove like normal, nice and smooth. Got home and turned it off, and turned the key back on (not start, just the ON position) and the fuel pump kept running, and clicking off here and there. Then turned off and on again, and it primed like normal. Did this about 50 more times and it primed like normal every time.

    I'm beyond stumped. Sounds like a loose connector but I have no idea what to check. Ignition switch?


    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  16. #16

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    Wow, helping the neighbors grandson with a very similar problem car. This car will run/drive well for 30-45 minutes, bring her home, sometimes cuts off, else we key off and she will not restart until a cool down. Amazingly similar PITA.

    TFI ... check
    Ignition coil ... check
    Distributor ... check
    Battery ... check
    Ignition switch ... check
    ECM ... check

    Above list represents renewed or confirmed good items. I listened for EEC and FP relay activity with some contentment, yet do need to confirm grounds. Will probably replace the two before mentioned relays (one at a time, of course) tomorrow.

    Dang it ... need to beat this one, also. Back soon.
    Last edited by StangItMan; 08-14-2015 at 07:15 AM.
    Featured 4 Eye: 84 Tu-Tone 5C/1E - Dedicated project resto-mod for my son Cameron Lee. :tu

    4 Eye past:83 GT - project, traded for a boat load of goodies to finish other cars.
    86 Coupe - Gave to a friends son - being restored. 86 GT - Gave to another friends son ... finished.
    Our Current Fords: 66 F100/FE, 84 Coupe/Tu-Tone(5C-1E), 87 Coupe/408 drag car, 89 GT/347, 90 Coupe/347/Supercharger, 94 Ranger, 98 Explorer/5.0, 04 Cobra SVT, and ...

    Ford Fun-a-tic / Lithia, Florida

  17. #17

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    Drove great tonight to a car show/cruise in. Acted up again upon start up. Got so desperate to fix it, pulled chip (that it has the tune stored on), squeezed the terminals together a bit (female) and reinstalled it. Started up great, ran, after several shut offs and re-starts, went to a local joint for one beer, started up after - still ran perfect.

    At this point, not counting my chickens until it runs for 2 weeks flawlessly. I will report if it acts up again.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  18. #18

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    I would just like to also say if your fuel pump is having a hard time shutting off or turning on there could be carbon buildup on the inside terminals of your fuel pump relay that weld themselves together if to high of a current is being presented. Chances are this is not it as you would have probably walked out to a dead battery by now. Easy way to check if it happens just tap the relay with a screwdriver or solid object and it should free the points and if that works just buy a new relay. In my 90 thunderbird it's in the trunk next to the fuel inertia cutoff switch.

    Sent from my ASUS_Z00AD using Tapatalk

  19. #19
    FEP Super Member gr79's Avatar
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    Had a similar problem with my Ranger.
    Replaced both relays. They work together. Fuel pump and PCM.
    Was part of the problem. Internal arcing due to loose connections slowly ruined them?
    They were working their way out of the sockets due to bumpy roads.
    Remove and reseat. Ran fine for a while. Random engine quit but would restart.
    One day, when going across a bad section of road, truck acted up. Check engine flash. The relays again?
    Found the problem:
    The relays would work their way up to the cover and stop- loose just enough to cause stall/miss issues.
    Either one or the other or both. Push down, all was well.
    Added camper foam tape inside the cover to press down the relays.
    The foam tape eliminated the gap between the top of the relays and the bottom of the box cover.
    Now they stay seated. No more problems since.

  20. #20

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    As anticlimactic as it seems, my last solution was the final one. Something with the chip was ever so misaligned and I think grounding/touching the computer's metal case. Ground out the metal case some more around the chip opening, cleaned all terminals, no problems driving to the moon and back (and track) for going on 3 years now.


    Sent from my iPhone using Tapatalk
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  21. #21
    FEP Super Member erratic50's Avatar
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    84StangSVT came over with his fluke amp loop equipped meter and what we found was vast fluctuations in current on the ground side.

    Knowing what I know now - the block to body flex strap ground cables wears out over time and without any predictable interval.

    My sons 1986 GT ragtop has 110K and his is shot. My car has 440K and it's just fine - go figure. You can bet I'm adding a cable to mine and rewiring it the next chance I get.

    Ground from battery to front of engine cover like is stock but then add from front cover bolt to core support or K member.

    Cut out the wires from stock fender ground connector for the weird 4 wire smash connector. Add a loop connector and a second nut to the negative lead. Crimp then solder in a new heavy wire. Trim the new wire at the 4 wire smashup, wrap the wires together with an oversized crisp then solder. I used another loop connector I cut into a C then brought down to tension and soldered the hell out of it.
    Last edited by erratic50; 04-18-2017 at 01:50 AM.

  22. #22
    FEP Super Member xctasy's Avatar
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    rock4451 Sean P!


    Your sub 12 second, 116 mph, 350 plus rwhp machine suffers from Ford being smart enough to power up parts of the ECU from different sources. Nothing anti climatic about doing that with stock Ford parts and TFS heads.


    The Aussie Ford modification groups have found the EEC a very tough nut to crack due to the low voltages that can upset the whole module. It's no Delco P4 Cal Pac. In Impcos LPG TSB book from 1984, it siad the EECIV was very easy to fuse, since it was a lot more advanced than other CPU's and used much more mirco-chip control. Luckily, its MIL/CEL light functions are below the radar. It ws the real time 126 Thexton / 3225OTC Electronic Engine Control-IV Breakout Box that allowed a Ford tech to isolate faults that gave borth to trouble shooting without replacing parts.



    Most issues are compounding earthing issues. As long as the capacitors aren't burnt out, you have to go through the earths. Explorers and Rangers are simply the worst for earths being faulty right from the factory. After a few years of duty, so are Foxes, but there is a lot more info, and if we get fed up, people do rewire or drab another ECM.

    Fuel pump earthing is a special Explorer problem due to 5 white box fuel pumps in a hard to get to fuel tank. The EECIV AND EECV indeed has multiple voltage feeds.

    Same issue applies with the variations in transmission controllers on 4 and 5 stage auto cars.

    The blessing I've had is being a technician that has used Silcon valley US computers since 1987, the EECIV and EECV are just the same as Troxler Nuclear Density meter computers, same kind of parts. Your US industry has all the answers!


    I have a wonderfull bunch of guys who do my US vehicle services, and almost had the business owner running for cover when I dropped of my Green XLT 4.0 98 Explder for a service with 5 gallons of gass in the tank.

    He said that thing had cost him three days of fault finding after a 5R55 geabox repacment. He said the pinouts connected, but the transmiussion wouldn't take over drive and had sporadic other problems which resulted in him pulling it out, and sourcing another replacment just to get it "out of his hair"

    I found in 5 minutes a problem that this very cleaver guy had delt with for five years on an Explorer just like mine....


    1. a faulty pump earth that stops the truck picking up fuel when parked up a 10% slope.

    2. The Over drive/TPS earth continuity change between the 1997 and 1998 versions.


    Ford does little changes, and sometimes, certain batcjhes suffer some really big problems that you don't find in TSB, EVTM's, but you do find with people on forums that talk with each other.


    Thanks for the advice!

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