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  1. #1

    Default TAB/ TAD headache

    Hello all:

    I may have found the reason for my engine running hot and giving me all sorts of trouble. Corrected a few things but looks like I have something wrong with the TAB and TAD solenoids. Here goes:

    I've read over plenty of factory and some non-factory literature and can't figure out how these gizmos operate. Should be easy. Solenoid is either on or off allowing or not allowing vacuum to flow, thereby operating, or not, some component. I always have Thermactor air going upstream and after thoroughly looking at the setup on the car, an 86GT, its a mystery.

    What do they do and when is my problem. If they are both off normally, how is any air flowing? According to my books, the TAB is closest to the fender with three wires. The other is TAD. Check. But the vacuum line routing is reversed. This would be my fault from a few years back. But if that's the case, how is air getting upstream? I pulled the old solenoids off to check them, plus a replacement. Both don't really hold vacuum but the shop manual says that is normal. Both solenoids work when tested. On both assemblies. I do need to clean the terminals but since I have no codes and vacuum seems fine, why the upstream air all the time?

    I even checked the new diverter valve. It allows air to the downstream port without vacuum, upstream with vacuum.

    If vacuum is reversed, then the bypass valve should be bypassing all air and nothing should flow to the diverter.

    Quite confused obviously. A plain English description would be most welcome. I should just reverse the vacuum routing and see what happens but I want to be sure. Not really sure how the lines were switched.

    Thanks much. Cheers.

  2. #2
    FEP Super Member erratic50's Avatar
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    Default

    Watching this thread — I’m wondering if we are fighting with a similar problem!

  3. #3
    FEP Super Member xctasy's Avatar
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    Each year from 1978 to 1987, the TAB/TAD operation can differ because they used whatever parts Ford used for the year, and Then, they fiddled with the VECI diagram between the final State they were delivered to. So there is a lot that differs between 1986 Port EFI 5.0's. Upstream and Downstream AIR is relative to the Upstream side, the Thermactor bumps in the exhaust eight ports, and the downstream AIR, usually the lines to the upper cataylsts in the four Cat 86 onwards Port EFI 5.0 Mustang and Capri's.

    SMOG pump (Thermactor Air System)

    This pump brings air to the back of the heads and into the two rear catalytic converters.

    When the engine is cold, the thermactor air system pumps fresh air into the heads (there are bumps in each exhaust port in the head, air goes in from the back of the heads from the cross-over tube).

    When the engine is warmed up, the air is diverted to the cats which helps to create the catalytic reaction that converts hydrocarbons and carbon monoxide into C02 and water vapour.
    Its basically like this



    Without this system, the catalytic converters risk clogging up or at least not perform as they should. At WOT, the computer tells the bypass valve to open and dump the fresh air to help limit parasitic drag on the engine. The fox Mustang’s Thermactor Air System comprises of few parts:

    Air pump
    Thermactor Air Bypass valve
    Thermactor Air Diverter valve
    Thermactor Air Bypass and Diverter solenoids (TAB/TAD)
    Check valves

    Note that specfic to the passenger car Windsors, After 1978, Ford added Upstream Air to the 5.0 and 5.8 Windsor cylinder heads to make the Thermactor easier to control. Upstream AIR is sent to the back of the cylinder head on the passenger side via two lines to both heads. Down stream AIR, (if so equiped) is sent ubove the first cataylst by long tubes with a backfire valve(s).

    Since the 86 has four cats, long tubes divert air to a point above the first cataysts. The priority system for engergizing the TAD and TAD differs each year, even though the controls look the same. That's what causes most of the confusion, and there are Load Control Valves that vary between CA/High Altitude state 5.0's, and the other 48 or 49 state engines.

    See https://foxstang.com/fox-mustang-smog-system-help/

  4. #4

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    Great info. Wonder why things changed so much year to year. I think the solenoids and valves changed appearance for 88, not sure. 86 TAB and TAD are hard to find but I now have a backup since both checked out good.

    From my Ford books- shop manual and the EVTM, it appears that TAB is always 'on' meaning energized and therefore allowing air to continue, not overboard. TAD is 'on' only during warmup, sending air upstream to the heads, then 'off' sending air downstream to the cats. If that's the case with 86's, then I have the vac lines switched, which would easily explain the running lean codes a few weeks ago plus the overheating and just plain running hot.

    I'll switch them tomorrow evening and let the board know what happens.

    As a PS, the part number identifies the factory TAB/ TAD assembly as a Continental part. Many parts for the FI 86 come from T-bird, Cont, or even a few other models. Pieced together definitely but as some would say- Yeah its a hodge podge but its my hodge podge.

  5. #5
    FEP Super Member xctasy's Avatar
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    Ford had always intended to make the EFi system found on the 1980 to 1985 CFi Lincolns, Panthers, and Foxes into something very special. Rollout of the Port EFi had to await the domestic success of the Escort EFi, the SVO Turbo and the Turbo EXP Escort and LN7. Elseware, the V6 Euro Granada and Capri had used the Port EFi, so the 5.0 was a culmination of a lot of other parts.

    Ford makes money by having critical mass to spread and amortise the costs, so a Hopped up Mustang 5.0, from 1982 to about 1993 was a combination of MN12, S car Fox LSC and even truck components. So the same thing is always seen....part bin robbery by Robin Hood. The EEE guys who dyno tuned the fist 200 hp 5.0 had already done the Five Step Plan to Horsepower Nirvana way before 1982...1968 in fact, with Carol Shelby. They rework the M code engines time an time again for countless years, and delicately blended in other stuff form other car and truck lines.


    Under standing it becomes a little easier if you try an think how you can cost something. If its spread over the Panther, Fox and F truck and E van lines, you can make anthing a goer when the Boss says Yes. It was actually HeNry Ford II and Edsel Ford II who rubber stamped the 5.0 revitalisation. The saw what happened to V6 engines in Germany, the UK, and 5 liter V8 engines in Australia, so they knew a hotted up Port EFi engine was going to do the job.

  6. #6

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    The TAB and TAD were switched- vac lines went to the wrong valve. Switched them and all is good. No more excessive heat.

    Great info about the 5.0, especially the early 80s development. Had a hunch that the engine saw application elsewhere first and likely was knit together from parts bins and what worked for other car lines. Still plenty of fun.

    Cheers.

  7. #7
    FEP Super Member xctasy's Avatar
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    The Lincoln Foxes gave the SVO its brakes and wide track, the LSC the basics of the 86 GT Port EFi engine.

    The clues were all there in 1982

    https://www.youtube.com/watch?v=AqQ6ds8-BUw

  8. #8

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    Bit of a late reply, but it bears pointing out that the diverter valve in the diagram and photo above, are installed in the
    'default downstream' orientation, where vacuum is applied to bring the air to the cylinder heads. That configuration
    was used on the SEFI and CFI 5.0s, and I believe also the '83 4V. The '84 and '85 4V used the same valve but with the
    vacuum diaphragm pointing toward the front of the engine. In that configuration, the valve is 'default upstream', and
    vacuum is applied to switch the air to downstream.
    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

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