1988 f150 5.0 EFI auto problems - Ford Forum - Enthusiast Forums for Ford Owners

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Old 12-28-2011, 11:03 AM
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Default 1988 f150 5.0 EFI auto problems

Gentlemen, ive been helping a friend with his old ford.whats
going on is the trans wont shift into high gear unless i stomp on the gas and get the truck going about 50 or so then it goes into
4 gear or 5 not sure even what type of trans it has.. Replaced screens, has no vac. Modul. All electrical. Also when you slow down it doesnt downshift and makes engine knock untill you put in netural, then back in drive just gives low and 2nd again

even though doesnt have vac. Modul. Is the shifting controlled with vacume . These trucks with all the sensors and crap are a pain in the ***.. What was ford thinking . I miss the old 302 / 289s with out all the bs.. Best motors ever built. If any of you good ol boys
can give me a little info to set me in the right direction id be awful grateful
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Old 12-28-2011, 04:56 PM
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Location: Iowa
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I think the transmission is shifting with the electrical shift solenoids. They move the valves inside the valve body. The valve body is sending the oil under pressure to the various clutches and bands that perform the shifts.
Maybe the valves are a bit sticky. I would add some Lucas Oil Transmission Fix to the tranny fluid to see if it helps. I think that's less than 10 bucks, or 3 beers at the bar. Even if it doesn't work it is not much of a loss, unless the beer is very dear to your friend. ;-)
There is also a "Seafoam Trans Tune" product that can help with sticky valves. I saw it on Youtube.
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Old 12-28-2011, 06:11 PM
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Posts: 7,552

Something you can check, the plug that plugs on to the trans, check for corrosion and wiring condition.
I know you don't want to get into this , but if all else fails and you don't have the specs and tools to check the trans solenoid functions, with the trans pan removed check the wiring on the inside of the plug that goes to the shift solenoids.There might be a problem there. Have seen this before.
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Old 12-28-2011, 09:27 PM
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Location: Colorado, near Denver
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Yes, I work on these all day long, and I must agree, I miss the old 289 also. I miss the simplicity of the c-4 and FMX. However, no one would argue that the transmisions of today aren't better (and much smoother) then those of yesterday.
And yes, to be specific, what really happens in any of the transmissions in this particular truck is that the shift solenoid control oil flow to shift valves, which then apply/release whatever concerned parts are needed to hold/drive whatever needs to be done to obtain a specific gear.
Start with a code scan. Most of the transmission will set all kinds of codes when something is amiss. Usually (I know I'm going to get grief about this) an incorrect gear ratio code means that it's going to have to be taken out and overhauled.
What appears to be going on here is either a shift solenoid/pack problem (which explains the 2nd startoffs and lack of upshifting). This usually starts as a bunch of sludge that accumulates over time, then makes the valves stick, creating said problems. When it's cleaned out (usually with a trans service or a flush), not everything comes back all the way. Usually, it's the sludge that's holding the gearbox together. They'll run for a while after a service, but then inevitably start to slip sometime in the future due to clutch wear.
Sea Foam can work wonders for sticking solenoids and valves. However, it's not a miracle in a can. On something this old, it's problaby time for a rebuild.
The knocking you're hearing is most likely caused by a torque convertor. This is a common problem with these trans.
Good luck!
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