Here's my info
1991 F590F Super Duty, (5 ton) E4OD tranny, 7.3 IDI diesel, Dana 80, 5.13's, 14mpg, 10 lug rims, Duallies, 4 wheel disc, 83,500 miles.
Heres the scoop:
cold starts excellent, then you drive away. It shifts into 2nd gear pretty violent, then the OD light flashes and flashes. Engine's still cold. You enter the freeway and it revs a bit high because of those Effen 5.13's. Anyway it shifts into all four gears rather nice, except harshly, engine still cold. As you approach 60mph (almost my limit) the truck is in OD, the light is flashing and the temp is starting to warm up. You can feel/hear the tranny NOT locking up by the way the engine is revving. Mind you the tranny doesn't "slip" like a worn out tranny at all. But then when the engine is approaching warm status like 10 miles or so, you feel the truck softly lunging forward at the same time you feel the tranny softly locking up to the converter, but never on the first attempt. It takes sometimes up to 20 attempts for the tranny and converter to lock together. How do I know this. Cuz when it locks up, Everything becomes quieter like I just found a magical 6th gear. Then the OD light goes off like a good little OD light should. About 1/2 the time, I never get the two locked together anyway. This makes me think about my engine temp sensors (3 of them or something) especially the one that lets the torque converter lock up. the temp never rides higher than 25% off of cold. You can drive all day and take the cap off of the radiator and put your finger right in the water. Hot but not very hot. I changed the thermostat, no difference. Now after I have been driving for an hour or so lets go into the city for some slow driving now. as you slow down the OD flashes again. Now I am driving 30ish mph and the tranny "hunts" like cant decide if it wants to be in 2nd or 3rd constantly up and down, up and down, throbbing between gears. Quite annoying. I installed a new FIPL, set it correctly and no difference. I checked the positioning on the electrical thingamabob where the.. Gear Shift Selector position thing is on the side of the tranny. That was good too. I don't have an engine tach but I did check that magnetic tach pickup thing that goes to the big gear on top of the engine. It check'd out good too. (I swear I know the names of all these parts but when i need to say them, I forget instantly wtf is with that) I often wonder if my only problem is low line pressure. I bought a Banks Transcommander but never installed it. I don't personally think my tranny needs rebuilding. I honestly think some electrical component isn't talking to another electrical component. I don't know if its relevant, but my speedo is usually about 10mph off. So if my Speedo says I am going 60 I am really going 50. Alright what do you think the likely culprit is? Bad ground? sticky valve body? worn springs? keep playing with the fipl? that cold engine/tranny related sensor? All this cuz my radiator is too big? Only 83K, super clean truck. (used to be a pepsi hauler) wasn't used much but i know there is no dust in the tranny. Oh ya, after its all warm. sometimes it shifts through all 4 gears in 20'. HELP!

 

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old thread digging again Niles lol.

well this wont help the op,as im sure he probably resolved the issue (had too,the trans would have died shortly after since he just kept driving the truck with a flashing o/d light) but there is still much for others;

the first thing Krazymaan should have done here is to park the truck.put a code reader on and scanned for codes.for around 20-30 bucks you can pick one up at online or at your local auto stores.your just looking for the old OBD1 scanner.
most likely he had dirty connections at all the harness plugs with an old truck left sitting (a '91 w/ just 80k in '09)
whenever you get multiple codes for shift solenoids/tot sensor.always jump to the conclusion that the main solenoid plug needs a very healthy dose of electrical cleaner sprayed into the plug using the spray tube to flush it all out good,then leave it sitting full for an hour.then soak up the connector with preferably a lint free cloth.spray the heck out of the plug/pins side as well of course.then apply a little dialectic grease and make sure it fully snaps back in.address any other unrelated codes,clear codes,go for another drive.then trace out any more codes if the o/d light flashes again,or if you get strange shifting behaviors.
everything must have a flawlessly clean connection.if your trans wires/connections are not spotless first,then your chasing your tail.

the last thing you want to do with a flashing OD light,is to continue driving.this is a sure way that leads to requiring a rebuilt/replaced trans.depending on what it's doing,and how far you are from a trans shop/home,it may be best to call for a tow.

 

It was getting quiet.