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When my 90 Bronco (5.8L) sits for a while, it will only go into first gear by revving the engine. If I’m using it often, it’s not a problem. Once in gear, it shifts perfectly. This leads me to believe it’s a pump or oil pressure/vacuum issue.

I’ve checked and replaced my fluid and filter and it hasn’t solved the problem. It might have made it a little better, but not fixed.

It will go into reverse when cold with no problem. I’ve also tried turning off the OD and starting in 2nd gear but it doesn’t make a difference.

I’ve read that there is a check valve that keeps the fluid in the torque converter from flowing back into the transmission oil pan when the car is shut off and that valve can fail causing this issue.

I’ve taken it to a couple of transmission folks, but they are all over the place from head scratching to replace it to rebuild it. I don’t think any of them have experience with this specific transmission.

It just doesn’t make sense to rebuild as once it’s warm and the pump has oil pushed into the tranny, it runs fine. I think it’s either a pump issue, vacuum issue, or the check valve.

Does anyone have any thoughts about this?
 

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Yo Joe,
Welcome!
Ford's diagnostics call for checking for Diagnostic Trouble
Codes, so Try a Self Test for Codes by my pal, BroncoJoe19 @ Code Reader.....
The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test. Run it around to heat the engine up and shift thru all gears including Reverse. Make sure A/C is off and transmission is in Park (automatic); or in Neutral for a Manual and; release clutch. Then turn off engine, all accessories/lights (close driver's door) , etc.

Do KOEO test First. Post Code(s) here according to KOEO and KOER.

A helper can assist you by counting the codes. Some use their smart phones to record them.

BEWARE OF FAN, BELTS, PULLEYS, HOT HOSES, IGNITION HIGH TENSION WIRES, AND ENGINE COMPONENTS⚠

Or ask local mom and dad parts stores if they will test it for you.

Or purchase a coder reader such as Equus 3145 Innova OBD I Code Reader for Ford EEC IV Engines at Walmart & most parts stores.

Related issues or causes:
Low E4ODFluid Level;
"A fluid level that is too low will affect transmission operation, such as: slipping, slow engagements, damage to internal hardware. Low level may indicate fluid leaks that may cause transmission damage. "
"
  1. Observe color and odor of the fluid. It should be red, not brown or black. Odor may indicate overheating condition, clutch disc or band failure.
  1. Use an absorbent white facial tissue and wipe the fluid level indicator. Examine the stain for evidence of solid particles and for engine coolant signs (gum or varnish on fluid level indicator).
  • If particles are present in the fluid or there is evidence of engine coolant or water, the transmission pan must be removed for further inspection.
  • If fluid contamination or transmission failure is confirmed by further evidence of coolant or excessive particles in the transmission pan, the transmission must be disassembled and completely cleaned and serviced. This includes cleaning and flushing the torque converter and transmission cooling system. Repair or replace radiator." by Ford
Cold Start; Any Ford E4OD regardless of gas or diesel will not lock the converter until the coolant temp reaches 100 degrees. The transmission fluid temperature sensor is located on the solenoid body assembly in the transmission sump. It is a temperature-sensitive device called a thermistor. The resistance value of the transmission fluid temperature sensor will vary with temperature change. The powertrain control module monitors voltage across the transmission fluid temperature sensor to determine the temperature of the transmission fluid. The powertrain control module uses this signal to determine whether a cold start shift schedule is necessary. The cold start shift schedule lowers shift speeds to allow for the reduced performance of cold engine operation. The powertrain control module also uses the transmission fluid temperature sensor input to adjust electronic pressure control pressure for temperature effects and inhibit torque converter clutch operation during the warm-up period..." by Ford

Less likely;
Vehicle Does Not Move Diagnosis & Service Tips TSB 94-21-14 for 90-95 Bronco, Vans & F Series; "... may be caused by the check ball, located in the rear cooler line converter drainback check valve assembly, sticking...." by Ford

Here are the:
1990 Bronco Pre-Delivery Shop & Electrical & Vacuum Troubleshooting Manuals (EVTM), Partial by member Kingfish999 in Google Drive @ 1990 Ford Truck service manuals - Google Drive
&
1990 Ford Truck Emissions Manual.pdf by Ford via member 90.CaliBronco in Google Drive @ 1990 Ford Truck Emissions Manual.pdf

Suggest you download both for faster scrolling and to use the table of contents index.

1990 Ford Bronco Brochure by Ford via Dezo's Garage @ https://www.xr793.com/wp-content/uploads/2020/07/1990-Ford-Bronco.pdf

Register with VIN to see most Ford dealer maintenance/repairs done @ any dealership nation-wide @ Welcome to Ford Owner | Official Ford Owner Site

For any Bronco issues or to chat about it's planned modifications or build, it's better to post each seperately in Noobie Bronco Tech Questions. Flame free zone. This will get more attention and you can build up your post count to get into other sections such as Bronco and Ford Parts/Accessories that requires 75 non-padded posts to participate due to scammers who preyed on our members.

To save you time and for better responses, please fill out your Bronco info with location, year, engine size, transmission type, transfer case type (manual or electric shift), locking hub type (automatic or manual) info & major mods such as a Lift, etc. .
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Click your profile button in the top right and go to account settings.


On that first page, named Account Details, scroll down to "Vehicle Info" and type in up to 100 characters.

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➡See Baba Looey's Favorite FSB Links (lots and lots of tech links) ... includes such as, "Tailgate Window repair & troublehooting".

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Al
 

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It would seem to me that some sort of piston or actuator gets stuck if its been sitting for a while
I would start with a COMPLETE flush of the transmission. Read up on this because its not easy and many 'jiffy lube' type services are not complete or even close despite claiming such.
Look up what the complete volume is for trans replacement and use that as your guide
I also considered running something like Hot Shots 'stiction eliminator' thru there but after a few seconds of thought highly advise against it. Something like that could be TOO slippery and soak into the friction disks and make the thing now slip. Fix one problem and create another.

Too bad the transmission talent pool in your area is so poor
To me, it sounds like a problem in the actuation part of the transmission which is just the valve body you see when you drop the pan....very easy to drop and replace, not an entire rebuild.
 
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