Ok so my 1990 460 has about 140,000 miles on it. I bought the truck from my pops and new about this before hand. He's an old soul and doesnt see anything as a probloem untill its actual broken. Anyways my truck shifts really hard sometims, not all the time. Ecspecially right when i get off the freeway it revs pretty high sometimes to 4000 and kicks into the next gear rough. Like i said sometimes it shift smooth as can be but sometimes its quite rough. Ive changes all the fluids except for the tranny fluid which a lot of people dont recommend doing untill at least 150,000 miles. I've never changed tranny fluid before but dont know if it would help anyways.
Thoughts?

Thanks!

 

 

I'm thinking the vacuum modulator is bad or the connection is loose. If the modulator is bad or has no vacuum you will get maximum line pressure, which means it will shift hard and only at high RPM. In other words, the trans will act like you want wide open throttle acceleration (high RPM firm shifts) at all times.

There should be a vacuum line running down to the modulator on the rear passenger side of the transmission. Make sure that line is getting manifold vacuum, has no leaks, and is connected properly to the modulator. If that doesn't solve you're problem you probably have a bad vacuum modulator. They are fairly cheap and easy to replace. Make sure you follow instructions for adjusting them properly. If it is out of adjustment, your line pressures will be off and possibly cause damage to the transmission.

 

Line pressure(and everything else) is computer controlled in the E4OD and what you describe is a common symptom with multiple potential causes, so start by pulling the codes first and post up what you find.

 

To attempt to clarify the above two posts, the truck could have a C6 (vacuum operated) or more likely in a 90' is the fully PCM controlled E4OD. Diagnoses depends greatly on which trans you have. Is there an OD off button on the column shifter (indicates E4OD).

 

Sorry I just assumed he had a C6 3 speed. As others have stated, diagnosis would be completely different with the 4eod. I know the 4eod came out in '89 and was opitional with all engines except the 460. I do not know for sure what the first year was for the 460 4eod combo.

 

As others have said, if it is the E4OD tranny, start by checking the computer codes. It is actually very simple to do. A hint is to video the flashing light sequence with your cell phone so you can count the flashes later.


My '90 F150 has the exact same symptoms. Shifts fine (especially when cold) and then then shifts very hard at times. After running the codes, the computer told me there was a faulty throttle position sensor and neutral safety switch (manual lever position sensor). I changed out the TPS and the truck ran better. I will be changing out the MLPS this weekend and hopefully it will shift better. After that, my plan is to get the tranny flushed with a new filter installed and see how it goes.

 

Im sorry i should of stated that i have the E4OD Trans. Their is NO check engine light on as well.

 

There can be issues that would fail the Key On Engine Off (KOEO) tests as well as stored codes WITHOUT triggering a Check Engine Light (CEL). Run the KOEO tests and stored codes (CM) display.