My friend has 2000 Honda accord automatic transmission.
Car has about 150k miles
Runs recently we had a shop swap the transmission because old one was not shifting properly it was makeing crazy noise and all that throwing too many codes regards to transmission '

So we bought a used transmission from JDM depot ' they import them from Japan ' and it has about 50k on it '

We swapped old celinoids from the old transmission as the japanies ones won't work with US ECU '

We start the car it drives and shifts as it should ' it works perfect ' doesn't matter if the car is cold or warm '

After driving for about 20-30 minutes car down shifts to first on it own ' you could be doing 65 on a freeway and it will still do it '

But soon as you turn car off and back on its fine again ' but in another 7-10 miles it will do the same exact thing '

So basically resetting the car by turning it on and off solves the problem ' which makes me think it is computer related ' other wise it shouldn't just fix the problem right away ' I drove his car around my self and I never experienced down shifting to 1st but I did notice you car was downshifting rough and upshifting very lazy ' I stopped the car turned it off turned it back on right away it drove fine .

My guess brings me to that ECU is bad. Because 2000 hond accords

It will greatly be appreciated if someone can give me some advice before I have him go search for new ECU and possibly waste some money '

 

If it has the same problem with 2 transmissions, I doubt it's anything mechanically. If it is something mechanically, you have terrible luck with transmissions. My guess is either shift solenoids or the transmission computer. Since you said you reused the old solenoids instead of getting new ones that could be the problem. That's my guess.

 

if it's not the TCU it probably has something to do with the beat up old shift control solenoids that you swapped over from the trashed autotragic transmission.

Why do you say that the newer transmission solenoids won't work with the US ECU? They are newer and they are the correct solenoids to control that transmission. They work based off voltage signals sent from the TCU it doesn't matter what country the TCU comes from. As long as the TCU matches the shift points of the transmission.

If they have different connectors I can see that being a small issue. What is the transmission code number that you ended up with?

 

swap in a manual, then you never have to worry about it shifting when you don't want it to


just my $.02

your problem has something to do with the solenoids and the ecu not being fully compatable with that transmission, i used to work with a guy who swapped the trans in his prelude and didnt swap ECU's and it would randomly shift like ****, it idled all wonky, and he ended up messing alot of crap up in his drivetrain because of it, both electrically and mechanically

 

Check your TPS first, make sure it had a linear voltage output and no dead spots. If the TPS has dead spots it may cause the PCM to command an unwanted shift.
98-02 4spd ATs have several problems, differential bearings, third gear clutch pack prematurely wears out which causes larger bits of clutch material to clog ports and passages in the transmission. This can lead to erratic uncommanded downshifts. And the PRV valve is known to overshoot causing overheating in these transmisisons. A 'low mileage' unit from Japan is just as bad. Since the symptoms tend not to show up until the 40-60Kmile mark.

Verify that the shift solenoids, and pressure switches are functional.

Call up several transmission shops and ask for quotes on a rebuild if you bring them the old transmission, and ask them regarding fixes for the trouble spots on these later 4spds. If they cannot have a reasonable discussion on what the common problems are move onto the next shop.

 

My 4spd trans is on its way out and considering a JDM swap.So a "low mileage"wouldn't be a good option vs a rebuilt one? If i went with a JDM tranny and I regularly did routine maintenance how many miles would i get out of it? So buying a rebuilt would definitely be better? I'd go with a manual swap but it costs way too much for me.