Hey guys, Ive been visiting this site quite a bit over the last year or so for advice and it never seems to disappoint in helping me find what Im looking for, so hopefully this problem shouldnt be an issue. Car is a 90 accord DX, original automatic trans with 320,xxx~340,xxx on it failed about a month ago, just put in a 90 LX supposedly with 90,xxx on it from a reputable source myself and Ive been having a few issues with it, hard shifting and an odd grinding noise at certain rps/gears. Before the trans swap I was getting a tcu code 15, indicating the failure of the nm sensor, but the trans completely failed before I had a chance to look more into it. New trans is in, and Im still had the code. I tried to test both my old and "new" sensor just by measuring the impedance, with 400-600 being the norm for these things. I was unable to get an accurate reading off of either. Took the sensor out and cleaned all of the metal shavings and crud off of it, gave it a lick of silicone spray and put it all back together and enjoyed a little bit smoother shifts for a little bit, but not for long. Still have the code and hard shifts, but rockauto lists this part around $100 and I was hoping to not have to throw another Benjamin at my new trans so quickly.


And now for the summary:
-Hard down shifts in most every gear
-Reverse / parking work fine
-Runs like butter on the highway
-I get a grinding sound when Im cruising in 4th. right at ~2,000 rpm, so just about 40 mph. The engine seems to bog down a bit here and is almost "stuck" but after that everything is fine.

I had read that if the previous owner had used an aftermarket atf fluid then then the friction material would be permanently saturated in it, causing issues even if the correct Honda fluid was used.

Sorry for writing a full novel for my first post haha Im by no means an expert mechanic, but I like to thing Im pretty mechanically inclined and knowledgeable, as long as its a 1990 honda accord that that is haha

 

If you have a code 15 wiht both the old and new trans, and both sensors checked out, check your wiring harness. If something fell or hit the wiring it may be damaged. The connectors at the main harness can sometimes have filth or corrosion, pull them apart, inspect, clean and repair if needed.

 

Sorry about the late reply, but I when I went to check the connections I no longer had any code from either the tcu or ecu. Its still shifting a little harder then I would like and the grinding noise in 4th. is making me a little worries, just got back from the beach, good ole north myrtle, and the majority of my driving put me right at 1800-2000 rpms and ~40 mph, where this grinding noise lives. I assume its just something inside this tranny and in which case theres nothing I can really do about it.

 

Pull the two right side cover sensors. If they are covered in magnetic slurry the TCU may not pickup the correct signal and may be trying to command an unwanted shift.
Pull clean and reinstall.
Have you tried driving at 40MPH in D3 rather than D4?
Does the noise change, stay the same, or go away?

 

I pulled the one on the front of the trans, the nm I beleive, I always get the two mixed up, and it had some crud on it. I cleaned it up best I I could when these problems started, but I hadn't done the one on the back. I can lock it down to d3 and it will run through just fine. I'm about to change the fluid again and see how much crud is on the magnet from just this past month, hopefully not too much. I'll try and get the the other speed sensor and see what shape that guy is in, but as of now I'm not getting any codes what so ever.

 

D4 is the overdrive gear
i had an issue with the D4 light and climbing shallow hills. D4 and trans slipped D1 and all was fine?

anyway i changed trans fluid and pulled the fuse under the hood for 20 sec. no problem since. the fuse u wanna look for is the ECU fuse. under the fuses cover u will see a guide to the fuse placement.

more than likely the ECU is holding the trouble code from the last trans and pulling the fuse will create a whole new ECU/fuel shifting chart for the car erasing the old

or if it is mechanical pull trans and return for a working one

 

The battery was disconnected for two days during the trans swap, that would be more than enough time to discharge anything within either the ecu or the tcu. It seems like a mechanical issue inside the case, but I did the swap in my garage by myself and a buddy so I'd really rather exhaust every other possible cause for this before I take it out and repeat this whole process.

 

And so the plot thickens! I noticed if I had the car in "sport" mode, this would inhibit it from shifting into 4th. overdrive a little bit later, avoiding the 2k rpm and 40 mph spot that the grinding occurs. There is some noise as it engine brakes, though it is not very loud, its not as smooth as it is supposed to be. At this point I think I just got a bad pick from the junkyard, so I may take advantage of the 6 month warranty that was the deciding factor in originally choosing this particular one.