90 EX Automatic transmission issues

[stupidhurts]

A friend and I bought 90 Accord EX that has 83,000 original miles that has a transmission issue for cheap. The Previous owner said the Sport light was on and we did our research (using this site and others) before we arrived and had a few ideas about what possibly could be the issue.

The car would start and drive fine then then the transmission would start to slip, then it would rev like it was in neutral and not put any power down at all. It did this in D4, D3, 2 and 1. Once you turned the car off and let it sit for a minute and turned it back on it would run fine for a few minutes before it would start doing the same thing again.

Before we bought it we checked the trouble codes and we got code 15 on the Sport light which is the trouble code for the NM speed sensor.

We got the car back to the shop and pulled the TCU looking for the common leaking capacitor problem. The TCU was built in Georgia. Everything looked good inside. Nothing leaking, burnt or swollen. Somebody else had the same idea as us because they unbolted the bracket that holds the two computers and didn't bolt it back in.

We moved on to the speed sensors, taking them off the car and reading the resistance they were both between 400-600 ohms. We pulled both solenoids off the car to test them with a battery. The lockup solenoid tested fine but the shift solenoid was dead, with no audible click. I went to my local u-pull-it and pulled both speed sensors and both solenoids that all tested good for $20.

I installed the new shift solenoid, drained the transmission and poured in some fresh fluid. I still have the same issue. Starts and drives fine then start to slip then nothing at all. No trouble codes were thrown either. I noticed when I would pull the car out then place it into park for a few minutes then put it into drive it would act if it were in neutral and wouldn't even try to move.

The only other things I can think of being bad is the TCU, which looked good from a visual inspection but I don't think there is a way to test them and I don't have a know good working TCU. I really don't think it could be a mechanical issue since it only has 83K but I've seen stranger things. Could the main relay be the culprit?

Cliffnotes:
-Bought a 90 Accord EX with transmission issue, slipping in each gear selected, eventually revving like it was in neutral and not move.
-Trouble code 15 pulled from Sport light (NM speed sensor)
-Inspected TCU and looked ok visually
-Tested both speed sensors and solenoids, found bad shift solenoid and replaced, drain and fill transmission.
-Still having same issue, no trouble codes this time.

[deevergote]

Slipping is usually mechanical. Sometimes a fluid change fixes it (only Honda ATF should be used.) If that didn't fix it, then the transmission is likely damaged.

Many CB7 automatics are in poor condition because they are sensitive to the correct fluid, and they are sensitive to proper fluid changes. Many owners don't even think of changing the automatic transmission fluid! It's possible that the fluid in that transmission was well over 20 years old before it was changed for the first time (probably once problems started becoming apparent.) Even at 83k miles, the transmission is 23-24 years old. If it was running old fluid, or the wrong fluid, for all those years... things will wear out.
Rebuilding or replacing the transmission is probably going to be the only solution. You seem to have done a pretty decent job of ruling out all other common possibilities.

The only thing that might be worth trying is to find another 90-91 TCU that you know is working properly.

[stupidhurts]

The yard had 8 90-93 Accords last time I was there. Does the TCU have to be from a 90-91 EX or will any EX/LX/DX unit work from that generation?

Is there an easy way to do a fluid exchange on the transmission or is drain and fill the only method? I did the initial drain and fill with Valvoline Maxlife Dex/Merc which is listed Honda ATF Z1 compatible.

We really don't want to swap transmissions in the car. We bought it as a quick flip hoping the issue was electronic. The exterior is decent shape cosmetically and the interior is in excellent condition with quite a few OEM Honda accessories inside and out. If a new TCU doesn't solve the problem hopefully we can get our total investment back.

[ktaylor660]

I had almost the exact same issue. Ypu're gonna need a new transmission. I picked one up for $200 at the yard.

[deevergote]

There's really nothing electronic that will cause a slip. That's mechanical.

The 90-91 models were the only ones with the Sport function. The 92-93 TCU won't work 100%, so it's best to avoid one of those. Any 90-91 should work, regardless of trim level (there are minor transmission differences, I believe... but not enough to make a big difference.)

[C91BLX7]

Had the same problem with my 91. The trans was shot. I remember taking out the dipstick and there was metal shavings all over it.

[oni_cb7]

That sucks bro. I hope it isn't the trans itself.

If it helps, I had a problem with my TCU and it took me about 2-3 hours to actually find the leaky capacitor. It was really hard to find.

[stupidhurts]

Had the same problem with my 91. The trans was shot. I remember taking out the dipstick and there was metal shavings all over it.

The dipstick is clean. There was buildup on the drain magnet but I'm not sure what's normal.

We popped the transmission cooler line and performed a flush so the trans is full of fresh fluid and it didn't seem to help. Nothing looked out of the ordinary with the old fluid. It actually looked pretty good. Like before, it would drive fine when you selected a gear then it would eventually start to slip and then nothing. We got it running fast enough to notice it wasn't shifting either. It wouldn't shift out of first when it was in D4.

We think their is some kind of blockage because it will run fine at first then something gets restricted and starts to slip. Once the car is off for a minute it will move fine until it it starts to slip again.

We're going to pour some Lucas Transmission Fix in and see if that helps. It won't hurt as the trans is probably toast anyways.

That sucks bro. I hope it isn't the trans itself.

If it helps, I had a problem with my TCU and it took me about 2-3 hours to actually find the leaky capacitor. It was really hard to find.

We'll pull the TCU and inspect again. I'll take a few photos and post them on here.

[NVmyCB7]

If you live in California I have my old auto that Il let go s**t cheap. That's even cheaper than dirt cheap. It's just sitting in my garage since I did my manual swap. That's if your trans is bad.

[schierholz]

yep my tranny started this stupid stuff a week or 2 ago. did that neutral feeling but went forward slowly (this happened once so far after a 200 mile drive to the bay area). and every now and then reverse grinds unless I let it sit in neutral for a sec or 2 others it can be put in just normal. I am going to try a new shift linkage im not sure where to find a tranny that has ben taken care of.... after thinking about it, it started after my rear seal went out and replaced.

[dooey52_91CB9]

I'm having the same exact problem with my 90 ex. I thought it was something electrical also but its not.

I've switched out both the ecu and tcu with 3 other pairs and it still does the same thing.

Had my brother look at my car and when we drained the fluids there was alot of metal shavings in the drain pan.

The transmission is TOAST. Second 1 in a year to do that to me.

5 speed swap is next.

[illinois_erik]

its bad to do a "flush". there is an internal filter, usually you push the shit back out of it. Drain refill drain refill. repeat, you can do the initial 3 quarts to refresh it, and then the 9 and drive to totally replace all the fluid. NEVER take it to be flushed when you even suspect a problem. Maybe the torque converter is at fault lucky scenario, but it sounds like either way a transmission needs dropped

[oni_cb7]

I'm having the same exact problem with my 90 ex. I thought it was something electrical also but its not.

I've switched out both the ecu and tcu with 3 other pairs and it still does the same thing.

Had my brother look at my car and when we drained the fluids there was alot of metal shavings in the drain pan.

The transmission is TOAST. Second 1 in a year to do that to me.

5 speed swap is next.

Did you ever drain and refill it? I do this every oil change (already rebuilt my auto and I do not want to do it again, and installing a trans cooler soon [will extend the life]). This has kept my tranny in good shape since the rebuild. Maybe you just got a bad trans from the start. If its bad when you put it in, then it won't last long.

[stupidhurts]

I got a chance to work on the car last week. We decided to try some Lucas transmission fix. The stuff was extremely viscous. Instructions said to add 12 ounces in a transmission that that is warm and running. It seemed to work, kinda. It would hold power for longer but the same old symptoms would emerge.

I'm heading over the the shop this afternoon to start pulling the transmission.