98 Accord tranny trouble

[Thumper27]

My friend's 98 Accord V6 automatic (I'm pretty sure it's a 98, could be a 99- We haven't been talking long!) has some issues. It began two months ago sticking between first and second, taching up to around 4000-4500 before finally shifting. Then, later, it started not wanting to take off at all from a stop, like at a stoplight. So, to the dealership. They say, need a new tranny. To two independent shops. New transmission. By the way, the car has 109K. So, she finds a used one with 45K, and has it swapped in. No luck, the car does the same thing. Now, her dad wants to find yet another transmission and do it again. Question: Is this just an obscene coincidence, or is something else wrong? I was thinking about shift control, related to the rpm of the motor, but wouldn't that be computer controlled instead of a vacuum or valve sticking? Any ideas? I'd hate to see her spend another $1500 unnecessarily.

[jeffcoslacker]

I'd look hard at the TCU and wiring before doing anymore swaps...something fishy here.

You shouldn't have a vacuum modulator on that, but it's worth a look. It would be down low near the pan and have a vacuum line or hose connected to it. It should have a leak-free connection all the way up to the intake manifold.

Usually a modulator fault will result in no shift until the throttle is dropped, at which point the vacuum level rises sharply and overcomes the leak, initiating the shift finally. Sounds different from what you are describing.

Also check that the transcooler in the radiator isn't blocked...it could be restricting fluid flow.

[jeffcoslacker]

Originally Posted by Thumper27

I was thinking about shift control, related to the rpm of the motor, but wouldn't that be computer controlled instead of a vacuum or valve sticking? Any ideas? I'd hate to see her spend another $1500 unnecessarily.

The tranny uses a computer module (TCU) that controls shift points by commanding solenoids to open and close in the valve body of the tranny. The valve body works by hydraulic pressure by default, so without computer intervention, the tranny will upshift at certain engine RPMs regardless of vehicle speed or load.

Before computer control became the standard, upshift modification was carried out by vacuum modulator or a transhift cable that changes the valve body's function depending on throttle opening.

A faulty Throttle position sensor can affect upshift funtion as well on TCU controlled trannies, so that could be suspect also, but will usually light the Service Engine light when it goes bad....