Torque converter woes
 

Hello! I have a ’95 BMW 325i convertible with an auto tranny (GM made A4S 310R model I believe). 89,000 miles. I'm having a problem where the transmission doesn't "like" having the torque converter locked up. When I'm cruising on the highway in 4th gear (say, at 60 mph), the torque converter will normally NOT lockup, so the engine runs around 3,000 RPM. However, if I press on the gas a bit to accelerate, the torque converter locks up! Makes no sense... If I then push the throttle around halfway down, the torque converter unlocks (makes sense), and if I push further it drops to 3rd gear (also makes sense). The problem is that I would think the torque converter should be locking up when I'm cruising at highway speeds, and should unlock only when my foot comes completely off the gas or I'm asking for significant acceleration.

I spoke with a local transmission shop, and they suggested that the throttle position sensor may have a "flat spot" in the resistance measurement it sends to the computer, so the computer thinks I'm barely touching the gas and doesn't lock up the torque converter. Since this isn't a throttle-by-wire car, I thought this made a lot of sense, so I tried a new TPS sensor. No change.

I purchased this car in 2005 (66,000 mi) and changed the trans. fluid and filter back then with Redline D4 ATF. I changed it again last month to see if the torque converter behavior would change, but no luck. Has anyone noticed this with their car? Any ideas/suggestions? Thanks in advance!

--Bryce
'95 325ic

I personally don't drive a car with an automatic transmission, but I did come across this little tidbit that might be a simple fix: locate the wires that send the signal from the throttle position sensor to the engine computer and trace them to the connectors. Then, with the connector apart, bend the spades for those wires slightly so that they make better contact with the female side of the connector.

It could be as simple as that, keep your fingers crossed. Are you getting any error codes?

Unfortunately, no, no error codes. Well, no lights on the dash anyway, I don't have a BMW OBDI error code checker. Could the computer have error codes in it that don't trigger a light on the dash? I have a friend that does have a code reader, but I haven't had a car before that ever had stored codes but no idiot lights illuminated.

I'm afraid that the next step will be to try to replace the solenoid that engages torque-converter lockup in the tranny, but that's $300 bucks, and the transmission shop I spoke with said that if that was the problem, I most likely would have a tranny service light on the dash. Thanks much for the connector idea, though!

--Bryce

Possibly something like "TRANS PROGRAM SEE OWNERS MANUAL" would have come up on the onboard computer display, but no idiot lights. Your buddy's code reader might be a help, as not all errors display on the OBC (there is a technique to get the codes by depressing the accelerator a certain number of times on OBD I cars, but it's never worked for me). The solenoid is a logical, and rather simple, next step. I getting beyond my knowledge to contribute anything more that might be useful, so good luck, hope it's a quick and simple fix.

Hi, I own a '94 320iA with ZF A5S-310Z and usually mine locks up at 5th when cruising, say around 100km/h (60MPH) ONLY if I'm slightly on the gas and doesn't unlock if I release it unless, of course, deccelerate below 80km/h (50MPH) then it unlocks automatically. The only way to unlock it at such speeds is to push it more than half-way. I would think both trannies work the same way, mine is throttle by wire. So, what your tranny is doing I would say is absolutely normal, to lock it press on the gas just a bit!

Hope this helps,

Jorge
'92 325i ECE
'94 320iA ECE
'73 2002 ECE

Hello Jorge! Rats, I think your tranny is doing exactly what I want mine to. The difference is that mine will drop out of lockup as soon as I stop accelerating, just crusing down the highway at 65-70MPH will NOT keep it locked up. Even if I push down the throttle some to lock it up (and I have to push it at least a quarter of the way down), as soon as I let up a bit (or push the throttle down further) it unlocks. Without pulling the tranny, I think changing the lockup control solenoid is the only other option I have at this point. Thanks much for the advice guys, I appreciate it.

--Bryce

Oh, OK, now I understand, of course that is not normal, unlocking when releasing the accelerator, the most logical and maybe cheapest solution is to change this solenoid, I understood the opposite as you stated at the first post "The problem is that I would think the torque converter should be locking up when I'm cruising at highway speeds, and should unlock only when my foot comes completely off the gas or I'm asking for significant acceleration"

You're welcome and good luck!