Part Throttle Surge
Thread Starter
Instructor
Joined: Aug 2002
Posts: 198
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From: Yucaipa CA
Part Throttle Surge
With my '90 L98 automatic in "D" (3rd) going downhill off-throttle at around 41 mph the car surges like it's hunting for another gear or the torque converter is locking and unlocking. It does the same thing, though not as noticibly, on level ground, at lightly loaded part throttle. This does not occur in OD (4th) as it shifts to OD at 41 mph and runs smoothly off-throttle or lightly loaded. Could it be the TPS?
Melting Slicks
Joined: Aug 2003
Posts: 3,399
Likes: 395
From: Lakeville MI
If you're hovering at 41 mph you're right at the normal tcc lock/unlock speed.
Note:These values are taken from an 86 bin, but I suspect the tcc is calibrated in a similar fashion for all the auto trans cars.
41 mph is the typical lock up speed
40 mph is the typical unlock speed
There is basically no hysteresis with only 1 mph separating the two modes. The tps should not have much effect unless you are over the 41 mph lock threshold.
For example at 44 mph: it will unlock at > 65% throttle, and lock < 45 % throttle.
In 4th (OD) I would guess you don't have enough engine braking to drop you back under 40 mph and unlock. This could explain why it stays locked up.
I would suggest you drive this particular road differently, faster, slower use 2nd or 4th gear, or have a chip made to add hysteresis, or raise the lock up mph, so as not to be annoying in this case.
Note:These values are taken from an 86 bin, but I suspect the tcc is calibrated in a similar fashion for all the auto trans cars.
41 mph is the typical lock up speed
40 mph is the typical unlock speed
There is basically no hysteresis with only 1 mph separating the two modes. The tps should not have much effect unless you are over the 41 mph lock threshold.
For example at 44 mph: it will unlock at > 65% throttle, and lock < 45 % throttle.
In 4th (OD) I would guess you don't have enough engine braking to drop you back under 40 mph and unlock. This could explain why it stays locked up.
I would suggest you drive this particular road differently, faster, slower use 2nd or 4th gear, or have a chip made to add hysteresis, or raise the lock up mph, so as not to be annoying in this case.
