4th gear slip
04-27-2010, 12:36 PM
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4th gear slip As I drive my 98 Z28 down the freeway it does good for about 20 minutes. Drives perfect. Then you hit the gas a little bit and the rpms will go up without the trans catching. If I manually shift into third it does great for about 10 minutes again. I only have this problem on the freeway at cruising speeds 60+. Any insight would be great. I dont know what is causing it. The car is completely stock except a lid. The first time this happened I came home and checked the fluid and everything seems fine.
04-28-2010, 12:32 PM
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TCC "slip learning" is the devil. The PCM will pull back
pressure seeking to "barely slip", meaning that if some
condition changes (like even fluid viscosity w/ temp)
you may get into slip until it "learns" some more, and
perhaps step into an immature slip code that would
put the TCC unlocked until next key-on.
At low cruise on the freeway you will see 0% line
pressure commanded. Not true zero, but mighty low.
That's marginally OK for stock and not at all OK for
most aftermarket converters.
pressure seeking to "barely slip", meaning that if some
condition changes (like even fluid viscosity w/ temp)
you may get into slip until it "learns" some more, and
perhaps step into an immature slip code that would
put the TCC unlocked until next key-on.
At low cruise on the freeway you will see 0% line
pressure commanded. Not true zero, but mighty low.
That's marginally OK for stock and not at all OK for
most aftermarket converters.
04-28-2010, 10:18 PM
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Going into broken record mode----
How many miles on the transmission?
Any modifications done at all especially recently?
Does it shift hard in other gears when 4th stops working?
Are you positive it's fourth and not the converter lock up?
When you read the codes does anything come up?
Can you duplicate the problem by going down the road and pushing the brake pedal enough to turn the lights on?
Or when it runs normal can you duplicate the problem by putting the shifter in 3rd?
Does the check engine light ever flash while driving?
Is the engine in good running order? Plugs, wires, filters?
Misfires can cause loss of lock up, missing gears, etc.
How many miles on the transmission?
Any modifications done at all especially recently?
Does it shift hard in other gears when 4th stops working?
Are you positive it's fourth and not the converter lock up?
When you read the codes does anything come up?
Can you duplicate the problem by going down the road and pushing the brake pedal enough to turn the lights on?
Or when it runs normal can you duplicate the problem by putting the shifter in 3rd?
Does the check engine light ever flash while driving?
Is the engine in good running order? Plugs, wires, filters?
Misfires can cause loss of lock up, missing gears, etc.
