auto trans shifting late

Jan 23, 2006 6 Replies
N

Hi- I have a 93 Saturn SL2 which shifts late 2nd-3rd and 3rd-4th. The engine has to rev way up (3300-3800 rpm) before it shfits. Shifting 1-2 does not seem to be a problem. It used to shift at maybe



2500 rpm before. The transmission is not slipping just shifting later than it should.

Sometimes even if I am going 40-45 and take my foot off the gas, it will still not shift into 4th, which it used to do. The transmission is in "normal" not "perf". I checked that.



My question is, what controls the transmission shifts? Is it the throttle position sensor? I know the older cars (which I am much more familar with) had TV cables, but this transmission is computer controlled.



I am at a loss as to what is wrong. I changed the fluid and this did not help it.



The car has other issues (it has 160,000 miles on it), such as a lack of power, reduced gas mileage, and an occasional misfire, which new spark plugs, wires, and a new oxygen sensor did not take care of. Perhaps the issues are related. I do not get a check engine light or any computer codes.



If anyone is familiar with this type of problem on this car and can offer advice I'd appreciate it.



Thanks in advance!



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J

hi njot I dont know what controls the trany shift but it may be vacume, Has the CTS coolant temp sensor ever been changed, that will make it run rich and if its runing rich it may not have correct vacume also the throtle body may need to be cleaned, CTS is a cheap item! Also a bad CTS will not cause a computer error! I have a 93 sl2 with 170 thousand original owner! Good luck with your problem! I just put another starter on mine today.

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B

I'm not familiar with the '93, but I know my son's '96 SL has a "performance" or "economy" switch on the dash. The performance setting does exactly as you describe to increase HP before shifting to the next gear. (It also burns more fuel as well.)

Bob

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N

I think you may be on the right track for sure. I just replaced the coolant temp sensor 3000 miles ago because the cooling fan was coming on too late.

Now what I think may have happened is the catalytic converter is blocked on it. If it ran rich from the CTS being bad, this could have blocked the cat.

If the cat is blocked, it would lack power and the vacuum readings would be off. Not sure if the MAP sensor controls transmission shifting, but if it does, faulty readings would affect this, I would think. It would make sense that the MAP and TPS sensors would control transmission shifting- I'm just not sure that;s really how it is.

I have been very lucky and haven't needed a new starter yet. Actually I have had very few problems with the car until it got past 145,000 miles, so I'm not complaining.

Thanks!

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N

Actually you are right. My car has this switch, too, but it's shifting late even though it is in "economy" (or "normal" mode on my car). Thanks.

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B

So the obvious question: Is the switch working? Sounds to me like it is not. If there were a wiring problem or the connection to the computer was not there, it would appear as an open. So, if the switch is open is that the performance mode and if closed, then in economy mode?

Bob

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N

This is a definite possibility. I'll have to look into this. Thanks!

Bob Shuman wrote:

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