Tranny shifts between 3rd and 4th Gear

Cappy · #1 02-27-2008, 12:35 PM

Hi Chris,
I'm hoping you can give me a guess with the problem I've been experiencing. When I'm driving at a sustained speed of anywhere between 45 and 55 mph, my car will often and unexplainably downshift into 3rd gear. At first I thought it was me maybe pressing down the accelerator, but no, it's the car. It seems to shift back and forth between 3rd and 4th even when I'm on a straight and level stretch of road, and my gas pedal is constant.

My first inclination is to check (and remove?) the aftermarket shift kit I put in years ago - it had always thrown the blinking power code at startup after I put it on, but never behaved this way until recently. Next, I'm thinking it might be a badly out-of-adjustment TPS. Am I on the right track? What else might be the problem?

To avoid these shifts on these icy mornings, I've started driving in 3rd gear only, unless I'm on the freeway and going over 60mph. Will that hurt anything? (Other than lowering my mpg from 23 to 18!).

As always, THANKS for your help.
Cappy

Hocrest · #2 02-27-2008, 12:38 PM

Yeah, check the TPS.

Are you sure it is going from 4th to 3rd and not just the torque converter unlocking.

immortal_suby · #3 02-27-2008, 07:16 PM

To check if it is the torque converter locking/unlocking or shifting 4th to 3rd, next time it appears to downshift, pull the gear selector back to 3rd and see if it downshifts again.

nextse7en · #4 02-27-2008, 07:53 PM

Anybody think that its kind of ridiculous that this forum is still here? Lots of talk about rolling it into Technical Q&A, but never any momentum.

-Patrick

dcarrb · #5 02-28-2008, 06:28 AM

Quote:

Originally Posted by nextse7en

Anybody think that its kind of ridiculous that this forum is still here?

Second that.
dcb

Cappy · #6 02-28-2008, 12:15 PM

Yep, I'm sure it's shifting between 4th and 3rd. When it's in the high RPM phase and I slip it into 3rd, there is no downshift. I too was hoping it was just the Torque Convertor, but no such luck.

dcarrb · #7 02-28-2008, 01:58 PM

Quote:

Originally Posted by Cappy

Yep, I'm sure it's shifting between 4th and 3rd.

A new throttle position sensor fixed this problem for me.

dcb

Cappy · #8 02-29-2008, 11:17 AM

Thanks!

I'll check the voltage to make sure my old one is shot.

One more dumb question....Until I get a new one, can I continue to drive the car in D3 at speeds up to 60mph without messing up my tranny?

Hey Jason...got a spare TPS?

Trevor · #9 02-29-2008, 03:32 PM

Quote:

Originally Posted by Cappy

Thanks!

I'll check the voltage to make sure my old one is shot.

One more dumb question....Until I get a new one, can I continue to drive the car in D3 at speeds up to 60mph without messing up my tranny?

Hey Jason...got a spare TPS?

Simply checking the voltage will not properly test the TPS, particularly in respect of the fault you describe. This is more likely to be caused by faulty contact as the TPS moves. Do some research in the how too section for cleaning and testing advice.

Cappy · #10 03-01-2008, 03:07 PM

Ok, before I tore into things I decided to check for a fault indicator. Guess what? I found one, but it's not the one I expected. It's fault code 11 "Duty Solenoid A". If I'm looking at the manual properly, it looks like it's INTERNAL to the transmission! Just for laughs, I disconnected the aftermarket shift kit, and sure enough, the 16 blinking power lights went away. But the shifting problem remains, and the code 11 is still there. Does this mean I need a new tranny?

Trevor · #11 03-01-2008, 03:31 PM

Quote:

Originally Posted by Cappy

Ok, before I tore into things I decided to check for a fault indicator. Guess what? I found one, but it's not the one I expected. It's fault code 11 "Duty Solenoid A". If I'm looking at the manual properly, it looks like it's INTERNAL to the transmission! Just for laughs, I disconnected the aftermarket shift kit, and sure enough, the 16 blinking power lights went away. But the shifting problem remains, and the code 11 is still there. Does this mean I need a new tranny?

Solenoid A controls the line pressure. It is what I had hoped for rather than expected and it is good news. The solenoid valve can be replaced without removing the transmission from the car.

Cappy · #12 03-01-2008, 07:02 PM

Sweet! I'll change it out and let you know how it turns out! Thanks!

Cappy · #13 03-25-2008, 01:22 PM

Just to let you all know, I worked on the car last weekend, and was able to test the Shift resister. It registered 0 ohms!. So did the "Small car Parts" resistor. So I removed the SCP aftermarket kit, cleaned up the ceramic OEM resister, and measured it again. Now it reads 15.4 ohms, so all is good.

Next, I removed the Throttle Position sensor, cleaned it up with LPS spray, and reinstalled it, making sure it was set at the midpoints of the recommended ranges. Damn! I broke the brittle hose coming off the auxiliary air contrl valve when I tried to move it away from the TPS connector, so I put a piece of silicon hose I had lying around on in it's place. Buttoned it all up, and I NOW HAVE AN ENTIRELY DIFFERENT CAR!

First of all - all that crazy shifting in and out of 3rd gear has completely gone away. Now it shifts right up to 4th gear, and doesn't downshift until I tromp on it, or slow way down.

secondly - my "SVX disease" has been cured! you know...the one where it idles rough, and occasionally misses for no apparent reason. After two years, I was getting used to that "shudder", and I actually didn't figure out what was different for a a while. I thought something seemed wrong - here it was RIGHT!

The only things I noticed that are different and NOT good, are the way the car seems to shift hard occasionally, the way that the tires seem to spin when I'm starting out and making a hard turn as I back up in my driveway from the garage, then pull forward with a full turn the other way (never did that before), plus the fact that when I fisrst start her up in the morning, she wants to stall untill I pump the gas pedal once or twice to rev it up.

Heck, I can live wit these things. The car is running sweet! Who knows? I might make it to 200,000 yet!

cappy

dcarrb · #14 03-26-2008, 05:54 AM

Quote:

Originally Posted by Cappy

Buttoned it all up, and I NOW HAVE AN ENTIRELY DIFFERENT CAR!

That's exactly how I felt when I replaced the TPS on mine; it completely changed the character of the car for the better. Best money I've spent on the thing.

dcb

Trevor · #15 03-26-2008, 06:58 PM

Good news Cappy,

Unfortunately you corrected two possible problems before testing. I would bet on the main cause being the “shift kit” fault. The dead short you describe will have intermittently upset the line pressure in a serious way. I have never been a fan of the “shift kit” mod.

As you have found brittle tubing, I would suggest you check all the tubing connected to the inlet manifold, as being a likely source of your idling issues.

Restoration of line pressure to normal, may now have brought to light, something not previously obvious. Drive with this in mind for a bit and see if things settle down. If not, investigate further in order to guard against possible damage.