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  #1  
Old 06-18-2012, 02:15 PM
David Cohen's Avatar
David Cohen David Cohen is offline
My car/My project: red '96 LSi
 
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Location: Seattle, WA
Posts: 68
Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

I have a '96 LSi with about 167,000 miles on it; I've owned it for the last 55,000 or so of those miles. And now I have a very worried look on my face because my tranny is failing to stay engaged in fourth on the freeway.

The Symptoms:
At steady speeds of 60-75 MPH in fourth gear (about 2000-2500 RPM), I've noticed two issues:

A. THE BIG ONE: While cruising along in D, the transmission disengages from fourth and starts a spontaneous, inappropriate downshift to third. The engine suddenly revs--and then, before third is fully engaged, the transmission slides back into fourth. For about a second it's not in either gear (sometimes it stays in third for half a second before upshifting again). This is starting to happen with extremely disconcerting frequency. I worry that this is Very Bad News.

B. THE LITTLE ONE: Even when the tranny remains in fourth gear, the RPMs jump up by about 200-300 RPM, stay there for a while and then fall back down; according to other threads I've found on this site (41328 and 59909), the torque converter is unlocking and locking. No idea why the TC (TQ?) won't stay locked at cruise or what kind of problem that signifies.

The Context:
A couple of weeks ago I was halfway from Spokane to Seattle when I noticed my SVX leaving a trail of smoke behind me. Transmission fluid was dripping from all over underneath the car. At a gas station I bought Dexron III-labeled ATF ($3 or $4 a bottle), and pouring in a couple of quarts got my car the rest of the way to Seattle with no warning lights on the dash. A shop diagnosed and repaired the problem the next morning: one of the transmission fluid hoses had split at the radiator and was spraying fluid onto the engine. The shop cut about an inch off that hose and topped it off with another 4 quarts of transmission fluid.

So I was definitely running with low fluid for a while, perhaps some hundreds of miles. It's full now; the automatic transmission fluid dipstick is currently showing a hot level slightly (maybe 1/4") above the "High" dot.

I have not been good about changing my transmission fluid or filter(s), I'm afraid. Or differential fluid/oil.

The Research:
Similar problems have been reported here (threads 35574 and 59742), and someone else posted what sounds like my exact problem in thread 40291 and concluded it was probably the throttle position sensor (TPS); they didn't verify any solutions. But thread 35350 claimed some success from cleaning out the TPS.

Unfortunately because this is a '96 (OBD II) I don't have a way to read ECU or TCU codes or even to know whether any codes have been thrown (the CEL isn't on, at least).

The Questions:
1. If this might be a throttle position sensor (TPS) issue, should I try to clean it, repair it, replace it with a used one from a salvage yard (30-day warranty), or buy a new one?

2. If it's not the TPS, is my whole transmission totally hosed? Is the clutch for fourth gear (Drive) shot? A boatload of money to fix?

3. I suppose it would be a good idea to drain and replace the transmission and differential fluids and change the transmission filter (and buy new hoses connecting the trans to the radiator). It's about time for an oil change; should I have a Jiffy Lube also do those services, or would I be better off asking a repair shop to handle it?
3a. Does the '96 4EAT have an internal filter, an external filter, or both?
3b. Do I need synthetic ATF and/or diff oil/fluid?
3c. Should I replace anything else like the solenoids?

4. If I need to overhaul or replace the gearbox, I'd like to get a 4.44 (4.444?) final drive installed. I'm definitely not going to do it myself; any recommendations for getting that done in the Pacific Northwest?

The Promise:
When I find out what's wrong and fix it, I will report back here afterward so that others with similar symptoms can benefit and not have to guess what worked and what didn't!

Thanks.
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  #2  
Old 06-18-2012, 02:45 PM
1986nate 1986nate is offline
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Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

Based on all of the information here, I would suggest doing a complete drain and fill of the fluid and replacement of the internal transmission filter. (no gaurantee this will work however) Using synthetic trans fluid would be a good idea, but in this case, I would stick to a normal "cheap" trans fluid until you are sure that the transmission will last. (no sense wasting extra money) If you had similar symptoms related to a possible TPS before the transmission fluid leakage, then the TPS could be a possible culprit but it really sounds like the friction surfaces have received some extra heat and wear. No need to replace any solenoids at this point unless you decide on doing an overhaul of the current transmission.
4th gear is engaged by the brake band in addition to the high clutch with the brake band being the probable problem here. If it needs to be replaced, it would include pulling the transmission and a proper rebuild to be done.

I believe there are a few forum members in the NW that could assist or know of a good place to have work done. (including a 4.44 swap) As for the fluid exchange, I would stay away from jiffy lube or any such similar place and go to an actual garage, preferably one that knows their way around Subarus.


Edit: By the way, I just want to thank you for including such detailed facts pertaining to the situation as well as doing some research of your own. This really helps your chances of getting a proper diagnosis and help from the experienced members here.
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  #3  
Old 06-18-2012, 06:03 PM
oab_au oab_au is offline
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Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

Quote:
Originally Posted by David Cohen View Post
The Symptoms:
At steady speeds of 60-75 MPH in fourth gear (about 2000-2500 RPM), I've noticed two issues:

A. THE BIG ONE: While cruising along in D, the transmission disengages from fourth and starts a spontaneous, inappropriate downshift to third. The engine suddenly revs--and then, before third is fully engaged, the transmission slides back into fourth. For about a second it's not in either gear (sometimes it stays in third for half a second before upshifting again). This is starting to happen with extremely disconcerting frequency. I worry that this is Very Bad News.

B. THE LITTLE ONE: Even when the tranny remains in fourth gear, the RPMs jump up by about 200-300 RPM, stay there for a while and then fall back down; according to other threads I've found on this site (41328 and 59909), the torque converter is unlocking and locking. No idea why the TC (TQ?) won't stay locked at cruise or what kind of problem that signifies.

The Questions:
1. If this might be a throttle position sensor (TPS) issue, should I try to clean it, repair it, replace it with a used one from a salvage yard (30-day warranty), or buy a new one?


Thanks.
First I agree with Nate on the good description.

The two symptoms of " changing back to third and the converter lock-up" susggest that the TPS could be the problem.

The changing back and forth from fourth to third, could be the lack of line pressure, but the locking,unlocking of the converter, points more to the TPS than line pressure.

I would cross your fingers, and buy as new TPS, see if that fixes the problem.

Harvey.
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  #4  
Old 06-18-2012, 06:54 PM
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svxfiles svxfiles is offline
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Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

Also take the ground wire off of the back of the intake manifold, by the vacuum line to the FPR, wire brush it, cover it with dielectric grease, and reconnect it.
Don't break the vacuum line, and make sure the ground is tight!
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  #5  
Old 06-19-2012, 02:02 AM
David Cohen's Avatar
David Cohen David Cohen is offline
My car/My project: red '96 LSi
 
Join Date: Aug 2006
Location: Seattle, WA
Posts: 68
Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

Because my TPS is under suspicion, I tested it with a multimeter according to an online copy of the SVX transmission service manual (instructions on pages 196-197).

Voltage from the TPS on connector B67 pin 8 [at the TCU] vs. ground (ignition on, engine off):

Code:
                   Throttle fully closed*    Throttle fully open* [WOT]
                   (no accelerator)          (accelerator fully depressed)
Specified*:        1.6 V [0.7 - 1.7 V]       4.7 V [4.4 - 4.8 V]
Actual:            0.36 V                    4.12 V
After adjustment:  1.27 V                    4.59 V
*(To make this just a bit more interesting, the specs have "open" and "closed" backward.)

My values looked low, but the voltage changed steadily and smoothly throughout the range from 0.4 to 4.0 volts as I pressed the gas pedal.

Resistance between pins 1 and 2 of the throttle sensor itself (unpowered):
Code:
                   Throttle fully closed     Throttle fully open [WOT]
                   (no accelerator)          (accelerator fully depressed)
Specified:         4.3 kΩ                    1 kΩ
Actual:            5.45 kΩ (see below)       1.26 kΩ
After adjustment:  2.3-5.2 kΩ (see below)    0.70 kΩ
Here I found a smoking gun when I first measured the TPS: as I started to lightly press the accelerator, the resistance values started going up, not down. After increasing to around 8 kΩ, the readings shot through the roof; and then dropped back down to 3 or 4 kΩ and gently declined as I pressed the pedal the rest of the way.

I realized I might be able to both get my TPS into spec and largely avoid the spot where the resistor had worn out by twisting the unit all the way counterclockwise on its mounting. So far, so good--it seems to be behaving. I've disconnected the battery to reset the ECU and TCU, so they can start learning the new TPS sensor values. I'll report back on whether this has addressed my problems after I've taken the SVX on another cross-state drive.

Thanks for the guidance!

By the way: $235 for a freaking potentiometer?! Are any throttle position sensors from other Subaru models compatible with the SVX EG33 engine throttle body? It looks like Subaru changed the shape of the shaft in the late '90s, and then changed the design entirely; but surely there is some way to get a cheap replacement!
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  #6  
Old 06-19-2012, 02:25 AM
Chuckls's Avatar
Chuckls Chuckls is offline
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Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

We should sticky this and make it a must-read for all new people whom come in asking questions.

This is a fine example of how you ask
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  #7  
Old 06-19-2012, 04:48 AM
dcarrb dcarrb is offline
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Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

Quote:
Originally Posted by David Cohen View Post
By the way: $235 for a freaking potentiometer?!
Unless prices have spiked since my last purchase, you should be able to get an OEM-equivalent TPS from an aftermarket retailer for about $50 less. I got one from AutoZone online and paid something like $185, with "free" shipping. It was visually identical to the unit that came off the car, down to the serial number molded into the case.

dcb
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  #8  
Old 06-19-2012, 09:33 PM
David Cohen's Avatar
David Cohen David Cohen is offline
My car/My project: red '96 LSi
 
Join Date: Aug 2006
Location: Seattle, WA
Posts: 68
Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

Quote:
Originally Posted by David Cohen View Post
I realized I might be able to both get my TPS into spec and largely avoid the spot where the resistor had worn out by twisting the unit all the way counterclockwise on its mounting. So far, so good--it seems to be behaving.
A little tip: Don't do this.

It turns out that turning the TPS all the way counterclockwise will physically prevent the throttle from returning to a fully closed position, which will give you a really fast idle, which will eventually cause the ECU to complain.

I've turned it back a bit, which brought the idle back down to its usual sedate self. Voltage values from the TPS are now 0.967 V with throttle closed and 4.43 V at WOT, which is within spec. Hopefully in its new position the worn spot in the TPS won't be a factor.

More news as it happens.
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  #9  
Old 07-22-2012, 12:02 AM
David Cohen's Avatar
David Cohen David Cohen is offline
My car/My project: red '96 LSi
 
Join Date: Aug 2006
Location: Seattle, WA
Posts: 68
Smile Re: Uh-oh... '96 Transmission trying to shift itself out of 4th. TPS?

Twisting the TPS eliminated the worrisome downshifting behavior and let the torque converter lock up properly. Hurrah! Unfortunately, the computer finally noticed the wonky throttle position readings and lit up the check engine light. Passengers seem to like letting me know that my CEL is on. Sigh.

I ended up replacing the TPS with one I bought from another SVX World Network member (thank you, Galen!), and that definitively solved my problems. My SVX is driving and shifting perfectly now.

Thanks to everyone who offered help!

—David
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