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Discussion Starter #1
I have a 1994 Taurus with a 3.0L Vulcan and an AX4S transmission. This is my daily commuter, so I need to fix it quick!

Here are the symptoms:
1.) At highway speeds, if the tranny needs to kick-down (to pass or climb a hill), the Torque Convertor will come out of lockup but the tranny will remain in 4th. If I move the shift lever to D, the transmission will follow and downshift into 3rd.

2.) When I come to a stop, the tranny will downshift into 3rd, then 2nd, then 1st, although slightly rougher than I remember.

3.) If I accelerate lightly, the transmission will go through the gears smoothly. But once in 4th, it wants to remain in 4th.

4.) If I try to accelerate briskly, the transmission will stay stuck in 1st (with the engine screaming) until I lay-off the gas pedal; then it will jerk into 2nd.

5.) The tranny doesn't seem to be slipping, only not shifting at the correct times.

I see three possibilities, although I'm quite a novice at this and could be completely off-base:
1.) Inputs to the computer are correct, the computer is telling the transmission to shift, but the transmission is unable to obey.

2.) Inputs to the computer are correct, but the computer is miscalculating the shift points and the transmission is obeying what it's told.

3.) Inputs to the computer are not correct, so the computer is not getting good data and miscalculating the shift points based on incorrect data, and the transmission is obeying what it's told.


Here's what I've tried so far:
1.) The tranny fluid was not low, and it is pink in color. No burnt odor.

2.) At highway speeds, the cruise control works as before, which tells me that the Speed Sensor is working. I had that sensor fail on me once, and it was not pretty.

3.) I tried replacing the TPS, and nothing changed.

HELP!!
:(
 

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I'd want to get the VSS checked to make sure it's working properly, since it can cause a lot of weird shifting issues. Also get the MLP checked, since it could cause the tranny not to shift. If both of those are ok, then i'm out of ideas.
 

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Discussion Starter #3
Please forgive my ignorance.... I don't understand how the MLP would prevent the trans from downshifting.
:dunno:

I could not find a Manual Lever Position switch on the Rockauto website. Is this aka "Neutral Safety Switch"? It's about $30.
 

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Please forgive my ignorance.... I don't understand how the MLP would prevent the trans from downshifting.
:dunno:

I could not find a Manual Lever Position switch on the Rockauto website. Is this aka "Neutral Safety Switch"? It's about $30.
[/b]
Yea, it is the Neutral Safety Switch
 

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Discussion Starter #5
Do you agree that the MPS is the problem?

I hate to belabor the point. But the fact is that if the problem is the tranny, the car is going to the scrap yard. I don't want to waste $30 on a part, if I'll be taking the car to the scrap yard anyway!
 

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You can test it. It seems the only problem would be the D position as it manually down shifts OK.
 

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I like both of Nidan's ideas.

My acting out, but not completely failed speed sensor, caused some of the shifting symptoms you describe, so just because the cruise control works, don't rule the speed sensor out just yet.

I had intermittent drop out on the cruise control & harsh up & down shifting & later on in the failure mode, on occasion it would hang up in 1st & bump the rev limiter kinda like you've described!!!!

With a Actron CP-9145 scantool attached, I had the wife drive it, while I rode shotgun & monitored the speed sensors PID output to the computer & caught that bad boy hanging up at 37 mph, right where some of the rough up shifts had happened!!!! So closely check out that speed sensor.

Seeing as how you can get it to act fairly normal, by shifting out of OD, to D, I agree the MLP/Neutral Safety switch, or it's wiring/elecreical connector, or mechanical connections, belong on your suspect list.

I suppose you could have more than one problem & maybe the tranny has some gum, varnish, or sludge deposits that are confusing things too.

Even with regular "severe service" timed tranny fluid pump outs & filter changes, I've had up & down shifting problems over the years, that have responded favorably to a dose of "SeaFoam Trans Tune" cleaner upper, until the acting out ceased, (sometimes a couple of days, sometimes a couple of weeks, or months) then did a full fluid pump out, with filter change & she'd be ok for a few more years.

So just because the tranny fluid level is right & the fluid looks & smells ok (mine did too), doesn't mean you couldn't have some small tranny deposits causing shifting problems.

So maybe keep the deposit thing in mind, if the previous two things Nidan suggested don't completely clear things up.

A bunch more thoughts for pondering.
 

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Discussion Starter #8
UPDATE:
I changed the VSS and the MLP last night. No improvement!!

So unless I hear back from you guys, I'm gonna junk the car. It' not worth replacing the transmission.
:(
 

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Well before I'd trash the daily commuter, I'd try a as specified, dose of Seafoam Trans Tune in it. Just don't overfill the tranny.
It can be had for less than $10 around here at the likes of most autoparts stores & even my Wally Worlds.

If the problem is deposit related, you should see some change in a commute or two.

If the problem improves, drive it until it stops acting out, then do a pan drop, filter change & full tranny fluid pump out/fluid exchange.

Let us know how it goes.
 

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I like both of Nidan's ideas.

My acting out, but not completely failed speed sensor, caused some of the shifting symptoms you describe, so just because the cruise control works, don't rule the speed sensor out just yet.

I had intermittent drop out on the cruise control & harsh up & down shifting & later on in the failure mode, on occasion it would hang up in 1st & bump the rev limiter kinda like you've described!!!!

With a Actron CP-9145 scantool attached, I had the wife drive it, while I rode shotgun & monitored the speed sensors PID output to the computer & caught that bad boy hanging up at 37 mph, right where some of the rough up shifts had happened!!!! So closely check out that speed sensor.

Seeing as how you can get it to act fairly normal, by shifting out of OD, to D, I agree the MLP/Neutral Safety switch, or it's wiring/elecreical connector, or mechanical connections, belong on your suspect list.

I suppose you could have more than one problem & maybe the tranny has some gum, varnish, or sludge deposits that are confusing things too.

Even with regular "severe service" timed tranny fluid pump outs & filter changes, I've had up & down shifting problems over the years, that have responded favorably to a dose of "SeaFoam Trans Tune" cleaner upper, until the acting out ceased, (sometimes a couple of days, sometimes a couple of weeks, or months) then did a full fluid pump out, with filter change & she'd be ok for a few more years.

So just because the tranny fluid level is right & the fluid looks & smells ok (mine did too), doesn't mean you couldn't have some small tranny deposits causing shifting problems.

So maybe keep the deposit thing in mind, if the previous two things Nidan suggested don't completely clear things up.

A bunch more thoughts for pondering.
[/b]

Pawpaw,

At your suggestion I used Trans Tune, it did no good.

Tranny still shifts hard sometimes and sometimes it kicks me on 3 - 2 down shift, on cold days.

When it shift hard, it bahave like that for few days, and then gets normal on its own.
 

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So before you decided to add the TransTune, had you confirmed that the speed sensors PID signal to the computer is good & steady????

Leave the Trans Tune in there & make sure you drive it long enough for the tranny fluid to get good & warm, so the Trans Tune can begin to slooooowly soften any deposits that may be hanging up a shift solenoid, or a pressure valve, ect.

It may take a few days if your drive cycle is such that the tranny fluid never gets fully warmed up, or the deposits are hardened into varnish, carbon or sludge.
If things are just gummed up a little, it'll have an easier time of it & you might begin to notice a change a little sooner.

My tranny was clean inside, but it still took about 4-5 days to begin to favorably respond the first time I used it & maybe 5-6 weeks to completely stop acting out the first time, but then I only used 1/2 a can of Trans Tune.

As I'd never used an aftermarket tranny fluid additive, I wanted to be careful & slooooowly dissolve any deposits, lest a chunk break loose & clog something important up, or cause other problems.

If deposits aren't your problem, then Trans Tune won't fix it, but the tranny will be squeeky clean inside, so when you do find out whats wrong & fix it, tranny shift quality improvement will likely be noticeable.

Seeing as how the problem is intermittent, it could be a number of things, so be sure to closely check that speed sensors output & any external wiring or electrical connectors that may be messed with by ice, snow, or salt.

Will be interesting to hear what you find is wrong, so keep us posted.
 

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Discussion Starter #13
PawPaw,

I haven't tried the TransTune yet. The car is parked for now, and I've been hitching rides into work. My transmission is completely full, so I will try the additive when the weather gets warm enough for me to crawl under there and drain a few ounces -- probably next week.
 

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PawPaw,

I haven't tried the TransTune yet. The car is parked for now, and I've been hitching rides into work. My transmission is completely full, so I will try the additive when the weather gets warm enough for me to crawl under there and drain a few ounces -- probably next week.
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No need to crawl underneath to remove tranny fluid.

Just remove the tranny dipstick, insert a length of tubing long enough to reach the bottom of the tranny pan + a few comfortable working inches, ( also long enough in case you drop it, enough is sticking out to get hold of), down the tranny dipstick fill tube, attach a hand pump siphon tube to the tubing & pump out any quantity of fluid you want.

Over the years I've attached the siphon tube of anything from the pump on a windex spray bottle (slow going), to a liquid soap hand pump (a lot faster) to my outboard marine lower unit lube pump( A lot faster), to remove whatever amout of fluid from a tranny you want.

You could also remove the tranny fluid return line at the cooler connection, drivers side, just in front of the front wheel & idle the warmed up engine & it'll pump out 1qt/15seconds at warm idle.

Will be interesting to hear how it goes, so keep us posted.
 

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Discussion Starter #15
Pawpaw,

Thanks for the suggestions. :)

About 25K miles ago, I changed the tranny fluid to Amsoil Synthetic ATF. While I had the pan down, I added a drain plug. That will make my task of removing a few ounces very easy!

But it's still COLD out!! Yesterday, it was about 0° with a wind chill of -10° here. I was outside for about 40-Minutes changing the MLP, and I froze. I work outdoors, and my driveway has about 3/8" solid ice on it. Not ideal ideal working conditions. (Yeah, I know, I'm a wimp.)
 
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