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Discussion Starter #1
Sticky, sticky subject. Bottom line: while cruising around 40 - 45, if I step on the accelerator the car seems to lose power - falters. I have to step on the accelerator to shift down in order to gain power. And, I've noticed the tach occasionally may increase 500 rpms momentarily, and go back down while I'm cruising. ONLY occasionally, not all the time. Doesn't seem to happen when car is cold - only when warmed up. Typical climate - 40 to 75 degrees.

Longer story: I've replaced LOTS of stuff to try to run this down.

1999 Mercury Sable Wagon
3.0L 24 valve Duratec engine (232k total miles)
AX4N trans (rebuild 12k miles ago)
 

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What you are describing is characteristic of the transmission although the degree of issue may be exaggerated in yours given it's age / rebuilt status. Also note that at around 40mph, the throttle cable will resonate and you will feel a vibration in the pedal. There was a tsb to fix the issue.

I would consider doing either a full fluid exchange with licensed Mercon V or three or so drain and fills.

What parts have you thrown at the problem so far?
 

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What you are describing is characteristic of the transmission although the degree of issue may be exaggerated in yours given it's age / rebuilt status. Also note that at around 40mph, the throttle cable will resonate and you will feel a vibration in the pedal. There was a tsb to fix the issue.

I would consider doing either a full fluid exchange with licensed Mercon V or three or so drain and fills.

What parts have you thrown at the problem so far?
I exchange fluid with the jug shown in the pic. Takes about 20 minutes total suck out and refill. I remove the vent cap for this as it makes refill much easier. Vent cap needs cleaning and put back on carefully. Just on the first bulge, and wobbly loose. For vacuum, I remove the inlet filter from my small air compressor and use that for vacuum. I have sucked on it with my mouth and it can be done.
-chart-
 

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Discussion Starter #4 (Edited)
What you are describing is characteristic of the transmission although the degree of issue may be exaggerated in yours given it's age / rebuilt status. Also note that at around 40mph, the throttle cable will resonate and you will feel a vibration in the pedal. There was a tsb to fix the issue.

I would consider doing either a full fluid exchange with licensed Mercon V or three or so drain and fills.

What parts have you thrown at the problem so far?
RJacket - I'm sorry, I don't follow your comment about the vibrating cable at 40 mph.

Further detail : As I'm cruising, (doesn't happen while accelerating) at most speeds actually I. E., neighborhood speeds, 25, 30, 35, and even at 50, and 60 - so when I'm not accelerating up to speed, I encounter this faltering, like too much air in the fuel mix, a drop off in power, but no backfire or miss that I can tell. And, no hollow vacuum sounds, as it might make if it were truly starved of fuel. It's a little hard to explain.

So, the following is what I've done to determine if I'm dealing with a transmission issue, or something masquerading as a Trans problem :

Shop Fluid change with mercon V about 5k ago. Followed up with 3/4 of bottle Lucas transmission slip fix.
Changed out plug wires/plugs.
Changed coil pack (it has been missing upon startup and while cold). Still missing, but may be due to recent SES P0174/0171
Replaced VSS
Fuel filter
Air filter
Cleaned MAF with electronic contact cleaner and let air dry.

Fuel pressure is within spec.

Coil pack and VSS were suggestions given as fixes for missing /low power, as well as symptoms that mimic slipping Trans.
 

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Replaced VSS
I hate to be sound like one of those guys but when you replaced the vehicle speed sensor, did you do so with a Ford OEM sensor? I replaced one in mine, as the car was unsure of which gear to use, at parking lot speeds, with transmission hot. After replacement, it was the same thing with transmission cold. Swapped it out for another brand and it gave me the same issue. Swapped it out for an OEM, and haven’t had a problem since.

If it is happening at slower speeds, which you said it was at 25, 30, etc. bring it down to first gear. Is it happening where it’s not changing gears or is it only happening when the car needs to decide what gear to be in? That data should determine engine/fuel system versus transmission. If it doesn’t give you a problem at that point, double check the VSS. When I switched from the first replacement to the second replacement I also made sure to swap out the harness. The old one had seen it’s days.


Sent from some little thing that I hear voices from. Oh, and his name is Blüe Longroof
 

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How long have you owned the car and when did you notice this issue?

I would look at cleaning the throttle body and checking for slack in the throttle cable. Run a bottle of techron concentrate or gumout regane in the fuel to clean the fuel system and injectors. I would even go to Walmart and get the $20 fuel injector service which is more about cleaning up the combustion chamber. All this ensures that your fuel and air is operating properly. You could also give the mass air flow sensor a clean (with the correct spray).

The 500rpm rise you see when warm and not cold is the torque converter unlocking. The AX4N is programmed to lock up as soon as you're no longer accelerating for fuel economy reasons, even when you're going slow. The Duratec also has less torque below 2500rpm so once the torque converter locks, even at a speed of 60mph, it can feel unwilling to accelerate.

It's even worse at 25mph but the torque converter will unlock if it needs to and gears will shift down also if you press hard enough. Having slack in the throttle cable, a dirty throttle body, dirty injectors will mean you'll need to depress the throttle pedal even more when cruising to get a response.

One easy way you can get a more responsive experience, especially below 45mph, is to select the other "D" ie Drive instead of Overdrive.

The other thing is why is there a Lucas additive in a transmission that was rebuilt 12k miles ago? I would want to fully exchange the fluid so that it is virtually 100% new Mercon V. I would also want to (first) drop the transmission pan, inspect and clean it and change the filter. There could be all sorts of contaminants in the system as a result of the rebuild.

Lastly, disconnect the battery which will give the PCM a chance to relearn everything.
 

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Codes 171/174 = vacuum leak 99.8% of the time. Check LTFTs on both banks at hot idle and with engine under load with a good scan tool. High positive trims at idle that drop toward zero with engine under load = vacuum leak. Since you have both 171 and 174 codes, vac leak effects both banks. Look for split vac lines, split / rotted PCV hose, etc.
 

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Discussion Starter #8
I hate to be sound like one of those guys but when you replaced the vehicle speed sensor, did you do so with a Ford OEM sensor? I replaced one in mine, as the car was unsure of which gear to use, at parking lot speeds, with transmission hot. After replacement, it was the same thing with transmission cold. Swapped it out for another brand and it gave me the same issue. Swapped it out for an OEM, and haven’t had a problem since.

If it is happening at slower speeds, which you said it was at 25, 30, etc. bring it down to first gear. Is it happening where it’s not changing gears or is it only happening when the car needs to decide what gear to be in? That data should determine engine/fuel system versus transmission. If it doesn’t give you a problem at that point, double check the VSS. When I switched from the first replacement to the second replacement I also made sure to swap out the harness. The old one had seen it’s days.


Sent from some little thing that I hear voices from. Oh, and his name is Blüe Longroof
Hi McSteven,

The VSS was a 3rd party part. I'm sorry but I don't remember the company, but it was not from a Ford dealer, though the company I purchased it from (CostLess Auto Parts - Orchards, WA State), is a reputable company that is very popular here in the Vancouver area, and I've dealt with them for 20+ years.

I took the car out (warmed up) and tried staying in 1st gear, but at 1500 rpms the car wants to shift. I did not notice the idiosyncrasy that it typically shows with the engine faltering. Additionally, I mis-spoke about the "slipping". I said it varies 500 rpms when it slips. Actually, it varies 50-100 rpms at most. Not 500 rpms.

I'm still mystified.

Thanks for weighing in!
Rob
 

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Discussion Starter #9
How long have you owned the car and when did you notice this issue?

I would look at cleaning the throttle body and checking for slack in the throttle cable. Run a bottle of techron concentrate or gumout regane in the fuel to clean the fuel system and injectors. I would even go to Walmart and get the $20 fuel injector service which is more about cleaning up the combustion chamber. All this ensures that your fuel and air is operating properly. You could also give the mass air flow sensor a clean (with the correct spray).

The 500rpm rise you see when warm and not cold is the torque converter unlocking. The AX4N is programmed to lock up as soon as you're no longer accelerating for fuel economy reasons, even when you're going slow. The Duratec also has less torque below 2500rpm so once the torque converter locks, even at a speed of 60mph, it can feel unwilling to accelerate.

It's even worse at 25mph but the torque converter will unlock if it needs to and gears will shift down also if you press hard enough. Having slack in the throttle cable, a dirty throttle body, dirty injectors will mean you'll need to depress the throttle pedal even more when cruising to get a response.

One easy way you can get a more responsive experience, especially below 45mph, is to select the other "D" ie Drive instead of Overdrive.

The other thing is why is there a Lucas additive in a transmission that was rebuilt 12k miles ago? I would want to fully exchange the fluid so that it is virtually 100% new Mercon V. I would also want to (first) drop the transmission pan, inspect and clean it and change the filter. There could be all sorts of contaminants in the system as a result of the rebuild.

Lastly, disconnect the battery which will give the PCM a chance to relearn everything.
Hi! I've owned the car from 2005. The transmission was replaced with a rebuild in 2015. A week later, the trans guy changed the fluid with Mercon V to handle any contaminants.

I had a shop change the fluid ( not a flush) with a Mercon V fluid 3.5 years after, when it began to manifest the aforementioned problems. A couple of months afterward, it was still 'slipping? / doing what it's doing', so I took a chance with the Lucas Transmission fix - siphoned out a total of about 3/4 of a quart, a little at a time - which I replaced with the Lucas, a little at a time. No joy. The car has not been used a lot since the trans replacement since I've been employed on/off and am not using it every day.

Regarding your comment about responsiveness - the problem occurs in inverse 'D' (overdrive), and 'D2', no difference. When I'm cruising at 40 to 55 and, say, I want to add a few mph, I lightly step on the pedal, and that's when I notice the problem. It can happen when I reach cruising speed as well, and am just trying to maintain speed, it will falter - begin to lose power. I'm using the Android Torque Pro app with an ELM327 OBDII adapter as well, if anyone cares.

When I changed the plugs/wires recently, I pulled the exhaust manifold to get to the back 3 plugs, and cleaned the throttle body, and Intake just past/near the throttle body, as well as cleaned the buildup in the 3-port, half-moon circle of the intake manifold which mates with the throttle body. It builds up with carbon deposits and plugs the small 3 ports on the bottom, and throws a code when it's plugged. It had not thrown a code, but I felt as long as I had the throttle body off, I might as well clean it. The 3 ports and that half moon channel was completely plugged. I also cleaned the large port that leads to the EGR valve, I believe. It, too, was 1/2 way plugged with carbon deposits. I checked and lubricated the EGR to make sure it was functioning using a hand vacuum pump. And, of course, cleaned around the venturi.

The throttle cable is sound, adjusted properly and spring is in place. I run Top Tier gas in the car 100% of the time, and felt that should clean injectors, no? If you/anyone thinks an injector cleaner should be added, I can do that, but felt it was overkill as I didn't believe there was a problem there. Especially after checking the condition of the plugs at last change interval about 9 months ago. After the car was performing this circus act. What do you/anyone recommend for an injector cleaner? RJacket - you mentioned Wal-mart.

Thank you for weighing in! It's wonderful to have some ideas to try.
 

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Discussion Starter #10
Hi! I've owned the car from 2005. The transmission was replaced with a rebuild in 2015. A week later, the trans guy changed the fluid with Mercon V to handle any contaminants.

I had a shop change the fluid ( not a flush) with a Mercon V fluid 3.5 years after, when it began to manifest the aforementioned problems. A couple of months afterward, it was still 'slipping? / doing what it's doing', so I took a chance with the Lucas Transmission fix - siphoned out a total of about 3/4 of a quart, a little at a time - which I replaced with the Lucas, a little at a time. No joy. The car has not been used a lot since the trans replacement since I've been employed on/off and am not using it every day.

Regarding your comment about responsiveness - the problem occurs in inverse 'D' (overdrive), and 'D2', no difference. When I'm cruising at 40 to 55 and, say, I want to add a few mph, I lightly step on the pedal, and that's when I notice the problem. It can happen when I reach cruising speed as well, and am just trying to maintain speed, it will falter - begin to lose power. I'm using the Android Torque Pro app with an ELM327 OBDII adapter as well, if anyone cares.

When I changed the plugs/wires recently, I pulled the exhaust manifold to get to the back 3 plugs, and cleaned the throttle body, and Intake just past/near the throttle body, as well as cleaned the buildup in the 3-port, half-moon circle of the intake manifold which mates with the throttle body. It builds up with carbon deposits and plugs the small 3 ports on the bottom, and throws a code when it's plugged. It had not thrown a code, but I felt as long as I had the throttle body off, I might as well clean it. The 3 ports and that half moon channel was completely plugged. I also cleaned the large port that leads to the EGR valve, I believe. It, too, was 1/2 way plugged with carbon deposits. I checked and lubricated the EGR to make sure it was functioning using a hand vacuum pump. And, of course, cleaned around the venturi.

The throttle cable is sound, adjusted properly and spring is in place. I run Top Tier gas in the car 100% of the time, and felt that should clean injectors, no? If you/anyone thinks an injector cleaner should be added, I can do that, but felt it was overkill as I didn't believe there was a problem there. Especially after checking the condition of the plugs at last change interval about 9 months ago. After the car was performing this circus act. What do you/anyone recommend for an injector cleaner? RJacket - you mentioned Wal-mart.

Thank you for weighing in! It's wonderful to have some ideas to try.
Oh, RJacket, I now see that you mentioned the Techron additive, and Gumout. I used to do that with my dad on his '71 Ford truck back in the day. We dump some in the carb, rev the engine until the white smoke would clear up out of the exhaust, and repeat the process until the can was empty. But, we'd have to pull the plugs and clean them after that. Please don't tell me I'll have to pull the plugs after I run the injector cleaner, OK? ;o)
 

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The Gumout with Regane / Techron complete fuel system cleaner would go into your gas tank and you wouldn't have to pull the plugs. The Walmart $20 fuel injector service is more about cleaning the combustion chamber, and is something I did that removed a noise (presumably some carbon) that was still there after Gumout and Techron did an otherwise excellent job. But my issues were a result of years of short trips and non top tier fuel. Since you've been running top tier, I would think your injectors and combustion chamber will be fine.

Nonetheless, running a complete fuel system cleaner is a good way to ensure your injectors are as clean as possible and can clean other deposits and is very cheap maintenance.

But back to the problem you're having, I think Jeff K's reply should be the basis for your investigation. Do you still have the 171 / 174 codes? If you have a vacuum leak, then that's going to throw your air / fuel mixture off.
 

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Discussion Starter #12
Well, it certainly couldn't hurt to run an injector cleaner through it, even if it doesn't fix the problem.

I had noticed high long term fuel trims for a while now. My various efforts to try to run that down have been fruitless. I've done all the usual.

Now, I'm in the process of building a smoke machine to try to find the vacuum leak.

Thanks
 

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Hi McSteven,

The VSS was a 3rd party part.
...
I took the car out (warmed up) and tried staying in 1st gear, but at 1500 rpms the car wants to shift. I did not notice the idiosyncrasy that it typically shows with the engine faltering.
If the engine is not faltering, then it sounds like a transmission issue. I’m sorry, I should have noted to shift manually but at an RPM higher than the automatic would shift it.

The place you bought the VSS may be reputable. I buy from reputable people/stores all the time. I still think it’s the sensor.

That said, I am NOT a mechanic. I don’t even play one on TV. When I replaced mine the first time, and the problem switched from hot transmission to cold transmission, I thought there had to be something else. Searching here and other Ford forums led me to try a different sensor.


Sent from some little thing that I hear voices from. Oh, and his name is Blüe Longroof
 

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Discussion Starter #14
Well, that's kind of a bummer. The Trans doesn't exhibit the same behavior in first gear as it does in D and D2. If that's the case I can't see spending the money on an OEM VSS.

I'll continue to search for the vacuum leak so at least it's not throwing the code.

I will certainly NOT put another Trans in it. And tearing it down to prove that it's a Trans problem isn't is the realm of my anorexic finances. Trans shops are in the swapping business these days, not the quality of repair business.

On the off chance it could be something else, is there a definitive test that can be done to verify that this is/is not a transmission problem?
 

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An issue that sounds similar to yours:

 

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Discussion Starter #16
That's interesting. Though the engine is the DOHC Duratec and not the Vulcan, it could still be the problem. Man! I've never plugs in that shape before.

The problem he's experiencing is similar to mine. Could it be that easy?
 

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^ Nice video! Carbon-tracking is another issue to check for.
Plugs and wires go together. Carbon tracking on the plug leaves damage on the wire boot. New wires and new plugs may fail in a year.
Wet plug was loose in the threads and from the factory that way.
Both cars had the same symptoms but no codes. The wet plug was COP, other one DOHC with wires.
-chart-
 

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Another thought: Have you tested for the faltering in 2nd gear?
 
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