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Discussion Starter #1 (Edited)
My 1997 Thunderbird Sport 4.6 liter V-8 (147,000 miles) has a strange problem that I'm thinking is transmission related. I'll describe the problem and I'd like some opinions on the cause, if anyone has any!

When I am cruising down the road, say at around 30-50 m.ph. (I haven't really noticed if it does this at other speeds, yet) and I lift my foot off the gas, the car suddenly begins to feel like it's slowing down. By slowing down, I mean much more quickly than it should be if it's coasting. It almost feels as if the brakes are dragging or that the transmission has downshifted. I know it is NOT the brakes for two reasons - this noticeable deceleration does not happen for 1/2-1 second after lifting my foot off the gas and my brake parts (calipers, pads and rotors are new at all 4 wheels, with less than 2,000 miles on them). The transmission is also not, to my knowledge downshifting - at least, it doesn't feel like it's downshifting (the car just starts to slow down as if it downshifted).

There is a "Service Engine Soon" light illuminated on my dash, but when I had AutoZone read the code, it came back as a malfunction detected in the vapor canister system - a faulty pressure sensor or purge valve. I haven't fixed that yet, but I don't think it's related. I'm wondering if it could possibly be something to do with the lock-up torque converter?

Anybody else ever experience something like this?

Thanks,

Dennis

P.S. - I think I should add that in every other respect my trans seems to be operating normally!
 

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If you put your foot on the brake just enough to put on the brake lights but not enough to engage the brakes, does that make the car seem to coast more when you let off the gas? If the EVAP code is the only code, then it shouldn't cause any drivability issues.
 

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Discussion Starter #3
If you put your foot on the brake just enough to put on the brake lights but not enough to engage the brakes, does that make the car seem to coast more when you let off the gas? If the EVAP code is the only code, then it shouldn't cause any drivability issues.
I'm not sure - I'll have to try that!

Thanks,

Dennis
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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I think I know what Dennis is talking about and it happens to me too, although it cures itself after a second or two and seems intermittent. Get up to 40 MPH and cruise there for a minute or so, then let your foot off the gas - and the transmission will go into a state where, like Dennis said, it feels like it's downshifting into 3rd gear, but doesn't. Like that lurch you get when you do coast down to 3rd gear, but it lasts longer. Almost feels like the transmission is going to downshift but changes its mind. :confused:
 

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When you touch the brakes at speed, the torque converter unlocks, even the slightest touch. Stay off the brake pedal when you check that.
 

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That is what he should be testing, it sounds like for some reason it isn't unlocking (if it really should be that quick), I am not sure how fast it should unlock when you get off the gas, I have a tune on mine and it is totally different than before I got the tune, and my 2000 Grand Marquis with 2.73s and mush tuning and no tach, I can't feel it when it shifts up or down, WOT or manual or anything.

I don't know what all the PCM uses to determine it should unlock the TC, only thing I know for sure is application of the brakes.

Just like testing for TC shudder or a misfire, I would get up to the target speed and hold that speed, lightly press the brakes only enough for the lights to come on, watch the tach for the 100-200 rpm raise, then let off the gas and see if you still feel the same sensation. Again, I don't know that there is actually anything wrong, I get a lot more engine braking (feeling anyways) in this situation in my 97 Cougar than I do in my 2000 Grand Marquis.
 

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I'll be up in talmadge in a few weeks. If you want to bring it over I'll take it for a drive and tell you what I think. From your description I have no idea.
Alan
 
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