94 Grand Marquis- "Grab" = harsh downshift?

[UncleS2]

I drove Mom's 94 Mercury Grand Marquis(4.6 L V8, AOD trans) yesterday for about 80 miles. Got tires rotated & rebalanced, etc. She had said it felt like it was hesitating, or missing(her words), but I never saw or felt it before. Got a tuneup & few other things done at the local Ford dealership(exc sevc dept)last week, it's been really running good. But yesterday, I finally discovered what she had tried to describe. A big "bump" or "grab" when the dar slows down, sometimes when braking, sometimes not. Feels like maybe a harsh downshift to me, though the engine revs don't seem to change that much. Also felt like it tried to do it(you know, it was "thinking about it" ) when topping a steep hill on a highway later at about 65 mph. Any ideas? Something that can be fixed with a fluid change & band adjustment? She wants to start a 500 mile round trip *tomorrow* with that car. I sure hope it dowsn't eat the trans & strand her!

 

[55Test]

Hmm, the AODE/4R70W was well known for torque converter shudder, so that could it be. A flush with Mercon V should clear that up. Try and describe the 'grab' a bit more, by chance does it feel like it's bucking or snapping hard? My 93 Crown Vic did that for a while, turns out in my case it was a defective ignition module.

 

[UncleS2]

Thanks, 55. It was harsh enough that the first time it did it, I ck'd the rear view mirror to see if I'd run over something. Speeds were slowing down from ~35-45 mph in city traffic. Buck & snap? I dunno. Maybe instead of a harsh downshift, it's trying to put itself into *Park*??? It's at the dealership again now, maybe I should call & ask about/suggest the ignition module. They couldn't get it to do anything wrong so far. gonna call 'em now.

 

[punisher]

A defective MLP sensor will cause intermittent shift concerns, jerks/bucks, intermittent neutrals etc. It won't set a code either. Some sensors and harness connectors had problems with water intrusion and corrosion. A converter shudder will happen most often under light throttle about 35 mph, often mistaken for an ignition miss. Some Grand Marqs/Crown Vics/Town Cars had a "trailer hitching" concern during throttle off decel due to the PCM shutting off fuel to the injectors. Ford finally called it "normal operation".

 

[UncleS2]

Punisher, you win the kewpie doll! When I called back, they said they had ck'd & the MLP sensor(I *think* that's what he said) was bad. Gotta pick up the car tomorrow morning. Thanks to 55 & punisher for the advice & help.

 

[TheTanSedan]

I'd still add some LC-20 or ARX.

 

[UncleS2]

Funny you should mention that, TS. Some years back, when I first found BITOG, this same car was beginning to have some transmission problems- it would hunt for the right gear, downshift much too early, etc. This was happening about a year to 18 months after a fluid & filter change, band adjustment, etc, all done at that same dealership. On Bob's recommendation, I gritted my teeth & poured about 6 to 7 oz of Schaeffer Neutra 131 into the trans & then drove the car for about 100 miles without shutting it off. All the bad stuff went away, and since it hadn't blown up, I went ahead & added the rest of my last remaining 12 oz bottle of Neutra to it, bringing the total dose up to about 10 oz.(the rest had been used in the lawn mower's engine as an oil purge). That was over 4 years ago, I think , & the trans has given no problems until very recently. Also: as recently as 6 to 8 months ago, the trans dipstick *still* smelled like Neutra, whether cold or hot. when I looked at it today, I noticed that it no longer smelled like Neutra- not at all. A few years ago, when I met Odis Beaver, he recommended using Lube Control in an automatic transmission, said 3 ounces was just right. So, late this afternoon, I decided to mix up a little brew for that trans, & will add it before Mom leaves on her trip. The mix? 5 oz of Neutra, plus 3 oz of LC. So, Yup, I'm taking your advice- at least partly!

 

[TheTanSedan]

I use LC-20 (also per Odis) every 10,000 on the auto trans and power steering; when fluid changes following ARX runs are at 20-25,000 miles.