99 mountaineer bucking under load

[jscope399]

Can anyone help me I am having a prob with my 99 mountaineer ,, when i reach a speed of about 40mph the truck starts to buck like it wants to shift but wont
when i accelerate i will shift..it seems to happend more under a load ..
I am about to get rid of my prob by trading it in But i love the vehicle

thank you

 

[Tom G]

Might be the throttle position sensor.

Which engine?

 

[gavin]

have you checked the tranny fluid level?

 

[jack1.1]

try new plugs and wires

 

[gavin]

surprised my first suggestion wasn't to scan for codes
even if the CEL isn't on, there may be a stored code in there, and it just hasn't actually tripped the CEL yet.

 

[jscope399]

302 5l

 

[jscope399]

mercury mountaineer

try new plugs and wires

did a plug and wires change,,, not a miss in it when i accelerate,, only when going in to downshift or between shifting from 35 to 40 mph

 

[96eb96]

did a plug and wires change,,, not a miss in it when i accelerate,, only when going in to downshift or between shifting from 35 to 40 mph

THis is a very common issue with that trans pre-98, but a very similar trans is used to this day in crown vics/TC and the issue still prevails.

If you touch the brake pedal very gently (make the lamp go on) does it make any difference or stop the problem? If the answer is yes, you have torque converter shudder. 35 is the magic number, that is when the TC starts to lockup. The TC needs a very special, intact fluid to do its magic.

If not, there are other things to consider (engine sensors, egr, etc).

When did you change the fluid last?
You have to do a complete fluid exchange with a good brand of Mercon V fluid (no jiffy lube stuff). Older trans had Mercon, and the fix from ford was to switch to mercon V. But even mercon V will break down and lose the friction modifiers after so many miles.


You have to drop the pan/filter and either empty the converter or flush it all out the cooler line.

 

[gavin]

I forgot about that...
what 96eb96 said.

does it only do it with the overdrive ON?
and does not do it with overdrive turned off?

I had this problem with my truck a few thousand miles after I got it.
luckily it was still under the used-vehicle warranty (or maybe there was a TSB on it? can't remember).
atleast, when I had the problem, it only occured with overdrive on, doing about 35-40. If I turned o/d off, it would not do it.
which makes sense... since the t/c doesn't lock with o/d turned off

had to take it to the stealership for work, and whatever they did cleared up the problem.

 

[96eb96]

I forgot about that...
what 96eb96 said.

does it only do it with the overdrive ON?
and does not do it with overdrive turned off?

I had this problem with my truck a few thousand miles after I got it.
luckily it was still under the used-vehicle warranty (or maybe there was a TSB on it? can't remember).
atleast, when I had the problem, it only occured with overdrive on, doing about 35-40. If I turned o/d off, it would not do it.
which makes sense... since the t/c doesn't lock with o/d turned off

had to take it to the stealership for work, and whatever they did cleared up the problem.

97 would definately have this issue full blast. They did a fluid change and I believe a computer update to change the T/C strategy. The other issue you could have is a harsh 1-2 shift. If it isn't smooth there is an easy fix for that.

 

[jscope399]

Easy fix

97 would definately have this issue full blast. They did a fluid change and i believe a computer update to change the t/c strategy. The other issue you could have is a harsh 1-2 shift. If it isn't smooth there is an easy fix for that.

what would the easy fix be ?

 

[Glen4X4]

I've got to try and drain the fluid from my converter since its doing the same thing. 96eb says to do this through the cooler line, what do I need to do to get all the fluid out of the torque converter for it all to drain out?

 

[gavin]

you should actually have an access hole in the bottom of the bellhousing.

hand crank the engine until the drainhole bolt gets to a spot you can get at it.

remove bolt, let it drain. Will take a long time since it's a small hole.

Re-insert bolt. Put rubber cover back on. Refill. :biggthump

 

[Glen4X4]

Alright, thanks Gavin

 

[gavin]

when re-filling, you still do not want to over-fill the transmission pan.

I believe the pan holds about 3-4 qts?

so dump in 3-4 qts. Start engine, shift between all gears, waiting about 5-10 seconds between shifting. When I did this, I think I shifted forward and back about 3 times. Add another 3-4 qts, repeat.

When draining the TC, it will require (iirc) about 14 or so qts, depending on the engine/tranny combo.

 

[Glen4X4]

Alright thanks, hoping this helps. Because another thing it does is when and if I put it in 1st to go down over a steep hill on bad snowy roads or anytime the torque convertor doesn't hold back at all it does in 2nd gear but not 1st and I know the trans is in 1st. So I'm hoping that it will help cure that too.

 

[Cobraguy]

Alright thanks, hoping this helps. Because another thing it does is when and if I put it in 1st to go down over a steep hill on bad snowy roads or anytime the torque convertor doesn't hold back at all it does in 2nd gear but not 1st and I know the trans is in 1st. So I'm hoping that it will help cure that too.

Hmmm...I need to think about that with that particular trans, but that could be a band problem...not a converter. Something isn't right there. It shouldn't free wheel in manual low.

 

[Glen4X4]

Ok, I thought maybe it had something to do with the convertor like the bucking is. But yeah when I put it in 1st manually it will fly down over with no resistance the rpms drop as if its in neautral, I thought before that 1st went out so I got on the gas and sure enough its in gear just no resistance.