transmission shudder or engine misfire?

[windeye]

Need your experience and help.
Car is 2000 Mazda MPV. Ford Duratec 2.5L V6 engine, 4speed auto trans. Over 175000 miles on clock. Owned since new.

Symptom is as follows: at around 50 mph crusing on high way with light throttle, trans is in lock-up mode (torque converter lock-up), a mild incline would trigger trans kick down but could not hold on to the lower gear (well I felt like that) so it up shifts immediately, and then repeat. I can let go of gas pedal or give more gas to break the vicious cycle.

It does feel quick like driving onfreeway rumble strip, it's more like hitting small speed bumps.

Trans fluid is Mazda M-III, OE. Exchanged 40k miles ago in 2010. Fluid level is good. Color still is red.

Plugs were changed at tge same time as ATF, FORD OE plugs. Wire is original, coilpack also original. Resistence checked, within range.

No recent major repairs. Coolant still OE dark green, no atf leaking to coolant. Only repair recently was replacement of bank1 sensor1 O2 sensor by Denso, original sensor was denso as well. I did it myself. Scan tool show O2 switching normally. No idle priblems.


I am thinking it might be TPS sensor....your opinion is greatly appreciated. Thanks.

 

[gregk24]

It sounds like a torque converter issue. I rode in a Honda Odyssey once with the transmission shudder problem, just like you described it had the feeling like going over rumble trips on the side of the highway. It required a "reflash" of the torque converter.

 

[Taildragger]

Have an F-150 that I would have sworn had a trans shudder. Turned out to be a failed spark plug.

 

[windeye]

I mistyped... it does NOT feel like driving on rumble strip. It's more like a stumble. Lower frequency. I had some mis-spelled words but can edit the original post any more. Using cell phone key pad. Sorry.

One more thing: no CEL whatsoever.

 

[irad]

Check the ignition coils. I replaced two for a neighbor with the same car. The strain of the incline causes the failing coil to misfire. If you have an obd meter with non-continuous diag (mode 6) look at tid 53, this will display misfire count for each cylinder. Mazda uses ford OBD software.

 

[Rand]

From your description..

could it be unlocking the TC then downshifting?

can you be more descriptive.. giving rpm, load, throttle, description etc for each step when this occurs.


I'd suspect ignition but I'm not there and this is one of those WAG type things just going by your description isnt really detailed enough to even guess IMO.

 

[refaller]

Should be easy to determine if it is the TC. My Odyssey had it, but it occurred in specific situations and rpms so I knew it was when the TC was locking. Simple solution was to step a little harder on the go pedal. If it ignition, then it will be more random then that.

ref

 

[windeye]

Originally Posted By: irad
Check the ignition coils. I replaced two for a neighbor with the same car. The strain of the incline causes the failing coil to misfire. If you have an obd meter with non-continuous diag (mode 6) look at tid 53, this will display misfire count for each cylinder. Mazda uses ford OBD software.

Thanks for your note. I do have a obd scanner, but it does not do particular event id as you ssuggested. No CEL so far.

 

[windeye]

Originally Posted By: Rand
From your description..

could it be unlocking the TC then downshifting?

can you be more descriptive.. giving rpm, load, throttle, description etc for each step when this occurs.


I'd suspect ignition but I'm not there and this is one of those WAG type things just going by your description isnt really detailed enough to even guess IMO.


It occurs at speed at 40 to 50 mph, rpm at 1500 to 2000. Car warmed up, with light throttle just enough to maintain speed. Road incline triggers the event with no change on throttle. I can give more gas or let go of gas which would break the stumble cycle.

 

[windeye]

Originally Posted By: refaller
Should be easy to determine if it is the TC. My Odyssey had it, but it occurred in specific situations and rpms so I knew it was when the TC was locking. Simple solution was to step a little harder on the go pedal. If it ignition, then it will be more random then that.

ref


I was thinking it's the TC untill I read a lot on many ford vehicles where people was saying it's coil pack. The engine/trans were used in cogar sable etc in late 90's. I was thinking it could be trans internal problem where line pressure of atf could not be maintained properly due to internal leaks around atf pump. In which a higher viscosity atf might be the cure.

 

[zzyzzx]

I would test the TPS first.