2012 TDCi Engine RPM varying ("Heartbeat")

[AlCan]

I hope Just Bill isn't lurking here - after his nightmare, I bet he's had enough of Mondeo's to last a lifetime - and he probably won't want to see this.

Anyway, in one of his earliest posts, he described this. I have the same / similar thing on a different car.

Not the same extent of power loss, but I'm sure, it's a progressive thing. I suspect there will be a lot of agreement on the cause and the solution, but how about the explanation? I have a theory...

https://photos.google.com/share/AF1Q...NqbUVpdVZ0TWdR

Tried to keep the throttle as constant as possible, but still got an acceleration from about 48km/h to about 67, stable in the last half of the video.

Tried it with Cruise Control but found manual control showed it better. It's very hard to distinguish any change in power level, but sometimes you can feel it, especially during decel, surprisingly. As you can see, this was in 3rd gear, but happens in all (higher gears anyway).

[AlCan]

Sorry, I forgot to mention:

It's a Powershift / 6DCT450 Transmission.

[AlCan]

Ok, looks like no one is game to comment, so here's an update.

I changed the DCT Fluid yesterday / day before. What I mean is I drained it the day before and left it overnight.The fluid was black, of course.
Then I found the Volvo video...
That shows the guy checking the transmission temperature (before? after?) refilling with new fluid. Holy moly. Is it necessary for the transmission to still be warm when refilling?

It makes complete sense to drain it when warm, but no one seems to know why you need to do 20-second step throughs of all the gears before draining, though of course it would have to be critical after refill. I guess just another Mondeo / DCT mystery.

Anyway, nothing I could do about that, so just refilled it.

And...?

Well, it drives a bit better, but the throbbing, pulsating Engine RPM is not cured. I think it's improved, in the sense that I think it now happens at higher power levels. Not sure if the surging on deceleration is better or not. That's still very noticeable in some situations - it feels as if there's a Gremlin playing with the brakes - but maybe it's because I was pushing the car much harder. That's a definite improvement, at least. Before, I didn't feel able to push the car hard at all, and I think the truth is that it was going into a silent limp mode at the higher throttle settings. I think this parallels Just Bill's original symptoms.

So, while I'm here, let me have my rave about what I think is happening.

Rave: On

As I see it, there are three or four possibilities to explain the throbbing Rev Counter.

1. Instrumentation fault. There's something wrong with the electronics. Maybe a duff RPM gauge. (Gauge Sweep seems to work fine.) Maybe a faulty sensor. Maybe a flaky ECU. A loose wire just doesn't fit, nor, really, does a sensor fault. I don't believe it's any of these faults.

As far as I can tell, it depends on various factors relating to engine power / torque.

The RPM readout seems otherwise normal/correct. I tried running in Self-Diag mode, but the Digital RPM display moves too fast to see what's happening and drive at the same time. I'd have to video it again, but couldn't be bothered, sorry.

2. Control Fault. Sometimes it feels (esp during decel) as if the other clutch is suddenly, intermittently, dragging, but that doesn't make sense. Can the trans remain in two gears after a change is complete and not throw an Error Code? If not, then it wouldn't matter if the other clutch is dragging.

It could also be insufficient clutch (hydraulic) pressure, but don't know how that manifests. I have never seem a "Transmission Limited Function" or any other Display warning, and no Engine Check light.

[I forgot to bring my OBDC Dongle, but only 3 common Chassis codes showing in the Self-Diag menu - though I know/believe the TCM doesn't save codes. Another mystery - why not?? Daft!]

When I very first drove the car (its delivery voyage) and saw the pulsating RPM, I thought Clutch Slip. I still think it's clutch slip, but we'll get to that.

Thinking that's what it was, I figured slip will produce heat - like it sure does in a dry clutch. So, after about half an hour of noticing this, I stopped and checked the trans temp by hand. It was warm, but not hot. Interesting. I would have expected much hotter.

Anyway, I removed the underpan to allow better cooling and carried on. That resulted in a slight improvement, but the further I went, the worse the problem got. Had to stop and let cool a couple of times. So, it's temperature related, and it worked fine (apart from rough changes) while cold.

3. It's not really a fault. This is my current thinking. Yes, it's a problem, and it's showing there's a problem, but I think this is entirely deliberate, designed in.

I currently believe the problem is really either the wrong trans fluid, or, it's just never been changed and is dirty / worn out. So, the clutches slip because the fluid is no longer providing whatever is required for adequate clutch grip.

Now, as above, slipping clutches are normally a terminal situation. They heat up and burn out... But apparently, the crafty designers of this transmission were well aware of this so decided to build in some protection.

In my view, it's just like Traction Control. For example, if you put a much bigger or smaller tyre onto one wheel, you're likely to get persistent Traction Control activation, and the car will go into Limp Mode until the wheel slip ceases. Since it doesn't, Limp Mode continues...

Traction Control works by comparing the speeds of the different wheels, and if any are too different, it activates. I guess it's a similar thing here, but to detect clutch slip, you have to compare engine speed with clutch output speed. I know there's a speed sensor somewhere in that vicinity, and maybe this is the one that's used, but I don't know.

Anyway, to compare two speeds (clutch input against output), you need time. You have to compare the number of turns of both elements over a period of time. If they are different, then you know there must be slip - or a faulty sensor - or the clutch is disengaged, or something is broken...

Okay, let's say you detect clutch slip. Then what? Maybe you can increase clutch clamping pressure, or maybe it's already at maximum.

Then what?

Here's what I think. It's clear to me that the engine and the transmission "talk" to each other. I imagine the trans is more the master, the engine more the slave, since the engine's job is simple - make power according to throttle setting and load. The trans on the other hand has a much more complex job - to engage and disengage clutches and gears nicely and appropriately, and if it disengages a clutch with the engine at full power and no gear ready to take the load, well... possibly Messy!

I believe this "talking" is what causes cars with failing transmissions to "stall" or baulk during changes. I've had the 2011 do that a few times. Like, when the transmission can't engage the next gear within a certain time, it tells the engine "HEY! IDLE" while I sort this out. Then, the engine speed drops and when the gear is ready for the clutch to supply drive, the engine is running too slowly and you get a jerk or a jolt while the engine speeds up again. Maybe the TCM firmware could use improvements in that area.

Anyway, when you think about a control system, how do you deal with a slipping clutch without simply throwing an error and quitting?

Here's my take. First, you have to continually monitor for clutch slip, at all times except when switching between clutches. (Or in P or N, I guess.)
Maybe you do this once per second, or even more frequently. Then, as soon as you detect unwanted clutch slip, you have to take action to avoid clutch burnout. If you can't increase clutch pressure, there's really only a couple of possible choices.

If you can choose a lower gear and you're in Auto mode, then drop down a gear (or stay in that gear longer). This means the same amount of torque (which is the cause of clutch slip) can deliver more power since the RPM will increase (as Power is Torque x RPM). This fits with Just Bill's description of high revving during acceleration.

The second available choice is also an essential one, whether you can drop a gear or not: Reduce Power until clutch slip ceases. Tell the engine: REDUCE POWER! The TCM probably keeps saying Reduce Power until the clutch slip ceases, no matter how low that power level is.

Now what?

Well, a car is a highly dynamic machine, things are always changing. On top of that, you have a driver trying to command power. Chances are, the TCM's command to reduce power is the opposite of what the driver is commanding.

At this point, the TCM has things under control and has no need to keep commanding the engine to reduce power. The driver has his foot down more than the current power setting, so naturally, if the Boss is silent, the ECU will start increasing power to satisfy the 2IC, i.e. the driver.

So, clutch slip then resumes fairly soon. And the TCM then detects Clutch Slip again, and the whole cycle repeats.

I surmise that this is what is going on with this car. Once clutch slip begins, the engine starts to rev up. The TCM then throttles the engine back until slip ceases. Clutch holds for a moment, until engine torque is overwhelming again... So, Revs increasing, then dropping, increasing, dropping.... ...

If this is what's really happening, then I think it's pretty impressive. My hat's off to the transmission designers.

As AlanM said in Just Bill's thread, changing the oil may not be an instantaneous fix. He suggests that the TCM "learns" to adapt to the dirty oil. I can't argue with that, except that if my theory is correct, then my clutches are still slipping, despite the new oil*.

My suspicion is that the wrong or dirty oil causes glazing of the clutch plates and this might be why they are still slipping. I'm hoping this will wear off and all will be well.

Hope this was worth the read!

Rave: Off.

[AlCan]

*New Oil: Petronas Tutela Multi DCT 700.

Anyone else used this? Comments? It meets the Ford Spec.

[AlCan]

OK! Another update.

First drive since yesterday.

The symptoms are different. Whereas in the video, the Rev Counter can be seen going up then down, pausing, then going up again, then down... now, it's different. Maybe sitting overnight with fresh oil on them has rejuvenated the clutch plates somewhat.

I don't know if it's me or the car - maybe I've unconsciously adapted to this behaviour, though I think it's more the car. What happens now is that under acceleration, the RPM goes up in steps. It doesn't seem to drop back like it did. It's like this: the RPM goes up as if the clutch is slipping, but then it pauses and stays there, as if the car's speed is now catching up to the engine. Then it steps up again... repeat...

The lunging on deceleration is still there, like that gremlin is still dancing on the brake pedal (as I'm not touching it), but apart from these things, it's like a new car.

It has regained buckets of power, despite the continuing clutch slip issue.

Even if the clutches are not quite holding yet, I think the theory still is. ;-)

We'll just have to wait and see. Keep you posted.