Torque converter lock-up question

usmcdoc14 · **Posted:** Wed May 17, 2006 6:14 pm

Is this thing working right? :lol:

Lock-up happens around 55-60mph in I believe 3rd gear (not enough space in traffic to start from a stop) and will keep the rpms up until 50mph when it will let go and the rpms will drop back to "normal let off the gas rpms"
It feels like it is locked up because I get some slight engine braking (or I am loosing my mind)

sorry this is the first automatic I have owned in a while. The only other auto I drive is my roomates lifted waggy and it acts like a "normal" auto and coasts/rpms drop when I let off the gas.

build date FEB 06, no other issuses

groucho · **Posted:** Thu May 18, 2006 2:34 pm

Since your build date is 06, it is likely working correctly. Are you talking about the CRD with the 5 speed transmission? I cannot feel lockup on my 06. Before the latest flash, I couldn't even feel the shifts. If you are doing 55 with OD not locked out, should be turning about 1700 rpm I think. If the torque converter is screwed up, it'll break soon enough.

Again, if you have the CRD, there is not much in the way of engine braking with a diesel. Compression ratio is a bit high for that. If it feels as though it is "holding back" when coasting in D, that is the combination of the air drag of the "box" and all the power train components manifesting their presence. "4 wheel drive" comes at a cost, even when all that stuff is disengaged.

Semper Fi

usmcdoc14 · **Posted:** Thu May 18, 2006 9:04 pm

groucho wrote:

Since your build date is 06, it is likely working correctly. Are you talking about the CRD with the 5 speed transmission? I cannot feel lockup on my 06. Before the latest flash, I couldn't even feel the shifts. If you are doing 55 with OD not locked out, should be turning about 1700 rpm I think. If the torque converter is screwed up, it'll break soon enough.

Again, if you have the CRD, there is not much in the way of engine braking with a diesel. Compression ratio is a bit high for that. If it feels as though it is "holding back" when coasting in D, that is the combination of the air drag of the "box" and all the power train components manifesting their presence. "4 wheel drive" comes at a cost, even when all that stuff is disengaged.

Semper Fi

yup. 06 CRD with the 5 speed.
its not significant engine braking but enough that made me notice the unlocking of the torque converter.

I am used to 4wd drag on a vehicle in 2wd with the aerodynamics of a brick. There is a lifted grand waggy in my household :lol:

Cowcatcher · **Posted:** Fri May 19, 2006 10:17 am

After reading the topic here on RPM's at 60 MPH it didn't make much sense to me as everyone was quoting different ranges. A couple of nights ago I had to punch it on a rural highway and got up to 3200 RPM's and just shy of 70 mph then slacked back off to about 60 mph. My RPM's generally run at about 1850/1900 at 60 but this time pulling a long hill I was doing 1650. Having now experimented a few times it seems that the only way I can get this thing to lock up and run at reduced RPMs is to do that.

This rig has no trouble running at 1650 or less at the 55 > 60 MPH range but I don't think you should have to wrap it up to 70 to get that to happen.

IndyCRD · **Posted:** Fri May 19, 2006 10:57 am

usmcdoc14 wrote:

Is this thing working right? :lol:

Lock-up happens around 55-60mph in I believe 3rd gear (not enough space in traffic to start from a stop) and will keep the rpms up until 50mph when it will let go and the rpms will drop back to "normal let off the gas rpms"
It feels like it is locked up because I get some slight engine braking (or I am loosing my mind)

sorry this is the first automatic I have owned in a while. The only other auto I drive is my roomates lifted waggy and it acts like a "normal" auto and coasts/rpms drop when I let off the gas.

build date FEB 06, no other issuses

Mine is an '05 and it does the exact same thing. I believe that it was inteded to be that way.

Here's a theory....

I'm thinking that part of the reason that the torque converter locks in at 4th and 5th gear may be done for fuel savings. I may be wrong about that. You would think that it would be the other way around since the RPMs are held up higher with it locked. Here's why I think that it might be the case:

On my VW diesel (with a manual transmission), the way I understood it was that when the car was coasting in gear, the car would automatically shut off the fuel pump temporarily as the engine kind of slowed the car down in gear. The momentum of the car turned the engine and it didn't need any fuel. When you hit the clutch on that car, the rpms would drop and you could feel the fuel pump kick back on.

I could very well be wrong....I probably am....but the torque converter locking up in those gears would allow the same effect to happen on an automatic transmission, thus saving fuel.

What do you think about that theory?

Oldnavy, you are a resident expert. Could this be the case on our Jeeps also?

oldnavy · **Posted:** Fri May 19, 2006 12:51 pm

Well with the VW we had VAG-COM and could tell everything happening in the car, here we don't have that option. My guess is like the VW's when you let off the power fuel flow was cut to idle flow amount or about .4 liter per hour, best I remember it never completely stopped fueling the engine in the automatic cars or the sticks either. That would not make sense unless it was working with an electric motor for aux power like a hybrid. By nature without the likes of a Jake-brake diesels do not compression slow like a gasser, because in a diesel the fuel pump is in reality the throttle and is turned by engine RPM. It is more complicated then that but that gives you the idea, and there is electronic controls to vary the timing of the pump. Most people don't realize it but a diesel will rev quicker then a gasser. I hope I answered this in an understandable fasion without going into a lot of detail.

Average over the road diesel burns about 1 gallon per hour at idle if I remember correctly, but this could very by mfg and size. I would imagine our CRD would be in the 1 liter per hour range is all, maybe a smiggen less.

DZL_LOU · **Posted:** Fri May 19, 2006 1:25 pm

oldnavy wrote:

My guess is like the VW's when you let off the power fuel flow was cut to idle flow amount or about .4 liter per hour, best I remember it never completely stopped fueling the engine in the automatic cars or the sticks either. That would not make sense unless it was working with an electric motor for aux power like a hybrid. By nature without the likes of a Jake-brake diesels do not compression slow like a gasser, because in a diesel the fuel pump is in reality the throttle and is turned by engine RPM. It is more complicated then that but that gives you the idea, and there is electronic controls to vary the timing of the pump.

Let's take your hypothesis a bit further. If the fuel pump flow rate is controlled by the engine RPM, then is it possible that the jerking engine experience noticed after heavy acceleration is due to the fuel pump changing the flow rate from an acceleration flow rate to and idle flow rate?

oldnavy · **Posted:** Fri May 19, 2006 1:29 pm

DZL_LOU wrote:

oldnavy wrote:

My guess is like the VW's when you let off the power fuel flow was cut to idle flow amount or about .4 liter per hour, best I remember it never completely stopped fueling the engine in the automatic cars or the sticks either. That would not make sense unless it was working with an electric motor for aux power like a hybrid. By nature without the likes of a Jake-brake diesels do not compression slow like a gasser, because in a diesel the fuel pump is in reality the throttle and is turned by engine RPM. It is more complicated then that but that gives you the idea, and there is electronic controls to vary the timing of the pump.

Let's take your hypothesis a bit further. If the fuel pump flow rate is controlled by the engine RPM, then is it possible that the jerking engine experience noticed after heavy acceleration is due to the fuel pump changing the flow rate from an acceleration flow rate to and idle flow rate?

Yes. That is probably the reason for the ECU reflash done on that one TSB to better control the fluel flow drop.

LibertyCRD · **Posted:** Fri May 19, 2006 2:56 pm

IndyCRD wrote:

usmcdoc14 wrote:

Here's a theory....

I'm thinking that part of the reason that the torque converter locks in at 4th and 5th gear may be done for fuel savings. I may be wrong about that. You would think that it would be the other way around since the RPMs are held up higher with it locked. Here's why I think that it might be the case:

I could very well be wrong....I probably am....but the torque converter locking up in those gears would allow the same effect to happen on an automatic transmission, thus saving fuel.

What do you think about that theory?

Oldnavy, you are a resident expert. Could this be the case on our Jeeps also?

No, when the converter locks it DROPS the RPMs. That's why my CRD will turn less RPMs at 59 than it will at 55. That's why you will get better fuel economy at 60 than you will at 55 in these things. they are odd creatures...

jeep06 · **Posted:** Fri May 19, 2006 4:21 pm

Mine always locks up at 64 mph, then if I let off the gas it will run at 1700rpm's at 60. If I baby it, the TC will stay locked up on level ground, but if you tweak the throttle, it un-locks the TC and runs about 1900rpm's at 60. Mine jerks too after hard acceleration, and then running at 55-60 mph. I wonder if it also has something to do with this butterfly on the intake horn? Who knows, more marvals that DCX has thrown on a good engine.......Cummins included). Just my $.02.

oldnavy · **Posted:** Fri May 19, 2006 5:07 pm

DZL_LOU wrote:

oldnavy wrote:

My guess is like the VW's when you let off the power fuel flow was cut to idle flow amount or about .4 liter per hour, best I remember it never completely stopped fueling the engine in the automatic cars or the sticks either. That would not make sense unless it was working with an electric motor for aux power like a hybrid. By nature without the likes of a Jake-brake diesels do not compression slow like a gasser, because in a diesel the fuel pump is in reality the throttle and is turned by engine RPM. It is more complicated then that but that gives you the idea, and there is electronic controls to vary the timing of the pump.

Let's take your hypothesis a bit further. If the fuel pump flow rate is controlled by the engine RPM, then is it possible that the jerking engine experience noticed after heavy acceleration is due to the fuel pump changing the flow rate from an acceleration flow rate to and idle flow rate?

Well I tuned the ScanGage for the CRD and went for test run, 66 mph was 1972 RPM's and the MPG's were showing 34.4 MPG on level ground. Not sure of just how accurate that is, but it's probably within +/- 2% as avertized. The one thing I was looking to check was what it would show for mininum GPH of fuel flow when suddenly letting off throttle. What it would show is if you eased off the throttle it would drop to 0.1 GPH sometimes 0.2 GPH, if sudden let let off fuel it would go to 0.0 GPH for a short period then come back to 0.1 or o.2 GPH. So even taking in possible gage error it appears to me fuel is not shut off when coasting, that very well may have caused the bucking some reported when letting off the throttle when fuel was shut off completely and then engine might try to restart when a small shot amount was injected then fuel shut off again all this in rapid sucession.

bhysjulien · **Posted:** Fri May 19, 2006 5:52 pm

Let's take your hypothesis a bit further. If the fuel pump flow rate is controlled by the engine RPM, then is it possible that the jerking engine experience noticed after heavy acceleration is due to the fuel pump changing the flow rate from an acceleration flow rate to and idle flow rate?[/quote]

An interesting hypothesis. My experience in my 06 has been this:

Accelerate in overdrive to around 70 and back off, I can feel a slight surging around 65. It doesn't feel like the transmission is slipping or hunting, it feels like the engine is surging due it fuel management issues. It doesn't do this all of the time

With the OD off I acclerate to 50 and back off, at 45-46 there is noticeable surging that will continue until I either back off the throttle until it stops or accelerate slightly. By slightly I'm talking 2-3 mph, if I back off after the acceleration there isn't any surging. I can make the Libby do this on command.

I've had automatics let go on me in the past so I know what that feels like. This doesn't feel like that to me. Anyone else had this experience in 4th gear?

oldnavy · **Posted:** Fri May 19, 2006 6:43 pm

I forgot to mention that stopped in drive at idle the fluel flow rate was 0.7 GPH and when shifted to neutral or park the rate dropped to 0.4 gal per hour. That was the same as the '02 Jetta 1.9L TDI, and this engine has a liter on the VW engine, kind of makes me wonder.

IndyCRD · **Posted:** Fri May 19, 2006 6:59 pm

LibertyCRD wrote:

IndyCRD wrote:

usmcdoc14 wrote:

Here's a theory....

I'm thinking that part of the reason that the torque converter locks in at 4th and 5th gear may be done for fuel savings. I may be wrong about that. You would think that it would be the other way around since the RPMs are held up higher with it locked. Here's why I think that it might be the case:

I could very well be wrong....I probably am....but the torque converter locking up in those gears would allow the same effect to happen on an automatic transmission, thus saving fuel.

What do you think about that theory?

Oldnavy, you are a resident expert. Could this be the case on our Jeeps also?

No, when the converter locks it DROPS the RPMs. That's why my CRD will turn less RPMs at 59 than it will at 55. That's why you will get better fuel economy at 60 than you will at 55 in these things. they are odd creatures...

Sorry....I wasn't clear.

What I meant was that when the converter is locked, the RPMs are held up higher when you let off the accel pedal and coast. When the transmission is below 4th gear and the converter is not locked, the RPMs want to fall near idle when you let off the pedal and coast.

That probably wasn't any more clear. Sorry.

retmil46 · **Posted:** Sat May 20, 2006 1:48 am

LibertyCRD wrote:

IndyCRD wrote:

usmcdoc14 wrote:

Here's a theory....

I'm thinking that part of the reason that the torque converter locks in at 4th and 5th gear may be done for fuel savings. I may be wrong about that. You would think that it would be the other way around since the RPMs are held up higher with it locked. Here's why I think that it might be the case:

I could very well be wrong....I probably am....but the torque converter locking up in those gears would allow the same effect to happen on an automatic transmission, thus saving fuel.

What do you think about that theory?

Oldnavy, you are a resident expert. Could this be the case on our Jeeps also?

No, when the converter locks it DROPS the RPMs. That's why my CRD will turn less RPMs at 59 than it will at 55. That's why you will get better fuel economy at 60 than you will at 55 in these things. they are odd creatures...

That's only part of the reason for better fuel economy. A direct mechanical linkage (ie, clutch/manual tranny, locked up torque converter) is more efficient than a viscous coupling (standard torque converter/auto tranny). You have less power loss between the engine and the wheels.

BLake · **Posted:** Sat May 20, 2006 1:01 pm

Oldnavy,
When you talk about scangage, are you talking about this one http://www.scangauge.com/ ? They say that fuel functions don't work on the CRD. Just wondering if they really do.

oldnavy · **Posted:** Sat May 20, 2006 1:27 pm

Their fuel functions have always worked on mine, and on the Jetta. I did have a problem with one of the fuel fiunctions, but it was when shifting between the functions in the Trip Computer mode. Had same problem with it in my Magnum, but the unit was worth the money for the gages. In gage mode it works fine with MPG's & GPH, never had a problem that way and it checked with VAG-COM on the VW.

Torque converter lock-up question

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