Diesel engine poor start/cut out - my story - now fixed

[DMGRS]

I'm pretty sure that engages Cruise on the Auto doesn't affect the state of lockup - if I sit at 70 on the motorway and engage cruise, engine load, RPM etc doesn't change in the slightest when viewing the diagnostics on the IPK.

[James.uk]

There is no logical reason why the autobox should behave differently when cruise is engaged. innit...

Surely cruise works in conjunction with the car pedals and has no direct input to the autobox. The autobox works off the pedals whether cruise is engaged or not..
...

[HarryM1BYT]

Originally Posted by James.uk

There is no logical reason why the autobox should behave differently when cruise is engaged. innit...

Surely cruise works in conjunction with the car pedals and has no direct input to the autobox. The autobox works off the pedals whether cruise is engaged or not..
...

It behaves differently because the box is bypassed completely - when you press the cruise button it uses Hyperdrive.

[madone]

Originally Posted by James.uk

There is no logical reason why the autobox should behave differently when cruise is engaged. innit...

Surely cruise works in conjunction with the car pedals and has no direct input to the autobox. The autobox works off the pedals whether cruise is engaged or not..
...

ColinW enlightened me and others a few years ago about CC on a diesel auto

http://forums.mg-rover.org/showthrea...ight=convertor

[SD1too]

Originally Posted by madone

ColinW enlightened me and others a few years ago about CC on a diesel auto ..
http://forums.mg-rover.org/showthrea...ight=convertor

Thanks for the link Graham which I asked for earlier. I have read the whole thread. Please read post no. 3 by ColinW again very carefully. You'll see that he does not agree with what you said in post no. 2:

Originally Posted by madone from '.org'

The torque convertor only kicks in when the cruise is on in 5th gear.

Colin explained to you how torque converter lock-up is engaged. As he suggests, you are confusing the terms 'torque converter' and 'lock up'. Colin also hasn't made it crystal clear that lock-up can, and does occur when cruise control is disengaged as well as when it is engaged. So unfortunately you appear to have the idea that lock-up and cruise control go together, but they don't.

Back to this forum, the confusion increased when you posted this:

Originally Posted by madone

5th in an auto does not have the torque convertor working unless cruise is on.

This is the opposite of what you said on the other forum! It seems that, despite your confidently worded posts, you still don't understand the torque converter's function and consequently what the lock-up system does. It has nothing to do with cruise control or whether the car has a diesel engine. Cruise and lock-up work in exactly the same fashion on both petrol and diesel 75s and ZTs.

I am sure that there are basic explanations of how automatic transmission works on the internet. You might like to have a look at some.

Best wishes,

Simon

[madone]

Thanks Simon for enlightening me further as I don't profess to be an expert, I only post what I think is right or what I have read.

I know Colin did not agree with me in my old post but the fact remains that when cruise is on at say 70mph the box does not lock up when under load eg going up an incline. The revs pick up by 2-300 rpm to maintain the speed where as without cruise on the engine does not increase if maintaining the speed manually.

Does a petrol version do the same????

Whilst on the topic does a petrol engine 75 with an auto box disengage when braking whilst going downhill (coasting) or does it drop a cog to assist?

The diesel coasts.

[SD1too]

To answer your points:

Originally Posted by madone

... when cruise is on at say 70mph the box does not lock up when under load eg going up an incline. The revs pick up by 2-300 rpm to maintain the speed ..

The 200 - 300 rpm change in engine speed you noticed is most likely the lock-up disengaging.

... where as without cruise on the engine does not increase if maintaining the speed manually.

You must be mistaken. If the car's road speed falls whilst ascending an incline and the driver presses on the accelerator pedal to compensate, then the engine speed must increase.

Does a petrol version do the same?

As I said in my last post, the automatic gearbox functions in the same way irrespective of the type of engine.

... does a petrol engine 75 with an auto box disengage when braking whilst going downhill (coasting) ... The diesel coasts.

We covered this misunderstanding in a lengthy thread earlier this year. The automatic gearbox never "disengages", akin to travelling in neutral using a manual gearbox. This is what "coasting" is and no automatic car does it, including your diesel 75/ZT.
When you're travelling downhill and you lift off the accelerator pedal the engine speed should fall considerably. Depending upon which gear is selected at the time by the automatic gearbox you may, or may not, experience an effect called "engine braking". If the car is in 5th gear, you won't experience it. This does not mean that the car is "coasting", it isn't. However, if you use the brakes the car's ECU is programmed to tell the automatic gearbox to change down to provide engine braking, but this will depend upon the precise driving conditions at the time. The braking effect will never be as strong as with a car with a manual gearbox (unless you manually select a much lower gear for the road speed).

Simon

[madone]

Thanks Simon just wish I still lived in Ruislip then I could show what I mean.

It does look like others have experienced what I have though http://www.the75andztclub.co.uk/foru...light=coasting

Dragrad the same here http://www.the75andztclub.co.uk/foru...oasting&page=2

More diesel owners also here http://www.the75andztclub.co.uk/foru...light=coasting

My wifes CRV petrol auto behaves differently to mine when going downhill. The box drops a gear to use engine braking.

[BaroqueMoon]

I think that simply reading the user manual, specifically in reference to the auto gearbox would be a fine place to start.

[SD1too]

Originally Posted by madone

It does look like others have experienced what I have though ..

As I have said the engine always remains connected to the driving wheels via the torque converter, even when you lift off the accelerator and the engine speed drops to near idle. If you choose to define that as "coasting" then it is.

My wifes CRV petrol auto behaves differently to mine when going downhill. The box drops a gear to use engine braking.

Yes, Mrs. SD1too's Citroën is even better. The gearbox will sequentially change down on the flat as road speed gradually reduces with my right foot off the accelerator pedal. I put it down to better executed gearbox control software, but the less powerful engine is probably a factor too.

Graham, you've pointed out the number of people with diesels commenting on this phenonemon. This might be because the later CDTi develops its maximum torque at 1,900 rpm whereas the petrol engines (excluding 1.8T) develop it considerably higher at 4,000 rpm. I suspect that the petrol ECUs might be designed to change down earlier in order to keep the engine within its useful torque band by maintaining higher revs. The diesel has less need for the lower gears due to its torque characteristics, but I imagine that they're there to standardise gearboxes across the range. My petrol SD1 V8, with its above average torque, needs only a 3 speed automatic transmission.

Simon