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Clutch & low gear cruising.
B0bbyEwing
Forumite 758 Posts
in Motoring
1) Cruising may be the wrong term but it's not the term used isn't the key point here & I'm sure by the end of the post people will know what I mean anyway.
2) <blah> "You should drive to the conditions of the road & be in the appropriate gear for those conditions and the speed you're doing" </blah>. Yes but be that as it may, it doesn't answer my question...
Ok so I'm wondering why my current car will judder like mad & then cut out if I take my feet off all pedals & just cruise, coast, whatever you wish to call it. I've never had it happen before with anything I've driven.
All other vehicles - take your foot off the clutch & it goes, forwards. Don't touch the accelerator and the car will just keep going forwards. You could be first gear, second gear, doesn't matter, it just goes forwards.
This car - a Mondeo diesel, it forces you to shift down else it will judder-judder & then cut out. In fact, i'm pretty sure it also does it in 1st gear so it forces you to dip the clutch and stop. Literally NO other vehicle I've driven does that so as this one is the oddball, I'm simply wondering why it's the case purely out of curiosity, nothing else.
* Little 1ltr petrols
* 2ltr petrols
* Sporty cars like R32s, Focus STs, Civic Type Rs
* Non turbo diesel cars, turbo diesel cars
* Transit vans, combo vans, Sprinter vans, Iveco vans
* 7.5ton DAFs, Iveco's
* 18ton DAFs, Ivecos
* Artic 44ton DAFs, Iveco's, Volvo's, with & without trailers.
* Manuals, Automatics
I've driven the lot. Some of those (the 7.5s upwards) were only on private land so I wasn't in the highest gears but this question isn't about getting speed up.
Literally did not happen with any of those at all. Only my current vehicle.
Just wondered why. @Goudy I know you had one, did you experience this?
2) <blah> "You should drive to the conditions of the road & be in the appropriate gear for those conditions and the speed you're doing" </blah>. Yes but be that as it may, it doesn't answer my question...
Ok so I'm wondering why my current car will judder like mad & then cut out if I take my feet off all pedals & just cruise, coast, whatever you wish to call it. I've never had it happen before with anything I've driven.
All other vehicles - take your foot off the clutch & it goes, forwards. Don't touch the accelerator and the car will just keep going forwards. You could be first gear, second gear, doesn't matter, it just goes forwards.
This car - a Mondeo diesel, it forces you to shift down else it will judder-judder & then cut out. In fact, i'm pretty sure it also does it in 1st gear so it forces you to dip the clutch and stop. Literally NO other vehicle I've driven does that so as this one is the oddball, I'm simply wondering why it's the case purely out of curiosity, nothing else.
* Little 1ltr petrols
* 2ltr petrols
* Sporty cars like R32s, Focus STs, Civic Type Rs
* Non turbo diesel cars, turbo diesel cars
* Transit vans, combo vans, Sprinter vans, Iveco vans
* 7.5ton DAFs, Iveco's
* 18ton DAFs, Ivecos
* Artic 44ton DAFs, Iveco's, Volvo's, with & without trailers.
* Manuals, Automatics
I've driven the lot. Some of those (the 7.5s upwards) were only on private land so I wasn't in the highest gears but this question isn't about getting speed up.
Literally did not happen with any of those at all. Only my current vehicle.
Just wondered why. @Goudy I know you had one, did you experience this?
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Cruising is just lifting off the accelerator entirely, but with the car still in gear.
It happens all the time in low gears for me. For example, there's some sets of lights around here where you can generally judge when they're going to switch to green. What I've done in the past is knock it down to 2nd & just basically keep rolling very slowly rather than driving to the lights & hitting the brakes, then setting off again.
Absolutely can't do that with this car. If I knock it to 2nd and roll, it'll start juddering so I then have to either knock it to 1st or stop. If I knock it to 1st and roll, eventually when the speed is low enough it will again judder then cut out so I have to then either put my foot down reading to pick up (not what I'm wanting when the lights are on red) or dip the clutch.
I found it hard to believe that it was some kind of design issue on this one car as in that's just the way this car is supposed to be based purely on the number of different vehicles I've driven and not a single one had this.
Another thing I've noticed with this car, which is probably a separate thing & probably just me, is I've never stalled a car so much in my life, even after owning it a couple years. I've stalled this car more times in a 6 month period than I have done in the 10+ years I owned my last car. Setting off from lights (or just a standstill) can be a nightmare at times. Got to the stage where I just stick plenty revs on which I know isn't a great thing but there we are.
A bit pointless getting rid of it now because it works, but when the day comes when it no longer works & needs to go to car-heaven, I'll certainly not be sad to see this one go.
There is no "throttle" (valve in the airway into the engine) as such, air just get sucked/blown into the engine and the pedel is connected to the injectors which adds fuel.
I think the term "on the over run" is better than cruise or coast.
This when you take your foot off the throttle pedal and the vehicle decelerates, in gear. Engine braking might be another term.
You use the wheels to spin the crankshaft and the pumping of the engine slows you down, a little or a lot depending on gear and road speed.
Modern cars will inject little or no fuel when it's in this over run state, it's only when you dip the clutch as you get too slow that the fuel starts to be injected again.
So this process is speed and gear related.
Try it in a high gear at a slow speed and the car will judder and perhaps stall as the turning wheels can't spin the crank fast enough to keep the engine running.
Try in at high speed in a low gear and gearbox will likely crunch and the rpm will redline or more, none of this is good for the engine or gearbox.
Nearly every car these days will increase their own rpm if you lift the clutch from a standstill in first gear, this aids a smooth get away.
It's not by much, but it is usually enough to get you actually moving without any throttle pedal input.
Older cars didn't do this or not as much, depending on age.
A worn clutch can cause a problem with this creeping, there's just not the meat on the clutch plate which tends to either slip or cause it to act a like a switch and the cars weight and rolling resistence over comes the cars engine, so it stalls.
If you have a worn clutch you usually need to work the engine and clutch pedal carefully to get it to pull away.
Again, your car being a diesel this stalling on the over run is a bit odd if you aren't flogging it in too high a gear.
There could be many reasons for this but would suspect the EGR valve first.
This over running is bad for emissions, NOx tends to be more more prolific when the engine pumps air without fuel, it's just too hot.
To get around this the EGR valve diverts exhaust gas back into the engine intake so it is no longer pumping air, but exhaust gases which cools this pumping process.
So now on the over run the EGR is open and if it's failing to close when you slow to idle or reaccelerate, the engine iis starved of the air it needs so stalls.
Of course there could be many other causes, but knowing the Duratorq engine, it's a good place to start.
Blowby (oily gases) from within the crankcase vent into the air intake to get burnt, this mixes with the soot from the exhaust via the EGR and the horrid gunk plays havoc with the EGR valve.
As diesels are compression ignition, they tend to suffer a lot more blowby than a petrol engine so do tend to throw out a lot of oily gas.
Depending on year and the Euro regs at the time, EGR operations may or may not be linked to the cars on board fault/diagnostic system.
I think there were at least 4 different EGR valves fitted to this engine, from the early vacuum operated one, to a special motordriven, hightech one fitted just to the autos with a couple more in between.
Cannot be good to force an engine to drive in 4th gear at tickover.
Thanks a lot for the reply Goudy.
My EGR is electronic on a 56 plate. Relative had same engine but 54 plate which was vacuum so I've seen the difference.
Also my EGR is duff and has been blanked. I've removed the blank and the car cuts out immeditaley on start so I put the blank back (bought the car already blanked).
Caprikid - if that post was to me and not anyone else who has replied, then as said, this car suffers this in low gears at low revs. Not just high gears low revs.