Defender "slow race" - TDCi vs TDi

[tact]

Gang - would be VERY interested to test empirically whether the TDCi is faster or slower than TDi at idle in low first and low reverse.

Has anyone got both vehicles? Mind doing a test? Of course having similar size tyres and no gearing mods would be a prerequisite.

Reason for asking:
- TDCi's have this feature that should be transparent to vehicle operator and it's called "idle jack"
- idle jack in TDCi simply raises idle speed from 800rpm to 1100rpm but only in low first and low reverse (and when clutch pedal is fully up)
- the reasoning from LR for this feature is that apparently the TDCi gearing in low 1&R is lower than older models, apparently deemed to low for safely driving steep descents, and so they raise engine idle to compensate.

Some TDCi owners feel the vehicle speed in low 1&R is too high, higher than older models, and I'd love to test this empirically.

Can you help?

[PAT303]

I've got both,the TDCi is slower.Mine only rev's up when anti stall kicks in,I've found it's better to let the clutch right out and let anti stall do it's thing when pulling a heavy load off idle or driving over a rough piece of ground.The Tdi stalls. Pat

[Dervish]

https://www.aulro.com/afvb/images/imported/2016/09/828.jpg

I ran the numbers, as Pat says the TDCi (dotted line) still travels a touch slower even at 1100rpm than the TDi (solid line) does at 800-850rpm. We're talking a fraction of a km/h though (TDCi at 2.65 km/h, TDi at 3.25 km/h - again, purely mathematically [on 235/85r16s]).

[tact]

https://www.aulro.com/afvb/images/imported/2016/09/828.jpg

I ran the numbers, as Pat says the TDCi (dotted line) still travels a touch slower even at 1100rpm than the TDi (solid line) does at 800-850rpm. We're talking a fraction of a km/h though (TDCi at 2.65 km/h, TDi at 3.25 km/h - again, purely mathematically [on 235/85r16s]).

Hows about the numbers for low range reverse gear? What does that look like?

[tact]

I've got both,the TDCi is slower.Mine only rev's up when anti stall kicks in,I've found it's better to let the clutch right out and let anti stall do it's thing when pulling a heavy load off idle or driving over a rough piece of ground.The Tdi stalls. Pat

Hey Pat - are you saying the TDCi moves slower than the TDi in low first and also in low reverse?

[Dervish]

TDCi reverses at 2.95 km/h (1100rpm), TDi (R380) at 3.2 km/h (850rpm).

[MrLandy]

TDCi reverses at 2.95 km/h (1100rpm), TDi (R380) at 3.2 km/h (850rpm).

Is that on the flat? ...Are you able to factor in a steep downhill descent, so that engine braking, or lack thereof, in low reverse comes into play, rather than just acceleration speed? IME the higher rpm is the issue reversing down hill in low in the Tdci compared to the 300 Tdi. .

[tact]

Is that on the flat? ...Are you able to factor in a steep downhill descent, so that engine braking, or lack thereof, in low reverse comes into play, rather than just acceleration speed? IME the higher rpm is the issue reversing down hill in low in the Tdci compared to the 300 Tdi. .

There is no shortage of compression braking available with the TDCi 2.2 engine in my experience. Where there is good traction - mine reverses slowly down the steepest inclines and doesn't start to run away at all. (On a slippy steep slope - have to use some throttle at times to keep wheels turning at a rate that approximates vehicle speed to avoid uncontrolled sliding)

I wonder if the TDCi behavior that has you worried is that other behavior I wrote up in the other thread: the one about how the TDCi takes its time to drop revs to back to idle (any gear, low or high range, on or off road).
( http://www.aulro.com/afvb/90-110-130-defender-county/228170-idle-jack-dangerous-low-range-reverse-puma-5.html#post2584061 )

This does give the impression of a lack of compression braking available in the TDCi. But what is really happening is the electrickery just takes its merry time to drop right back to idle revs. (And as described in the other thread - this is a pure GOLD asset on slippery descents in any gear)

[PAT303]

TDCi reverses at 2.95 km/h (1100rpm), TDi (R380) at 3.2 km/h (850rpm).

Mines much slower,mine doesn't do the 1100 rpm bit until it loads up and then anti stall takes over. It trundles along until it hits a rut,the rev's kick up as it goes over and then settles down again,the Tdi labours and then goes over or stalls.I find the TDCi to be excellent when towing,feet off all the peddles and just steer,the low rev's and deep gearing are light years ahead of the Jap crap. Pat

[tact]

Mines much slower,mine doesn't do the 1100 rpm bit until it loads up and then anti stall takes over. It trundles along until it hits a rut,the rev's kick up as it goes over and then settles down again,the Tdi labours and then goes over or stalls.I find the TDCi to be excellent when towing,feet off all the peddles and just steer,the low rev's and deep gearing are light years ahead of the Jap crap. Pat

That's interesting, Pat. In low first/reverse, mine ramps up to 1100 rpm a few seconds after its feet off pedals - Every time. Then it behaves as you describe with anti-stall doing its thing to keep revs at 1100 (I don't think it ever overruns 1100).

(Of course in other gears its ~800rpm, not 1100)

You have a 2.4 TDCi, right? Mine is a 2.2. I wonder if LR made some changes along the way...

[rick130]

The Tdi gearing is higher than the Tdci (unless you fit Maxi Low range gears or Ashcroft's Underdrive) The granny low in the MT82 makes a world of difference.

With 255/85's on the old Tdi the Maxi low range gears made a world of difference idling along.

Interestingly I remember Lowranger commenting that he preferred the Tdi off road to the TD5 comparing like for like, reckoned it would lug at lower revs before stalling.

[MrLandy]

I wonder if the TDCi behavior that has you worried is that other behavior I wrote up in the other thread: the one about how the TDCi takes its time to drop revs to back to idle (any gear, low or high range, on or off road).
( http://www.aulro.com/afvb/90-110-130-defender-county/228170-idle-jack-dangerous-low-range-reverse-puma-5.html#post2584061 )


Yes that's exactly what it is and that's why it's dangerous IMO. In low reverse on a steep hill there's no time to let the revs drop, because by then you're either on your way far too fast down hill or you've slammed into the rock wall or trees at the bottom. It's counter intuitive as to what low range is designed for in that situation. ...going up hill or on the flat, sure the idle jack can be useful. Downhill and especially in reverse I reckon its dangerous.

[tact]

Yes that's exactly what it is and that's why it's dangerous IMO. In low reverse on a steep hill there's no time to let the revs drop, because by then you're either on your way far too fast down hill or you've slammed into the rock wall or trees at the bottom. It's counter intuitive as to what low range is designed for in that situation. ...going up hill or on the flat, sure the idle jack can be useful. Downhill and especially in reverse I reckon its dangerous.

Ok. Gotcha. In this case there are two distinctly different situations and really you just have to know your vehicle, know the right driving techniques, know your own limits:
Situation 1. Very tight situation like manouvering a trailer in reverse on a steep driveway. To avoid the slow return to idle:
- don't touch the accelerator in the first place. In low reverse you cannot stall the engine and in such a tight place why would you touch the throttle.
- if you never quite get the clutch pedal fully up (because it's THAT tight) idle Jack won't even kick in and anti stall is your best friend.
- be aware that if you have room to let clutch right up revs will gently go up from 800 to 1100 a second or two after the pedal tops out. Know your vehicle, and know you are still moving slower than a TDi.

Situation 2. Offroad where you are on a long slippery hill in low first or reverse and basically just want to be able to keep one of the vehicle's pointy ends facing travel direction, and maybe have just enough control of the long slide as to aim off from big trees...:
- idle Jack does no harm and brings no surprises, it actually helps keep the wheels turning at a more useful speed. And the slow return to idle after any throttle you use to control the vehicle direction during the sliding descent is a pure gold asset. (I.e. Sudden! reduction in wheel speed will break what ever traction you gained with the counter-intuitive throttle action and put you more out of control again. The TDCi slow return to idle revs minimizes this driver error)

[MrLandy]

Thanks Tact good info for newbies, but I'm very aware of technique.

In my situation there was no throttle. Letting the clutch out alone, combined with gravity in reverse, raised idle. And braking had little effect whether clutch in or out. The idle jack was fighting the brakes until it subsided. Engine braking was non existent due to idle jack.

[tact]

Thanks Tact good info for newbies, but I'm very aware of technique.

In my situation there was no throttle. Letting the clutch out alone, combined with gravity in reverse, raised idle. And braking had little effect whether clutch in or out. The idle jack was fighting the brakes until it subsided. Engine braking was non existent due to idle jack.

Which brings us back to (10mths ago in the other thread:http://www.aulro.com/afvb/90-110-130-defender-county/228170-idle-jack-dangerous-low-range-reverse-puma.html#post2452525 ) :- That just doesn't happen in my vehicle. If I don't touch the throttle and let the clutch out nicely in reverse low: the vehicle begins to move very slowly (much slower than a stock TDi) at idle around 800rpm. Then a second or two later the revs gently rise to 1100rpm (vehicle speed, by all accounts, still slower than a TDi).

If yours (or any one else's) behaves differently then maybe there is a problem that needs LR to fix.

[filcar]

If yours (or any one else's) behaves differently then maybe there is a problem that needs LR to fix.


Neil
My MY12 operates exactly as you have outlined in this thread. Super slow and controlled on steep inclines with the idle jack at work both in low reverse and low 1st. The Puma motor has heaps of compression braking.

The only time I have had a serious lurch on a steep slope such as described by MrLandy is when not key starting from stationary and operator error (me) in stuffing up the brake and clutch release coordination. Gave myself a big fright but then the engine braking took over and all was well again.