TD5 engine over-run on gear changes

[Cloughy]

Guys, would appreciate an help you can offer!
When accelerating and changing gears, the engine runs on for 2 to 3 seconds before revs drop. Thought originally that the potentiometer was at fault, repaced it to no avail.
Motor still runs on.
EGR removed, DPF/Cat removed, no other mods yet.
Does any one have any ideas as no faults or codes show on the Nanocom.

Cloughy:confused:

[sierrafery]

You should have asked before spending money on a TPS cos it's most probably the clutch switch(MSK500020), if the D2 is facelift it's screwed into the bottom of the master cylinder if not it's on the fluid line near the fusebox(like in the attachment)... if you move with talent and keep the pedal depressed while you swap it you may escape without bleeding

[towe0609]

Same symptoms if you use an auto ECU in a manual (MSB ECUs that is)

[sierrafery]

Same symptoms if you use an auto ECU in a manual (MSB ECUs that is)
Guess why ;)

...cos the auto ECU doesnt have the hardware for the clutch switch input:cool:

[towe0609]

Guess why ;)

...cos the auto ECU doesnt have the hardware for the clutch switch input:cool:

Yes, exactly.

[gazk]

Another way to check the clutch switch (assuming you have a manual transmission Engine ECU) is to set the cruise control then press the clutch - the cruise control should disengage.

[Cloughy]

Took Disco for a drive today and tried Gazk's test - cruise on and set, depress clutch and guess what ....... cruise disengaged instantly, but engine still ran on for a second or two. Does this suggest the clutch switch is functional and is not the cause of my woes? The vehicle has very k's (140k) so one would think not mechanical, but then again it is 14 years old and age can be as telling as Kms on vacuum lines etc. Should I change the clutch switch or look elswhere?
Any advice would be appreciated.
Cloughy

[sierrafery]

Just confirm are you 100% certain you didnt touch the throttle or brake by reflex at that very moment?...cos if you are then the switch seems to be ruled out, make one test more to be 100% positive with it, unplug it and make a test drive then if still the same bridge the pins in the plug and see then(leave cruise controll alone during these tests) if no change the switch is OK and then it's above my imagination what can be the culprit.

[Cloughy]

Thanks for your post Sierrafery,
Tested clutch switch disconnected - still have over run.
Tested Clutch switch bridged - no over run.
Found oil is connection, suspect switch is starting to weep, which may be the reason cruise disconnection is still operational - voltage may be enough to disconnect cruise, but not enough to cut fuel. New switch is on its way and will go in when it arrives - Thanks for your help.
That is what makes this forum so great - knowledge from those that have gone before us!

Cloughy

[sierrafery]

It's good to know how this thing worked for you cos it's really odd how it disables CC but not good enough for the surge damping and even if i had a suspicion it will be that way i had less hope it can be like that but that's another lesson for all of us to not quit after a first test of something electric as long as it's not 100% certain.... let's hope the new switch will be the cure, update please cos that's really interesting

[Cloughy]

New switch should be here early next week , will let you know how it goes.
PS... have been driving daily with the switch unpluged and the contacts bridged on the plug - all is as normal (without CC obviously).

[sierrafery]

Logically it should be a bit underfuelled this way

[Cloughy]

You are 100% right, down on power a little, but if you take it easy you dont really notice it. Just a short trip to work on the few days i go! We will see the difference next week!
That is if the clutch switch ever turns up, cheap prices in the UK, but don't be in a hurry for delivery (well not with this supplier anyway - no names mentioned)!
Cloughy

[Cloughy]

As promised, Update on the new Clutch Switch.
Fitted it last evening and went for a drive today - all symptoms of over run on gear change gone, and Cruise works fine. Obviously a faulty switch, but still cannot understand how the old one would disconnect cruise control, but not defuel the engine for gearchanges?
Thanks for all your help guys, particularly Sierrafery!
Cloughy

[sierrafery]

:thumbsup: I'm glad it's fixed, as about the oddity with the CC i think the old swicth closed but with a certain resistance due to the oil ingress and as you said in a previous post: "voltage may be enough to disconnect cruise, but not enough to cut fuel" with the correction that it's not about voltage but about voltage drop as the switch closes to earth so the only explanation i can find is that to disengage CC for the ECU is enough a voltage drop on that circuit while to cut fuel it needs solid earth .... never mind, important is that it's working now:cool: