I have found that the idle on my 2.5TD (which was already rather high at 1000 rpm) has increased even further when I run it on veggie oil (to 1200 rpm) now that represents a fair speed at the low gear ratios this car has.
There doesn't appear to be any mechanical adjustment at all on the pump and Haynes BOL is as usual, useless - doesn't even mention adjusting idle speed on either of the electronically controlled XM diesels.
Has anyone here discovered how the idle speed is adjusted?
//NiSk
Idle adjustment on (XM) 2.5TD?
Moderator: RichardW
Nisk,
The idle adjustment is made in the programming of the ecu. You can change it if you have access to an Elit or Lexia programming tool.
However, I suspect that the setpoint stored in the ecu has not changed. Therefore the ecu thinks
either
1. the engine is turning slower than it is
or
2. the setpoint is artificially raised for some reason
1. Check your Top Dead Centre Sensor on the top of the clutch housing (impossible to get to without taking off the plastic flow and return air pipe assembly to/from the intercooler). Otherwise fish around until you find the connector plug and test it electrically. Expect around 1000 Ohms. If you need an exact figure I'll measure mine if you wish.
2. The engine will increase revs temporarily for two main reasons. Either the ecu thinks its cold or the ecu thinks the air conditining is switched on. Check the air temperature sensor mounted on the plastic assembly mentioned above. Check the water temperature sensor on the complicated casting with all the pipes on the right hand side of the cylinder head as you look at it from the front of the car. With the aid of a wiring diagram check the signal usually sent from the A/C to the engine ecu to tell it when the A/C is running. It might be stuck on. (do you have aircon?).
I'd also check all of the above measurements both at the sensor, and more importantly, at the ecu connector plug. Give me a shout if you need the pinout list.
Do you have access to a proper diagnostic tool? A test might reveal a faulty or intermittent sensor. Not all faults bring up the yellow engine management light on the dash.
Hope thats a starter for 10.
Cheers
Norrie[8D]
The idle adjustment is made in the programming of the ecu. You can change it if you have access to an Elit or Lexia programming tool.
However, I suspect that the setpoint stored in the ecu has not changed. Therefore the ecu thinks
either
1. the engine is turning slower than it is
or
2. the setpoint is artificially raised for some reason
1. Check your Top Dead Centre Sensor on the top of the clutch housing (impossible to get to without taking off the plastic flow and return air pipe assembly to/from the intercooler). Otherwise fish around until you find the connector plug and test it electrically. Expect around 1000 Ohms. If you need an exact figure I'll measure mine if you wish.
2. The engine will increase revs temporarily for two main reasons. Either the ecu thinks its cold or the ecu thinks the air conditining is switched on. Check the air temperature sensor mounted on the plastic assembly mentioned above. Check the water temperature sensor on the complicated casting with all the pipes on the right hand side of the cylinder head as you look at it from the front of the car. With the aid of a wiring diagram check the signal usually sent from the A/C to the engine ecu to tell it when the A/C is running. It might be stuck on. (do you have aircon?).
I'd also check all of the above measurements both at the sensor, and more importantly, at the ecu connector plug. Give me a shout if you need the pinout list.
Do you have access to a proper diagnostic tool? A test might reveal a faulty or intermittent sensor. Not all faults bring up the yellow engine management light on the dash.
Hope thats a starter for 10.
Cheers
Norrie[8D]
Thanks Norrie!
This will give me something to look at this weekend. The car has A/C but I do not have access to any diagnostic electronics (and I hate to have to admit that to any of the Cit workshops around here - they are generally completely useless at finding or fixing anything). A suggestion from another (Swedish) forum was that one of the temperature sensors is givinga faulty (= low temp) signal. The DK5 engine is a gigantic lump and very crowded - not easy to find all the obscure sensors that seem to be fitted to it!
The interesting thing is why the engine speed increased by 200 rpm when I switched to veggie oil (modified rapeseed oil). I might try filling the tank with city diesel and see if it goes back to the original speed again.
//NiSk
This will give me something to look at this weekend. The car has A/C but I do not have access to any diagnostic electronics (and I hate to have to admit that to any of the Cit workshops around here - they are generally completely useless at finding or fixing anything). A suggestion from another (Swedish) forum was that one of the temperature sensors is givinga faulty (= low temp) signal. The DK5 engine is a gigantic lump and very crowded - not easy to find all the obscure sensors that seem to be fitted to it!
The interesting thing is why the engine speed increased by 200 rpm when I switched to veggie oil (modified rapeseed oil). I might try filling the tank with city diesel and see if it goes back to the original speed again.
//NiSk
Just to add a twist to the story . . . I filled the tank up with city-diesel once the rapeseed oil was used up. The idle immediately returned to 750 rpm. Explain that!
I then filled up with 30 liters of rapeseed oil when the tank was empty again - idle went up to 1200 rpm! Then added 50 litres of city-diesel - idle dropped to 750 rpm again.
I'm now going to progressively add rapeseed oil until the idle rises again so I can see where the limit lies.
Still can't understand it though!
//NiSk
I then filled up with 30 liters of rapeseed oil when the tank was empty again - idle went up to 1200 rpm! Then added 50 litres of city-diesel - idle dropped to 750 rpm again.
I'm now going to progressively add rapeseed oil until the idle rises again so I can see where the limit lies.
Still can't understand it though!
//NiSk