Lumpy tickover

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

Post Reply
bernie
Posts: 882
Joined: 10 Apr 2001, 02:25
Location: Southampton United Kingdom
My Cars:

Lumpy tickover

Post by bernie »

My 1992 BX turbo diesel has a very lumpy tickover.
It runs very well whilst driving.
Is there an ajustment on the roto pump just for tickover to weaken the mixture as in a petrol engine?
Bernie
User avatar
AndersDK
Posts: 6060
Joined: 21 Feb 2003, 04:56
Location: Denmark
My Cars:
x 1

Post by AndersDK »

There is no "choke" on a diesel for idle mix.
Instead you have the coldstart device which slightly offsets the injection timing at cold idle. This is the rather clumpsy cylindric device in thermostat housing with a bowden cable connecting to the roto pump.
With cold engine this cable attachment is adjusted against endstop. You can then mark up (white paint) the inner cable exactly where it protrudes - to check it moves out at warm engine - thus moving/releasing the lever it attaches to.
The ferrule is used for fine adjusting the tension on cable at cold.
If it does not move (some 6mm) - the device needs replacement - a common wear problem.
bernie
Posts: 882
Joined: 10 Apr 2001, 02:25
Location: Southampton United Kingdom
My Cars:

Post by bernie »

Sorry Anders I should have said the problem is when the engine is hot.
I have adjusted the cold start cable to give slack when hot.
jeremy
Posts: 3959
Joined: 20 Oct 2002, 16:00
Location: Hampshire, UK
My Cars:
x 2

Post by jeremy »

The principal of the diesel engine is that fuel burns in excess air - which means that the power output of the engine (and hence its speed) is simply controlled by the amount of fuel injected - so there is no throttle valve as found in a petrol engine and no mixture to adjust.
On the assumption that the engine is not idling too slowly and is otherwise healthy and not smoking excessively I wonder if you have an air leak in the fuel system.
Jeremy
DLM
Posts: 524
Joined: 13 Aug 2001, 03:01
Location: United Kingdom
My Cars:

Post by DLM »

Does the BX have the newer or older fuel supply + filter setup?
Older = push-button filter on l/h side
Newer = Priming bulb on l/h side, filter on top of thermostat housing
I've had problems with the newer setup - leaking filter + occasional fuel starvation as a result. Also - are the metal fuel lines under
the car in good order? These tend to corrode and can let in air.
User avatar
AndersDK
Posts: 6060
Joined: 21 Feb 2003, 04:56
Location: Denmark
My Cars:
x 1

Post by AndersDK »

Bernie -
The coldstart cable MUST be adjusted when cold - such the cable is exactly tight. Otherwise the hot idle timing is wrong.
Another common problem is simply too slow hot idle - which is adjusted on the throttle end stop.
Hot idle to be 750-800rpm
Cold idle to be 900-1000rpm
- for both n/a & turbo.
Donno if your '92 engine still has the old generation Citroen diagnostic test connector - with a TDC magnetic sensor at flywheel.
If this is fitted - you can tap the rpm from this sensor.
bernie
Posts: 882
Joined: 10 Apr 2001, 02:25
Location: Southampton United Kingdom
My Cars:

Post by bernie »

Thanks for your replies.
If there was an air leak and I presume air bubbles in the fuel would it cause the lumpy tickover?
When I say lumpy, it ticks over very steady and rythmicly but laboured as if over rich and shakes the car. The engine mounts are good.
At present I have adjusted the cold start with plenty of slack when hot so it is not interferring with the hot running.
I have the tickover at approx 850 rpm.
As I said before the engine preforms well above tickover, very smooth and quiet.
Dave Burns
Posts: 1915
Joined: 14 May 2001, 05:30
Location: United Kingdom
My Cars:
x 2

Post by Dave Burns »

Either uneven fuel injection or a dodgy valve or tight clearance.
Injectors where the springs have gone a tad weak will open earlier and send it out a wack, plus some could have poor spray patterns causing cylinders to be a bit lame at low speed.
Dave
bernie
Posts: 882
Joined: 10 Apr 2001, 02:25
Location: Southampton United Kingdom
My Cars:

Post by bernie »

Thanks Dave I'll check for air leaks.
The injectors are new.
DLM I've the older button push on filter
Bernie
DLM
Posts: 524
Joined: 13 Aug 2001, 03:01
Location: United Kingdom
My Cars:

Post by DLM »

Hi Bernie - was just asking from my own personal experience as I've only had fuel/air problems on the newer type of BX feed/filter. I guess it can't be that bad as it was fitted to all Xantias..
Also thinking about it, when I've had problems it's only been cold start + tickover - not hot tickover.
Post Reply