Diesel "clatter" at idle speed

ScottFromNZ · Post by **ScottFromNZ** » 20 Sep 2004, 02:06

Over the last few thousand miles my BX TZD Turbo seems to have more diesel "clatter" at idle and at very light loads just above idle speed, particularly when the engine is cold. I cannot pinpoint exactly when this started to happen.
I have been using a diesel fuel treatment (Morey's) in the last few tankfuls which among other things raises the cetane of the fuel by 3 to 5 points. Also In new Zealand a month or so ago they reduced the sulphur levels in our diesel. It is still high by European standards but alot lower than it was.
The diesel clatter is the only change. The engine starts and runs perfectly and is returning a consistent 50 - 51 mpg.
Could the additive or the change in sulphur level in the diesel have caused this change in noise? Should I be concerned about it and go to a diesel specialist? The car has only done 67,000 miles so hopefully the injectors are still O.K.
Is it possible that the pump timing needs adjusting slightly for the change in fuel we have had?

AndersDK · Post by **AndersDK** » 20 Sep 2004, 02:19

Try if any help in this article : Diesel coldstart device
Failing coldstart devices sneaks in on your engine over a couple of weeks, and may be the cause of a change in the engine noise scheme.

ScottFromNZ · Post by **ScottFromNZ** » 20 Sep 2004, 02:34

I have read the article about the cold start device. I think mine is working O.K. The idle speed when cold is about 1000 - 1100 rpm and as it warms up the idle speed drops to the normal 800 rpm. This is how it has been all along even before the diesel clatter got louder.
One of the supposed benefits of the Morey's fuel additive is that it "increases compression by improving piston ring sealing" In theory if this has happened could it increase cold idle noise? The engine uses no oil between changes and never any blue smoke when running.

Kowalski · Post by **Kowalski** » 20 Sep 2004, 16:21

How can a fuel additive improve piston ring sealing?
It'll get burnt just like the fuel it is dissolved in and disapear out of the exhaust valve.

bxbodger · Post by **bxbodger** » 20 Sep 2004, 16:33

The noise is most likely down to the fuel change, and if there's no change in MPG and performance I wouldn't worry about it, but are you sure its diesel clatter and not just something loose?
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Is it possible that the pump timing needs adjusting slightly for the change in fuel we have had?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Don't fiddle with the pump- it causes more problems than it cures. Its the old carburettor twiddling syndrome!!!

Robin · Post by **Robin** » 20 Sep 2004, 17:07

Scott, the increase in diesel clatter could be down to a few issues - The additive increases the cetane rating of the fuel which will burn with a more 'explosive' characteristic when cold.
The reduction in sulphur will not affect the engine but the process of removing the sulphur also increases the cetane rating.
The additive will clean the injectors and this increases the injectors ability to break up the spray into finer particles which also burn faster at cold especially with the cold start in operation and this increases the clatter.
I would suggest you cease using the additive and leave things alone,
Robin.

NiSk · Post by **NiSk** » 20 Sep 2004, 18:41

If your BX has a Bosch pump with a small shock absorber type thingy hanging on the throttle wire connection, remove it! They don't do any good and often make a clattery sound at tickover.
//NiSk

ItDontGo · Post by **ItDontGo** » 20 Sep 2004, 21:57

The claims magic potions makers make!
If it does improve piston ring sealing then I reckon you would need a pretty fantastic rolling road to be able to spot the difference.

jeremy · Post by **jeremy** » 21 Sep 2004, 12:17

Many years ago in my youth I purchased a very tired Hillman Hunter and after changing the head gasket someone kindly gave me a tin of Wynns additive which I duly used feeling that I hadn't got much to loose. In fact the difference was remarkable and I had to slow the idling down several times over the first week.
Presumably the rings were gummed up and the additive was a solvent which removed the muck and compression improved.
Mind you modern engines may be made of sterner stuff. My BX TD does not get any additives - nor seem to need any at 196,000 miles.
jeremy

john alexander · Post by **john alexander** » 22 Sep 2004, 17:18

Have read anders link to cold start device. when I got my Xantia est 98 it idled too fast , so I turned it down using the r/hand screw at the back of the pump(bosch) now after reading the link I think the cold start is not working.I only get 41 to the gal.what other effect does it have on the engine ie pulling power ,top speed etc thanks in advance ,my knowledge of diesels is limited to the obscure fact that the first compression ign eng was built by an englishman akroyd stuart who used powdered coal

jeremy · Post by **jeremy** » 22 Sep 2004, 19:19

Cols start device on the TD does exactly what it says - assists cold starting. It has no influence when the engine is warm and is there to prevent stalling and with luck reduce smoke on starting.
So if your problem is when the car is hot then its not the cold start.
the device is operated by a thermostatic device which screws into the thermostat housing and pulls a cable by about 5 mm. Follow the cable to the pump and see what happens with a cold and warm engine - the cable should extend as the engine warms - if not replace the unit (about £20.).
Jeremy

john alexander · Post by **john alexander** » 22 Sep 2004, 20:02

thanks ,but if the cable is always pulled on does it not have some effect or else why make it go off when the engine is hot.

Robin · Post by **Robin** » 22 Sep 2004, 21:14

The function of the pull off/on device is to increase the idle speed slightly when the engine is cold and if you have air con it increases the idle speed again when A/C is on to avoid stalling and keep the compressor running at a useful speed.
The increase is around 150 to 200 rpm. It is controlled by an elctro solenoid device at the rear of the engine bay. Two of these devices if you have air con. Check for split hoses and a functioning vacuum pump.
Robin

davek-uk · Post by **davek-uk** » 23 Sep 2004, 15:38

I always thought that the cold start device increased the revs by advancing the timing slightly. If that is the case then if the device has failed then the pump will stay in the cold start, advanced state all the time. Personally I never notice much difference when this happens - other than the idle speed of course. As I STILL haven't replaced my unit, I'm constantly running in 'hot' mode as I have the vacuum device fitted directly to the cold start diaphragm. I have has this set up for a nearly a year now and I had no problems starting in the cold of last winter although with the aircon working I do have to be a bit careful hill starting – the aircon really seems a drain on the engine.

jeremy · Post by **jeremy** » 23 Sep 2004, 21:55

Early Roto-Diesel pumps used the thermostatic device to open the throttle a little. TD's and ZX 1.9D use it to operate an electric switch which in turn advanced the timing. Not sure about Bosch. Without it working I found my TD tended to hunt at idle when cold.
jeremy