knocking diesel engine

[simdel1]

Another possibility...

If the lower engine mounting has become excessively worn, it could be alowing the exhaust to hit the car causing a knocking noise. Some CDT owners have reported a 'death rattle' when switching the engine off which has been cured by replacing the lower engine mount.

[COLVERT]

Originally Posted by Roverron

DON'T AGREE.

So the injectors aren't working any harder - well they're opening alot more often, and experiencing higher fuel pressure the higher the rpm and torque demand. That suggests they are indeed under more stress.....

You've missed the point anyway so I won't be taking you advice - your'e fired.

The whole point of thrashing the engine is to get as much cleaner through the injectors as vigorously as possible to clean them. Some owners have had a result by filling the fuel filter with neat cleaner.

A leak back test is no use if its just partially clogged nozzles.

He hasn't mentioned starting issues so I've no reason to blame leak back, though it can affect the idle, but not knocking noise which is due to dribbling.
(if not maf related).

If it was me, I'd send the injectors to lynxdiesels.com for complete overhaul.

Ron

Ron. Sir. Touches forelock deferentially.

Can I talk about your first sentence as a point of discussion and not an argument, please ??

I mentioned 3,000rpm in my post. Whether your foot is flat on the throttle wizzing down the road or you are stationary surely the injectors will only open the number of times necessary for those revs ???
The fuel pressure from the HP pump has a maximum governed by the pressure release valve. Without this valve the pressure could vary and allow different quantities of fuel through even though the electrical pulse supplied by the ECU remained of a constant width !!
The increase in fuel supplied is directly due to the length of time the injector remains open and has little to do with engine ( ie. 3,000rpm ) speed or fuel pressure.( Which needs to remain constant. )

Colvert.

Please, can I have my job back now, pretty please ?????????



Oh ! and a bit more grovelling. Lol.

[COLVERT]

From my first post about a leakback test. If one of the injectors has suffered more wear than the other three then on tickover it could be slightly underfueling one cylinder and giving a mildly erratic tick over.

Colvert.
Maybe !!

[Gate Keeper]

Thanks for getting back to me in the thread Ron. I will print this off to revisit and study your suggestions. On checking the sensor it appeared to be intact after using the air can. I had seen on another post how fragile it is. Clearly I need to do some more research again on my sensor before putting in an order for the correct number to see if it is an 029 or not. The car is up to 103K now, so maybe it would be prudent to have the injectors serviced as well.

[wuzerk]

My CDT was vibrating throughout the car on tickover and it was not the lower engine mount, so I followed all the advice and sent the injectors to Lynx Diesels. They told me that one of them was only producing a dribble at tickover pressures so I had the set rebuilt and balanced. Since then the engine still vibrates at tickover and now it knocks very loudly at low revs too! Now that was a disappointment! But, if I disconnect each injector in turn at tickover the resultant shuddering is exactly the same.

[COLVERT]

Originally Posted by wuzerk

My CDT was vibrating throughout the car on tickover and it was not the lower engine mount, so I followed all the advice and sent the injectors to Lynx Diesels. They told me that one of them was only producing a dribble at tickover pressures so I had the set rebuilt and balanced. Since then the engine still vibrates at tickover and now it knocks very loudly at low revs too! Now that was a disappointment! But, if I disconnect each injector in turn at tickover the resultant shuddering is exactly the same.

The weight on the crankshaft pulley is bonded on. Has this started to become loose and out of balance ???



Colvert.

[Roverron]

Originally Posted by COLVERT

Ron. Sir. Touches forelock deferentially.

Can I talk about your first sentence as a point of discussion and not an argument, please ??

I mentioned 3,000rpm in my post. Whether your foot is flat on the throttle wizzing down the road or you are stationary surely the injectors will only open the number of times necessary for those revs ???
The fuel pressure from the HP pump has a maximum governed by the pressure release valve. Without this valve the pressure could vary and allow different quantities of fuel through even though the electrical pulse supplied by the ECU remained of a constant width !!
The increase in fuel supplied is directly due to the length of time the injector remains open and has little to do with engine ( ie. 3,000rpm ) speed or fuel pressure.( Which needs to remain constant. )

Colvert.

Please, can I have my job back now, pretty please ?????????



Oh ! and a bit more grovelling. Lol.

You are still wrong!

The fuel pressure does NOT remain constant - believe me I logged it 5years ago when developing the Synergy. It increases with rpm even on full throttle and levels out only at around 3000rpm.

Also, the injectors do not open just enough to maintain the rpm, they open at the start of every cylinders power stroke - so more rpm = more injection pulses, the duration depending upon throttle position ie driver demand.

When I said 'thrashing' I meant it - ie full throttle through the gears so both fuel pressure, number of injections per minute and injector opening time are maximised to flow as much fuel and hence cleaner as possible.

Its pretty obvious that when you drive a car harder and faster it uses more fuel, so more must be flowing through the injectors, which is the aim.

Now get the idea??
Ron

[Roverron]

Originally Posted by wuzerk

if I disconnect each injector in turn at tickover the resultant shuddering is exactly the same.

That would tend to point to another component - in order of cost and probability.

Crank pulley

engine mounts

dual mass flywheel

Also be worth checking the exhaust flexipipe and exhaust mountings.

Ron

[COLVERT]

Originally Posted by Roverron

You are still wrong!

The fuel pressure does NOT remain constant - believe me I logged it 5years ago when developing the Synergy. It increases with rpm even on full throttle and levels out only at around 3000rpm.

Also, the injectors do not open just enough to maintain the rpm, they open at the start of every cylinders power stroke - so more rpm = more injection pulses, the duration depending upon throttle position ie driver demand.

When I said 'thrashing' I meant it - ie full throttle through the gears so both fuel pressure, number of injections per minute and injector opening time are maximised to flow as much fuel and hence cleaner as possible.

Its pretty obvious that when you drive a car harder and faster it uses more fuel, so more must be flowing through the injectors, which is the aim.

Now get the idea??
Ron

Thanks for your reply Ron. The first paragraph I find interesting. I guess the ECU must compensate for variable pressure up to around 3,000 rpm by holding the injectors open that fraction longer .

The rest of post what I was trying to say but in a different way to you.

Thanks again. Colvert.

[wuzerk]

Thanks Ron, that's what I thought re equal effect on disconnecting each injector in turn. Mine is an Auto so the dual mass flywheel is off the list.
I have checked engine mounts and replaced bottom one. The Crank pulley
sounds likely. The knocking disappears once the revs reach about 1800 so I was leaning towards a duff hydraulic tappet, would a duff pulley act the same?