D24TIC Timing in degrees

[tfb]

I have picked up a 2nd hand diesel timing light. It works by fitting a transducer around the pipe to No.1 injector and the transducer picks up the slight swell/shockwave/whatever as fuel is pumped to the injector.
Now, I can find lots of info on setting the timing on the pump with a dial guage, but none that gives me the timing in degrees BTDC, any one know what it should be?

Regards
TFB

[Paul Clifton]

In theory diesel engine timing reading will be 0deg but in practice is controlled by the injection pump on older systems and ECU 's on the more modern systems and depending on the system can be governed by a number of sensors. Therefore i'm afraid that your 'timing light' will not be much use on a modern diesel as the timing will be whatever the system deems it necessary to be at that time and conditions.

Paul.

[tfb]

ECU??? what's one of those? . The only electrical signal my engine needs(once it's running) is the voltage to hold open the fuel supply valve on the pump!.

There must be a value for the advance when the engine is idling and I can't see why I could not adjust the advance buy rotating the pump while the engine is running and lighting up the timing marks, or am I missing something fundamental?

To me, at least, it seems that setting the timing with a dial guage is akin to setting the static timing on an old petrol engine by twisting the dizzy until the points begin to open. I would have thought a timing light would have been far more accurate as it is on a petrol engine. Then again, if I had a dial indicator and not a timing light I may think the opposite

Regards
TFB

[outnumbered]

Originally Posted by tfb

ECU??? what's one of those? . The only electrical signal my engine needs(once it's running) is the voltage to hold open the fuel supply valve on the pump!.

There must be a value for the advance when the engine is idling and I can't see why I could not adjust the advance buy rotating the pump while the engine is running and lighting up the timing marks, or am I missing something fundamental?

To me, at least, it seems that setting the timing with a dial guage is akin to setting the static timing on an old petrol engine by twisting the dizzy until the points begin to open. I would have thought a timing light would have been far more accurate as it is on a petrol engine. Then again, if I had a dial indicator and not a timing light I may think the opposite

Regards
TFB

lol
mike

[Paul Clifton]

TFB. At the moment I cannot think of any diesel pump that you can adjust with engine running and I have not seen any figures for timing diesels this way.
Common rail diesels are all electronic, ecu controlled with solenoid operated injectors.

Paul.

[outnumbered]

Originally Posted by pc654

TFB. At the moment I cannot think of any diesel pump that you can adjust with engine running and I have not seen any figures for timing diesels this way.
Common rail diesels are all electronic, ecu controlled with solenoid operated injectors.

Paul.

hi paul
i adjust the pump timing with the engine running whilst hooked up to the vol fcr program, this enables me to get it withing the parameters.
mike
850 tdi

[tfb]

Originally Posted by pc654

TFB. At the moment I cannot think of any diesel pump that you can adjust with engine running and I have not seen any figures for timing diesels this way.
Common rail diesels are all electronic, ecu controlled with solenoid operated injectors.

Paul.

Hmm...unsure why you mention Common rail, ecu's etc. as they are not applicable to a D24T. I can see the timing light would not even be able to trigger from a common rail system.

However, the timing must have a static advance of n degrees and the management system (or in my case some spinning weights, I imagine) will alter this value depending upon the conditions and demands placed upon the engine. The static advance is usually very similar to the dynamic advance at idle, perhaps a few degrees difference.

I can't see the base value being 0degrees as this would allow no time for the fuel to burn, which however quick does take a measureable amount of time, before the piston travels downward. As I understand it, the optimum time for ingnition or injection is a few degrees before TDC, so that the fuel is completely burnt/burning at TDC, thus generating the maximum amount of pressure inside the cylinder.

I found some info in an Autodata book that gives the value of 14 degrees @750rpm for n. This does seem quite advanced (I am used to petrol engines at about 6-10 degrees), but if it stops raining tomorrow I'll have go and see what the timing is currently set to and then try advancing/retarding it to 14 degrees and see what difference it makes to the car. It would be nice to get rid of the clouds of smoke I sometimes leave behind me, although it is VERY useful if I am being tailgated on the motorway

I'll try and scribe some lines on the pump housing and bracket before altering anything, just in case it all goes wrong!

Regards
TFB

[Mapleleafer]

Ooooh, bad idea!

If you review the correct procedure, you'll note that timing is adjusted by loosening the camshaft sprocket with cam positioned at TDC by a locking plate and then positioning the pump sprocket to the position that causes a specified lift of the pump, and then locking the cam sprocket in place. It is NOT performed by rotating the pump body.

Unlike the short duration of a spark event, diesel fuel is injected over a period of time - starting prior to TDC and continuing after ignition has commenced. Also significantly different is that as engine speed rises and injection begin point is advanced, the end point is simultaneously delayed. This longer injection cycle results in a greater quantity of fuel per injection as engine speed rises.

For example (specs from the VW 1.6L/Audi 2.0L NA version of the same engine, plunger set to 0.6MM at TDC);
At 1000 RPM injection starts at 5° BTDC and ends at 13° ATDC. Injection event is approx. 18° rotation.
At 2000 RPM injection starts at 7.5° BTDC and ends at 20° ATDC. Injection event is approx. 28° rotation.
At 3000 RPM injection starts at 11.5° BTDC and ends at 23° ATDC. Injection event is approx. 34° rotation.
At 4000 RPM injection starts at 13° BTDC and ends at 27° ATDC. Injection event is approx. 40° rotation.

Your timing light senses the noise created by the sudden pressure rise in the injector pipe but there is no telling exactly what point in the injection stroke is actually triggering the light. Trust in the concept that the engineers at VW and Bosch might have known exactly what they were doing. The dial indicator is a tried-and-true method of setting the VE injection pump.

[tfb]

Thanks for some good info and an explanation, much appreciated. It was interesting to hear about the duration expanding that much with engine speed.

I will take issue on one point though. Re-reading the Volvo manual it does tell you to "slacken pump mounting bolts and turn pump inwards to obtain correct value", if the reading is low and outwards if the reading is high. I would guess that there are too many variables for the timing to be spot on by just locking off the cam and the pump sprockets.

Looking out of the window, I don't think I'll get a chance to try anything today. I am interested in seeing if the timing light does trigger on a consistent part of the injection cycle. If is a consistent trigger, then the timing marks should appear to be static under the strobe, if it is inconsistent then the timing marks should appear to bounce and jitter all over the place. I'll try attaching the transducer to various parts of the pipe to No1 injector and see if that also makes a difference.

I have no doubt that the Bosch engineers know far more than I do, but I doubt that they enjoy experimenting as much as I do!. And yes, I am fully prepared for it to all go hideously wrong and end in tears (as it so often does!).

Regards
TFB

[tfb]

Well, the skies have cleared for half an hour. So I've been out and tried making a measurement.

I cleaned up the flywheel with a little toothbrush sized wire brush and highlighted the zero mark with some paint from the daughter's "Paint with Barbie" kit although tippex would have worked better.

The strobe was lighting up the timing mark in a very consistent manner (as Mapleleafer said I don't know what part of the injection cycle was triggering it). I tried putting the piezo-electric transducer on various parts of the pipe and using various torque's to clamp it with and the reading remained consistent.

Using the offset function of the light, the timing was reading at 15.2 degrees with the rpm at 780, which is similar to the value in the Autodata book.
I will try and get hold of proper dial indicator and fitting(I do have a standard dial indicator, but I couldn't mount it in a suitable way) and verify the readings. Though the ideal way to verify things would be to set the timing using a dial indicator on several cars and then make readings with the light and see if they matched. The likelihood of getting a few D24T's together to do this is remote though.

Regards
TFB