setting injector pump timing by ear

[greg lousy]

Setting IP timing while running is the funnest work I've ever done on a car.

"exactly just before marbling" seemed, with my tweaking, to be kind of a maximum power setting. I think I was doing a little better mileage wise retarded a smidge more. Does this sound right?

Also, I gotta ask. What exactly is making that marbling sound?

[TylerDurden]

Also, I gotta ask. What exactly is making that marbling sound?

Diesel knock is the hi pressure event occurring before TDC.



http://enginecombustion.blogspot.com/

[surfcam]

Boy O boy a picture is a 1000 words. It looks like that poor engine is trying to go backwards.

[greg lousy]

this is the part where I pretend to be smart enough to make sense of that graph

[TylerDurden]

The linked article is thorough, but for the tl;dr folks:

The term premixed combustion refers to the rapid premixed combustion of a portion of the fuel injected during the ignition delay period. This period is indicated as b→c in Figure 2 [fig]. This portion of the fuel would have undergone atomization, evaporation, and the pre-ignition chemical reactions. It would also have mixed with air to form a fuel-rich mixture that is ready to ignite once the proper temperature (autoignition temperature) is reached. When autoignition occurs, the premixed fuel burns at a very high rate, producing high temperature and high rates of pressure rise in the combustion chamber. The rate of premixed burning is governed mainly by chemical kinetics.

The characteristic noise of the diesel engine is also associated with this premixed burn phase. It is generally accepted that the rate of pressure rise resulting from the premixed combustion is proportional to the noise intensity in diesel engines.

[Quantum-man]

Strictly speaking the graph is referring to a DI engine. IDI with swirl likely to be different.

[TylerDurden]

Maybe in flame pattern nuances....

They all go knock-knock.

[surfcam]

I wonder if it's possible for a diesel to turn over backwards like gas engines sometimes do?

[air-cooled or diesel]

usually caused by too far spark advance

[30dodgeboy]

Has anyone put a timing light on (or dial indicated their pump of) their engine after setting it to the point just short of where it sounds like marbles? Just curious what number of degrees advance it was at. I do understand that it will vary some from engine to another due to tolerances.

[TylerDurden]

Some folks attest that ~12 degrees BTDC is common for start of injection.

The piezo-pickups for timing lights are available on Amazon or ebay.

[30dodgeboy]

Thanks again TylerDurden!

I set mine to 0.95mm and then put a light on it. The dial was at 10 degrees when the marks lined up. It also proved my suspicion - the timing advance is not operating when I revved the engine. That is another job for when I get some time, besides a compression check and flywheel TDC mark verification while I have the injectors out.

Are the TDC marks on the flywheel typically pretty accurate? Just wondering, but I will set the timing by ear next opportunity I have.

[Quantum-man]

Dodgeball,
It could be that at idle the pump is already fully advanced, especially if you have raised internal pump pressure, and advance spring is weak through age. Try pulling advance lever with engine off and compare it's stiffness with pulling at idle
Ooops make that Dodgeboy

[30dodgeboy]

Thanks for the reply Q-man. I did not have time to measure the pump pressure yet, but I am willing to bet it is low. I know for certain that the cold start handle pulls out the same whether the engine is running or not.

[Quantum-man]

Thanks for the reply Q-man. I did not have time to measure the pump pressure yet, but I am willing to bet it is low. I know for certain that the cold start handle pulls out the same whether the engine is running or not.

Is it harder to pull than to push back in?