injector timing

[acfloors]

I have been watching these forums for about a year. I have seen a lot of talk about injection timing and how changing it can help your diesel. What exactly does it do? How is it done on an electronic injector pump? Is it something someone with an average mechanics ability can do or should it be taken somewhere? I really enjoy this forum and have seen a lot of very helpful posts. I have always been a gasser mechanic and a diesel is a little different animal.
Thanks for any help.

[97GMC6.5Z71]

You'll need a scan tool to read the timing like a snap-on MT2500 or GM TechII

[DA BIG ONE]

Or, CarCode OBD-2 software to put on your own PC, or laptop it reads and can reset timing, timing offset and lots of others things and the price is cheap too....

[Hubert]

http://public.ca.sandia.gov/ecn/orifice.php Thats mostly newer generation injection events but shows some comparisons of the event.


Go to the above website and look at the time of the injection event. Then do some calculations of the time it takes the piston to move over about 4 degrees of crank rotation at different rpms to appreciate the scale of the time event.

Basics its my understanding is the "pop" of the combustion event seals the rings. The temperature rise determines the pressure rise in the cylinder (everything else the same). Too early of timing and temperature is higher and so is pressure (too much fuel along with early timing can stress headgasket and engine because the combustion chamber is actually still getting smaller ahead of center and is growing slower while the crank is at TDC comparitively while crank is near top of rotation) too late and combustion is slower and pressure lower. As the crank rotates and piston goes down the chamber grows faster with rotation and pressure begins to drop due to volume increase (for the pump action).

Temperature of cylinder air IAT and compression, pressure (boost and compression) , injector nozzle orifice, injection pressure of fuel, fuel atomization, Cetane etc all play a part in the actual combustion events speed. As RPM changes the scale of the event changes too. Here in lies the need for "electronics" to try and optimize all the factors and adjust timing accordingly.

[Hubert]

The 6.5 adjusts timing with rotation of cam ring and IP plunger pumping action. Its clocking compared to crank. Similar to a distributor in a gasser.

Newer common rail engines the electronic controlled injector controls timing independantly of IP fuel pressure.

How .... the optic sensor and stepper motor etc but thats a long post.

[acfloors]

Thanks for the explination. It is still a little to technical. Could it be explained in plain english.

[97GMC6.5Z71]

Thanks for the explination. It is still a little to technical. Could it be explained in plain english.

First you'll need a scan tool or OBD-2 software to get a timing reading to see where the timing is set at. Then you can change the setting.
But if its running good now you may not gain anything by changing the timing:D

[Robyn]

Simply put
The engine has a crankshaft sensor that tells the computer where the crankshaft is and the injection pump has an optical sensor that tells the Computer whats happening there.
The Injection pump is still mechanical but the fuel rate and the timing are adjusted by the Computer based upon what RPM the engine is running at and the engine load based on the gear the tranny is in and the position of the throttle.

There are inputs from the different sensors like the coolant temp, atmospheric pressure sensor, Manifold pressure sensor and intake air temp sensor. All this nice stuff feeding data to the computer that will ultimately effect timing and fueling.

The timing is set to a base value similar to that of a gasser.
The DS4 uses a timing stepper motor in the injection pump that is controled by the computer to change the timing value based on all the inputs it gets.

There you have the simple version of how it happens. :eek:

A scan tool is a necessary piece of equipment if you want to get serious about finding and fixing any anomalies on these systems.
There are times that retrieving a code and a little WAG method will get it fixed but not always.

Now on the DB2 pumps. 6.2's and 92-93 6.5's had mechanical advance on the timing and you simply lined up a couple marks on the pump and the housing to get the base timing. You could check the value with a timing meter that either worked off a pulse trigger sensor or a liminosity probe in the glow plug port to run the unit.
Timing could then be set to specs. this way.

All the advance on these was mechanical based on throttle position.
The only electric controls on the timing were the cold start advance unit that raised the pressure in the IP case some that gave more timing on a cold start to avoid a smokey warmup and poor running.

Hope this simple explanation helps some.

On the later stuff there is no simple hammer and screwdriver fixes on it.
Takes techy tools to do it. :)

Now to answer your question, Yes you can do almost everything under the hood at home, IFFFFFFFFFF you have a good tech tool like has been mentioned.
Here is the biggy, if the check engine light is not on, there is really not much you need to be doing. The computer will let you know with that wonderful little amber light if it sees something out of spec.

Other than ordinary service such as filters and fresh oil there really is not much to do.
You can replace high mile injectors and glow plugs with no particular need for any high tech tools.

" If its not broke, dont fix it" :D
If you can work on a gasser these little diesels are a snap, They are pretty much the same old stuff, just dont have spark plugs and they run on thin oil is all.

The internal like rods, pistons, valves, cams and such all look about the same. The injection system is not real mysterious just stuffs fuel under very high pressure into the engine at just the right time when the piston is real close to TDC and the heat of compression (400 PSI) in a little teeny weeny chamber ignites the fuel as it hits the hot air.

Diagnostics on the electronic controls can get a little intense but its still not something thats all that difficult to master and work on when need be.




best

Robyn