Super (Duty) -Visor advice on cold start

[KYSlowhand]

I'm a bit late to this party, but...
As already pointed out, our IDI's do not have any throttles in the air intake.

DrCharles Good info on MB using vacuum control. Been reading the Engine Service Manual; Amazing how a basically mechanical device can efficiently supply fuel in a tough working environment/ without a brain. The Corvette had such a system back in the day which used more refined fuel. I had a Corvette with the Fuel Injection insignia on the fenders but someone put a carburetor on it.

 

[Booyah45828]

Sorry that I'm now seeing this. We went over this when I was in school years ago. You go half or full throttle on cranking in order to retard the injection timing. This allows the piston to go higher up in the cylinder, creating more pressure and heat in the process. Since these engines are heat/compression ignition, the more heat created before fuel injection, the easier it will be to light off.

This idea is present on a lot of mechanically injected diesel engines, so it's not really rare, just uncommon now-a-days.

The reason the timing is retarded when adding throttle is intentional. The more fuel you add, the more volatile the combustion event, so you retard the timing so the pressure increase occurs at the right time ATDC.

Timing is advanced with higher rpm. That's because the combustion event occurs in a relatively fixed amount of time. Therefore as rpm increases, the injection has to happen earlier so that, once again, the pressure increase occurs at the right time ATDC.

 

[KYSlowhand]

Sorry that I'm now seeing this. We went over this when I was in school years ago. You go half or full throttle on cranking in order to retard the injection timing. This allows the piston to go higher up in the cylinder, creating more pressure and heat in the process. Since these engines are heat/compression ignition, the more heat created before fuel injection, the easier it will be to light off.

This idea is present on a lot of mechanically injected diesel engines, so it's not really rare, just uncommon now-a-days.

The reason the timing is retarded when adding throttle is intentional. The more fuel you add, the more volatile the combustion event, so you retard the timing so the pressure increase occurs at the right time ATDC.

Timing is advanced with higher rpm. That's because the combustion event occurs in a relatively fixed amount of time. Therefore as rpm increases, the injection has to happen earlier so that, once again, the pressure increase occurs at the right time ATDC.

BOOYAH thanks for simplifying by explaining the -IDI Visor Instructions; too simple, to justify 10 Sensor Input controllers. and interesting also is ignition occurring ATDC ???

This knowledge negates my usual inclination to tinker with fuel settings, truly if it ain't broken / or you have special hi-intensive training: Let It Be.

 

[Thewespaul]

Sorry that I'm now seeing this. We went over this when I was in school years ago. You go half or full throttle on cranking in order to retard the injection timing. This allows the piston to go higher up in the cylinder, creating more pressure and heat in the process. Since these engines are heat/compression ignition, the more heat created before fuel injection, the easier it will be to light off.

This idea is present on a lot of mechanically injected diesel engines, so it's not really rare, just uncommon now-a-days.

The reason the timing is retarded when adding throttle is intentional. The more fuel you add, the more volatile the combustion event, so you retard the timing so the pressure increase occurs at the right time ATDC.

Timing is advanced with higher rpm. That's because the combustion event occurs in a relatively fixed amount of time. Therefore as rpm increases, the injection has to happen earlier so that, once again, the pressure increase occurs at the right time ATDC.

Exactly right, more advanced would be a colder explosion. Couldn’t have explained it better myself. Glad they are still teaching something about the old mechanical engines in tech schools.

 

[austin92]

I may have missed something but are we saying the throttle retards timing when starting but advances after engine is running? If retarded timing helps with starting why do we have a cold advance?


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[Thewespaul]

I may have missed something but are we saying the throttle retards timing when starting but advances after engine is running? If retarded timing helps with starting why do we have a cold advance?


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The light load advance piston retards timing with throttle, but as engine rpms increase the hydraulic advance takes over and advances total timing as transfer pressure builds. With just cranking rpms you’re set at one rpm and set at a certain transfer pressure, so the only change in timing will be mechanical with the throttle.

 

[Macrobb]

Also, at this point, a lot of things are worn out which is why some IDIs will not start when at half/full throttle - it becomes *too* retarded.

 

[Booyah45828]

BOOYAH thanks for simplifying by explaining the -IDI Visor Instructions; too simple, to justify 10 Sensor Input controllers. and interesting also is ignition occurring ATDC ???

This knowledge negates my usual inclination to tinker with fuel settings, truly if it ain't broken / or you have special hi-intensive training: Let It Be.

I really don't know on an idi. I know on gas engines ignition begins BTDC. But the idi timing is so close to TDC it could start before or after.

Actually if I think about it, ignition on an idi starts ATDC because if you've ever read about timing these engines via luminosity probe, you're specs are all given ATDC. So based off that I would assume ignition would occur ATDC.

 

[Booyah45828]

Glad they are still teaching something about the old mechanical engines in tech schools.

This was taught in a 6 week class dedicated to old mechanical engines. The gentleman that was the instructor had to have been in his 60's and forgot more about diesel engines then most will ever know. The only reason he went over any of it in detail was because I asked him about it, because like others here have stated, it seemed backwards to me at the time.

Sadly, Most kids in the class could have cared less about it. They were either drunk/high/on a free ride, too dumb to write their own name, or were only interested in which chip to put on a cummins.

 

[KYSlowhand]

The light load advance piston retards timing with throttle, but as engine rpms increase the hydraulic advance takes over and advances total timing as transfer pressure builds. With just cranking rpms you’re set at one rpm and set at a certain transfer pressure, so the only change in timing will be mechanical with the throttle.

Also, at this point, a lot of things are worn out which is why some IDIs will not start when at half/full throttle - it becomes *too* retarded.

Gentlemen ... Thank Y'All; Think I'll L@@K for a Diesel Tech. also a donor vehicle.