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Old 11-21-2018, 09:28 AM   #1 (permalink)
Gunfreak25
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6.2 light load advance lever

Can someone explain to me how the DB2 light load advance works on the 6.2? I've read the manuals and it's still confusing to me. This is the lever on the side of the pump actuated by a face cam connected to the throttle shaft.

It's called a light load advance however it clearly retards the timing by rotating the internal cam ring in the direction of pump rotation.



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Old 11-21-2018, 09:37 AM   #2 (permalink)
Sixtwotonnetonn
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I believe you are taking about the fast idle.
Helps warm it up.
Green wires.
Some people put it on a switch.
Good glow plugs and you don't need it.

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Old 11-21-2018, 10:06 AM   #3 (permalink)
Gunfreak25
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No not the fast idle, there is a lever on the passenger side connected to the throttle via a ramped face cam ring, this pushes on the servo plunger on the bottom of the IP which is where the housing advance piston and springs are located.

Common sense tells us more advance is necessary at higher RPMs to allow the fuel more time to burn, yet this advance lever actually retards the timing the more the throttle is pressed which seems backwards to logic.

I know someone out there can explain this to a boob like myself.

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Old 11-21-2018, 11:59 AM   #4 (permalink)
Sixtwotonnetonn
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Ya sorry.. over my head lol..
Hopefully someone else will chime in.

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Old 11-21-2018, 12:07 PM   #5 (permalink)
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Info here:

https://www.dieselplace.com/forum/63...ml#post3490062

A light load advance mechanism provides advance when the engine is operating at low speed or under light load, when the transfer pressure is too low to move the advance piston.
The light load advance is actuated by an external face cam and rocker lever assembly when the throttle shaft rotates (on the 6.2L and 6.5L engines, this mechanism is on the passenger side of the pump). The lower end of the rocker lever pushes on the end of the servo advance plunger.
As the throttle shaft rotates, the face cam pushes on the rocker lever using a “see-saw” action, which depresses the servo plunger and advances the timing through the power plunger’s linkage to the cam ring. At a predetermined angle, the face cam flattens out, so that additional throttle movement does not affect the servo.
After the light load advance mechanism ceases to act on the servo plunger, advance action is regulated by transfer pump pressure.
The housing pressure cold advance (HPCA) solenoid is one of three solenoids that affect the operation of the injection pump. The HPCA solenoid makes it easier to start a cold engine by reducing housing fuel pressure in the advance mechanism.
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Old 11-21-2018, 01:17 PM   #6 (permalink)
Gunfreak25
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[/QUOTE]
As the throttle shaft rotates, the face cam pushes on the rocker lever using a “see-saw” action, which depresses the servo plunger and advances the timing through the power plunger’s linkage to the cam ring.[/QUOTE]

That info is incorrect, I believe. It actually retards the timing, not advance it. This is evident by pressing on the lever with a screwdriver while running, the result is retarded timing and quieter operation.

Still Stanadyne calls it a "light load advance" but as far as I can tell it has nothing to do with advancing per say.

I adjusted my face cam so the lever retards the timing much later, the result is a lot more pep and a little extra clatter, less exhaust haze too.

I suspect it is more of an emissions feature in disguise as there was a lot of emissions regulations mandates in the early 80s. If I recall, higher advance timing in a diesel makes for higher NOx emissions which the EPA dont likey.



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Old 11-21-2018, 05:50 PM   #7 (permalink)
upsmoker
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I have deep convictions on this subject> I actually took a road trip to a stanadyne dealer a few years ago and hired the tech for an hour to explain these little buggers. The hour turned in to almost 2 !!
The term "advance" lever is a misnomer, it does advance the ring in the direction of pump rotation which in turn retards the fuel event. The mechanical advance of the ring is only temporary until increased pump speed builds pump pressure to overcome the advance of the ring. If I were to write about it I would most certainly step all over myself and confuse the issue
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Weeeellll a 6.2 and 5.7 have 3 things in common, you put oil in the pan, antifreeze in the block and it burns diesel
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Dang it ... your making the quote wrong, 4 things 5.7's and 6.2's have in common, flex ring failures ....

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Old 11-21-2018, 06:10 PM   #8 (permalink)
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http://www.trucktrend.com/how-to/exp...njection-pump/

That's a good read to help understand.

The LLA lever is only there to maintain proper timing when the transfer pump pressure is too low to properly advance advance the cam, at higher RPM the transfer pump takes over.
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Old 11-21-2018, 06:21 PM   #9 (permalink)
upsmoker
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Quote:
Originally Posted by jdla140 View Post
http://www.trucktrend.com/how-to/exp...njection-pump/

That's a good read to help understand.

The LLA lever is only there to maintain proper timing when the transfer pump pressure is too low to properly advance advance the cam, at higher RPM the transfer pump takes over.
Mmmmm?

"The mechanical advance of the ring is only temporary until increased pump speed builds pump pressure to overcome the advance of the ring."

The "advance" lever protects the engine by retarding the timing before an onslaught of fuel hits the pistons at a low rpm advanced position
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Quote:
Originally Posted by Bigboytoys View Post
Weeeellll a 6.2 and 5.7 have 3 things in common, you put oil in the pan, antifreeze in the block and it burns diesel
Quote:
Originally Posted by Bigboytoys View Post
Dang it ... your making the quote wrong, 4 things 5.7's and 6.2's have in common, flex ring failures ....


Last edited by upsmoker; 11-21-2018 at 06:24 PM.
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Old 11-21-2018, 06:38 PM   #10 (permalink)
Gunfreak25
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Makes sense now. Engine protection was the only thing I could think of as far as purpose. It does indeed retard it initially however as you said, once RPMS rise, the rise in transfer pump pressure overcomes the servo spring force and advances appropriately.

When this all happens is controlled via the face cam ramp which is adjustable on the throttle shaft. I adjusted mine fully forward which means the throttle has to be opened quite a bit before any retarding takes place.

I'm pretty easy on the truck and it's not a tow vehicle, I dont believe engine damage can result from this and it sure has a lot more pep around town. A little clattery at 2000rpms so I may dial the face cam to come on a little sooner.

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