the question about fuel adjustment screw of cucv 6.2 diesel engine

[als804]

hello
i have seen so many writings about adjusting fuel screw valve to increase in fuel supply to injectors.
but i am wondering "is this really effective?"
i don't know the difference between doing this and putting the pedal more.
putting the pedal more deeply also can supply more fuel to injects.
why people do adjust that?

fuel screw adjustments is to increase the fuel at the same rpm?
please let me know!!

 

[LT67]

If you were to turn up the fuel delivery within the injection pump, the engine is going to get more fuel regardless of throttle position.

 

[Keith_J]

While the throttle pedal indeed varies the injected quantity, normally from 4 to 52 cubic millimeters, the high limit is set by the screw you mentioned.

There are two plungers which pump this injected quantity, the length of the stroke is the upper limit. When the screw is tightened, it straightens a curved leaf spring, the ends of this spring are what limits injected volume by fixing the plunger stroke.

This must be done carefully as higher exhaust gas temperature can cause damage. This engine loses volumetric efficiency above 3000 RPM, this increases combustion temperature. More air is needed, this dilutes the combustion temperature. Hence the need for forced induction, normally via turbocharging.

Injected volume decreases above 3400 RPM and is nearly eliminated above 3700 RPM via the governor in the front end of the injection pump.

 

[Chaski]

Keith did a nice job of explaining it.

The injection pumps diesel using two little opposing pistons inside the rotor, as the rotor turns the pistons are pushed in by rollers as they make contact with the cam ring. The pistons and the "leaf spring" are highlighted in the photo.

Turning the screw clockwise flattens the leaf spring looking gizmo on the rotor.

Leaf spring looking gizmo limits the travel of the opposing plungers in the injection pump rotor.

The flatter the leaf spring - the further the plungers can travel - hence the more volume they pump. The rollers that push the pistons in only contact the high spots of the cam ring, on the low spots they don't contact. The leaf spring gizmo limits the travel and holds the pistons in, therefore allowing you to adjust the max pumped volume.


I wouldn't mess with it unless applying a turbo.

 

[als804]

Keith did a nice job of explaining it.

The injection pumps diesel using two little opposing pistons inside the rotor, as the rotor turns the pistons are pushed in by rollers as they make contact with the cam ring. The pistons and the "leaf spring" are highlighted in the photo.

Turning the screw clockwise flattens the leaf spring looking gizmo on the rotor.

Leaf spring looking gizmo limits the travel of the opposing plungers in the injection pump rotor.

The flatter the leaf spring - the further the plungers can travel - hence the more volume they pump. The rollers that push the pistons in only contact the high spots of the cam ring, on the low spots they don't contact. The leaf spring gizmo limits the travel and holds the pistons in, therefore allowing you to adjust the max pumped volume.


I wouldn't mess with it unless applying a turbo.

View attachment 828212

i feel like i got it,.

so... i know this injection pump controls the fuel based on RPM. As rpm is reached to the degree set by an accelerating pedal, fuel supply will be automatically decreased by the pump
max fuel is pumped right after pushing the pedal more.
max pumped volume is adjusted by this Allen screw that controls the leaf spring gizmo directly related to the travel length of two pistons.


is that right?

 

[als804]

While the throttle pedal indeed varies the injected quantity, normally from 4 to 52 cubic millimeters, the high limit is set by the screw you mentioned.

There are two plungers which pump this injected quantity, the length of the stroke is the upper limit. When the screw is tightened, it straightens a curved leaf spring, the ends of this spring are what limits injected volume by fixing the plunger stroke.

This must be done carefully as higher exhaust gas temperature can cause damage. This engine loses volumetric efficiency above 3000 RPM, this increases combustion temperature. More air is needed, this dilutes the combustion temperature. Hence the need for forced induction, normally via turbocharging.

Injected volume decreases above 3400 RPM and is nearly eliminated above 3700 RPM via the governor in the front end of the injection pump.

oh easy to understand with the injection pump picture .

thank so much.

 

[Keith_J]

Injection quantity is based on throttle pedal position until engine speed nears 3600 RPM. If the engine is at idle and you floor it, the amount of diesel injected on each cylinder cycle goes from 10 to 55 micrometers, nearly instantly. The reason for the RPM cut out is engine protection.
The limit on injected quantity is due to the sharp decline in volumetric efficiency. Full load exhaust gas temperature at 1800 RPM is around 950 °F. At 3600 RPM, 1100°F. The cylinder just cannot fill completely with air at high speed because diesels must have both valves closed at top dead center and suffer high speed performance.

 

[LT67]

Injection quantity is based on throttle pedal position until engine speed nears 3600 RPM. If the engine is at idle and you floor it, the amount of diesel injected on each cylinder cycle goes from 10 to 55 micrometers, nearly instantly. The reason for the RPM cut out is engine protection.
The limit on injected quantity is due to the sharp decline in volumetric efficiency. Full load exhaust gas temperature at 1800 RPM is around 950 °F. At 3600 RPM, 1100°F. The cylinder just cannot fill completely with air at high speed because diesels must have both valves closed at top dead center and suffer high speed performance.

High speed and CUCV are mutually exclusive to each other lol

I'm just not brave enough to turn a 6.2 diesel over 3000 rpm. I want my 6.2's to stay in one piece...

 

[Keith_J]

The 6.2 is perfectly happy turning 3600 RPM as long as the harmonic damper is not age hardened and the air filter isn't clogged. The poor volumetric efficiency and resulting high BSFC are the only reasons to avoid this speed range.

 

[LT67]

The 6.2 is perfectly happy turning 3600 RPM as long as the harmonic damper is not age hardened and the air filter isn't clogged. The poor volumetric efficiency and resulting high BSFC are the only reasons to avoid this speed range.

So if I were add a turbo to a 6.2, it would be safer to turn 3000 rpm vs NA?

 

[Keith_J]

Turbo or not, 3000 RPM is fine. CUCVs have no intake silencer so it sounds rough, the intake manifold is past its prime so noise is high.

What kills the engine is torsional vibration from age hardened dampers. All engines suffer this malady, diesels the most. The worst regime is idle speed. Wide open at 3600 rip ems is the easiest job for crank, block and bearings.

Now cooling system? That is a whole other issue. Normally aspirated means the most cylinder head heat rejection. Which is why 2100 RPM is your goal if coaxing the most distance from a certain volume of diesel is your goal. It won't happen in first gear or in any gear factory equipped..stay tuned for news.

 

[Dispatcher7]

Turbo or not, 3000 RPM is fine. CUCVs have no intake silencer so it sounds rough, the intake manifold is past its prime so noise is high.

What kills the engine is torsional vibration from age hardened dampers. All engines suffer this malady, diesels the most. The worst regime is idle speed. Wide open at 3600 rip ems is the easiest job for crank, block and bearings.

Now cooling system? That is a whole other issue. Normally aspirated means the most cylinder head heat rejection. Which is why 2100 RPM is your goal if coaxing the most distance from a certain volume of diesel is your goal. It won't happen in first gear or in any gear factory equipped..stay tuned for news.

Finding this thread very informational and hoping @Keith_J finishes the story. As my recently purchased 1985 M1009 is my first I have a lot to learn. This website has been amazing! Wanting to know how the engine likes to run and what I can do to keep it happy. Thanks.

 

[Barrman]

Something else to remember is that every single NA 6.2 seems to be different from every other one. I have a pair of M1009's that at one point in time were daily driven every day. There was a NA 6.2 2wd Suburban driven every day and my NA 6.2 M715 that got driven a few times a week. 4 6.2 engines and each had its own idle characteristics, power delivered traits, noises and fuel mpg.

Both M1009's had BFG 33x12 tires, stock everything else. One just fired up happy every morning. The other likes to puff some smoke but never used oil. The happy starting truck makes more noise at all engine speeds and was happy at 62 mph getting 21 mpg down the highway. The smoke truck idled so smooth, had gobs more power according to the butt dyno and never got better than 18 mpg no matter the speed. But, was happy at 64 mph on the highway. I think IP timing might be the difference but I just this month have gotten equipment to check and will have to write about that later. It could be a bunch of other things stacked up as well.

So, go about getting the truck sorted incrementally. Air filter, fuel filter, belts, balancer and all the drive line fluids. Since those are all consumables that must be changed you might as well base line them now. Then just drive it. If you find you want it to be in 3rd at 35 mph because that is the speed limit for a lot of your drive but you are always holding a bunch of throttle in to keep up with traffic and it won't shift to 3rd due to the mechanical vacuum control valve mounted to the throttle on the side of the IP. It might be changing the valve location makes things all perfect and no IP adjustment is needed. Keep in mind that if you see black smoke out the pipes at any time in a non turbo truck. You are pushing too much fuel and need to back off the throttle. Yes, you will see what you think is smoke in your mirrors when a car is behind you at night, but it isn't the visible black kind. Just the heat. If you never see black smoke no matter how hard you push it in the daylight. Then, maybe a little turn of the metering screw will give you a bit more power.

Just remember that this is an engine designed to fit where any big or small block Chevy would, get the same horse power as a stock 1982 2 barrel 305 gas engine and double the fuel mpg. That was the goal and it does it perfectly. Keeping up with a modern 200 hp 3000 pound Kia stop light to stop light isn't going to happen.

 

[Keith_J]

i feel like i got it,.

so... i know this injection pump controls the fuel based on RPM. As rpm is reached to the degree set by an accelerating pedal, fuel supply will be automatically decreased by the pump
max fuel is pumped right after pushing the pedal more.
max pumped volume is adjusted by this Allen screw that controls the leaf spring gizmo directly related to the travel length of two pistons.


is that right?

The injected quantity is based on skinny pedal position, not engine speed. IQ is only limited at maximum engine speed. If you are doing 73 MPH in a stock 1 ton CUCV, the engine is at 3600 RPM and the governor in the injection pump is starting to reduce injected quantity to limit RPM. Likewise, if you are doing 37 MPH in the same vehicle on a steep climb requiring full throttle, the injection pump is probably at the maximum volume for each injection event, 50 plus milligrams or so.

The throttle position controls torque as torque comes from cylinder pressure and cylinder pressure is from injection quantity. Adjusting the maximum quantity limit is something which should only be done when you have an exhaust gas temperature gauge because serious engine damage is possible. Anything over 1150 °F is excessive. You will see this in stock engines at maximum RPM and load because the cylinders lose air breathing capacity at high speeds.

 

[Skinny]

Both of my CUCV engines were severely under fueled. Its not tough but not super hard to get to the fuel screw if you are patient. I'd start with an 1/8 and be prepared to go to 1/4 if it didnt make light smoke at WOT. You will like the result.

Sent from my SM-T380 using Tapatalk

 

[als804]

Both of my CUCV engines were severely under fueled. Its not tough but not super hard to get to the fuel screw if you are patient. I'd start with an 1/8 and be prepared to go to 1/4 if it didnt make light smoke at WOT. You will like the result.

Sent from my SM-T380 using Tapatalk

Haha thanks I adjusted 1/4 the results are good
When i drive the specific highway ( a little steep ),

NA & no fuel up : speed was decreased 100kph to 70km/h

now turbocharged and fuel up 1/4 : no speed drop and i even could accelerate a little !

 

[Skinny]

Nice



Sent from my SM-T380 using Tapatalk

 

[LT67]

Turbo or not, 3000 RPM is fine. CUCVs have no intake silencer so it sounds rough, the intake manifold is past its prime so noise is high.

What kills the engine is torsional vibration from age hardened dampers. All engines suffer this malady, diesels the most. The worst regime is idle speed. Wide open at 3600 rip ems is the easiest job for crank, block and bearings.

Now cooling system? That is a whole other issue. Normally aspirated means the most cylinder head heat rejection. Which is why 2100 RPM is your goal if coaxing the most distance from a certain volume of diesel is your goal. It won't happen in first gear or in any gear factory equipped..stay tuned for news.

Just flip the intake portion of the air filter housing to the drivers side. It'll cut down on the noise from the intake.

 

[dougco1]

Just flip the intake portion of the air filter housing to the drivers side. It'll cut down on the noise from the intake.

Is that true? How so?

 

[LT67]

Is that true? How so?

I don't have an answer as to why it reduces the noise. I just know when I flipped the air inlet to the drivers side it cut down on the noise. Attaching some sort of an air induction hose to the air cleaner housing helps as well.