Diesel opacity tests for road vehicles

Poke around some of the diesel truck sites for instructions. I'm not familiar with the Chevy diesel, but on most mechanical injection pumps its a very simple adjustment.

Keith

#2 Diesel fuel at 60 degrees F weighs 820-950 kg. per cub. meter.

Kerosene at 60 degrees F weights 817 kg. per cub. meter.

Gasoline at 60 degrees F weighs 737.22 kg. per cub. meter

As I asked Keith, how is turning the MAX fuel rate screw down (backing it off) 1/6 of a turn going to affect smoke at PART THROTTLE, when the plunger stroke still will not be limited by the spring, even after setting it down 1/6 of a turn, since, at part throttle, it's nowhere's near max fuel rate (plunger stroke), anyhow????

But during the steady-state 40MPH opacity test, the metering valve is limiting the fuel flow to WAY less than the MAX stroke of the plungers, and since the plungers are not taking on a complete charge, and moving out against the leaf spring, moving the leaf spring inward a little, by setting the pump down slighly will STILL not put it in contact with the plungers, limiting their outward movement, and the fuel charge they are taking in, and delivering to the injectors.

If the plungers WERE taking on such a charge of fuel at partial load that their travel WAS being limited by the leaf spring, the engine would NOT be at "steady state", holding at "40MPH".

It would be accelerating at it's full horsepower capacity, otherwise known as WOT (Wide Open Throttle).

Please explain to me how TURNING DOWN THE PUMP will affect the smoke, at simulated highway speeds of 40 and 60 MPH????

The pump adjustment controls the MAX amount of fuel injected with the pedal to the floor, and would have NO EFFECT on the fuel rate at less than WOT.

Some common reasons for excess smoke from a 6.2:

Bad injectors

Late injection timing from wear in the timing chain and gears and/or a worn advance piston
and bore. SLIGHTLY advancing the pump static timing MAY help.

In the last several months, I have replaced the timing sets on 2 high-mileage 6.2's, and it's unbelievable how much better and CLEANER they run.

Even the crankcase oil may affect smoke, 'cause some of it gets sucked into the intake and burned, along with blowby. On one of the GM diesel boards, this was mentioned, and a suggestion was made as to a good oil choice for better results at the testing station, but I can't recall where I saw that!

"...have NO EFFECT on the fuel rate at less than WOT" NOT TRUE.

In a rotary injection pump, the length of the plunger stroke is constant regardless of the throttle setting, not controlled by the throttle setting like the old in-line pumps. The amount of fuel delivered in each stroke of the plunger is controlled by opening the metering valve some number of rotational degrees after the start of the plunger stroke, spilling excess fuel back into the pump housing. The point at which the metering valve opens is determined by a combination of engine speed and throttle setting. Essentially, fuel is delivered for some percentage of the plunger stroke.

What you're actually adjusting when you turn the pump up or down is the maximum stroke of the plunger, which does control the maximum amount of fuel the pump can deliver at wide open throttle, PROVIDED ENGINE SPEED IS BELOW GOVERNED SPEED. At top speed, the governor mechanism in the pump will start opening the metering valve earlier, reducing the total amount of fuel.

Since the opening point of the metering valve is at some percentage of the plunger stroke, as determined by the position of the throttle and engine speed (via the governor), a longer maximum stroke will result in greater fuel delivery at a fixed throttle position and speed. Conversely, a shorter maximum stroke, i.e., turning down the pump, will deliver less fuel at a particular throttle setting and speed.

Since a diesel has not throttle plate, air volume is a function of speed, and reducing the fuel at a give speed leans the burn, reducing smoke. Same reason they smoke at higher altitudes if set for a low altitude...thinner air results in fewer air molecules in the combustion chamber and a richer burn.

There's a relatively simple desription of a rotory injection pump operation at the attached link. The mechanical arrangement of the Bosch pump is different than the Roosa-Master, but the prinicple of operation is the same. I couldn't find a simple description of the Roosa-Master pump & wasn't going to spend a lot of time looking for one.

Hope this helps.

Keith

• Bosch pump operation

Simply put, your treatise does not apply, since you are discussing how a Bosch pump works, and this is a ROOSA MASTER. (STANADYNE)

Changing the maximum fuel rate on these pumps WILL NOT affect the smoke opacity at PART LOAD.

You say "controlled by opening the metering valve some number of rotational degrees after the start of the plunger stroke, spilling excess fuel back into the pump housing. The point at which the metering valve opens is determined by a combination of engine speed and throttle setting. Essentially, fuel is delivered for some percentage of the plunger stroke."

Actually, the position of the metering valve in a Roosa-Master is controlled only by how much you have your foot into the throttle, and where the engine speed is at in relation to the min-max governor, and the metering valve position DOES NOT correspond to the start, or end, for that matter, of plunger stroke.

Think about it... the Roosa metering valve is flowing only enough fuel to maintain the engine at the speed required for the 40 or 60MPH smoke test. The plungers in the rotary injection pump are at NO WHERES near full stroke, so they don't extend nearly out to the stroke limiting spring, and the spring never limits the plunger stroke, NOR WILL IT, unless you set the stroke WAY down, so fuel is limited to less than needed to maintain 40MPH on the test stand.

(In the Roosa rotary pump, the metering valve is NOT involved with the plunger stroke, such as it is in the BOSCH rotary pumps.)

And, your last statement, "hope this helps", doesn't, since we are discussing apples, and you have explained oranges! You haven't cleared up a thing, with your linked explanation of a VE BOSCH pump, since it's plunger and metering valve are one, and are axial with the head and rotor, and the Roosa metering valve is separate of the plungers, and remotely located from the plungers, which are RADIAL to the head and rotor. The BOSCH plunger/metering valve moves back and forth to inject, and rotates to control fuel delivery rate, while the ROOSA's metering valve only rotates.

Keith

I'd still like to see an explantion, though, how the max plunger travel leaf spring fuel adjustment on a Roosa-Master is going to affect smoke at a steady-state, part load, medium RPM condition!

I COULD agree with you, though, at a condition near maximum torque, but not at this steady-state, much less than full-loaded condition!

Thanks for the lively discussion, though, it's been fun!

Incidently, you wouldn't have a VE pump (Japanese clone, actually) for a Toyota Corolla lying around? I need the thermal "wax pellet" unit, heated by engine coolant, that attaches to the IP, and controlls timing advance at cold start, and fast idle. The part is obolete, both through Toy, and OEM, and I've had NO luck finding even a usable used one.

I'd still like to see an explantion, though, how the max plunger travel leaf spring fuel adjustment on a Roosa-Master is going to affect smoke at a steady-state, part load, medium RPM condition!

I COULD agree with you, though, at a condition near maximum torque, but not at this steady-state, much less than full-loaded condition!

Thanks for the lively discussion, though, it's been fun!

Incidently, you wouldn't have a VE pump (Japanese clone, actually) for a Toyota Corolla lying around? I need the thermal "wax pellet" unit, heated by engine coolant, that attaches to the IP, and controlls timing advance at cold start, and fast idle. The part is obolete, both through Toy, and OEM, and I've had NO luck finding even a usable used one.

1975 - Cold Start Accelerator - KSB
1982 - Temperature Controlled Idle Speed - TLA
1987 - Pneumatic Idle Speed Increase - PLA

I'm not familiar with any of it - mainly because I've never had a problem except with the coolant-sensor controlled fast-idle on my Isuzus. My Volkswagens - with the genuine Bosch pumps - have never had a problem - but I suspect, some control is manual. Both have a "cold-start" manual pull cable - works like a choke-cable for a carburetor. I don't even know what is does - since I never had a problem. But it's effect is - faster idle and seems to advance timing when cold. It might also add extra fuel - maybe I'll have to read the book sometime.

Keith