3B EDIC Overinjection position advances timing? (1 Viewer)

[Busted Crank]

When i had my 3b on the engine stand i experimented with the fuel control arm and found that in the over injection position it advances the timing. now my question is am I making things up here or has anyone else found this as well. Also i set my fuel screw just before it starts to advance and found it to have little power. The 3B is turboed and only hits 600 degrees F pre turbo so far. it could still use way more fuel but this advancing timing thing worries me.

Any thoughts?

 

[gerg]

How can over inject physically rotate the whole pump? I thought that was the only way to adjust timing. Am I missing something?

 

[duncanrm]

I'm pretty sure the 3B Inline pump is the same basic design as the 2H inline pump. There is no mechanism on the 2H pump that can modify the timing whilst the Fuel Control arm is in the Overfuel position.

 

[Busted Crank]

if the pump piston is cut a certain way then when rotated further than normal it can close the spill port earlier than normal, causing the timing to be advanced. however i have not dissembled one of these pumps yet to verify.

 

[gerg]

I'd pm yotahead. He's local to you, as in the same time zone, and is knowledgable of our pumps.

 

[lostmarbles]

When i had my 3b on the engine stand i experimented with the fuel control arm and found that in the over injection position it advances the timing. ...

We're certainly used to hearing only of advance/retard being achieved by rotating the pump (or by altering the relationship of its drive-cog with its camshaft as performed by the automatic timer mechanism).

How exactly did you confirm that rack movement also has a noticeable effect on the timing?

 

[RufusTheDufus]

On an inline pump the position of the plunger helix only controls the amount of fuel that's allowed to be delivered by the plunger. The up/down movement of the plunger is controlled by a camshaft. This cam sets the timing and phasing of the injection event. The rotational position of the plunger does not affect injection timing on an inline pump. An axial pump may be a different beast.

 

[Busted Crank]

when i was spill timing the pump i noticed the start of injection seemed to start earlier if the arm was in the over inject position. i just need to see a picture of the pump piston from our trucks to tell if I'm right or dead wrong I'm hoping it was just a weird coincidence. What I'm wondering is if the top of the piston has a groove cut in it to delay the injection event until you are in the over inject position. a Cut like the blue line in the picture. It makes sense to me that you would want to advance the timing for cold starting but only on a idi engine. ( over inject being the left side of the piston and idle being the right side of the piston.

 

[RufusTheDufus]

The over-inject position changes the governor to allow for more fuel, the same way putting your foot on the accelerator would modify the position of the control rack. Your injectors are designed to open at a specific pressure. The pump is designed to meter a specific amount of fuel at that very high pressure. When you use a spill pipe the piston is working against atmospheric pressure. Over-inject will tell the governor to move the rack to rotate the piston to deliver more fuel which "seems" to come out earlier because there's more fuel. But if it was working against the crack open pressure of the injector it wouldn't be any earlier.

The delivery plunger/piston doesn't know it's in over-inject mode or if it's 1/4 throttle on the accelerator.

 

[RufusTheDufus]

From the factory service manual.

 

[RufusTheDufus]

This isn't from the Toyota FSM but it is a typical inline Bosch plunger assembly.

 

[duncanrm]

This isn't from the Toyota FSM but it is a typical inline Bosch plunger assembly.

Thats a great pic, thanks for posting.

 

[lostmarbles]

when i was spill timing the pump i noticed the start of injection seemed to start earlier if the arm was in the over inject position....

I had a feeling that's what you must have done/seen...

... When you use a spill pipe the piston is working against atmospheric pressure. ... But if it was working against the crack open pressure of the injector it wouldn't be any earlier.....

Diesel is not compressible so wouldn't that mean negligible difference in spill timing for:

• against atmospheric pressure versus
• against crack-open pressure.

I've just been studying various line drawings of the way components in-line IPs work but I've got to admit that much of it is rather over my head.

(If I get the oportunity some time in the future I must verify for myself any change in spill-point/timing with the IP lever in various different positions.)

 

[RufusTheDufus]

Diesel is not compressible so wouldn't that mean negligible difference in spill timing for...

I did a poor job of describing why I referenced atmospheric pressure vs crack pressure. I was thinking more along the lines of the fuel following the path of least resistance and going out the spill tube instead of flowing into the spill port. But there's a spring and a delivery valve at the top of the plunger assembly that should accomplish that same task. I do know that the FSM references pump test nozzle holders for pre-test check and preparation that mimic the crack pressure of 1636 to 1778 psi. That's what led me to think that having no resistance on the spill tube might make things appear to be other than what they are. I don't know what happens in the pre-stroke phase if the rack is moved and there's no injector.

The spill port's job is to change the effective length of the column of fuel over the plunger. In a sense it changes the length of the stroke of the plunger. Maybe this this will explain things better than I can.

From the linked document:

Delivery of fuel ceases when the plunger helix passes the barrel spill port (or control port), and the delivery valve returns to its seat. During the remainder of the stroke, the fuel displaced by the plunger simply returns to the gallery via the vertical slot, cut away area and spill port. Thus fuel ceases to be injected when the helix uncovers the spill port.

Metering the fuel charge
Since the plunger is cam driven, its stroke is constant and cannot be varied to control the quantity of fuel injected per stroke. However, the effective part of the pumping stroke can be varied to control the quantity of fuel injected per stroke simply by rotating the plunger in the barrel.

Fuel delivery begins at the instant the top of the plunger covers the barrel ports and continues until the helix edge uncovers the spill port, at which point fuel trapped above the plunger is allowed to return to the fuel gallery. Thus the effective pumping stroke ceases when the spill port is uncovered, and is directly controlled by the distance through which the plunger must travel before the edge of the helix passes the bottom of the spill port.

Injection timing is set at the port-close time which is static.

 

[lostmarbles]

Thanks Rufus.

I thought I had a pretty good book (on IPs and how they work) in my library but those images are far better/clearer than what it shows (and therefore make it much easier for me to understand).

They show me clearly how piston/plunger rotatation alters the amount of fuel delivered (via that helix-groove) so if this is how our IPs are designed then I can see that having the rack in different positions POSITIVELY CAN'T alter the injection timing.

Thankyou again..



(The fuel must start getting pushed out towards an injector when the "cam-follower" is at the same point on the related cam regardless of how much fuel is going to get delivered.)

PS. I don't really have a "library" as such. But I do have a large pile of Land Cruiser FSMs and connected publications.

 

[RufusTheDufus]

You're welcome. I'm enjoying learning this stuff.

In viewing these photos it became very obvious to me how important clean fuel is. There's a lot of tiny moving parts in there with incredibly tight tolerances.