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- #81
Couple of PDF files thats show a few different mechanical governed bosch designs in detail.
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3B Rebuild and Performance Notes
- Thread starter yotahed
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The IP diaphram spring swap sounds appealing. What are the chances it works anything like the cummins fuel pins, which the aftermarket just re-indexes or increase the notch on it? (Denny T)
I'm hoping someone can post a bit more information about where you find it and what exactly you take apart to swap it over.
I'm hoping someone can post a bit more information about where you find it and what exactly you take apart to swap it over.
Sorry for the late reply.
On my brother HJ60 that was Auto to start it had the same pump arrangement as a 12HT the throttle is connected to the pump its self. We swapped a 5spd engine and trans in that is controlled the same way the 3B is with throttle plate set up.
I'm sure we could have made the auto set up work with the 5spd trans but did not bother trying. I had read reports of jerky throttle input and extream throttle sensitivity.
I may try one of those MB Springs in my brothers, not that fuel is a limiting factor on that thing though.... I only have it turned up 1.5 turns at 15psi and could use with a 1/4 turn less fuel. I'm waiting to see ring lands come out the exhaust.....
On my brother HJ60 that was Auto to start it had the same pump arrangement as a 12HT the throttle is connected to the pump its self. We swapped a 5spd engine and trans in that is controlled the same way the 3B is with throttle plate set up.
I'm sure we could have made the auto set up work with the 5spd trans but did not bother trying. I had read reports of jerky throttle input and extream throttle sensitivity.
I may try one of those MB Springs in my brothers, not that fuel is a limiting factor on that thing though.... I only have it turned up 1.5 turns at 15psi and could use with a 1/4 turn less fuel. I'm waiting to see ring lands come out the exhaust.....
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- #84
Cody C,
Different kind of pump that the cummins style. No aneroid for a fuel pin, But comparatively it would be a similar mod.
The spring is right under the rear diaphragm cap, very back of the pump, held on with 4 screws.
Just swap it out and away you go. I listed the part number a few times recently. Available from any mercedes dealer for around 10 bucks.
Sent with greasy fingers.
Different kind of pump that the cummins style. No aneroid for a fuel pin, But comparatively it would be a similar mod.
The spring is right under the rear diaphragm cap, very back of the pump, held on with 4 screws.
Just swap it out and away you go. I listed the part number a few times recently. Available from any mercedes dealer for around 10 bucks.
Sent with greasy fingers.
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I have a spare one here next tine you are over you can take a look.
After Reading through this thread I would like a couple things just laid out in plain. I think I have a very interesting idea.
I have replaced the diaphragm on a 3b diesel inline pump once before. It was a couple months ago actually. Went together quite nicely and had excellent results. What I noticed was that the bigger vacuum line seamed to pull on the diaphragm and against the spring pulling the fuel rail out. I didn't see or was aware of the reference line.
So first someone please explain a little better how the two work together on apposing sides of the diaphragm. When I look at it my thoughts are this:
When you push down on the accelerator pedal, the butterfly opens up, which alloys the engine to suck more air, which increases vacuum, which causes the diaphragm to move which sends more fuel. The reference line is on the opposite side of the of the diaphragm but also on the outside of the throttle body. The reference line gives smooth throttle response and seams to act as a shock absorber of sorts so that the diaphragm doesn't get slammed every time but has a slower draw.
So my idea then is simple. Switch the lines around, basically turning the vacuum system into a boost compensator. The vacuum line pushes against the diaphragm and spring and the reference line makes sure that doesn't happen to quickly. This is assuming my understanding of how the system works is slightly correct
I have replaced the diaphragm on a 3b diesel inline pump once before. It was a couple months ago actually. Went together quite nicely and had excellent results. What I noticed was that the bigger vacuum line seamed to pull on the diaphragm and against the spring pulling the fuel rail out. I didn't see or was aware of the reference line.
So first someone please explain a little better how the two work together on apposing sides of the diaphragm. When I look at it my thoughts are this:
When you push down on the accelerator pedal, the butterfly opens up, which alloys the engine to suck more air, which increases vacuum, which causes the diaphragm to move which sends more fuel. The reference line is on the opposite side of the of the diaphragm but also on the outside of the throttle body. The reference line gives smooth throttle response and seams to act as a shock absorber of sorts so that the diaphragm doesn't get slammed every time but has a slower draw.
So my idea then is simple. Switch the lines around, basically turning the vacuum system into a boost compensator. The vacuum line pushes against the diaphragm and spring and the reference line makes sure that doesn't happen to quickly. This is assuming my understanding of how the system works is slightly correct
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- #89
Rear port on pump=vacuum signal from throttle body venturi.... Open throttle> less vacuum> engine revs go up.
Front port=reference pressure line to throttle body. Usual at ~ atmospheric until boost.
Both come under boost pressure with a turbo and the large spring in the rear side is what essentially throttles the motor.
Youre on the right track, but its been tried and wouldnt work so well.
You need that vacuum signal at the rear to keep the idle, and keep the motor from revving out of control.
Once you apply unequal positive pressures to each side of the system you get either very sensitive or very sluggish response.
The best way that I have tested so far, is to install a needle valve in the reference side and only restrict/close it a very small amount from fully open/unrestricted.
I tried a bleed valve setup to bleed pressure from the reference side, but it surged really bad under any boost on the highway. It was great off the line, but sucked at higher Rpms.
My pump also has the longer mercedes main spring, which I would suggest you try out before fooling with the system further. Very nice difference.
Sent with greasy fingers.
Front port=reference pressure line to throttle body. Usual at ~ atmospheric until boost.
Both come under boost pressure with a turbo and the large spring in the rear side is what essentially throttles the motor.
Youre on the right track, but its been tried and wouldnt work so well.
You need that vacuum signal at the rear to keep the idle, and keep the motor from revving out of control.
Once you apply unequal positive pressures to each side of the system you get either very sensitive or very sluggish response.
The best way that I have tested so far, is to install a needle valve in the reference side and only restrict/close it a very small amount from fully open/unrestricted.
I tried a bleed valve setup to bleed pressure from the reference side, but it surged really bad under any boost on the highway. It was great off the line, but sucked at higher Rpms.
My pump also has the longer mercedes main spring, which I would suggest you try out before fooling with the system further. Very nice difference.
Sent with greasy fingers.
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Could a guy attach a valve to the throttle linkage, that dumps reference pressure or vaccum when you take your foot off the throttle to stabilize or keep it from wanting to run away after WOT?
I like the sounds of the power increase possible from this mod.
I like the sounds of the power increase possible from this mod.
- Thread starter
- #91
Yea you could use a throttle switch to open the valve up at 3/4-full throttle and close when coming off. I believe the solution is a lot simpler than that though.
Ill be doing some testing today.
Sent with greasy fingers.
Ill be doing some testing today.
Sent with greasy fingers.
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I think I understand a little bit here...so how is vacuum created when there's boost though...I really don't understand
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- #94
There isnt vacuum when boost is present. Once the system goes into positive pressure, it acts like a different animal. The vacuum side and reference side are both pressurized, although, the vacuum side sees a slightly lower boost than the reference side due to the smaller port of the venturi(restricted). The diaphragm spring throttles against this difference in pressure, but still has "less than ideal" resistance at lower revs and while building boost. Equalizing the pressure too much and the spring will throttle the motor eratically, too much difference in pressure results in poor response(too high on the reference side) or the boost throttling the engine(too much on the vacuum side).
There lies the problem I am trying to overcome. Get the pressures to rise closer to the same rate on acceleration, but still be able to hold at constant rpm and boost as well without the surging, and run on when releasing the throttle...
Sent with greasy fingers.
There lies the problem I am trying to overcome. Get the pressures to rise closer to the same rate on acceleration, but still be able to hold at constant rpm and boost as well without the surging, and run on when releasing the throttle...
Sent with greasy fingers.
You fellas are starting to paint a better picture of how this works. The Mercedes spring has a different spring rate, it allows the diaphragm to change position quicker allowing us to access more fuel, but after wide open throttle it doesn't snap the diaphragm back in some cases as it seems to be in a state of over fuelling and it acts like a runaway engine. Is this correct?
If it is the case, then perhaps a different spring with a progressive spring rate as opposed to a linear spring rate might be what we're looking for? Something softer like the MB spring at first, but stiffer as per the stock spring as the diaphragm is displaced?
- Thread starter
- #96
No. Youre getting mixed up here. The spring does not relate to these symtoms. Start reading further back in the thread.
The mercedes spring actually makes the stock system better for use with a turbo, without the need to modify the pump in any other way.
It changes the response and delivers more fuel than the stock spring at wide open and part throttle. Allows you to set your fuel screw lower and acheive a higher max delivery rate than the stock spring at the same screw position-> less smoke off the line, more fuel at WOT.
Now it all works just fine as is with the merc spring....
What im trying to do here is make the system even better. Because of the way it is, its very hard to get full delivery when you want it, i.e., "fuel rack to full load right now"
Instead you have an air system "cushioning" your pedal inputs and not giving you precise (not enough for me anyway) control over what you want the motor to do.
Moving the rack to full off the line would probably make even a mildly boosted cruiser spin tires if you kept your foot in it, but the system, as is, won't let it happen.
Unless you wind the fuel right up, of course, but then your efficiency kinda goes for a s***..
Seems too easy.
Sent with greasy fingers.
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you say the Mercedes spring is better, but didn't you say it wants to create a run away effect?
- Thread starter
- #98
You need to read from the beginning of the subject. That has nothing to do with the spring. I installed the spring almost two years ago.
It was tampering with the lines and altering airflow that caused a run-on condition...
Dont mean to be a dick, but really, just go back and read a little bit.
Sent with greasy fingers.
It was tampering with the lines and altering airflow that caused a run-on condition...
Dont mean to be a dick, but really, just go back and read a little bit.
Sent with greasy fingers.
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- Thread starter
- #100
Heres a diagram and explanation for anyone who doesn't know.
1. Diaphragm spring
-Sets fuel rate and initial rack position based on preload at a speicfied vacuum. Mercedes spring is roughly twice as long and the wire thickness is less.
2. Diaphragm
Seals the chambers and provides a direct link to the rack.
3. Rear(vacuum) Chamber
4. Idle Spring Capsule
-Adjusts minimum speed bumper/plunger. I believe this also prevents it from stalling if the diaphragm pulls back too far while pulling off the throttle.
5. Fuel Rack and Seal
-Rotates the plungers in the pump body to give more or less fuel. Forward for maximum, rearward for minimum or stop.
6. Front (reference) Chamber
7. Vacuum Generator
-Throttle plate has a small cutout around the vacuum generator, directing most of the airflow through it. Creates a "Venturi Effect" and thus you have a vacuum source.
Steady state:
"650rpm - 4"Hg 2500rpm - 5"Hg
Accelerating hard (any RPM):
0.5 - 1"Hg
Deccelerating hard (any RPM):
10"Hg"
(No Turbo)^^
8. Shaft and Throttle Plate (butterfly)
9. Reference Port
- Has a small "cup" notch in the end. Turning this in different orientations as well as placing further away from the throttle plate has affected throttle response
did i miss anything?
1. Diaphragm spring
-Sets fuel rate and initial rack position based on preload at a speicfied vacuum. Mercedes spring is roughly twice as long and the wire thickness is less.
2. Diaphragm
Seals the chambers and provides a direct link to the rack.
3. Rear(vacuum) Chamber
4. Idle Spring Capsule
-Adjusts minimum speed bumper/plunger. I believe this also prevents it from stalling if the diaphragm pulls back too far while pulling off the throttle.
5. Fuel Rack and Seal
-Rotates the plungers in the pump body to give more or less fuel. Forward for maximum, rearward for minimum or stop.
6. Front (reference) Chamber
7. Vacuum Generator
-Throttle plate has a small cutout around the vacuum generator, directing most of the airflow through it. Creates a "Venturi Effect" and thus you have a vacuum source.
Steady state:
"650rpm - 4"Hg 2500rpm - 5"Hg
Accelerating hard (any RPM):
0.5 - 1"Hg
Deccelerating hard (any RPM):
10"Hg"
(No Turbo)^^
8. Shaft and Throttle Plate (butterfly)
9. Reference Port
- Has a small "cup" notch in the end. Turning this in different orientations as well as placing further away from the throttle plate has affected throttle response
did i miss anything?
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