Bosch Pump - What do all the bits do?

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PJLarge
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Bosch Pump - What do all the bits do?

Post by PJLarge »

Hello again all,
Well I'm really liking my Volcane. It's a great commuting car.
I want to give it a bit more 'poke' on the motorway so I'm after a primer on the settings for the Bosch pump. I've seen the web page telling me to adjust both the master fuel and the boost compensator, I'm wanting to know what they actually do - ie the effect they have on things - specifically the boost compensator. Does anyone have any pearls of wisdom or resources on the web I can have a look at? I'm after a good glob of torque in the mid range whilst still retaining good economy. I realise these two things are at odds with each other in the real world but my lack of understanding of how the pump actually works is stopping me making an informed decision on what to adjust.
Thanks all,
Phil.
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davek-uk
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Post by davek-uk »

Do a search here for "diesel tuning", you’ll find lots of stuff - there are nearly two pages of conversation threads. One of the older threads has a lot of related links. You'll have to sift through the info to find what you need.
As I understand it there seem to be 3 main adjustments:
a. The turbo wastegate - on my KKK this was shortening the actuator rod (once unclipped it simply screws into itself);
b. Adjusting the maximum fuel setting on the pump - on the Bosch this is at the rear of the pump (the right hand end when looking in from the front of the car), I haven't changed this due to my AS3 pump having a security shield;
c. The boost compensator - the unit at the top of the pump. This has three settings itself. The unit has an initial setting using a screw in the top to press down on the internal components. Internally there is a sprung diaphragm that is pushed down by manifold pressure. It moves a pin in an eccentric cone to supply the fuel rate. Under the diaphragm is a toothed wheel that controls the spring strength. The three settings are:
<ul><li>Off-pressure boost is adjusted by a torx screw and locknut on the top of the unit under a metal cap (screw in to increase). </li><li>Boost-fuelling is adjusted by rotating the diaphragm (thus moving the shaped pin in the eccentric cone). </li><li>Boost-delivery is adjusted by turning the toothed wheel to change the spring pressure (move anti-clockwise to increase).</li></ul>I'll tell you what I have done so far:
Initially, I adjusted the 'off-pressure' boost (screwing in one turn) and the turbo wastegate (shortening five turns). This made the engine smoother at low revs and a generally more responsive.
Recently I adjusted the boost compensator (diaphragm turned 90º clockwise, toothed wheel turned 5 clicks anti-clockwise) and this had made a dramatic difference to the mid-range urge.
I haven’t had time to play with these adjustments yet but as I’m getting no black smoke I think I could adjust more aggressively at a later date.
DaveC
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Post by DaveC »

Ohhhh, thanks for that quick insight Dave UK...
That has kinda generalised it alot for me in a good way.
I kinda knew what must happen when the top screw was turned in and all that.
One thing that gets me though. The toothed wheel under the spring, I'm pretty sure that no matter how compressed it is, the rate is the same. Ie, it'll take the same pressure to push it the same amount. Or a better way to put it, it's deflection from rest is the same under the same boost pressure.
Therefore, we set it's rest position using the top screw, and it's maximum travel using the screw wheel underneath it.
Then we can alter the fuelling amount itself using the offset cone on the end of the rod.
So ideally I think, just guessing and from my own testing, that the toothed wheel may as well be right in, since we will always (if we do it right), have sufficient air for the fuel we pump in.
Setting the top screw out more, so the cone sits higher, will reduce fuel off-boost. Now, we have more travel, so at full-boost, the fuelling is the same as usual. Now, we can turn the cone, so it ups the fuel off-boost to essentially where it used to be. Now, we have the same base rate fuel, but on-boost, the fuel is much higher.
This is what we need to get the most out of the upped boost from a turbo, without it smoking lots when the turbo is off-boost.
Afterall, no matter what we do to the car, the off-boost fuelling and air intake is fixed quite stricktly. Only maybe a fancy air filter or what not will allow more low-end fuelling.
So even when we up-boost on the turbo, our off-boost fuelling needs to stay the same no matter how much we have turned up the turbo.
Thats what was getting me, and I wanted to know how to get more fuelling up top, but no more low-down. The only way I can see this being done is by altering the travel of the rod and diagphram, and thats why you must have to alter the top screw so at rest we can have the same fuelling, but when it defelcts it can allow more fuel...
This is just from my little experiments and what I've read.
Dave UK, do you have a KKK or a Garret turbo? I read 1 full 360 degree turn on the wastegate arm is 1 psi. So if you did 5 turns, you'll have ~18-20psi, or ~1.1-1.25 bar boost!?
Is that whole 1 turn = 1 psi boost thing reliable for a garrett? I think it's time I got a boost gauge just to make sure.
And I'm still getting that damn power-loss thingy, I can't seem to fathom it. I think maybe my wastegate has got weaker and flaps about, so it'd be a good time to tighten it up a few turns :)
Seya
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Post by gjb02 »

I think an adjustment in the spring pre-tension is what the toothed wheel effects.
By pre-loading the spring pressure the amount of boost required to initial compress it is increased, therefore the hystersis of the spring is effected, the spring wont compress as quickly or as much for a given level of boost.
The 'on boost' fuelling would come on later and take longer to reach its peak. This would marginally shift the power curve.
I would imagine this would be a good adjustment to make to compliment a rise in boost pressure along with the max load screw, and eccentric plunger adjustment.
If I'm mistaken please feel free to correct me.[:)]
DaveC
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Post by DaveC »

I'm not 100% about the spring pre-tension being of much relevance to how the pressure pushes on it.
If I screw my toothed wheel right in, I still have to press down to fit everything back on, so the plunger is already "primed" on the spring.
Since the spring is constantly coiled and of constant cross-section, the force it exerts is linear. So no matter how compressed it is already, a 2psi pressure change would always deflect it the same amount, no matter how compressed it already is.
Afterall, if this is wrong, then there is no obvious way we can turn up on-boost fuelling while leaving off-boost fuelling the same, which is what must be done when we up the boost pressure lots.
Ie, if I run 1.25 bar boost, I need lots more top end fuel, but hardly any more bottom end otherwise it would black smoke loads before the turbo kicks in.
To do this, we need either the plunger to go down further (which it admittedly will with more boost), or to start higher up, and be turned also so that the "pin" that presses against the plunger is in a similar position to usual when off-boost (ie, start further up the plunger cone, letting the pin out more, but turning it so that it is pushed back in again against the eccentric offset of the cone).
OK, having more boost will press it down more, which is maybe why you want to turn the toothed wheel so it can actually go down more.
The problem is, at peak boost (where the plunger is pressed most), the rpm and fuel mixture and air are at a given ratio.
As we increase rpm, we gain no more boost, so we have to reduce effective fuelling per cycle (even though overall consumption goes up). To do this, I don't know if the pump relies on some other mechanism, or relies on the dropping boost to cut it back!?!?
I think trial and error is the best solution, and try extremes and see the effects on power delivery and smoking etc.
The main problem on mine right now is slight smoke just off-boost, but totally clean on-boost. I could do with more top end fuel, but less bottom end. There is only the overall fuelling screw, or the eccentric plunger which is also an "overall" fuel change. I need to turn up the top end only, the on-boost, and to do this I assume we let the plunger come up more, reducing overall fuelling, but having the same deflection maximum, keeping top end fuelling. Now we can up overall fuelling either by turning the plunger or the screw, bringing base-line fuelling back to normal, and on-boost fuelling up...
Thats the only way I can see it working anyway, and again, if I'm wrong, let me know :)
Shame Alan Allard or Diesel Doctor guy don't visit here :(
Seya
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Post by rossd »

Even if they did visit, they wouldn't say much I expect, they wouldn't have an income if they did! The Derv Doctor frequents the PSOOC forum and he doesn't tend to answer specific questions. Same with Allard, I emailed them with a query just like this and they said "We would have to see the car"
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Post by RichG »

Dave,
Whilst you are correct that the 'spring rate' of the spring will be linear throught its range the pre-load will make a difference. If the only adjustmant is to screw the star wheel down then this pre-load will be decreased. The fuel off boost will be the same but the diaphragm will start to move at a lower boost pressure (force = pressure x area)hence more fuel will be applied whilst on-boost. However the diapragm will stop moving when it hits the nlyon ring below it or the spring gets coil bound. I have read of a guy in the USA who sanspapered the nylon ring to get more movement!
If the diaphragm is rotated to give a greater slope towards the pin then the top adjustment screw must be wound out to keep the same fuel off boost. I am not sure whether the max fuel screw alters the fuel throughout the range or just the maximum.
If the dimensions of the cone, body and spring rate were known then the relative differences made by adjustments could be calculated as there must be a boost pressure above which no more movement of the diaphragm is possible.
Richard
DaveC
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Post by DaveC »

Hmmmm...
So, is the cone shape non-linear in it's angle with the pin that slides against it?
Ie, is it steeper as it is turned?
As far as I could visibly see anyway, it just looked offset, so I assumed turning it just altered the fuelling constantly across the travel of the plunger.
I did think, if you were a clever person with the right tools, you could make your own plunger, with a profile just right for what you wanted, and a spring with just the right force to be fully deflected at your peak boost.
Anyway, back to reality...
I notice on the cone is a groove where the pin which controls fuelling presses against. This pin has got an obvious "travel" on the cone, and so we can assume that the plunger moves that much.
To turn up the fuelling overall, we can (assuming it's gradient profile is linear around the plunger, just offset) turn the rod to turn up the fuel, essentially letting the pin come out more. Now we have more fuelling, a bit like the fuelling is ahead a bit relative to where it was in relation to the boosting. Ie, 10% more across the range.
Now we are just getting black smoke at the bottom end, so thats ok, but we have loads more air at the top end, so how do we pump in more fuel to get the power?
I don't know if this can be achieved with that top screw thing or not. The only way to properly achieve it any way you look at it is to increase the travel of the plunger.
Thats what is confusing me :) I suppose if we take the top screw out, we are de-tensioning the spring, but we are never the less reducing fuelling off-boost, while still attaining the same deflection assuming no spring stop or spring binding.
I guess that the plunger will have more movement off-boost now there is less pre-compression in the spring. But it should have no more overall deflection until it catches up to where the pressure was enough to resume defelction of the plunger when it was in a pre-compressed state.
I think I'm confusing myself now... I really wonder if this is the only way to adjust it. A good indicator may be that the top plunger screw is marked and totally covered on some pumps, almost as if it is a VERY important part to alter/mess up. Might point towards it being quite important for tuning purposes (ie, they cover up what they don't want you touching).
I suppose if I get the Allard Top mount intercooler kit and boost adjuster stuff, the leaflet will explain it all for me. Will definately do a DIY job, Bristol is so far from Leeds :)
Mind you, Mi16 rear axle and new shocks first I think!
Seya
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davek-uk
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Post by davek-uk »

Dave, as you say fuelling off-boost should stay the same; that is why once the cone/pin is adjusted to give more fuel (at any one point) you have to turn the top adjuster back to raise the starting position of the diaphragm to lessen the fuel again. This would also give you a larger overall movement of the diaphragm, as it is higher at rest. I have also heard of shaving the bottom stop.
I didn’t have a lot of time to play when I did my adjustments so I don’t know for sure how the toothed wheel adjusts the spring. I only turned it 5 notches and the wheel must have 40 or more around it. Now, does the wheel go up and down to shorten or lengthen the spring or does it wind the spring up or unwind it (unlikely)? A diagram on this page may help http://dodgeram.org/tech/dsl/more_power/Power_ve.htm
When I had a look at mine and tried some of the adjustments I had read, I couldn’t decide exactly what I was looking at. The diaphragm was screwed to the bit under it. Under the diaphragm rim was a cone effect and a spring with the toothed wheel below. As I couldn’t see any dirt and muck in there I assumed that this top part never came into contact with fuel; therefore the cone and pin that let the fuel through must be under all this – is this correct?
How do you adjust the cone and pin configuration? Do you merely turn the diaphragm and assembly as a unit or do you have to unscrew it to turn the diaphragm against the cone under it?
I must stress here I have a late pre-facelift with the infamous XUD9TE "DHY" code engine, a Bosch AS3 pump and a Garret turbo (not KKK as I said earlier).
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