1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot down?

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kenbw2
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1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot down?

Post by kenbw2 » 06 Jan 2018, 18:28

On my XUD9s and my DW8, the Bosch pumps allowed you to fiddle with the fuelling to get a bit of extra oomph. I'm sure many of you know the way - keep putting it up till you get black smoke, then back it off a bit.

I understand that that adds more fuel into the air/fuel mixture. But then isn't that all the throttle does? Is there a difference?

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by MikeT » 06 Jan 2018, 18:48

What throttle are you meaning? If you're talking about the accelerator pedal on a diesel, that controls fuelling only, there is no control on the air intake.
Its different in a petrol as that has to have the air controlled, thus "throttled" with a butterfly.

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by kenbw2 » 06 Jan 2018, 19:24

Yea that's kind of what I'm getting at. When I press the accelerator pedal down, that adds more fuel to the combustion chamber. I understand that nothing controls the amount of air going in.

So what does that adjustment do, if not just exactly the same thing as the accelerator pedal?

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by MikeT » 06 Jan 2018, 19:27

Your right foot is "tempered" by the fuel pump's internals, mainly the governor which controls fuelling based on rpms. So a factory-set pump may deliver x-amount of fuel for given conditions, whereas a "tuned" pump will likely deliver a little bit more - and so across the whole range of conditions.

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Michel
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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by Michel » 06 Jan 2018, 19:32

It increases the time the fuel is injected for when you open the screw, thus allowing more fuel in. It's not the amount of fuel specifically that changes, but the time it's injecting fuel in..

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by MikeT » 06 Jan 2018, 19:39

It depends which control you're talking about Michel, of which there are a fair few, not including addtions according to application (ie, LDA for instance). I'd assume you're talking about what's commonly referred to as the Max Fuel screw?

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by Michel » 06 Jan 2018, 19:50

MikeT wrote:
06 Jan 2018, 19:39
It depends which control you're talking about Michel, of which there are a fair few, not including addtions according to application (ie, LDA for instance). I'd assume you're talking about what's commonly referred to as the Max Fuel screw?


I am indeed talking about the screw :-) One can mess about with the LDA too, but that's more involved and fiddly. A common XUD Turbo mod was to turn the screw and adjust the wastegate to up the boost too

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by MikeT » 06 Jan 2018, 20:06

Michel wrote:
06 Jan 2018, 19:50
MikeT wrote:
06 Jan 2018, 19:39
It depends which control you're talking about Michel, of which there are a fair few, not including addtions according to application (ie, LDA for instance). I'd assume you're talking about what's commonly referred to as the Max Fuel screw?


I am indeed talking about the screw :-) One can mess about with the LDA too, but that's more involved and fiddly. A common XUD Turbo mod was to turn the screw and adjust the wastegate to up the boost too


Most find that screw first and are entirely satisfied with the results (as you say, if turbo fitted, then wastegate next) for a good performance hike.
It is pretty potent for a simple bit of screwing/spannering ! 8-)

And yes, the LDA tweaks are other tunable items if it has a turbo fitted. More involved and fiddly, but equally as satisfying imo. And there's even more that most don't bother with.

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by kenbw2 » 07 Jan 2018, 01:00

Still feel a bit lost with this I'm afraid. I guess there are other ones to adjust the advance, but that's probably (I don't think so anyway) the one I'm referring to.

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by Peter.N. » 07 Jan 2018, 12:12

You can't generally adjust the advance without changing parts as its preset when the pump is originally made and there is no point really. The Bosch fuelling is easily adjusted by the screw between the pipes on the back but it goes anti clockwise to increase the output but if you overdo it you get a lot of smoke which might not only get you stopped but doesn't do the engine a fuel consumption a lot of good either, the smoke will reduce as the turbo comes on song as that increases the air input.

If you seriously over fuel it its not kind to the engine, it will produce more power but will also get hot, that and the increased power output could lead to head gasket failure and all the soot produced doesn't do it a lot of good either. I would leave it alone if I were you, increase it a little if you like but not to the point that it seriously smokes.

To answer your original question, yes the 'throttle' does control the amount of fuel you inject but only up to the maximum allowed by the 'max fuel' setting on the pump, if you adjust it will increase the max allowable input.

Peter

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by MikeT » 07 Jan 2018, 16:05

kenbw2 wrote:
07 Jan 2018, 01:00
Still feel a bit lost with this I'm afraid.


Assuming you're still unsure about the accel pedal vs max fuel setting, perhaps a more simplistic comparison will help?

Think of a garden hose with a trigger gun outlet connected to a standing pipe tap.

The max fuel screw is akin to the restriction that is the standing pipe tap.
The accelerator pedal is akin to the trigger gun on the other end of the hose.

If you fully open the trigger gun (accelerator), you will only get the maximum flow that is restricted by the tap (max fuel screw).
By opening the tap further, you increase the max flow that you can control at the trigger.

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by Peter.N. » 07 Jan 2018, 17:17

That'l do :wink:

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by kenbw2 » 07 Jan 2018, 18:50

MikeT wrote:
07 Jan 2018, 16:05
kenbw2 wrote:
07 Jan 2018, 01:00
Still feel a bit lost with this I'm afraid.

The accelerator pedal is akin to the trigger gun on the other end of the hose.


Ah, so the answer is that there is no difference between the two, but the max fuel screw means that the top limit is raised a bit. Makes sense.

I did have mine adjusted once and I've had some jiggery pokery with my pump advance and noticed it's not smoking at all at the top end anymore. Was considering doing it again so that I can get that extra bit out of it. God knows the DW8 needs it. But it made me think, surely it's just the same as putting my foot down a bit more.

It could be just right as it is, but I'd like to have a play to push it as high as it can get without wasting fuel.

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by MikeT » 07 Jan 2018, 19:24

kenbw2 wrote:
07 Jan 2018, 18:50
MikeT wrote:
07 Jan 2018, 16:05
kenbw2 wrote:
07 Jan 2018, 01:00
Still feel a bit lost with this I'm afraid.

The accelerator pedal is akin to the trigger gun on the other end of the hose.


Ah, so the answer is that there is no difference between the two, but the max fuel screw means that the top limit is raised a bit. Makes sense.
No, not just the top end, the whole accelerator range.
Think of the trigger gun held at 50% open; when you open the standing pipe tap more fully, more water will flow out the gun without moving the trigger.
kenbw2 wrote:
07 Jan 2018, 18:50
I did have mine adjusted once and I've had some jiggery pokery with my pump advance and noticed it's not smoking at all at the top end anymore. Was considering doing it again so that I can get that extra bit out of it. God knows the DW8 needs it. But it made me think, surely it's just the same as putting my foot down a bit more.

It could be just right as it is, but I'd like to have a play to push it as high as it can get without wasting fuel.
Yes, there are many settings that affect others and these need to be balanced to obtain the best tune. The factory setting not only needs to take power into account but engine longevity, emissions, passenger comfort and noise outputs too. changing one compromises others, as already advised by other posters.

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Re: 1990s Bosch diesel pumps allowed for increasing fuelling. What's the difference between that and putting your foot d

Post by Paul-R » 07 Jan 2018, 19:40

You'll also find that if you increase the fuelling on the mixture screw that you'll have to reduce the tickover. It went up when I had my old Montego tuned.