 Attempts
kfz-tech.de/PDM34
No, actually, the distributor pump doesn't belong on an injection pump test bench. After all, what are you supposed to check and adjust, such as the delivery rates for the individual cylinders? You can't change
those here anyway. However, there was a Bosch mounting kit available, presumably to check before a possible replacement or to analyze the control behavior.
But the test bench has proven itself to be very useful for training purposes. Pictured above is a conventional pump that measures the internal pressure with a pressure gauge filled with glycerin, with the display
showing particularly little wobble. This allowed a direct correlation to the adjustment of the delivery pressure.
We took things much further. At some point, electronic diesel control with the corresponding distributor pump came along. But where would the control unit get its information regarding engine speed and the
position of the crankshaft and camshaft? Then we noticed the test bench's comparatively large flywheel, and by gluing metal pieces in two rows, it was actually possible to fool the control unit into thinking it
was in a real BMW engine compartment.
| Even though none of the glued metal pieces ever came loose, a protective device is still
necessary. |
Here is an electronically controlled VE pump for manual operation, of course with weaker springs.
kfz-tech.de/PDM35
You have to be careful. Is it a signal from the camshaft or the crankshaft? For the latter, twice as many are needed. But the two sensors aligned to the respective metal circuits performed their duties without
complaint. The way was clear to take a closer look at the control unit and its programming. If you look closely, you can see some of the metal pieces that were obviously not needed for this pump.
How does the injection quantity alter when you change the fuel or coolant temperature? The latter obviously has a much greater influence. How does the engine speed control work in the lower range?
Apparently, the BMW engine had an acoustically unpleasant range, which it was essentially overcome by separating the accelerator pedal and the quantity control. This is, of course, only a small part of the
findings.
You see, the (expensive) injection pump test bench was worth it, especially afterward with the recording of signals through the (storage) oscilloscope. Of course, the same applies, or perhaps even more so, to
the in-line pumps. In comparison, the systems sold by some teaching aid companies are clearly inferior, for example, because the motors aren't as powerful. If the engine speed drops during a flow comparison
measurement, you can't tell whether it's due to that or the control system.
Experimenting with electronic diesel control might even have allowed you to discover for the first time what a characteristic map actually is. In the beginning, there weren't as many parameters as there are
today, for example, where you don't know exactly which information sent to the control unit caused this or that.
The easiest way was to determine the idle and governed speed. You only need to measure the fuel quantity at the relevant speeds, either at full throttle (cut-off) or at idle. Then you can see that, above a certain
speed, the injection quantity decreases (cut-off) or increases (idle), and you know you've exceeded the desired speed.
If you're not working in a well-ventilated workshop, you can also use odorless silicone oil. This is also safer than diesel fuel. However, the initial fill of the fuel injection test bench's tank is quite expensive. This
is another reason why you should try to minimize waste as much as possible. Tests with diesel injection alone also demonstrate how noisy it is.
kfz-tech.de/PDM36
Smaller and more affordable test benches are also available for common rail. In the chapter 'One Screw' you'll find an example of how to implement something similar on a diesel engine.
kfz-tech.de/PDM37
And then, of course, there are proper test benches for common rail. Before you start thinking, though, the price of a now-ended eBay auction was already €69,000. So how much might the original Bosch price
be? Here's a look inside . . .
kfz-tech.de/PDM38
kfz-tech.de/YDM13
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