How to check the fuel pressure

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Member since: May 10, 2010


Germany

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This post was moved to this forum by the moderator Weiß-Blau-Fan-Rude on May 16, 2010 at 19:51:32 from the forum "3er BMW - E36".

can someone tell me if and how you can check a petrol pump to see if it is defective

Edited by: Weiß-Blau-Fan-Rude on May 16, 2010 at 7:51:32 PM
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Hello krecki,


is the question still relevant?

There are many ways to check the function of a fuel pump.
To what extent the various methods are meaningful is a different story.

I assume you mean a normal intank pump. No high pressure pump,
Main pump, tandem pump or similar pump variants.

On the one hand, the applied voltage is measured first. That always happens (!)
in parallel with a connected pump. Unplug the plug and just use a multimeter
Placing it on the pins for plus and minus may result in a numerical value, but
there is no load, so to speak, the load on the current, and the result is not
one hundred percent meaningful. Even if there is only one functional cable in one cable
If a strand is present, the nominal measurement result is correct, a load, i.e. more operational
Pump, but this strand is not able to cope. To it physically (it is nothing else
namely) to express: The "cable" would be too thin and could burn through.

Of course, instead of the pump, you can pull out the plug and use one
Connect load resistor. In the case of an in-tank pump, a 21 watt lamp is sufficient.
An H7 lamp is also suitable should this be on hand.

If it can be determined during this measurement that the existing voltage is not present,
is to investigate. The reference voltage is always the on-board voltage present.
When the engine is not running, the battery voltage. The rule of thumb is that for each supply line,
i.e. positive or negative cables, 10 percent voltage drop form the limit values.

A simple circuit can also be switched with suitable cables.
It is important to ensure that the correct cable cross-section is used
are best secured with a fuse. In case of doubt: thicker cables
use. It is important to ensure that the polarization is correct. This means,
that you connect the plus pin of the pump to the voltage plus. Otherwise
if you reverse the polarization, that is to say so, and the pump no longer pumps
but sucks.

The following measurement is also possible, you can use it to make an initial assessment
but I personally recommend that you follow this up with further tests:
Place a clamp meter over a power cable, regardless of whether it is the plus or minus side, and
The flow rate in pressure can be inferred from the amperé value determined.
However, this is not a verifying measurement, but an approximately calculated one.
As a rule of thumb, a functioning pump approx. 1-2 amperes per one bar delivery rate
Requires electricity. If a pump is supposed to have a delivery rate of 3 bar, then it is allowed
There is a 3-6 Amperé power requirement. If more amperes are needed, the pump is one
first assessment firmly. This is because there is an increased internal resistance
is present under load without a corresponding delivery rate.

If you want a trivial solution, you can of course check the delivery rate. This is different and can always be found in the relevant manufacturer's documents.
So, so to speak: hose off, power to the pump and the fuel run into a cup
to let. A certain minimum amount must be promoted within a certain period of time.
This is called the defined delivery rate.

In the last place, and only for the sake of completeness, I mention the ohmic measurement
the winding in the pump. Add an ohmmeter to the dead (!) Pins of the
Place the pump and read off the value. If the nominal value is in the megohm range, this is it
equate to an interruption. Infinite resistance is an interruption.
A result in the milliohm range is a short circuit. These three states, correct measurement
and a very good ohmmeter presupposed, oh and no noise can me as measurements
are designated. All other values ​​that can be determined are not real
meaningful. This is due on the one hand to the windings of the pump and on the other hand to the ohmmeter,
because there are simply too many differences in quality with these. The main reason, however, and
it depends, is simply the one that comes from this simple, plain, trivial measurement
No final (!) statement can be made for a long time, as other factors are involved
cannot be determined and therefore taken into account.


All right ?!




Greetings Bardock

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