Electric Fuel Pump Issues

[marthur]

8 years? My boat was built in 1979. The A4 still has the original electric fuel pump. Seems to still be going strong.

You might want to take a look at the diaphragm on that pump during your annual maintenance. On my 1977 the pump worked great, but the diaphragm was showing its age. I think it might have worked for a long time, but they will eventually fail. So I installed the Moyer rebuild kit to get another 35 trouble free years out of it.

[Administrator]

Originally Posted by ndutton

Only if the ignition system wiring is too small. That's the definition of voltage drop.

Yep.

Bill

[sousou]

So I managed to make it out to the boat for a few minutes today and took some readings.

Volts at Coil: 13.6 at high RPM in gear (i don't have tachometer)
Ohms: 3.3-3.5
Does that look OK? The coil is definitely hot to touch. I can touch it maybe 3-4 seconds before crying uncle.

Any reason a 3 ohm coil would measure 3.5? Maybe I need to head back and take a better reading?

[ndutton]

It's pretty common for coil resistance to vary around 10% of specification, don't know why, it just does.

Do you have electronic or points ignition?

[romantic comedy]

Tolerances.

You meter may be a little off. The coil may be a little off.

Nothing is ever exact. Drill a 1/2 hole in a piece of steel. The drill was 1/2 inch at what temperature. The hole will vary with temperature......etc.

Guys here will measure the coil and then accept that as the absolute fact. There is always some error.

[ndutton]

Originally Posted by romantic comedy

Guys here will measure the coil and then accept that as the absolute fact. There is always some error.

. . . . but doesn't measurement give us the best information possible? If not by actual measurement then what??

[romantic comedy]

Neil, it depends on the instrument.

I have an expensive fluke multi meter that I trust. We never get the exact answer. That may sound weird, but that is the way it is. Things are designed with tolerences. There is always a plus and a minus.

There is a lot of discussion about coil voltage and resistance. Sure we can measure the coil and calculate the required resistor to add to the system. There again is an error present. But the coil also has a working tolerance. it may be a variation of several volts.

I also have a few cheap multi meters. i have measured a battery charging at 15.5 to 16 volts with the cheap meter. I go and check with my fluke and it measures 14.4 volts.

[ndutton]

Please keep in mind we aren't taking the calculations to the razor's edge. We factored in a 15% margin of safety in the ballast resistor calculator and thus far the solution has been successful regardless of who measures what with whatever test instrument.

[romantic comedy]

I have wondered what measurement is more accurate with our meters, resistance or amperage.

For the ignition sysytem some are adding a resistor to control the current. 4 amps is the max. The coil resistance is measured and a current is calculated. A resistor is added and the current is assumed to be what the calculation found.

I would prefer to measure current to find the proper resistor to add. Then measure the curent after it is added.

Then again, we have plenty of wiggle room. The resistor can vary quite a bit.

The answer is that Yes measurement is the best way for us to find the resistance.

[HalcyonS]

yes, I'd wondered about the tolerance in coil resistance readings. Most electronics components have a tolerance range - they're mass produced after all. Resistors and eletrolytic capacitors are usually +-10% or 5%. That is why resistors come in those odd values 2.1, 3.3, 4.7 etc...That is the bounds of their precision. And certainly, heat etc will change values. The coil is a power element, and inductive - the rules for induction are different from resistance - inductance is a bit arcane. just my two cents.