Fuel Pump Waveform - BAD

[sly dvl]

Just thought I'd share this. Scoped the fuel pump on my ZR2 today and confirmed my suspicions, time for a new pump.

The waveform should resemble the example in the top right corner of the scope screen. As you can see, mine looks NOTHING like the example.

Between the #1 & #2 vertical lines represents one revolution of the pump. There should clearly be 8 humps. I suspect the brushes are just about done in this pump

 

[sly dvl]

Re: Fuel Pump Waveform - BAD

Well, replaced said bad fuel pump this week. Ha! No wonder the waveform looked like it did.
Check out the pics...

That should be a flat surface, not deeply grooved.
I suspect this pump was the original, with over 250,000 Km's on it.
Replaced it with a Walbro.

The brushes resemble an old Fisher Price record :rotf:

 

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Re: Fuel Pump Waveform - BAD

x2

 

[sly dvl]

Re: Fuel Pump Waveform - BAD

Current ramping is the latest and greatest diagnostic tool. I've been using it for years to diagnose bad grounds, poor connections, shorted windings etc. Basically, you're measuring current draw, but on a Digital Storage Oscilloscope (DSO), as opposed to a DVOM. Lots of good info here:

http://www.lindertech.com/fuelpump.htm

You can determine the RPM of the pump by placing the cursors at the start and finish of one revolution (see post 1, pic 2), looking at the time frame, and then doing the math. Since most pumps have 8 commutators you just count 8 humps. My pump was so bad I had trouble counting 8 humps, so I just looked for a common repeating pattern and used that as a start finish point. Most stock fuel pumps run between 4000-6000 RPM.

I'm going to scope the new Walbro pump so I have a comparison and post pics in the near future.

I agree, Dave. I'm sure this was the original pump and was just suffering from normal wear & tear.

 

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Re: Fuel Pump Waveform - BAD

Where'd you get a DC inductive I probe?

Another reason to save up for that pc based waveform analyser.

 

[sly dvl]

Re: Fuel Pump Waveform - BAD

Where'd you get a DC inductive I probe?

Another reason to save up for that pc based waveform analyser.

Most Electrical supply stores should carry one. However, if you're looking for one that will plug into a laptop, you'd have to shop around a bit.

I was using a Snap-On VantagePro DSO with a Blue-Point low amp current probe.

 

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Re: Fuel Pump Waveform - BAD

Thanks,
They have analyzers that plug into the usb port that are overkill for automotive use unless your trying to analyze ecm signals. They should be able to read the blue point probe since it has a mv output.
They cost a little more than I want to pay though. Probably about as much as your snap on dohickie.