checking fuel pumps as maintenance

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  • ephratah service center
    Senior Member
    • Oct 2007
    • 143

    checking fuel pumps as maintenance

    Do any of you guys check fuel pumps with amp clamp as part of regular maintenance. I had a jeep in and customer asked if there was a way to test the fuel pump and if they ever go bad. I put an amp probe on the pump and sold a new pump based on the wave form I showed customer wave form of old pump and wave form of new pump. It looks to me like there was 1 segment on its way out on the old pump
    Attached Files
  • Witsend
    Banned
    • Nov 2012
    • 2942

    #2
    Well it still works 6 days a week

    Be Like Impeaching "Carter" before his term is up because one day a week he's down at the peanut farm

    Comment

    • Crusty
      Senior Member
      • Dec 2007
      • 2450

      #3
      There can be many factors affecting fuel pump testing. In your case here, the amperage "seems" a bit high (aprox 7.5 to 9.0 amps), but what is "normal" for these vehicles-??
      In SSC, you can use the cursors to analyse what you have recorded in more detail. The second from the right white button, at the bottom of the shown screen, changes the SSC view to three different views. One of those views will show the details of the trace, and you can activate the cursors and move the cursors to see exactly what the high and low amperages are between each pump motor segment. This will also show the frequency, and when you select an entire revolution, be it six segment pump, or 8 segment pump, or 10 segment pump, you can calculate the pump speed as well. Again, what is "normal" for this type of vehicle-??
      I have seen better appearing waveforms, and I have seen worse appearing waveforms too.
      If you can post up the waveform for the new pump, how much difference is there-??
      Most of the pumps I have tested this way are running about 2 amps less than what this vehicle is, but may not be definitive. The only way to know is to build your own "known good" for a particular vehicle type or category. Pickup trucks may be different than cars, or Ford may be different than Toyota.

      Comment

      • diesel71
        Senior Member
        • Feb 2008
        • 921

        #4
        that pump is an 8 segment pump and id say yes you have one bad segment.
        I always found it useful to have a known good screen shot and compare it like crusty said.

        Comment

        • derktins
          Member
          • Oct 2012
          • 37

          #5
          I would not have replaced the fuel pump based on that waveform alone. Unless there is a major dropout in the waveform, I don't like to condemn a pump based solely on this test.

          I think it was Jim Wilson who once said on iATN "There are 2 kinds of fuel pump waveforms, 'obviously bad' and 'other'"

          I think this one qualifies as "other".

          Lots of perfectly good pumps have waveforms like this one, where one segment looks a little bit "wonky". Try scoping some new pumps, and you will see what I mean.

          What I prefer to do as a "health check" on pumps is the current waveform test along with a pressure and flow test. If it's an engine that is difficult to connect a fuel pressure gauge to, then I would do the current ramp test and also a few WOT runs with the scanner. If the waveform is "other" and the O2's all stay high during a WOT run, then the pump is probably OK.

          Comment

          • sbreland73
            Senior Member
            • Jan 2009
            • 1076

            #6
            One more thing to consider: many a new vehicles are now using modules to PWM the pump to regulate fuel pressure. This will in turn affect the waveform based on load. While this test does serve as a relative indicator of health for a standard pump, I would not roll the dice on this alone.
            S. Breland

            Comment

            • ephratah service center
              Senior Member
              • Oct 2007
              • 143

              #7
              Here is the new pump after I installed it in the jeep the waveform looks much better amps are still on the high side but like the wave form.I have a 2 TB hard drive with a ton of files saved just did not have a jeep fuel pump in my data base. Thanks to Crusty for teaching me to build my own data base and when I test drive a car to grab as much data as I can. Crusty has been a good mentor for me over the years that I have known him and has been a big help when I get the ones that leave me scratching my head he has always given me sound advise and has kept me focused to dig a little deeper and find the real issue.
              Attached Files

              Comment

              • greasybob
                Senior Member
                • May 2008
                • 1590

                #8
                I would say that you made the right call. Did you replace the filter also or is it part of the pump assembly. The only thing that I would have done differently is to check the amp draw as you did and check the wave form integrity at a lower amp setting and set the scope to AC coupled. A pump as shown in the first screen shot could have the unfortunate luck of stopping in just the right spot to need a "thunk" on the tank to get it started again.

                Comment

                • Witsend
                  Banned
                  • Nov 2012
                  • 2942

                  #9
                  I think it's a good call too, but like people , just because one might hang a little lower or be a different size , it don't mean it still can't do the job with a good slap on the bottom.

                  Comment

                  • Crusty
                    Senior Member
                    • Dec 2007
                    • 2450

                    #10
                    Originally posted by ephratah service center
                    Here is the new pump after I installed it in the jeep the waveform looks much better amps are still on the high side but like the wave form.I have a 2 TB hard drive with a ton of files saved just did not have a jeep fuel pump in my data base. Thanks to Crusty for teaching me to build my own data base and when I test drive a car to grab as much data as I can. Crusty has been a good mentor for me over the years that I have known him and has been a big help when I get the ones that leave me scratching my head he has always given me sound advise and has kept me focused to dig a little deeper and find the real issue.
                    That is a much nicer looking waveform. The amperage "may" be normal for this type of vehicle. Also as mentioned, with the Fuel Pump Control modules varying the pump speeds, things are not carved in stone.
                    As you are doing, taking data from "known good" vehicles gives you something to measure against at a later date.
                    Quite often, when a regular customers vehicle is in for service, and I have time, I will grab data and save it. Sometimes a vehicle is fine for several years, then something misbehaves, and looking back at that same vehicle history files, shows where there is a difference.
                    This capability (saving data), along with SSC, is probably the strongest argument in favour of the Snap On equipment. It is something many, if not most, OE tools do not have the ability to do and it is so easy to do.
                    Sometimes I have seen waveforms such as the first one, yet the vehicles are fine, and have remained fine for several years. I don't think the waveform by itself warrants changing a pump out. I have also seen brand new, both OE and aftermarket, pumps appear as the first waveform.
                    The customer must have had some reason for asking. If that was the case, and the pump could be the culprit, the first waveform supports something that is not optimal, and thus a change out wasn't a bad idea.

                    Glad to be helpful. This website does away with all the "drama" evident on other websites and sensible discussions are possible.
                    Thanks to Snap On for hosting this site, and thank you for reliable capable equipment that in many ways puts OE equipment to shame.

                    Comment

                    • wrenchtamer
                      Junior Member
                      • May 2017
                      • 9

                      #11
                      I like the thread so far. Clearly there are a lot of knowledgeable folks here. I have done this before as well and have scoped probably at least 100 plus fuel pumps. I,too make a habit of doing it if it's a customer that I know would rather spend the money than risk a breakdown. My good customers know I do a lot of testing in ways that other shops don't and usually dont really care to know how I make a determination after the first or second explanation. A word of caution though. Many commutator style fuel pumps will have a waveform that looks terrible on a new pump until it is well broken in. I am actually surprised at how nice the one above looks. Anyway hats off to you gentlemen. This forum is great.

                      Comment

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