When a ground wire does not make a good contact, can it have the affect of damaging the fuel pump?

waltpairwaltpair Posts: 1
edited August 2017 in Mitsubishi
I own an automotive repair facility in Georgia. The purpose of this letter is to get opinions on a procedure that we did on a 2002 Monterro Sport. Customer brought truck in by tow for a no start. After charging the battery we could crank over the engine but it would not start. Next, to see if it was a fuel, electrical, pcm, theft system, ignition switch or some mechanical issue. Sounded like it had compression so we moved on to fuel as the suspect. With a few sprays of carb cleaner we could get the engine to run for a few seconds. With this we are pretty sure of a fuel issue. After removing tank and then pump, we were able test the pump by energizing and grounding to a 12 volt battery. Pump would run for about 1 second before it would stop. It seemed like it was binding internally. Put in new pump, replaced tank, cranked and truck ran fine. Test drove and called customer to pick up. 2 hours after customer drove away, she called me and said truck would not start. Truck is towed back and we began to check and double check. We narrowed our search to the fuel pump relay in the kick panel and replaced it. Truck started and ran fine. Test drove may times to make sure of repair. Customer, again, drives away. About 4 weeks later I get a text from the BBB saying that the customer wants all their money back. She said she drove the truck for 2 weeks and then it would not start again. She then had the truck towed to the dealer and they said that they found a ground wire that was bad. They made the statement that the fuel pump and pump relay was not the problem. Our position is "yes" a ground wire could be an additional problem, but because of the test we did to the original fuel pump it was confirmed bad. The dealer of course had no access to the original pump and therefore could not rule out its failure. What do you think of our procedure and is it possible that the fuel pump failure could cause the pump relay to malfunction and also cause damage to ground wire?














Answers

  • thecardoc3thecardoc3 Posts: 5,422
    Based on how you described your testing routine it cannot be proven that the ground wire was not the fault the whole time. With a solid routine that takes advantage of modern tools problems like this can be avoided. One of the first things that I would recommend is join the iATN and spend time studying and interacting with the technicians in that forum. Had you have done that a long time ago your testing routine for proving the state of health for the fuel pump and it's control circuit would have included using a low amps current probe and a digital oscilloscope.
    waltpair said:

    I own an automotive repair facility in Georgia. The purpose of this letter is to get opinions on a procedure that we did on a 2002 Monterro Sport. Customer brought truck in by tow for a no start. After charging the battery we could crank over the engine but it would not start. Next, to see if it was a fuel, electrical, pcm, theft system, ignition switch or some mechanical issue. Sounded like it had compression so we moved on to fuel as the suspect. With a few sprays of carb cleaner we could get the engine to run for a few seconds. With this we are pretty sure of a fuel issue.

    While that is a quick test to see if the engine would run if it had fuel, it is insufficient to justify the next step of pulling the tank to test the pump manually as you describe in the next section. This is the point where the scope should be attached to measure the power supplied to the pump, the ground circuit voltage drop and the current flowing through the pump all at the same time along with the fuel pressure should any be produced. If the pump was electrically failed or binding as you suggest the current flow and pump speed would be incorrect while source voltage and the ground circuit would not have displayed excessive voltage drops.
    waltpair said:


    After removing tank and then pump, we were able test the pump by energizing and grounding to a 12 volt battery. Pump would run for about 1 second before it would stop. It seemed like it was binding internally.

    The biggest problem right now is that this test did not include the power nor the ground circuit on the vehicle. There may have been a fault in your test connections resulting in the pump not operating as expected and tricking you into thinking that it was failed. Had you of tested correctly in the car with the scope and current probe you would be able to reproduce testing data supporting your diagnosis like this.

    This is a bad fuel pump.



    Here is a car that has a good pump but the fuel pressure is dropping because of a restricted tank sock.





    Had that vehicle been losing power or ground, the current flowing and the pump speed both would have dropped. These captures show the pump speed increasing as the current drops so it isn't a ground or power supply problem.
    waltpair said:


    Put in new pump, replaced tank, cranked and truck ran fine. Test drove and called customer to pick up. 2 hours after customer drove away, she called me and said truck would not start. Truck is towed back and we began to check and double check. We narrowed our search to the fuel pump relay in the kick panel and replaced it.

    How exactly did you test this? Describe your usual steps to prove if a relay is good or bad.
    waltpair said:


    Truck started and ran fine. Test drove may times to make sure of repair. Customer, again, drives away. About 4 weeks later I get a text from the BBB saying that the customer wants all their money back. She said she drove the truck for 2 weeks and then it would not start again. She then had the truck towed to the dealer and they said that they found a ground wire that was bad. They made the statement that the fuel pump and pump relay was not the problem.

    They don't actually know if there was any other problem on the vehicle or not, they are guessing and throwing you under the bus. However you don't have any data (scope captures, photo's etc) that supports your testing and findings either.
    waltpair said:


    Our position is "yes" a ground wire could be an additional problem, but because of the test we did to the original fuel pump it was confirmed bad.

    But you don't actually have proof, so it's a he said/ he said.
    waltpair said:


    The dealer of course had no access to the original pump and therefore could not rule out its failure. What do you think of our procedure and is it possible that the fuel pump failure could cause the pump relay to malfunction and also cause damage to ground wire?

    It is highly unlikely that a pump failing would have damaged either of those, however poor connections can result in a pump failure over time. The odds of the ground circuit being faulty combined with a flawed testing routine could result in a misdiagnosis especially if the ground circuit was disturbed during testing and that resulted in the ground making a temporary connection sufficient to allow the pump to run. Since you didn't measure the voltage drop across the ground circuit while the pump wasn't working there isn't a way to prove what was really happening at that time.

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