Repeated fuel pump failure

Hello guys,

Working on a 2019 Renault Logan MCV 1.5 diesel (K9K) odo about 250,000km

Before I got called, the car had 8 in tank fuel pumps replaced, (thing is a diesel, it has a low pressure in-tank pump and a high pressure pump under the hood), the story was the thing was "driving fine" until they shut it off and it never started again, then they changed the fuel pump and the thing started right up and drove for a week (it's a taxi so about 1,000km), they changed the pump again and the cycle kept repeating till the 8th one failed and they decided to find the real problem (lol), also another thing they said that it seemed to get worse with each pump (less and less time to failure)

Between one of those pumps the fuel filter (after pump one) was also changed, also the sock filters on the pumps were "clean" and replaced each time with the new pumps, I never saw the process because I wasn't there...

From the description the logical path was to go straight to the pump and check the wiring there, first thing I see when I lift the back seat is that the connector is missing and the 4 wires (+, gnd and sender unit to cluster) were cut at some point and extended with a different type of wire and soldered straight to the pins on the housing without the connector, the "connection" to the original wires was not soldered or crimped it was just twisted together poorly and covered with some tape, so obviously my thought process is we need to restore this wiring to factory first, because there are obviously voltage drops here, and this motor takes about 5amps, so the wiring overheats the pump overheats and dies..

So i found a new connector and restored the wiring to how it should be, then the garage where the car sits put in a new pump motor into the housing and called me, surprise - the car DOES NOT START..

I come check powers grounds all is good at the pump, pump turns on, crank no start... OK, check the fuel pressure on the high pressure side, we are not building enough pressure to start, had 70-100bar at the rail, when the desired is 280bar.. alright, thinking to myself this is weird because before they told me this thing starts right up after changing the pump.. anyway I go and start looking for why we are not building enough pressure to start this thing, long story short one of the injectors is dropping most of the rail pressure to the return line, tell them that and to call me when they have that injector replaced..

Few days later they call me, the car started right up with the replaced injector, pressure builds up all is good, we meet up, I code in the new injector, and I am thinking that the problem should be gone now.

Tried to come up with an explanation for myself why this happened the way it happened, only thing I came up with is that the injector started failing first, slowly dropping pressure and over working the high and low pressure pumps, that is why it kept getting worse with each new pump, because the injector got worse and also finally crapped out, and then they introduced this wiring problem later on when changing pumps every week, got rid of both problems, so car should be fixed right?

NOPE, yesterday got a call that the pump is dead again (almost exactly a week later after the "fix"), the driver also mentioned on the phone that before that happened he heard the pump making weird noises, it was loud then quite then loud again etc.. it was so bad that he said the passengers sitting in the back were asking wtf that noise was..

Today I will be going to that garage again, will check wiring again to make sure it is still good, i also want to cut open the pump to try to see why it failed this time.. my thoughts now is that this could be a mechanical problem, maybe there is debri or some type of contamination in the tank that the pumps keep sucking in, but from their words the sock filter was clean each time they took it out.. was also thinking to disconnect the line that goes from the pump to the filter under the hood and try to blow compressed air through it, maybe it's blocked and the pump is getting overworked (Doubt it)?..

Also another detail I remembered is that the pumps where all different brands and were bought in different places so can't be a bad batch, and not sure if this matters but they are using gasoline pumps in a diesel, but the first one they changed was an original replacement.


Anyone seen anything like this before? Do you have any thoughts?

Will keep you guys updated

Russell,
I have blessed little diesel experience, but in my experience repeated fuel pump failure generally comes down to, as you noted, poor wiring, contamination, or aeration/repeatedly running dry. Fuel is the lubricant for the pump and it will not live long without lubrication.
I would voltage drop test the power and ground with the pump running and inspect the tank for debris.
I'm curious to know if anyone has any thoughts pertaining to the use of a gasoline pump to move diesel. I feel like it should work, but again, very limited diesel experience.

Ok, so I was at the shop briefly and what I found out was that:

1. The pump is not completely dead, but pretty much.. it was brought back to life by hitting it a couple of times.

2. The lines are clean from pump to filter and from filter to high pressure pump.

3. It had half a tank of diesel which was pumped out of the tank, no obvious signs of contamination.

4. The old "killed pump" was drawing 2.65amps, we used it to pump out all the left over diesel out of the tank, when it pumped out all the diesel it dropped to about 2.30amps.

5. The new installed pump is drawing 5.74amps at idle (measured at the fuse) and 5.64amps at 2000rpm

The car started right up after putting this new pump in.

The owner cut open the last 3 failed pumps and the problem was with the brushes he says they were all about 3mm shorter and did not make good contact anymore, again I did not see this myself.. I am planning to take this last failed pump and disect it myself, it does sound like the brushes get burned out because when I hit it It came back to life (barely, but it did pump out half a tank).

This is what I am planning to do:

1. To rule out crappy fuel, I told them to use another brand of gas station the one they are using is not the greatest, and now we have a little problem with fuel (I am in Ukraine), the gas station they used till now used to get Belarusian fuel, not sure where they get it now.. so could have something to do with it..

2. I am planning to meet up with the driver everyday to measure the amp draw to see what it does and where it goes from the "new state" measurements, maybe this will give me a hint... I don't think the pump fails suddenly on exactly day 6 for example and goes to 2.65amp from 5amps I think it dies gradually from day 1 and only gets noticed when it gets too weak to bring up fuel to the hight pressure pump and get a crank no start.

Other than that, so far I have no ideas... ideas welcome guys, hopefully we don't kill this pump