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Over the last year I've gone through three in-tank pumps, two of which failed while on the road and caused me sputter to an inconveniently-situated halt. The first pump was manufactured in Sweden (I can't remember the name). I installed it myself with little difficulty, along with a new stepped-hose and a new fuel filter sock. During the installation the filter fell off into the tank where I could no longer reach or see it; however as the tank itself is pristine (no interior rust) and the fuel has no sludge (I looked in with a flashlight), I decided to forget the filter. I'm pretty sure this is not causing my chronic fuel pump failure, but of course I could be wrong...
The Swedish pump failed within six months and (after having the car towed sixty miles home) I replaced it with the Delphi pump from AutoZone--made in China. This too failed about three months later on the side of the highway, and (I was prepared this time with an extra Delpi pump in the trunk) I installed a second one. That was last week.
Every time a pump has failed, I've inspected the fuel in the tank (always clean) and the fins in the pump's intake turbine (among the three that failed in the last year the fins were all intact). The failed pumps would not spin when I connected them to the wires coming into the trunk (and turned the key), and I cannot rotate the turbine fins manually.
I can't figure out why the pumps are not lasting. Could it be extra strain and overheating caused by a poorly-functioning main (in-line) pump? Could the in-tank pumps be shorting out somehow? If they were shorting out, why is it that as soon as I install a replacement everything works fine?
 

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Have you been able to retrieve the filter sock? I dunno if it is vital but...

Have you changed the main filter (near the main pump)?

The in-tank pump is a low pressure helper. A faulty main (high pressure) pump would cause poor running I'd assume. Check for any restrictions between the in-tank pump and the main pump. That might strain the in-tank pump. Also check its electrical connections - a corroded or loose connection might be causing a low voltage problem.
 

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Have you been able to retrieve the filter sock? I dunno if it is vital but...

Have you changed the main filter (near the main pump)?

The in-tank pump is a low pressure helper. A faulty main (high pressure) pump would cause poor running I'd assume. Check for any restrictions between the in-tank pump and the main pump. That might strain the in-tank pump. Also check its electrical connections - a corroded or loose connection might be causing a low voltage problem.
I have not been able to retrieve the filter from the tank.
The main pump and all its electrical connections were replaced by my local Alfa specialist in the spring of 2018 so I'm assuming they're still good (the original one had shorted out because some pesky mice had eaten through the wires). Unsure about the main fuel filter--if it was replaced as well or not. I'll give the in-line pump the once-over anyhow. Either way, the car runs, pulls, and idles fine in traffic and on the highway.
 

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Update: the Delphi pump that I removed from the tank is working. Maybe it was an intermittent electrical connection--I'm going to clean all the contacts and connectors. It may also have been that there was something stuck in the fins of the pump that I somehow managed to dislodge; now it rotates, albeit with some stiffness. Either way the Delphi pump that I replaced last week was not shorted out.
 

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I'd fish the filter out the tank and use it where it's designed to be used....:)
a long piece of wire coat hanger and a decent slim flashlight ought to get it out in 5 minutes.
 

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About 8 years ago I had a similar experience on my '78 Spider. I cut the crimp off the top of the pump so that I could remove the can to examine the pump internals and what i found is that there are a pair of spring-loaded brushes that contact the armature. The brushes are housed in a close-fitting cavity in the upper plastic piece, each brush under its' respective electrical terminal. As the brushes slowly wear, the springs keep the brushes in contact with the armature. Any sort of contaminant that makes its way into the cavity will keep the brush from moving and as it wears, will eventually loose contact with the armature. In the picture below you can see where I modified the pump so that I can take it apart. I cut the crimp off the can and added 3 screws to reassemble. Each time the pump failed I would take it apart and find very fine grit in the brush holder cavity hanging up the brushes. The gas tank didn't look that bad (just a barely noticeable trace of rust on the inside) and I had replaced the filter a couple of times but somehow grit still entered the pump. I finally replaced the gas tank and all has been well since. Below is a picture that shows how I modified the pump so that i could easily take it apart.

DSC01801.JPG
 

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Just get a pencil magnet. There is steel on the sock cap. I've dropped mine and had to fish it out.
 
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