Failing aftermarket fuel pumps

processengr · #1 08-10-2012, 03:59 PM

My 3 rd aftermarket fuelpump failed (Bosch) after only 1 month. So far, I had an Airtex (9mo) 1st Bosch (3mo) now the 2nd Bosch has failed. 12VDC is there at startup. Is the voltage modulator unique to the SVX? The fuel tank is clean. Car is a daily driver. Fuel sources are the same as our other cars. Fuel filter replaced 30k ago, before the rash of failures. Strainers replaced after each failure.
Theories anyone?

oab_au · #2 08-10-2012, 06:12 PM

Quote:

Originally Posted by processengr

My 3 rd aftermarket fuelpump failed (Bosch) after only 1 month. So far, I had an Airtex (9mo) 1st Bosch (3mo) now the 2nd Bosch has failed. 12VDC is there at startup. Is the voltage modulator unique to the SVX? The fuel tank is clean. Car is a daily driver. Fuel sources are the same as our other cars. Fuel filter replaced 30k ago, before the rash of failures. Strainers replaced after each failure.
Theories anyone?

Did you find why they failed?
The Modulator has the resistor in the circuit at idle, it only gives the pump a direct ground with the pedal down, for full flow. So when you check the pumps voltage, the ground wire will be at a voltage of say 6V, instead of 0V.

Harvey.

processengr · #3 08-10-2012, 06:18 PM

Hi Harvey! I measured 12VDC only at 1st turning the key on, then it drops...the last two were under warranty, so I didn't disassemble them...The last one wouldnt work even when I disconnected I think the yellow wire from the modulator and grounded it. The pumps would not kick over at all...

processengr · #4 08-11-2012, 12:19 PM

Is the voltage modulator system used on all Subaru's? Could low voltage be burning out the pumps?

oab_au · #5 08-11-2012, 07:07 PM

Quote:

Originally Posted by processengr

Is the voltage modulator system used on all Subaru's? Could low voltage be burning out the pumps?

I wouldn't think so, as the added resistance lowers the current, just runs slower. I think it would be a bit hard to burn the pump out, when it is liquid cooled, but you never know.

Quote:

Hi Harvey! I measured 12VDC only at 1st turning the key on, then it drops...the last two were under warranty, so I didn't disassemble them...The last one wouldn't work even when I disconnected I think the yellow wire from the modulator and grounded it. The pumps would not kick over at all...

The system is not straight forward.The pump turns on 12V, with the ignition, for X amount of time then, turns off till the engine starts. It then runs 12V on load and reduced voltage on cruise.
As you have had a few with the same problem, I would think the problem lies in the cars wiring/relay/modulator area

, but if you find that the pumps won't run, even out of the car with applied voltage, I've NFI.

Harvey.

TomsSVX · #6 08-11-2012, 08:05 PM

I have seen some corrosion on the connector to tge tank cause misdiagnosed pump failures. Could also be a wiring issue from tank pigtail to the pump. Hace you been able to bench test the oumps failed?

Tom

processengr · #7 08-12-2012, 12:17 AM

Hi Tom!
The more I think about it, the more the pigtail to the pump sounds like the culprit. I had ground voltmeter probes to fit the connector to pump, and had measured voltage there, but did not bench test the removed pumps. Is that connector sold separately? Arcing in the tank sounds scary...

TomsSVX · #8 08-12-2012, 12:53 PM

Are you getting resistance across the pump motor? You can check pin tension for the connector to be sure. Dont worry too much about arching in the tank... air to fuel ratio has to be just right to make a bang. Gonna have to pull the pump and bench test it and the wiring to be sure

Tom

processengr · #9 08-12-2012, 01:37 PM

Pushing the topside connector on and off got the car to start and run, perhaps the flattened volt meter probes opened up the connection- Im going to use contact cleaner and a stylus to bend the connector sockets for more tension...

TomsSVX · #10 08-20-2012, 06:19 PM

Howd you make out gordon?

Tom

processengr · #11 08-20-2012, 07:13 PM

Hi Tom,
A bad connection was the problem- I wonder if the original pump was even bad! I cleaned and flattened the sockets in the connector on top, car is running fine...
Forcing the probes into the connector was a bad idea, have now ground a set of probes to the size of the male pins in the top connector.

TomsSVX · #12 08-20-2012, 07:16 PM

Glad to hear it... i never actually saw a pump fail... all were misdiagnosed... so your case definately caught my interest. Good fix!

Tom

processengr · #13 08-21-2012, 04:13 PM

Thanks for leading me to it!!!

Huskymaniac · #14 12-24-2014, 08:15 PM

Guys, this sounded like the most likely culprit in my latest SVX saga. Drove the car home last Friday with no issues whatsoever. The next morning it wouldn't start. The starter ran and the engine turned over. I "think" I didn't hear the usual fuel pump noise. Should this be the first thing to check? If so, how do I get to this connector?

Conn SVX · #15 12-24-2014, 09:13 PM

It is under the back seat. Actually if you fold down the seat and look under the carpet you should locate the pump..