Acceptable voltage drop off? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 5 Old 11-19-2011, 09:29 PM Thread Starter
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Acceptable voltage drop off?

Ran some voltage drop off tests today on my 86 GT.

From the starter relay to my fuel pump relay, had voltage drop off of appx 230ma. At the relay itself, originally had a 35ma drop, but after cleaning contacts its now down to 15.

After the fuel pump relay, there is another 200ma drop off from the fuel pump relay to the back fuel pump harness.

So, in total, 450milliamps of voltage drop off.

Also found two spots in the fuel relay wiring needing addressing. First right at the starter relay, dried and cracked wiring (but did'nt account for much lost current and also at the connection inside the drivers kick panel, some corossion and also a worn wire, where there was wiring being exposed.

I am suspecting one of these may be the cause of my fuel pump cutting out when the car gets warm, does anyone else agree?

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post #2 of 5 Old 11-20-2011, 04:37 PM
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Voltage drop measured in miliAmps?

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post #3 of 5 Old 11-20-2011, 04:49 PM Thread Starter
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My bad... mV..
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post #4 of 5 Old 11-20-2011, 06:30 PM
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Take a dedicated 12V wire (10ga or so depending on which pump and how far you are running) from your battery 12V directly to a new relay. Then a new 12V from said relay to the pump wiring in the trunk as close as you can to the pump.

Also ground the pump better by snipping the ground in the harness (again as close to the pump as you can) and either crimp and ground to a clean spot on the frame or run a dedicated ground directly to the battery with equal gauge wire as the +ve or larger.
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post #5 of 5 Old 11-20-2011, 08:48 PM Thread Starter
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We actually ran a dedicated temporary line to the pump harness to rule out wiring, of which we were successful in replicating the problem (loss of power after running a little bit, low pressure after running for a bit).

We dropped the tank, and it appears my new pump had crap inside the sock, clogging the screen inside the Airtex pump inlet. Replaced it with a new Edelbrock pump, and after a test drive it does seem there is 100% improvement, but I won't say its "fixed" until I get the opportunity to really drive it for a bit.

Thanks everyone for the feedback.
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