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Alan L's Avatar
 
Join Date: Apr 2006
Location: New Zealand
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wiring diag query

I have a voltage issue at my fuel pumps. I am getting around 11.5v at the front pump and 11v at the rear pump. This is with an independant battery source hooked in to the battery leads and engine running on independant source. 12.6V at the batt terminals and terminals on the 930. By the time the power gets to the pumps I am down to 11.5 and 11V. I have cleaned the fuse block terminals that supply the pump relays, and split the relay power source at the fuse block to two separate fuse terminals.
I am trying to find where the poor power transfer is. There is according to wiring diag 2 twin connectors in the power source to the rear pump, (and I think nil on the front - direct from fuse block). I have located the connectors and checked, cleaned and they look OK.
My query is to do with the power source to the fuse block. The wiring diag shows 3 red cables taking off from the battery terminal. I only have the one big one that feeds to the starter motor. So where does the power feed to the fuse block come from? I am guessing it must track via the starter motor to the alternator to....?
Looking for bad connections.
Thanks
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 01-15-2018, 04:00 PM
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found my 3 red wires - looped into an isolating switch. The hunt continues for bad connection.
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 01-15-2018, 05:01 PM
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Good time to relay those pumps or was wiring things that needs to be stock? Check grounds too.
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Old 01-15-2018, 08:56 PM
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Wiring can change. Yes - earths were the next on list - tomorrow. Not sure where each pump earths tho.
Figured best thing was to run pumps and pull earths off til they stop. Or, I was going to dummy in an extra earth and see if things improved voltage wise.
I guess with 35 yr old wiring, the crimps may be suspect as well as terminals. Hard to find these issues.
Regards
Alan
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83 SC, 82 930 (track) - Stock except for RarlyL8 race headers, RarlyL8 Zork, K27-7006, 22/28 T bars, 007 Fuel head, short 3&4 gears, NGK AFR, Greddy EBC (on the slippery slope), Wevo engine mounts, ERP rear camber adjust and mono balls, Tarret front monoball camber adjust, Elgin cams, 38mm ported heads, 964 IC. 380rwhp @ 0.8bar Apart from above, bone stock:-)
Old 01-15-2018, 09:33 PM
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gax gax is offline
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My voltages are exactly the same. 11.5v on the front and 11.2v at the rear pump with the engine running. 13.5v at the battery. Can anyone confirm if that's normal for a stock setup?
Old 01-16-2018, 12:09 AM
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Turbofrog
 
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IIRC the rear earth is below the left hinge at the wall behind the fuel filter.
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Old 01-16-2018, 01:43 AM
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start at the fuse block.
measure ALL voltage with reference to ground/chassis.
you can either pull the covers off the relays or slip the relays out a little to get a meter on the terminal.
if the voltage to or out of the FP relay is 12.6 and at the pump it is 11.5 then the wires have built up resistance.
sorry, I have measured voltage at my pumps I just don't remember want it was so I don't know if 11.5 is normal. it is seems to me that is what I have seen others say they have.

if you have ever stripped back and old wire and seen black stuff or anything on the strands, that will increase resistance and cause a voltage drop across the length of wire. what you want to see is shiny copper. I either use sandpaper or a wire brush to clean the ends if I cant cut off enough wire to get back to some that is clean.

with ground wire removed from pump, measure voltage at pump.

measure resistance across terminals of pump for me.
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Old 01-16-2018, 04:02 AM
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