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I need some electrical help...

OK, first and foremost, none of my wiring is STOCK. Everything is custom....

I'm blowing fuel pump relays (30amp). Where/how can I start to track this down....
I'd assume a grounding issue of some kind?

Front fuel pump is 6 months old or so, rear fuel pump is old, not sure how old...

Does anyone know the gauge of wire that should go to the positive/negative terminals on the fuel pumps? If so, I'll purchase some wire and re-wire to those points...


Brian
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Brian Keith Smith
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Old 05-15-2007, 11:42 AM
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Brian, it's highly unlikely that your wiring has gone bad.. Get a buddy, unhook your battery and with a meter start tracing things down..
I suggest starting at the relays...
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Old 05-15-2007, 11:54 AM
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No friends boss

Just me and the dog, and he doesn't have any thumbs...



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TEC3 EFI Conversion on 1983 930
Old 05-15-2007, 12:59 PM
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Compare ohms of front pump to rear ?
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
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Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

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Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

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Old 05-15-2007, 02:43 PM
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Then make yourself a looooong jumper cable so you can take some measurments... Something is shorted,, might be your fuel pump, good luck!!
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Old 05-15-2007, 06:17 PM
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Am I measuring number of ohms across the terminals of the pump while it has power? (I'm not an electrical guru....)

Brian
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Old 05-16-2007, 03:09 AM
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Don't measure while it's powered - you must have one terminal disconnected. The meter will measure the path of least resistance(current divider) - which would be another portion of your harness to ground.
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Last edited by turbocarrera; 05-16-2007 at 07:24 AM..
Old 05-16-2007, 06:28 AM
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Just curious, what was the last thing done to your car? Has this all come about (the fuses blowing) since the engine has gone back in...post rebuild? I hate electrical problems. I have good success with working backwards...i.e.: it used to work fine, now it don't what did I last touch?
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Old 05-16-2007, 07:53 AM
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SandMan:
yes pretty much last thing was putting engine back in....

I guess I'll pull it back out and see if problem goes away (kidding)

Brian
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Old 05-16-2007, 09:15 AM
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Quote:
Originally posted by briankeithsmith
SandMan:
yes pretty much last thing was putting engine back in....

I guess I'll pull it back out and see if problem goes away (kidding)

Brian
LOL!!! That's what I'm here for...
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back in the saddle: '95 993 - just another black C2
*SOLD*: '87 930 GP White - heroin would have been a cheaper addiction...
"Ladies and Gentlemen, from Boston Massachusetts, we are Morphine, at your service..." - Mark Sandman (RIP)
Old 05-16-2007, 10:59 AM
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I'm by no means an electrical expert, so I asked some of the guys at work.

The first thing they asked is what do mean by blowing the relay? Are the contacts welding closed so the pump won't turn off or is it burning up the wiring in the relay? They said it's most likely a problem with the pump drawing too many amps. Put your amp meter in series on one of the pump leads to check it.
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Old 05-16-2007, 12:04 PM
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When I turn on power to the car, the fuel pump relay is triggered by the ECU and should run for like 15 secs or so. What happens is, it will run for 1-2 seconds and cut out, and after that, power never makes its way to the fuel pumps. If I turn off power, and back on, same thing, it will run for 1-2 secs, then die. Relay is getting hot.


thanks for all the tips guys... keep 'em coming, just give me as much detail as you can... Its gotta be something simple....

Brian
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Old 05-16-2007, 12:09 PM
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How are your relays wired?

I used my stock fuel pump relays. Behind the fuse panel, I pulled out the two wires that sent the signal to the relays (blue and brown/red) and wired them to the ECU. Everything's been fine so far.
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Old 05-16-2007, 12:26 PM
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yeah, everything's been pretty much fine on mine for almost 3 yrs, just started blowing them....

I have a separate Fuse Block and relay block (2 relays, 1 for fuel pumps, 1 for coils).

When ECU turns on it powers fuel relay for 15secs, then it powers relay when ECU is "running", meaning engine is running.

There is a power lead from the harness/relay to the fuel pump(s). This lead goes to a fuse block and I have each pump on a separate fuse...

Probably doesn't make sense...

Brian
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TEC3 EFI Conversion on 1983 930
Old 05-16-2007, 12:30 PM
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If it's been fine and now it's not, sounds like a pump problem. Have they gotten louder? If they're starting to lay down, they start drawing more amps to run. I can't find the correct amps right now, but 4 amps comes to mind.
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Old 05-16-2007, 12:45 PM
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Front pump is new (less than 6 months old - Bosch OEM pump)
Rear pump not sure how old...

I'll try to measure the amps on each one tonight....

Brian
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TEC3 EFI Conversion on 1983 930
Old 05-16-2007, 12:48 PM
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I guess an easy way to see which one is blowing the relay would be to disconnect each one individually from the fuse block and see what I get...

Hadn't thought of that until now... (kinda slow on this electrical stuff I'm tellin ya)

Brian
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Old 05-16-2007, 12:51 PM
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If the pump is drawing too much current it should blow the fuse. I sounds like the ECU is cutting out first. So I would measure the voltage coming out of the ECU to the pumps and see if it is the ECU's fault.
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Old 05-16-2007, 01:43 PM
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Quote:
Originally posted by briankeithsmith
Am I measuring number of ohms across the terminals of the pump while it has power? (I'm not an electrical guru....)

Brian
I always disconnect both wires
+ & -
or
L & N
or
+ & Earth.

You then set your meter to read the ohms. X1 or X2 (depending on the meter) is not very sensitive. You can then try moving up the sensitivity to X10 or X20. Things like temp sensors usually need meter to be set at X1000 or X2000.

The lower the ohms the more current is being consumed.

Compare a courtesy light bulb to a headlamp bulb.

Measuring current is probably much more accurate but I am more used to working on 240V AC hehehe. I prefer to work with the power off
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 05-16-2007, 02:46 PM
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Thanks Dean (and Nathan)

Looks like the ECU is sending 11.94 volts to the Relay...

Brian
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Brian Keith Smith
Competition Custom Paint
1983 930
My Track Videos
TEC3 EFI Conversion on 1983 930
Old 05-16-2007, 03:47 PM
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