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Elombard's Avatar
 
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Chasing electrical drain - fuel pump(s)?

87 930

finally getting to the last of the issues on this car.

Battery drains in a few days, I am not too sharp on electrical but there is a ~3 amp (?) drain on one of the ~10 gauge red wires right off the battery (does not go through the fuse panel).

Took the wire off and turned the key and no fuel pumps, touch the wire to the post and the fuel pumps pressurize.

I looked at the wiring diagram from an 87 NA and I cant tell what is going on there; or if it is even the same.

ANy thoughts? Can the pumps start to fail and short like that?

What else is powered on that circuit?

Thanks

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Old 03-07-2010, 01:34 PM
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OK I figured out that wire makes the power seats and windows work, as well as the fuel pumps. I double checked pulled those fuses still see the drain

I disconnected both relays under the driver seat and it still shows a drain.

What else does that wire power?

I cant remember if a couple of diodes in the alt are fried wont you get the charge light on the dash with the key off or something?

I wonder if I am using the amp meter correctly?
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1994 Lotus Esprit S4 - interesting!
84 lime green back date (LWB 911R) SOLD
RSR look hot rod, based on 75' SOLD
73 911t 3.0SC Hot rod Gulf Blue - Sold.
Old 03-07-2010, 02:36 PM
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Anti-theft/alarm device?
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'85 930 Factory Special Wishes Flachbau
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Old 03-07-2010, 02:44 PM
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It does not have an after market device, how is the factory unit fused? I dont see it on the fuse list?
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1994 Lotus Esprit S4 - interesting!
84 lime green back date (LWB 911R) SOLD
RSR look hot rod, based on 75' SOLD
73 911t 3.0SC Hot rod Gulf Blue - Sold.
Old 03-07-2010, 03:38 PM
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Go to the fuses in the engine compartment. There should be only two of them. Pull one at a time and see what it does to your amp draw off the battery. If you've got a 3 amp draw onthe battery, that's a pretty serious drain.
I have a similar problem that I've never been able to entirely trace, but did note that when pulling those fuses the draw went away. Part of my problem is that the previous owner wired my MSD ignition onto a permanent hot wire, vs. keyed, so I get continuous draw to the tune of a couple hundred milliamps. But your 3 amps is something major. Rear window defrost, heater fans (I think) plus other stuff run of those fuses in the engine comp.
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Old 03-07-2010, 06:17 PM
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I pulled every fuse one at a time nothing changed the draw. If I am doing it right its on an un-fused circuit; starter, cold start, alternator.

I was convinced when I realized the windows and power seats wee on this circuit it was one of those! But I re-checked and pulled the fuses and no difference.....one of the passenger seat motors is not working and the passenger window wont go down so I figured a motor winding had come apart....Wouldn't pulling the fuse have detected that?

Here is another interesting point.

I turned the meter to the continuity setting and put one end on the wire that is showing the draw and the other on the fuses, one at a time.

Almost every fuse showed continuity.

Does that indicate its a dead short to the chassis somewhere?

I am wondering if its diodes in the Alternator again.
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1994 Lotus Esprit S4 - interesting!
84 lime green back date (LWB 911R) SOLD
RSR look hot rod, based on 75' SOLD
73 911t 3.0SC Hot rod Gulf Blue - Sold.
Old 03-07-2010, 07:13 PM
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Quote:
Originally Posted by Elombard View Post
..............edit for space..............................
I was convinced when I realized the windows and power seats wee on this circuit it was one of those! But I re-checked and pulled the fuses and no difference.....one of the passenger seat motors is not working and the passenger window wont go down so I figured a motor winding had come apart....Wouldn't pulling the fuse have detected that?

No, not if the circuit had an open. One of the most misused words in the English Language is the word "short". A short only occurs when you have a straight connection between Battery Plus (+) and Ground (Battery -). If you have a short, yes you would blow a fuse, but if it wasn't fused, you'd have a fire. Most likely when things break, it creates an "open"...device stops working, no harm no foul. Porsche in is infinite wisdom, didn't always fuse everything.....like footwell blowers, for example.
The windows not working may be the result of an open circuit, more than likely a broken lead on the window switch or mis-wired. Windows are a ignition switch enabled device and it sounds like you have a drain when the switch is turned off, yes?



.................................................. ............

I turned the meter to the continuity setting and put one end on the wire that is showing the draw and the other on the fuses, one at a time.

Almost every fuse showed continuity.

Does that indicate its a dead short to the chassis somewhere?
If you're drawing 3 AMPS, that means that somewhere on the car there's a circuit that is about 4 Ohms resistance. (Ohm's Law...I= E/R, where I is amperage, E is Voltage and R is resistance)
I am wondering if its diodes in the Alternator again.

Could be the diodes, but don't rule anything out.
Comments in Red above.
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Old 03-08-2010, 06:42 AM
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Thanks Dave,

I will have to check again but I think the seats and window work when the key is not on, I know the seats do....hmmm maybe some body messed with the wiring.
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1994 Lotus Esprit S4 - interesting!
84 lime green back date (LWB 911R) SOLD
RSR look hot rod, based on 75' SOLD
73 911t 3.0SC Hot rod Gulf Blue - Sold.
Old 03-08-2010, 06:58 AM
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erik,
Seats do work in the ign. switch in off, but windows should not.
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'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 03-08-2010, 07:01 AM
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wiring diagram

Erik, you need a wiring diagram for the power distribution for 87 930.

Can anyone email him one?
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Old 03-08-2010, 03:35 PM
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Hi Erik,
Did you resolve your electrical drain?
The window relay in my 86 930 went bad and I replaced it, but ever since then I have a drain that runs my battery down in about 4-5 days.
Never had a problem before.
Also, the relay is always warm....
mark
Old 08-25-2010, 05:12 AM
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The window relay is designed so the driver side window still gets power to put it up or maybe down once after the ignition is turned off. Or something like that...
I'm foggy on that one because i havn't tried it in a while but when it works right it does that.

Also the the interior light switches in the door jams are hot all the time and they ground the power going to the interior lights when the door opens.
The alarm system is somewhat of a mystery and it's hot all the time too so it seems it could be doing it.

Electrical problems are really frustrating... you can't see whats going on, just a mess of wires and lots of confusion, etc. ..kinda makes you want to just put a big solar cell on the roof and leave it parked in the sun to keep enough charge on it to start it.
Old 08-25-2010, 08:01 AM
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Hi JFairman, thanks for your input.
Went out to look at door jamb switches and noticed drivers side is broken.
I ordered part from our host and it got here really quick, 2 days
I will let you know if it worked.
Thanks, Mark
Old 08-28-2010, 04:24 AM
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Well,
I have said this before...... But.

My 930 has a Antenna booster on it from factory. When the guy before me installed a aftermarket CD player he hooked the constant on power lead to it.
Therefore, when the car was off, keys were out, the booster still was on.

After a few days the car battery was dead. Rewired the radio to a switched power (for the antenna booster).
No more problem.
1989 930 may be different than yours.......
Old 08-28-2010, 09:18 AM
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My door switch was my drain culprit. Design is that Windows will operate after you turn car off as long as you don't open the door. If your windows always work, look at the switch.
Old 08-28-2010, 10:16 AM
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Yes... The door switch.
By opening the door, it completes the circuit which shuts down the power to the relay....or something like that.
Back to normal, no power drain.

Old 09-04-2010, 04:33 AM
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