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930 Fuel Pumps not Running

Hey guys,

Ok my saga continues. Neither of my two pumps are running. Here is what I have done so far to diagnose.

1. When i press down on the air sensor plate (top of CIS housing) I feel the relay clicking in the rear fuse assembly. So the cis switch is working. No pumps.

2. When pressing down on the air sensor plate (friend doing it) I feel both relays up front clicking. No pumps.

3. Cleaned the fuse, fuse post and fuse wires to the pump(s). No pumps.

What next? Clean Positive and Ground connectors to each pump? If one pump is baked will the other run or not? Are they wired in series or separately? Remember this is a '76 930, so no shutoff switch on IC or other electronic dizmos.

Thanks guys.

Henry
'76 930
Old 08-30-2014, 10:12 AM
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Crotchety Old Bastard
 
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Does the CDI kick on when the ignition switch is in the on position?

You'll have to check everything in the path as it is a daisy chain. That includes the ignition switch. The fuse box and wires are nearly 40 years old. Hard to imagine I know ...
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 08-30-2014, 10:26 AM
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Henry, Have you tried jumping the 30->87 pins on the fuel pump relays to see if you can make either/both pump run? What's your battery voltage? Look at the schematic below. Some of the components are not applicable to your car but the basic power switching to the pumps is the same. I'm not sure who to credit for the schematic but it's very helpful to get a "visual" of what's going on.

Old 08-30-2014, 10:41 AM
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I no longer have a CDI, i run the electromotive hpv-1 twin plug ignition.
Old 08-30-2014, 10:43 AM
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Ok, i just jumped pin 87 & 30 for both pumps. Ignition on. Nothing. I assume that you do not have to actuate the air flow sensor plate? I tried anyway. Nothing.

What are the odds of both pumps dying? This problem has been intermittent for several weeks now, but i have always been able to get the car running. Once running it runs great.

Suggestions please.

Thanks,
Henry
'76 930
Old 08-30-2014, 11:01 AM
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Measure the voltage on pins 87 of the fuel pump relays with the jumper from 87 to 30 on. You should have 12V.

Check the voltage at the fuse labeled P above. You should measure 12V.
Old 08-30-2014, 01:22 PM
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Sounds like the 76 didn't come with a over boost switch ? It does seem very unlikely both pumps would fail at the same time. Any reason you can't put 12V pwr directly to the terminals on the fuel pumps to verify they're working ?
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Old 08-30-2014, 03:44 PM
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If you unplug the airflow sensor safety switch (F) and turn the ignition key to the second detent both pumps should run. No need to do anything with the air meter plate.
If the pumps do not run verify the fuse is receiving power (P).
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 08-30-2014, 03:47 PM
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Is it possible that the battery could be the culprit? Even if i have cranking, is it possible with insifficient amperage the pumps will not kick on? I have an Otima and it cranks the motor over well. It is on the tender now.

Henry
Old 08-30-2014, 05:37 PM
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One important clue is that both fuel pump relays can be heard to "click", which says that all various redundant circuits are trying to feed juice to the pumps...but it's not getting past the relays. Check the single fuse to the pumps....and/or sleep on it, let the ol' brain process it for awhile.
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Old 08-30-2014, 06:06 PM
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By chance is the fuse one of the old aluminum type? If so replace it with copper and clean up the contact points. Those old aluminum fuses can corrode to the point they malfunction.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 08-30-2014, 07:36 PM
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Fuses are all copper. Were all replaced when i finished the restoration 4 years ago.

I have power at terminal 30 (5 pin relay), but when jumped with 87 still no pumps.

Henry
'76 930
Old 08-30-2014, 08:30 PM
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Battery has 12.96. Volts
Fuse has 12.96 volts
Terminal 30 on both relays only has 10.01

Should the pumps be able to run on only 10.01 volts?

Henry
'76 930
Old 08-30-2014, 08:35 PM
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Have you refreshed the wire at both ends? By that I mean cut the terminal end of the old conection wire off and expose fresh wire for the connection.
The pumps may run at 10V but not well.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 08-31-2014, 04:50 AM
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No power to pumps

Hi Henry,

I have a 1976 930 also. It had a similar problem, no juice to the fuel pumps. It would intermittently stop running. I would check everything on the side of the road, checked voltage, changed the relays, checked fuses and CD. Eventually I would get it to run never knowing for sure what the cause was. Then it died on a spirited drive in the local hills and would not start for hours. After many attempts at a solution I accidentally found out it was the two small red wires connected to the positive side of the battery terminal that were loose. After cleaning and tightening the car ran fine.

Hope this helps,

Rahl
Old 08-31-2014, 08:06 AM
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Problem solved (I hope!!)

So after trying everything, including all of the above items plus removing the fuse panel to inspect behind for any wire damage, cleaning every ground on the car, cleaning each post on the front and rear pump (positive and negative) still nothing.

I got good power at Pin #30 but very little power at Pin #87 & volts.

What I did notice and have noticed for some is my ignition key feels quite loose in the ignition slot. It has been this way for years this is the original key - 38 years old) but the car started fine, you cannot remove the key. Anyway I dug out a duplicate key, stuck it in the ignition and boom the pumps were running.

Question - what is inside the ignition that controls the pumps? Are there specific tumblers for the pumps? Do I have to change the ignition assembly (what a PITA with anti-theft bolts and re-keying the entire car)?

Or do you think that the newer key will suffice?

Thanks very much for everyone's advice and help. Nothing like spending all day yesterday chasing this vexing problem.

Henry
'76 930
Old 08-31-2014, 09:56 AM
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Similar problem..Turned key over- nothing-no sound-just dead..turned it over a 2nd time it started instantly.. I thought it was a short.. Read in the 911 tech forums the tumblers get stuck in the key slot. I put mmo-marvel mystery oil with a dropper in the slot -let it sit-put key in and out. You could feel the spring action getting tighter when pulling the key out. No problems since
Old 08-31-2014, 11:42 AM
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Refer to Post#2. Too many electrical things go through that switch, when it gets worn all kinds of bad things can happen. I've got a jumper wire made just for the purpose of bypassing that switch. Changing the electrical part of the switch out is no fun at all. I made a couple tools for that event as well. You have to be a contortionist to get up in there.
Good news is now you should have a really clean electrical system for your pumps.

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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 08-31-2014, 12:06 PM
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Hey guys,

Well the fuel pump issue is NOT solved. Worked fine for a couple of days but I went to start her up this AM (started fine), backed out of the garage to warm up. Idled for a couple of minutes and then she died.

No pumps. I do not see on the above wiring diagram where the ignition switch operates the fuel pumps or which pins would be jumped to bypass the ignition switch.

Ugh, signed up for a DE next Tuesday and really want to go.

Any help would be appreciated.

Thanks,

Henry
'76 930
Old 09-03-2014, 11:34 AM
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Crotchety Old Bastard
 
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Chasing a failed connection is a lot easier than chasing an intermittent failure. That stinks.
The relay side goes through the ignition switch so you can bypass that by throwing 12V direct to the relay and see if the pump kicks on.
What about grounds, have you checked that? Be good if an EE would jump in here, I know there are better ways to troubleshoot this.
Old 09-03-2014, 12:24 PM
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