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Alan L's Avatar
 
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fuel pump relays

Should the front relays for pumps 1&2 be oscillating flat out on idle. I thought they would either be pulled in or out. The PO has obviously had issues, and rewired the pumps and had the relays dismantled - so you can see the contacts moving.
The end result is I'm getting low voltage at the AAR and WUR - like 2-4 volts. Since they are driven off the power supply for P2, I can only conclude this intermittent contact is dropping the voltage too low.
What would cause the relays - both 1&2 to pulse so extremely.
Thx
Alan
Old 11-26-2007, 07:34 PM
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Far canal! I think the relays should be either on or off too. Sounds like they're being fed AC instead of DC!!

There's a safety feature on later cars whereby the pumps are disabled when the motor isn't actually running (air flapper moved off the stop). So you should be able to push the flapper down and see what it does (should start the pumps running). Don't do it too much, it'll squirt fuel into the motor too...

Ddn't you take this all apart for the fuel distributor? Sounds almost like the switch is right at the point that it can't make up it's mind whether to be open or closed, although it surely wouldn't do that fast enough to make the relays oscillate...

I think the switch breaks the ground return for the control circuit fuel pump relays when the flapper is at rest, but i'm not sure.

If the relays are flapping back and forth, think you need to trace the circuit back until you're getting sane control inputs for the relays and rectify the last link in the chain

You might be well advised to check any rewiring that was done, too... Good luck!
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Old 11-26-2007, 08:12 PM
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The overboost yellow relay, the alarm, the flapper switch on top of the fuel distributor and the ignition switch can all get in the way of the fuel relays staying on. Pull the plug on top of the fuel distributor and rule that one out. Try replacing the magic yellow relay with a red one temporarily and pray it isn't the alarm (it's hard to get at behind the vent system (ask me how I know) :-)
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'86 930 Kokeln IC, K27-7200, SC cams, GHL headers, Fabspeed muffler, Short R&P , misc other mistakes made...
Old 11-26-2007, 09:25 PM
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Good suggestion - I tried it again with that in mind. It may be the air supply safety switch setting. I ran it again, and pushed the relays closed. They stayed there and I got my 12 v at the other end. I increased the idle revs and started it again, expecting it all to work. But they oscillated again at about AC rate. Maybe it has been doing this all the time.
My wiring is correct, I am sure. It is as per the factory scheme now. I removed relay jumper wires, reinstalled the safetys etc and the pumps now run from start up rather than ign on.
I will have a look at the air micro switch setting again, but I did monitor it when reinstalling the above. Had my multi meter over it watching it open/shut. I should be able to wire my meter into it's circuit with any luck.
Alan
Old 11-26-2007, 09:37 PM
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Andy, what yellow relay, and what alarm?
I have yet to find these things.
Alan
Old 11-26-2007, 09:41 PM
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The yellow relay is in the back of the car on that little electrical panel. It's got a delay circuit in it, but it's wired the same as a red one. The delay just keeps momentary inputs from the flapper from switching off the fuel pump relays. Search "magic yellow relay" for details. If you have a key switch in the edge of the driver's door then you have the factory alarm. The fuel relay runs through it as well ;-)
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Andy Glass
'86 930 Kokeln IC, K27-7200, SC cams, GHL headers, Fabspeed muffler, Short R&P , misc other mistakes made...
Old 11-26-2007, 09:49 PM
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The early cars didn't have a yellow relay in the back, it's red.
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Old 11-27-2007, 02:55 AM
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I only have one relay in the back panel - it is not yellow - red or black - can't remember. But it is wired to the fuel circuit. It is this relay that had the terminals jumped - and had the effect of wiring the pumps permanently on when the ign was on. I have unwired the jumper. The overboost switch is hooked into this circuit too, as is the CIS flapper. Both those bits work now. But possibly the delay function of the circuit there is not working. The lid of this relay had been removed previously too. So, I can watch it and see what happens. The car is an '82.
But I have yet to see the factory alarm - although there is an alarm - but have not found a key terminal. But the burnt out wiring in the car originated in the drivers door. Never worked out what it was.
Hmm. One day I'm gonna drive this thing.
Old 11-27-2007, 09:15 AM
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Mystery solved - Spuggy gets the prize. Thanks for the suggestion. I would have been a while finding this. Pulled the CIS flapper plug off and the fuel pumps kicked in with ign on. Started first shot and the relays pulled in and stayed in. When I did it again with the plug intalled, the relays oscillated again. This must be the original problem that caused the jumped relay. My rear relay is brown - but it is the same 87/87a that is used on the P1 & 2 and in various other places on the car.
Now I just need to sort this one out - delay circuit or micro switch.
Thanks
Alan
Old 11-27-2007, 10:02 AM
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Can you adjust the switch so it does not keep turning the pumps off until the engine does indeed stop?
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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.

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Old 11-27-2007, 12:44 PM
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I don't know. My manuals - Porsche and CIS say nothing about adjusting that switch. I intend to have a look - but hopefully without having to remove the fuel head.
My first thought is the height of the air flow plate - whether that would help -lower it slightly.
The switch must be adjustable in some sense - even if by fine shims. It must be right on the cusp for the amount of air drawn thru at idle. I need to measure the amount of depression of the plate from rest to idle. The delay relay must be working - because the pumps keep running. And when I switch the ign off, it takes a while to shut down. The real problem is the intermittent feed to the relays - which is caused by the air flow switch. The switch is working fine - on/off - so it must be the setting of the air flow plate, or the switch.
Will keep you posted.
Alan
Old 11-27-2007, 01:16 PM
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The ignition stays on for about a second when you turn off the key, this ensures all fuel is burnt. This is yet another relay on the LH panel in the engine bay.
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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 11-27-2007, 02:05 PM
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It's possible you have an air leak so the plate is being bypassed a little.
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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 11-27-2007, 02:06 PM
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I have found the cause, after a bit of frustration, just not sure how to deal with it.
Firstly, this would normally be a difficult issue to diagnose - so I will post some information here with some key words that would help others searching for similar issues. I was 'lucky' in that I could see the problem - the caps were off the relays for P1 & 2, by previous owner - so obviously he was struggling with this one too. Knowing what was happening - I can describe some symptoms which would otherwise lead you everywhere but to the problem.
The engine was rough starting. It would fire, cough, die, fire , cough die.....
Finally when it did get going, it was idling fairly sluggish and definitely too rich after a minute or two (the plugs were sooty black). The revs would also climb on idle. Over time it got faster and faster. The most tell tale sign of the relays oscillating was the low voltage at the AAR and WUR - consequently all the tuning was out of wack, and the AAR was not closing.
When I went to check the switch and plate settings, they were fine. The switch is opening as soon as the plate moves, and on idle the plate is open by about 1 mm - ie about 10 x what it took to trigger the switch.
So, I ran it again, and it went fine. Curse.
Put everything back and ran it again, and it went fine, until after a minute or two I could see the relays start to oscillate. While it was still running in this mode, I pulled the airfilter off and could see the problem - the air plate is vibrating furiously. If I stop it with my finger , it sits there steady and happy.
As soon as I blip the throttle , on closing, it oscillates again, and consequently so do the relays.
What the hell do I do with that?
Alan
Old 11-27-2007, 06:57 PM
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Allegedly, that's what the delay circuit in the yellow relay prevented. Though yours never had one of those and it's expensive. Something else is setting up that oscillation as mine doesn't oscillate. Mess with air and vacuum maybe?
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'86 930 Kokeln IC, K27-7200, SC cams, GHL headers, Fabspeed muffler, Short R&P , misc other mistakes made...
Old 11-27-2007, 10:12 PM
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I'm not sure the delay relay is the issue - in that the system is still operating under these conditions, rather than cutting out. It is more the fact the plate is vibrating so rapidly - you can just see it as a blur. The relay delay would not stop that, and clearly this should not be happening. My SC does not behave like that. There is a damper system in the fuel head to prevent that altho what you do to recify it, I am at a loss. I could pull the fuel head apart, but what I'm looking for I would hardly know - the manuals really don't go that far. I am mystified as to what would set this oscillation up. I don't know what cams are in it, but overlap would be more an issue at high revs I would have thought - altho lumpy cams do produce poor vacuum issues at low revs. But then, when I steady the plate, it stays steady. So, I suspect the damping in the fuel head.
Alan
Old 11-27-2007, 10:54 PM
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It might be time to consult someone who rebuilds/modifies fuel heads.
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--clutch-monkey
Old 11-28-2007, 04:20 AM
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Alan, do you have the Bosch Technical Instruction manual? (yellow cover)

Dunno if it helps, but from p20:

The control pressure acts through a
damping restriction on the control
plunger and thereby develops the force
which opposes the force of the air in the
air-flow sensor. In doing so, the restric-
tion dampens a possible oscillation of the
sensor plate which could result due to
pulsating air-intake flow.


(my emphasis).



So even if you do have lumpy cams, the damping should take care of it. Assuming you've checked/set the WCP to the correct value, it can only be the damping function of the control plunger in the fuel distributor not working as designed, no?
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Old 11-28-2007, 04:39 AM
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I have a couple of CIS manuals (copies of) , but not your one. But in general terms, they say the same thing. If it is the damper system fluctuation, rather than being caused by the air plate, I am wondering if I will see this in the pressures in the fuel head. Will try. If that is the case, I have something measurable to work off. I know of no one in NZ that rebuilds CIS units. I will hunt around if I need to - but I suspect I have the same manuals they have - that is where I acquired mine from. They will fault diagnose, and throw away a faulty part (I can do that too). But I don't know of anyone rebuilding them. The cleanest part on the car is the top of the fuel distributor.
Hmmm.
I may post this as a general query on the 911 board and see if we have some specific CIS expertise. Another fault symptom was a spikey tacho reading. Mine is an aftermarket tacho with shift light etc, so whether the standard tacho would suffer this, I don't know. But if your tacho spikes on idle, I would first suggest checking the voltage at the WUR and AAR, and hope they read 12.
Alan
Old 11-28-2007, 09:13 AM
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Does the engine have the stock camshafts? If the engine has cams with a lot of overlap, you are going to see the flapper oscillate. I would suggest go ask the previous owner what the heck he did to the motor besides screw up the CIS.
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Old 11-28-2007, 10:25 AM
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