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"Rebuild" Ignition Switch? Intermittent fuel pump circuit connection.

I have a slightly annoying issue that can become very annoying whenever it decides. My ignition typically will not trigger the fuel pumps to run continuously unless it is in a "sweet spot". If you simply turn the key to start you can hear the pump come on for a split second then once the car starts they go in/out ultimately deciding whether or not it will hold an idle. It's almost like there's a dead spot in the key turn just prior to ignition that is cutting off continuous connection to the pumps. Sometimes this takes several attempts before they will run continuously after the engine is fired.

Sometimes I can very carefully/slowly turn the key until I find the "sweet spot" just prior to actual ignition which will trigger the pumps to run continuously for several seconds then I fire it and it's typically gtg. It's important to note that this sweet spot does not always exist. Other times I simply turn the key to the "on position" and the pumps run continuously.

Is this something as simple as a lose wire/connection in the ignition? This is something I have just lived with as a quirk to the car for quite some time and honestly is not an issue ~75% of the time I'm driving but when it decides to act up it can be very annoying. Also worth noting the car has cut fuel/died on me while driving before which results in having to shift to neutral, fire the car, then release the clutch in appropriate gear to remain cruising. Simply letting the clutch out will not start the engine back up.

Ideas? I know the switches are not very expensive but would rather have all of my keys match etc. Thanks in advance!


Last edited by patina; 04-19-2018 at 08:53 AM..
Old 04-19-2018, 08:51 AM
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For later year 930s, the fuel pumps are not supposed to run before starting the car. Mine (an 88) used to do that, but Ronnie let me know that wasn't normal and it was the yellow relay causing my problem. Of course, you don't have a yellow relay, so I am not positive how your system would work. But, assuming it isn't supposed to run before starting either, that symptom is probably related to your fuel cutouts on occasion. No idea if the ignition switch is an integral part of that equation.
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Old 04-19-2018, 09:44 AM
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If I remember correctly (big IF), the actual electronic switch part bolts to the back of the keyed part. Therefore, replacing the (faulty?) electric switch part will not require you to change ignition keys.
Old 04-19-2018, 10:10 AM
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Being the guy I am I would try taking the switch apart and clean in.
If that's not possible I would just flood it internally with some electronic parts cleaner while turning and hope it's just dirt or corrosion in the switch. (Obviously while removed from the car)
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Old 04-19-2018, 12:58 PM
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Try some Deoxit D5

Quote:
Originally Posted by 1979-930 View Post
Being the guy I am I would try taking the switch apart and clean in.
If that's not possible I would just flood it internally with some electronic parts cleaner while turning and hope it's just dirt or corrosion in the switch. (Obviously while removed from the car)
+1

You can try spraying it with some Deoxit contact cleaner and move the key around in the tumbler. Being naturally lazy, I'd try this before taking the electronic switch apart. This stuff works well on vintage stereo switches and potentiometers to clean and lubricate the contacts. Then let it air dry - while you have it out, you can hook up a multimeter and check it.

https://www.amazon.com/dp/B0002BBV4/ref=twister_B07CG8YVFN?_encoding=UTF8&psc=1
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Old 04-19-2018, 03:16 PM
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Thanks guys - will start there.
Old 04-20-2018, 07:04 AM
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I have pulled mine completely apart. But be careful, from memory there are a bunch of springs and tricky bits in there. Nothing fatal, but take care when you open it to see how things go back. I spent a looong time reassembling it.
but I don't think your pumps should run until the engine does. I suspect you have another problem lurking.
Regards
Alan
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Old 04-20-2018, 11:45 PM
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Quote:
Originally Posted by Alan L View Post
I have pulled mine completely apart. But be careful, from memory there are a bunch of springs and tricky bits in there. Nothing fatal, but take care when you open it to see how things go back. I spent a looong time reassembling it.
Oooh. Now you've got me thinking... I frickin' hate the start interlock on the later electrical switches (with the 964 part #). But the older 911 part without the interlock is NLA (and was double the price for years before that).

I wonder it's possible to just remove the interlock from the electrical switch? (Some people say their interlock is in the locking portion, but on all 3 of mine, it's only in the electrical part);

Quote:
Originally Posted by Alan L View Post
but I don't think your pumps should run until the engine does. I suspect you have another problem lurking.
Ditto. Mine always did, but it was a transplant. Even when the plug on the back of the air sensor plate was hooked up, my pumps still ran with the ignition "on" - but it shouldn't have done; apparently some mismatch between the motor harness/car wiring.

You should probably check that the air sensor plug and the CSV plug are both plugged in and not swapped by mistake; they're in the same place and almost identical plugs (from memory, the air sensor plug is more blue-ish, and the CSV valve more green-ish). The car will likely start just fine with the wires swapped - e.g. without the CSV - because the TTV only kicks in at some very low temp. It's pretty common for the air sensor plate to be disconnected for diag or not replaced, for some reason. This is what stops the pumps from running until the motor is started (and the plate pulls off the stop). Assuming that everything is connected/working correctly...


That your pumps sometimes run and sometimes don't would worry me - enough to look into it, anyway. I had a Honda 750 that sometimes wouldn't switch on but mostly did; I pretty much just ignored the problem until the wiring harness released the magic smoke one day..

There's a bunch of other things it could be - but one possibility is that some contacts inside the switch may be worn/arced down inside, or the mechanism could be worn/flopping about and doing things it shouldn't. Yeh - that could be bad...

As Ollie says, the electrical portion can be replaced without touching the lock barrel, but it's a pig to get at the top screw... #1 the most awkward/frustrating job I've ever done on a 911 - and I've done it several times now. Replacing the hood shocks and adjusting the flappy air cables in the frunk - even the one behind the brake booster - pale by comparison...

If needed, bendy screwdriver or a very small ratchet is the hot tip. Once started, you'll probably do most of it with fingertips on the screwdriver bit anyway...

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Old 04-22-2018, 12:42 PM
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