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sney
Joined: 24 Sep 2010
Posts: 18
Location: Calgary, Canada
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 Posted: Tue Sep 28, 2010 3:31 am Post subject: Thermo Time Switch |
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Ok, so my '78 924 is experiencing some pretty severe cold start issues. I spoke to a friend of mine and he said the best way to handle it is to forget the thermo time switch and wire in a toggle instead, and that sounds like my kind of fix.
The problem is that I'm not sure where the thermo time switch is located, and Haynes is vague on the matter. I read a mention somewhere that it's plugged in towards the back of the block, and I followed the wires back to 1 plug that's in the aux air valve and another that's in another squarish component with 2 cylindrical protrusions that I forget the name of, but neither seems to jive with the "sensing coolant temperature" job that the thermo time switch supposedly does.
Can anyone point me in the right direction? I really want to get this thing going again. The wife is already mad at me for buying a car that doesn't work, lol.
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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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| Posted: Tue Sep 28, 2010 3:50 am Post subject: |
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Back of the block where the side coolant pipe and the heater pipes go.
That casting has the TTS in the bottom of it. Probably best from below.
It's a big brass hex with a plug on the top. It will be VERY stuck.
Might have to take the casting off to get it out.
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sney
Joined: 24 Sep 2010
Posts: 18
Location: Calgary, Canada
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| Posted: Tue Sep 28, 2010 4:16 am Post subject: |
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Very stuck, you say? Hmm. Well, I don't think I really need to take it out, just bypass it in the circuit. Guess it's the day to break in my new jackstands.
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Rich H
Joined: 10 Jun 2007
Posts: 2665
Location: Preston, Lancs, UK
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| Posted: Tue Sep 28, 2010 4:26 am Post subject: |
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Yep, if you want to leave it then do so.
One bodge is to just earth the other side of the CSV so the CSV fires during cranking. It's quick and dirty and your car MUST start easily or it'll flood in no time at all...
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1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec |
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Slam
Joined: 07 Jan 2005
Posts: 1690
Location: Wainwright, Alberta, Canada
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| Posted: Tue Sep 28, 2010 4:28 am Post subject: |
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Your cold start valve lives at the back of the intake - look for the injector with the connector 
You could wire a switch right to that CSV if you wanted, but in the long run you'd just be masking whatever the underlying problem is. Got vac leaks? Done a tune-up? Set the timing? Checked fuel pressures and such? And on and on...
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sney
Joined: 24 Sep 2010
Posts: 18
Location: Calgary, Canada
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| Posted: Tue Sep 28, 2010 4:59 am Post subject: |
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| Slam wrote: | Your cold start valve lives at the back of the intake - look for the injector with the connector
You could wire a switch right to that CSV if you wanted, but in the long run you'd just be masking whatever the underlying problem is. Got vac leaks? Done a tune-up? Set the timing? Checked fuel pressures and such? And on and on... |
the MFI system generally seems to be fine, since once it's running, it runs beautifully. No problems with warm start either. Anyway, the guy who sold it to me just came by to pick up his stereo - more on that later - and he was able to get it started, and showed me how, so the CSV issue has just moved out of the "urgent" column anyway. Apparently this very same starting issue would show up when he owned it every couple of months, though it was less of a big deal in his heated garage.
Thanks for the information, all.
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Tue Sep 28, 2010 5:39 am Post subject: |
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"MFI" actually doesn't apply to the 924NA-924Turbo(931) (unless the CIS system's been removed and replaced with some type of MFI).
CIS is a mechanical fuel injection system,with all four injectors spraying continuously, rather than pulsed and controlled electronically as is MFI.
I'd be willing to guess that the previous owners' trick to get it started involved holding the throttle to the floor while starting.. It's also mentioned in the owners manual.
I did myself a quick-easy test some time back to see if that would start it even with no help from the CSV. With engine cold after sitting overnight, I unplugged the CSV, and did the pedal hold down trick - it did start easily and within just a few engine rotations..
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sney
Joined: 24 Sep 2010
Posts: 18
Location: Calgary, Canada
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| Posted: Tue Sep 28, 2010 5:43 am Post subject: |
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| Smoothie wrote: | "MFI" actually doesn't apply to the 924NA-924Turbo(931) (unless the CIS system's been removed and replaced with some type of MFI).
CIS is a mechanical fuel injection system,with all four injectors spraying continuously, rather than pulsed and controlled electronically as is MFI.
I'd be willing to guess that the previous owners' trick to get it started involved holding the throttle to the floor while starting.. It's also mentioned in the owners manual.
I did myself a quick-easy test some time back to see if that would start it even with no help from the CSV. With engine cold after sitting overnight, I unplugged the CSV, and did the pedal hold down trick - it did start easily and within just a few engine rotations.. |
Heh, I was under the impression that MFI stood for Mechanical Fuel Injection ... though I'm wrong all the time so that's not new. And yes, he held the pedal to the floor and later pumped it a few times.
I don't have the owner's manual. Been meaning to find a copy. All I've got is Haynes and the internet.
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Fifty50Plus
Joined: 28 Feb 2008
Posts: 1424
Location: Washington DC area
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| Posted: Tue Sep 28, 2010 7:04 am Post subject: |
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My racecar has an MFI pump with pistons that squirt fuel based on load and RPM. Cold start manipulation is done by a timed cold start valve (CSV) and by temperature sensitive washers that expand when heated by air after it passes the cylinder heads (air cooled motor). The washers are connected within the pump to an enrichment device. Once the engine gets some temp in the heads, the MFI pump is leaned out a bit by the expanding washers.
The combination doesn't work very well with race headers so I replaced the washers with a fixed screw and put the CSV on a push button. Push and hold while cranking and for about 15 seconds after ignition gets the engine running. Several minutes of idle and the mixture is right for racing.
Highly NOT recommended for the street since a backfire might continue to be fed excess fuel by the dummy with the push button. 
Chuck
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Smoothie
Joined: 01 Jan 2003
Posts: 8032
Location: DE (the one near MD, PA, NJ)
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| Posted: Tue Sep 28, 2010 10:21 am Post subject: |
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| sney wrote: | | Heh, I was under the impression that MFI stood for Mechanical Fuel Injection ... |
Good point. My miss...I was actually thinking of "EFI". "MFI" can mean Mechanical FI. I was thinking Multiport FI, another thing that's associated with the abbr. "MFI", and which CIS actually is anyway.
Sorry for the confusions.
The pedal trick, I've found through extensive experimenting works best without pumping. -So if you ever find it extra stubborn in not wanting to start, try this: If you've already tried and it failed, begin by giving it an approx. 5-10 minute rest, then before you even touch the key, press and hold the throttle to the floor.. Now insert and turn the key to start. If it's going to go, it will within just a few engine rotations (, so don't push the issue). If-when it does start, of course let off the throttle.
Things I've found to not help and/or contribute to preventing it from starting -
(1) Trying the pedal-to-the-floor start too soon after a failed attempt. (Either a symptom of flooding, or on the flip side - possibly not enough fuel due to the TTS opening up, leaving the CSV in no-squirt mode.)
(2)- Pressing and holding the pedal to the floor -after- you've already activated the starter. (Don't know why this shouldn't work - I've just found it doesn't, and consistently.)
(3)- Pumping the pedal.
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