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'79 FI Cold Start Circuit
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gliderman
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PostPosted: Mon Dec 01, 2014 12:49 pm    Post subject: '79 FI Cold Start Circuit Reply with quote

The cold start circuit on my '79, Calif. Emissions bus is not working. Specifically, the cold start circuit on the double relay has failed twice now due to overheating, leading to melting of the lead trace on the circuit board. I repaired this once by soldering a wire around the damaged area and it worked for awhile, but now it overheated and broke in a different area of the board. Other than hard cold starting, the bus runs fine.

What can cause this to occur? The cold start injector tests out fine, but I haven't been able to test out the thermo-time switch due to its location, but all that does is to ground the circuit to allow the injector to fire.

Ideas anyone?

Tim
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Tcash
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PostPosted: Mon Dec 01, 2014 1:02 pm    Post subject: Reply with quote

Windings in the cold start. Did you do a ohms test
Bad crimp connector
Bad connections

Good Luck
Tcash
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Wildthings
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PostPosted: Mon Dec 01, 2014 1:53 pm    Post subject: Reply with quote

There is a heater circuit in the TTS, the power for which bypasses the cold start valve. If the heater circuit or the wiring for it were grounded out it would cause the problems you are seeing. I am not sure it is possible to swap the plugs between the CSV and the TTS, but if so that could be your problem as well. The plugs are physically the same shape so could be accidentally interchanged if the wiring harness would allow for it.
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Randy in Maine
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PostPosted: Mon Dec 01, 2014 2:33 pm    Post subject: Reply with quote

From the factory the CSV = blue, the TTS = brown, and of course the AAR= black

Last edited by Randy in Maine on Wed Dec 03, 2014 10:34 am; edited 1 time in total
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Tcash
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PostPosted: Mon Dec 01, 2014 2:46 pm    Post subject: Reply with quote

Cold start = Blue
TTS = Brown
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gliderman
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PostPosted: Tue Dec 02, 2014 3:19 pm    Post subject: Reply with quote

Tcash wrote:
Windings in the cold start. Did you do a ohms test
Bad crimp connector
Bad connections

Good Luck
Tcash


Did an Ohm test sorta. Had a spare used cold start; not known to be good. Both the spare and the installed (which I know works when energized) injectors exhibited the same resistance.

Tim
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Tcash
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PostPosted: Tue Dec 02, 2014 5:29 pm    Post subject: Reply with quote

As Wildthings posted. Maybe the TTS is shorted??
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gliderman
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PostPosted: Wed Dec 03, 2014 10:25 am    Post subject: Reply with quote

Tcash wrote:
As Wildthings posted. Maybe the TTS is shorted??


I haven't tested the TTS since its not easy to get to. However, would a shorted TTS even make sense as the cause of this problem? I mean after all, its function is to ground the cold start injector circuit for 7-8 seconds until the bi-metallic switch heats up enough to break the ground connection.

I will try to test it. Is there a certain resistance reading that I should look for?

Thanks

Tim
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Tcash
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PostPosted: Wed Dec 03, 2014 10:32 am    Post subject: Reply with quote

Wildthings wrote:
There is a heater circuit in the TTS, the power for which bypasses the cold start valve. If the heater circuit or the wiring for it were grounded out it would cause the problems you are seeing. I am not sure it is possible to swap the plugs between the CSV and the TTS, but if so that could be your problem as well. The plugs are physically the same shape so could be accidentally interchanged if the wiring harness would allow for it.


The heated circuit could be the problem.
Make sure the wires have not worn threw too.
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gliderman
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PostPosted: Wed Dec 03, 2014 10:38 am    Post subject: Reply with quote

Tcash wrote:
Wildthings wrote:
There is a heater circuit in the TTS, the power for which bypasses the cold start valve. If the heater circuit or the wiring for it were grounded out it would cause the problems you are seeing. I am not sure it is possible to swap the plugs between the CSV and the TTS, but if so that could be your problem as well. The plugs are physically the same shape so could be accidentally interchanged if the wiring harness would allow for it.


The heated circuit could be the problem.
Make sure the wires have not worn threw too.


Will do.

Could perhaps a bad diode in the double relay cause this problem (i.e. too much current through the double relay CS circuit)? I thought about buying a new double relay, but I want to make sure that I'm not going to toast it as soon as I install it
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Tcash
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PostPosted: Wed Dec 03, 2014 10:48 am    Post subject: Reply with quote

gliderman wrote:
Tcash wrote:
Wildthings wrote:
There is a heater circuit in the TTS, the power for which bypasses the cold start valve. If the heater circuit or the wiring for it were grounded out it would cause the problems you are seeing. I am not sure it is possible to swap the plugs between the CSV and the TTS, but if so that could be your problem as well. The plugs are physically the same shape so could be accidentally interchanged if the wiring harness would allow for it.


The heated circuit could be the problem.
Make sure the wires have not worn threw too.


Will do.

Could perhaps a bad diode in the double relay cause this problem (i.e. too much current through the double relay CS circuit)? I thought about buying a new double relay, but I want to make sure that I'm not going to toast it as soon as I install it

I don't know. I think the diodes protect the coil and the starter solenoid?
Take a look at this tech tip. Thanks to Amskeptic.
Double Relay Article
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Wildthings
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PostPosted: Wed Dec 03, 2014 11:44 am    Post subject: Reply with quote

The diode just prevents back feeding of power to the solenoid which would keep the solenoid activated after the points in the AFM close. It also keeps the CSV from getting power after the points close.
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Amskeptic
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PostPosted: Thu Dec 04, 2014 5:40 pm    Post subject: Reply with quote

gliderman wrote:

Could perhaps a bad diode in the double relay cause this problem (i.e. too much current through the double relay CS circuit)? I thought about buying a new double relay, but I want to make sure that I'm not going to toast it as soon as I install it


Possibly . . . A bad diode would allow the fuel pump run circuit to try to energize the starter solenoid. You would have to look at the path from 88Z to 88A (that is 12 volts battery to the AFM 36/39 switch) and see if the AFM to 86b circuit is continuous to 86. A diode tester would be easiest here. We want 12 volts supplied to 86b to not show up at 86 or 86a.
Colin
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