'78 weird problem - need help
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Intermediate
Joined: Jan 2004
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'78 weird problem - need help
OK. I am almost done getting my friend's car running. Now I have this bizarre problem. It is intermittant but here is the problem. You start it and it catches but when you let go of the key it dies. It did it about 4 times in a row. Then I found out if I keep the key in the start position(with the starter still running) It runs normally and revs - but as soon as you let go of the key it dies. My first instinct is that the lock cylinder is defective. Is there anything else I am overlooking?
Drifting
Joined: May 2001
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From: Owasso, OK
Check the resistors on the panel in front of the left wheel well. During cranking voltage is sent from the starter, through the .6 ohm resistor and on to the coil. When the key is returned to the on position voltage is supplied from the ignition switch to the .4 ohm resistor then on to the .6 ohm resistor then to the coil. So in your case, the switch (as mentioned earlier) or the .4 ohm resistor (or connections) are bad. Since the switch is functioning OK in the other positions, my bet would be the resistor or connections at the resistor are the culprit.
Dennis
Dennis
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Joined: Jan 2004
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Is there anything you don't know about this car. 
Thanks for the detail! I am going to check that tonight when I get home. It sounds like you are correct and would help explain the random no run condition.
Thanks again for taking the time!
Thanks for the detail! I am going to check that tonight when I get home. It sounds like you are correct and would help explain the random no run condition. Thanks again for taking the time!
Thread Starter
Intermediate
Joined: Jan 2004
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OK here is what I know And I have a couple of questions. I did find the wiring diagram in the porsche shop manuals he gave me. I checked the wiring on the resistors- moved it around etc. Climbed in the car - as soon as I got to the end of the driveway it quit. pushed it back in the garage and popped the hood - put the meter between the resistor and ground turned the key an wa-la the voltage is there - turned to start and it started right up. CLosed the hood went to back out it died. This happened 3 more times. The last time I left the hood popped with the meter attached and it didn't die. I drove it all around the neighborhood. Look at the attached pictures and tell me
A. are these part of a security system.
B. are they stock
C. If so will it kill the ignition.
A. are these part of a security system.
B. are they stock
C. If so will it kill the ignition.
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Drifting
Joined: May 2001
Posts: 2,747
Likes: 3
From: Owasso, OK
Checked the FSM but couldn't locate a picture of the hood trigger in either volume V or VI. IIRC the the alarm if triggered it will not let it start at all. Try connecting a jumper wire from the power block to the .4 ohm resistor where the single black wire connects. If it still dies on you, there is a break in the resistor coil which causes an intermittant contact. If it doesn't die, look for a bad connection or corroded wire between the ignition switch and ignition module or the ignition module and the resistor. Another possibility is that you are losing the 12 volt signal on circuit 15 that goes to the fuel pump relay which would kill the engine.
Dennis
Dennis
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