924Board.org

[stevekat]

When cranking my 1981 931, I have zero volts at terminal 15 on the coil. In the run position I have 10 volts or more. The car is very difficult to start, only starting with engine momentum after the key returns to the run position.

Currently there is no fuel pump relay in the car, I am waiting for this to arrive tomorrow, but I have the fuel pump jumper at the fuse relay block.

When I run a jumper wire from the battery + to the coil terminal 15, the car starts right up and runs fine when the key is returned to the run position.

How does one debug this problem?

1) If the ignition switch makes the engine crank, does this rule out the ignition switch as a suspect?

2) I understand the power for the coil comes from the starter or solenoid on starting...is there a relay or other interim step between the starter/solenoid and terminal 15 of the coil, or is it a direct connection?

3) Where is the take off from the starter/solenoid to the coil? Is it a separate wire from the starter/solenoid to the coil, or does the power come off a physical point elsewhere on the car? Does anyone recall if this is a push on connector, or is it a post and nut for this take off?

4) I have two wires into a single connector on terminal 15 on the coil, one is black and one is blue/black. Is one the run wire and one the start wire? Does anyone know the color of the start wire?

5) Where does the terminal 15 on the coil go, for run and start? To the fuse box first? Wanted to try to figure out where to trace next.

6) I know the fuel pump relay receives a pulse signal from the coil that keep the fuel pump running through the fuel pump relay, but does the fuel pump relay have any control over the power delivered to terminal 15 on the coil...I don't think so since lots of folks talk about jumpering the fuel pump relay terminals to start their cars when necessary.

Thanks for any help.

My prior post:
http://www.924board.org/viewtopic.php?t=26801&highlight=

[Paul]

See responses at the end of each question.

[stevekat]

Paul, thanks. Made some progress. I found a connector on the firewall, on the engine side, near the battery. There is a big fat red/black, and a skinny light blue wire. At the time I deduced that these come off the ignition switch and are activated in the start position. The light blue wire on this connector had a poor connection. I took apart the connector, cleaned the spades, and tweaked the female connector to make better contact. Once done, I was getting power to the coil terminal 15 on cranking. From this set up, it appeared the ignition switch provided power to the coil through the light blue wire, and it did not come from the solenoid, as you had confirmed.

I continued to have zero volts intermittently on testing cranking the engine, but maybe one in ten - a vast improvement. It is my understanding the prior owner had the ignition switch replaced. After fooling around, testing with the meter, etc., I discovered that one must turn the key all the way through the start position to get power to the coil terminal 15 when cranking. I had not consistently turned the key all the way to the stop, but had let up the turn when the starter began operating, and this occurred slightly before the ignition switch directed power to the coil. I thought about putting in another, perhaps better quality ignition switch, but I do not think it is failing, and is quite new...it is just a matter of understanding its idiosyncracy.

Tomorrow, if the fuel pump relay comes, I'll pop that in. Hopefully this shall permit removal of the jumper wire/switch that activates the fuel pump. I ordered relay 433 906 059 for about $20, that handles the 16 amps for the duel fuel pumps, but does not have the rev limiter.

I guess the question I have left, is if the light blue wire on the connector I found has any function for sending current to coil terminal 15 during cranking, where does it become the bk/bl - or is it an unrelated wire and I just imagined it has an effect on getting current to the coil on starting...