No-Start Issue - Part 2

frank · 11:06 AM

ISSUE SOLVED! See resolution below. Search for: *** Solution ***

I have narrowed my issue down to a peculiar symptom:

The Trigger / Ignition Wire only fails to provide voltage to the solenoid if it is connected. If I remove the wire and test the voltage on the wire I get 12.6 volts. Connected, the voltage is less than 1 volt.

Any thoughts?

frank · 10:23 PM

I tested every wire and scenario. I tested the path all the way through the relay board by removing the caps on the wiring harnesses to attach my multimeter. 12.6 volts everywhere UNTIL I connect the trigger wire to the solenoid on the starter. At that point there is almost no voltage.

I am stumped. Could my second brand new starter be bad too?

Is there an echo in here?

stinkindiesel · 02-07-2014, 10:29 AM

Somewhere along that circuit, you've got a high resistance connection. With no current flow (trigger disconnected) you get full voltage. With some current flowing, you see and excellent example of Ohms Law at work. Voltage at the source = battery voltage - (resistance in circuit) * (current drawn by the load)
That, or you got another shorted starter

Gary

John Rogers · 02-07-2014, 11:09 AM

I think it is the wrong starter and fails after a use or three.

frank · 08:48 AM

Voltage flows unobstructed until the solenoid is introduced to the circuit.

I am going to return this new O reilly's starter and get a Bosch. I'll pick up the troubleshooting from there if the Bosch doesn't fix the issue.

There us an abundance of complaints about failing new alternators and starters from O reilly's on the Net.

frank · 02-08-2014, 08:47 AM

Since it was Friday and no local shop has Bosch starters in stock I decided to get a third starter from the FLAPS... that and the fact that the guys at O reilly's told me I would have to get manager approval for a refund who happened to not be in at the time.

I didn't mount the starter. I simply attached jumper cables to the casing and the + post, then used an alligator-clip to connect the ignition wire to the S post on the solenoid. - Failed. Same issue, no voltage when the trigger wire is connected.

Is there wiring in the circuit aside from the yellow ignition wire that goes straight to the solenoid that I am not aware of?

I am going to take a lead and test the ignition wire path through the wiring harnesses in the relay board and all the way to the ignition switch. I will connect the lead to the contact at each of those 3 locations to see if I get the solenoid to trigger.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

74s and some 75s have the Dreaded Seatbelt Interlock Relay under the passenger's seat. This only allows current through the yellow wire when the seat belts are fastened. It can get corroded (especially if there are any leaks allowing water under the seat) and either fail to connect or give you a high-resistance connection.

Inside the relay board the starter circuit gets split and connects to part of the fuel injection. As you can see in the diagram here, the yellow wire comes in to pin #1 of the top connector, and goes to pin #6 of the right-rear connector. But the metal trace keeps going across to pins II and IV of the four-pin connector for the FI on the left-rear. Either of the first two connections could be dirty or corroded. I'm not sure how the FI connections could produce the sort of symptoms you're seeing, though...

--DD

frank · 02-08-2014, 10:32 AM

It's a 73 2.0, no Seatbelt Interlock Relay... BUT I just found the problem.

It's the relay board.

To test the ignition wire path I took the caps off the wiring harnesses that connect at the relay board.

I also took an ignition switch apart again to manually position the "Y" conductor to the contacts.

Without installing the starter and with an assistant:

1. I connected a lead from the ignition wire at the starter to the S post on the solenoid, a jumper cable (Red) from the + battery post to the + solenoid post, and the other jumper cable (black) to the starter housing. Turned the key. - Failed

2. I connected the trigger lead (ignition lead) to the yellow wire in the wiring harness that leads to the starter and turned the key. - Failed

3. I connected the trigger lead to the yellow wire on the wiring harness that comes from the ignition switch. - PASS

4. Although I had already tested this successfuly, which is what led me to this testing procedure, I connected the trigger lead to an exposed section of the yellow wire right at the harness that connects to the ignition switch and turned the key. - Pass

So it appears that the voltage falls off in the relay board circuit between the wiring harness that comes from the ignition switch and the wiring harness that leads to the starter.

I think this is pretty conclusive. I need a new relay board or I need to repair my own. Does anyone have one?

In the meantime I may be tearing my board apart.

frank · 11:45 AM

*** Solution ***

Looking at the wiring diagram for the relay board I saw that the path from the front yellow pin to the rear yellow pin was a straight shot along the bottom side of the relay board so using a pick hook I carved the tar away to expose the circuit. There were no breaks.

I tested continuity along the circuit and found that the readings fluctuated.

Putting pressure on the pin that connects from the starter switch gave me a better reading. I also noticed that it was the only pin where the gaps were completely closed. Using a razor I slipped it in and VERY gently set the gap to the same as the others but in doing so I noticed that the pin spins inside the receptacle. None of the others have this spin. Additionally, it was sitting higher than the other pins.

I tapped the pin head with the top of my screwdriver to press it in then checked continuity again... Continuity is a perfect 0 now... so that is good.

I put the relay board back in and turned the key. PASSED!

I'll fill-in the missing tar with plastidip.

WHAT A PITA THIS ISSUE WAS!

Thank you everyone for all your thoughts and suggestions. All were very helpful. I am very excited about this fix because the issue has been present since I purchased the car over 17 years ago only it wasn't anywhere near this bad... it exhibited more of a hot-start issue previously (even with a hot-start relay installed) but I would get stranded even when it was cold.

I am glad it is over... I learned things about my car I never wanted to learn.

now back to dialing-in my carbs, and replacing my headlight pivot.

Excellent resources for troubleshooting your own starter / ignition issues:

The absolute best starter diagnostics write-up: Testing the Starter (on the car): Symptoms and Diagnosis.

An excellent write-up on dissecting the Ignition Switch: Dissecting the ignition switch

Relay Board wiring diagram: Porsche 914 relay board wiring diagram

John Rogers · 02-08-2014, 11:21 AM

With some work and soldering skills you can get rid of the relay board easily. Find and aircraft type of multi pin sealed connector(s) and you might need two depending on how many pins you need to use? Make sure the wires run from the correct front plug to the rear plug and if I remember correctly the colors match so you are okay there. For the voltage regulator, fuses and any needed relays you can use spade lugs to connect them. We did this on my race car and many other racers do this as it makes it easier to pull the engine.

aclopez · 08-26-2014, 07:46 AM

I've been having a problem with no starts when the car warmed up. Having read your article and some trouble shooting, I found when cold, I was getting 12V on PIN 1 of the wiring harness on the Regulator Plate connector from ignition switch and 12V out on PIN 6 on the connector towards the starter solenoid. When the car was warm, PIN 6 showed no voltage.
I took the regulator plate out and indeed it was in poor shape. I dug out the trace very carefully and soldered both PINs to the copper trace...Voila!! Hard Start when warm is now fixed !!!