Jay,

For the CSV Circuit, power starts at the starter motor, then goes through the CSV via the yellow wire. The power then goes through the black/red wire to the micro switch. The micro switch (when closed) has the current go to ground to complete the circuit.

You need to be sure your test light or meter goes between the red/black wire and ground. With the microswitch open (hand throttle down), the lamp will light (or meter show 12v) when you hit the starter. With the microswitch activated (closed, hand throttle pulled up)), the light/meter will not light since the current will now go through the switch to ground instead of the light/meter.

Make sense?

Well Conceived Test Procedure….…..
 

Harry,

This is a well conceived test light procedure and would have done it differently but like this one instead. Thanks.

Tony

Right. I am putting the light point onto the tab on the microswitch that the black/red wire that goes to the microswitch. So when the starter cranks, that 12V should go through the tester light and the microswitch. At least that's what I'm figuring. Why would the wire being hooked up to the microswitch stop that from happening? It's like two light bulbs branching off the same wire.

I guess I could put it in line and see if that changes anything. I admittedly did not do well in Physics when it came to serial versus parallel electricity wiring.

And to be clear, when I take the black and red wire off of the microswitch and put the test light to it, and crank the engine, it does light up the bulb. Same wire. It's just that when it is attached to the switch, the light doesn't work.

Electricity always follows the path of least resistance.

Leave the wires attached to the microswitch.

With the test light on the red/black wire, the other side grounded, and the hand throttle down (the microswitch is open), the only available path for the current is through the bulb and when you hit the starter, it lights up.

When the hand throttle is up, the microswitch is closed and has less resistance than the bulb. When you hit the starter, the current goes through the switch to ground and the bulb does not see the current and stays dark (it may glow dimly).

Tony,

Thanks. As in many things in life, lots of ways to skin a cat. One is not necessarily better than the other.

Jay,

I think you already answered this but I have to ask. When you pull up the hand throttle, have you verified it moves the microswitch from off to on? Does the gas pedal move as well?

Yes, I'm certain the hand throttle is working and the microswitch is on. I'm measuring 5 ohms. I don't know the correct resistance for the switch.

Per Pete's question, no I have not tried starter fluid. Not even sure where to spray that in a CIS system? Take off the top boot and spray down throat, put boot back on and try to start? Would that delayed dripping starter fluid would do much?

As to it being an electrical issue, this car has been California garaged every day of its life and remains in great condition. I do not expect any material corrosion on the grounds or wires. But I can take a look. It is otherwise driving beautifully. I'd think there'd be some other ramification of such an issue. However, as I said, the starter switch though is balky now. Maybe when it is in the starter mode, the wire for the ignition is somehow not connecting well. But it connects better when in drive mode.

Starter spray: If you have a pop-off valve lift it open and spray in there. Otherwise, I use a straw on the spray head, push up the air metering plate, and spray it in there. If I'm lazy and don't have the air filter off already, I just give it about a 3 second burst into the air intake horn.

I consider starting spray the first diagnostic test when an engine won't start, or is hard to start. It's also the easiest test to do.

The micro switch is just a switch and should not have any significant resistance unless the contacts are pitted. The contacts should close when the throttle body just starts to open when either the hand throttle is pulled or the gas pedal is pushed. The cold start valve gets voltage when the micro switch is closed and the ignition is in the start position.
After a quick search using microswitch on the internet I found there are quite a few manufacturers of micro switches. It should be possible to find a much cheaper replacement with the originals basic dimensions.
The 73.5 was the first CIS and a bit crude. Later ones benefited by refinements added over the years, TTS, vacuum wur AAR AAV spider for cold start valve etc. The starting procedure where they say to fully depress the pedal while cranking is unique to the 73.5, and probably due to the fact that it has no TTS to shut off the cold start valve and Bosch figured the amount of air entering while the start valve is spraying would give approximately the correct mixture.

If you cross the leads of the ohmmeter, what do you read. My cheapo one reads a few ohms but I don't worry about it.

My ohmmeter gives 0 when directly crossed.

I will try the starter fluid next time I am out and have the starting problem.

There was a 73.5 micro switch on eBay I just picked up. It wasn't much money. We'll see how it tests and if it works any better.

Going back to the potential that the ignition is not getting correct power during the starting mode, anyone have a suggestion of where I can put my voltmeter during the starting process to see if it drops when the starter is spinning?

A red wire powers the CDI box. Connect your voltmeter to that circuit as close as you can easily get to the CDI.

Yes, I was just going over the wiring diagram. I came to that same concept - and found that on the #1 fuse in the 3 fuse box in the engine compartment, it is directly connected to red to the CDI. Thanks!

Just tested. 12.4V while ignition on. 11 V when starter spinning.

But still almost nothing for the red/black wire at the microswitch. But when that wire is disconnected, it shows 12V when the starter is spinning. Unless I'm misunderstanding how this works, that wire should show 12V there when attached too (and the microswitch is on).

11V when cranking is good.

Jay, did you finish sorting out whether the socket pins were reading correctly and the relay working correctly? That should not affect the car not starting, but it's one less thing that might be related to something else.

Where are your leads attached? If it is across the switch, it will read 12v when the switch is open (hand throttle down and cam on linkage not touching the switch) and 0v the the switch is closed (hand throttle up).

berettafan has my favorite signature: Well i had #6 adjusted perfectly but then just before i tightened it a butterfly in Zimbabwe farted and now i have to start all over again!

While your testing the cold start injector electrical, you also mention in posts 8, 25 that you saw it spraying, so I'm not sure if you acually have a problem. In the cold start thread I mentioned that there is a filter screen. You may want to pull it and maybe give it a quick cleaning to make sure it flows properly.
From looking at your post 28, pressures are pretty good. In the 73.5 injector thread, you mentioned you had a good spray pattern, but a slightly dripping injector. That could be a potential problem. It could lead to excess fuel to that cylinder and lack of fuel in the injector line.
I'm trying to think of any little issues that may contribute to the problem. You seem to be on top of most maintenance, have you checked to make sure the advance weights are working in the distributor? Setting the timing at full advance is standard, but is it correct at idle? You also seem to have checked for possible air leaks to eliminate that issue. Just curious, have you tested compression in all the cylinders?

Some updates. I got a replacement (used) CSV microswitch and installed it. I've been able to drive it a few times now. I'd say it is better, but not perfect.

But everything else is truly great as it's ever been. I don't have any of these issues, which I have had in the past:
- Idle is sewing machine smooth - I've had little burbles during idle here and there in the past.
- Full power all the way up to redline - it has tapered off above 5,000 rpm in the past.
- Smooth at all rpms - I've had slight flutters at constant throttle at one rpm or another in the past.
- No bucking when lifting the gas at any point.
- RPM drops and holds at idle and does not pulse (which should mean it's not too rich).

So with all of these working so well, I find it hard to believe that there is something major going on. And if someone said that perhaps it's too rich or too lean, I wouldn't touch it since the rest is so spot on.

But still, it doesn't snap to start like it did in the past. From my few drives, here is what happens. If I try to start without throttle (and without CSV), it doesn't start. But on the next two attempts, using throttle it seems to start - though still with some spinning. Starting the starter with no throttle, then giving some throttle while it is spinning doesn't change anything. But, I'm not sure if the CSV will trigger like that. Also, I note that when I do try to start it multiple times for many minutes with the throttle up, and it does finally start, I do smell gas - that is, that CSV must be pumping each time, and it still starts with that extra gas.

As to WURs, I did have a number of problems with WURs (as noted in my prior posts). I tried the 008, 009 and 129. I now have a nice old 001 on and since I put it on, it seems to drive better than any of the prior WURs. I don't know if this harder starting happened in conjunction with the 001 - but as noted above, this WUR performs right to spec for all specs.

To Pete, I did confirm the socket pins were correct. And stuck in a new relay just for the heck of it.
To Harry, I tested both old and new switches off the car and they read in theory correctly. But when I read the old on on the car, it gave odd numbers. I'm wondering if there is some issue inside of it, and hoping that this new switch solved it.
To Ed, yes, thanks for the detail in going over my old posts. The P&Cs and valves/guides are relatively new (like 10,000 miles), so I can't imagine compression issues there.

And no one has asked. But the spark plugs are pretty new - and last time I got them, I bought them straight from Porsche.

Congrats Jay. It's time to declare victory, go drive the snot out of it, and have a beer.

Thanks! Exactly. But I still don't like how much cranking it needs to start. So far it does seem to start after a little bit. We'll see Thursday when I drive to my 83 year old mom's and stay there for a couple hours. That's where I usually start thinking it will never start, and it takes many minutes to get it to start.