Weird cold start issue '74 CIS

[Tony V]

I've searched the bbs to see if anyone else has had the same problem. Nope.
Long story:
On the way to the Hill Country Rallye, our group took the back roads toward Globe Az. While we were enroute, I noticed the car's idle hanging a bit. When we settled in for the night, I took a look and found most of the throttle bushings were shot. Found an auto parts store and bought a bigger spring for the throttle. Snapped back fine and my right leg got a nice workout! Following morning, I had trouble starting the car. Nearly had to warm it up with the starter. Had the same cold start problem for the remainder of the trip. Got home and changed all the bushings: pedal cluster, bell crank and the ones on top of the engine. Still wouldn't cold start. Brought it in for some other work and had the mechanic check out the starting. He checked fuel pressure (fine) adjusted the lever between the seats and found that if he removed one of the leads, from the micro-switch, the car would start cold. When I picked-up the car, it did start. Next day some story. I reattached the wire for the micro-switch and it started right up. Removed the switch and tested it. Seemed to do what it was supposed to. also checked the switch in the drivers side cam housing and it too opened and closed with temperature. Now I've found, that before turning the key, if I remove one of the ground wires from the micro-switch and put it right back the car will start cold. Tempted to run a wire to a switch and do it from the cockpit. Make any sense?
Thanks,
Tony

[ossiblue]

Originally Posted by Tony V

I've searched the bbs to see if anyone else has had the same problem. Nope.
Long story:
On the way to the Hill Country Rallye, our group took the back roads toward Globe Az. While we were enroute, I noticed the car's idle hanging a bit. When we settled in for the night, I took a look and found most of the throttle bushings were shot. Found an auto parts store and bought a bigger spring for the throttle. Snapped back fine and my right leg got a nice workout! Following morning, I had trouble starting the car. Nearly had to warm it up with the starter. Had the same cold start problem for the remainder of the trip. Got home and changed all the bushings: pedal cluster, bell crank and the ones on top of the engine. Still wouldn't cold start. Brought it in for some other work and had the mechanic check out the starting. He checked fuel pressure (fine) adjusted the lever between the seats and found that if he removed one of the leads, from the micro-switch, the car would start cold. When I picked-up the car, it did start. Next day some story. I reattached the wire for the micro-switch and it started right up. Removed the switch and tested it. Seemed to do what it was supposed to. also checked the switch in the drivers side cam housing and it too opened and closed with temperature. Now I've found, that before turning the key, if I remove one of the ground wires from the micro-switch and put it right back the car will start cold. Tempted to run a wire to a switch and do it from the cockpit. Make any sense?
Thanks,
Tony

Very bizarre indeed and makes no sense if you assume the cold start valve is the problem--which it appears to be. However, it is not clear from your post if you had any firing at all of the engine during your failed cold starts. If there was no firing at all, have you considered it may be an ignition issue? Has anyone tested for spark during those times when the cold no-start symptom appears? Of course, if you got brief spurts of combustion but failure to run, then the ignition can be eliminated. Just throwing this out there.

Assuming it's the CSV, the micro-switch and TTS are wired in series as a ground circuit to the cold start valve. If either of them is "open," there will be no ground connection to the CSV and it will not inject fuel. This is why your scenario doesn't make any sense.

Removing a wire from the micro-switch creates an open circuit (unless the disconnected wire is somehow shorting to ground) and the CSV should not work--yet, apparently, it did when the mechanic disconnected it. The only way that could possibly happen is if the disconnected wire was the ground connection and the switch itself was somehow internally shorting to ground and sending that signal through the TTS to the CSV, or the TTS was shorting to ground.

That, however, doesn't explain the failure to start the next time and the successful start when you reattached the wire to the micro-switch. Certainly, removing and reconnecting a wire to the micro-switch, before any attempt to start begins, which results in a successful start, makes no sense at all.

So...based on the assumption the problem is the CSV failing to inject consistently, you may want to start by testing that component first. Before you do that, you may wish to try a simple experiment.

Remove the ground wire from the micro-switch and attach a jumper wire to the switch that is connected to a solid ground connection on the body. Do you get consistent cold starts now? If so, you likely have a bad connection through the ground wire to the micro-switch. If you see no differences in starting, continue, below.

Remove the two wires from the micro-switch and connect the ends together--removing the micro-switch from the circuit. Now you have a direct ground to the TTS and on to the CSV. See if you now get consistent cold starts. If you do, then the micro-switch may be the problem. If you still get failure, reconnect the wires to the micro-switch and join the wires from the TTS. See if you get consistent cold starts now. (If you remove the TTS from the circuit, remember not to pull the throttle lever up during warm starts. Your system is now wired like the first CIS in 73.5.)

Let us know any updates or test you perform. None of this makes much sense at this point.

[Joe Bob]

Check valve in the fuel pump neck? While mostly for hot start, residual fuel pressure could be an issue. CIS is mostly about fuel pressure to get a clean start and idle.

[Tony V]

Thanks guys. Will try a couple of things and report back. You are 100% correct on one thing: Just doesn't make sense!
Car always cold started on the first turn of the key. Problem started as soon as I installed the bigger spring.
Mis-spoke on one thing. Removing one wire from the micro-stitch, before attempting to start, doesn't work. Attempting to start and then removing/re-attaching the ground wire, does.
Thanks again for the assist.
Tony

[Tony V]

Finally got some time to continue investigating. Used a meter to test the leads to the TTS and the leads on the micro-switch. As I understand it, when cold, both leads on the TTS should have ground. (they do) One lead on the Micro-switch should have ground (coming from the TTS?) and the other should not have ground until the micro-switch is activated via the throttle lever. I find ground on all 4 leads when cold and the ignition off. Hard to get a peak at the cold start valve but the wires appear to be unobstructed and insulated. Would a ground on the front facing lead of the micro-switch point to a faulty cold start valve? The wires were removed from the micro-switch when tested and showed the same ground when reattached. Switch functions properly.
Thanks,
Tony