How long should cold start solenoid operate while cranking on '72?

LeeH · 01-17-2005, 05:55 PM

I hooked up a test light in the circuit just to see if power was getting to the cold start solenoid. The light stayed on for maybe two seconds while cranking. The car sounded like it was trying to start for those two seconds... then not. There never seemed to be a pattern for how long it would stay on - other than not for more than a second or two. Eventually it didn't seem to come on at all. I tapped the relay and it started coming on again... but only for a second or less.

How long should the solenoid open for a cold start? What controls the amount of time this circuit is running?

Bobboloo · Bobboloo's Garage

I know in the first version of MFI the cold start setup had a time limit relay that allowed only 2 seconds for the cold start valve to operate. The 72' version doesn't have the time limit relay however and it just has a thermotime switch that feeds the cold start relay that feeds the cold start valve. Since it's a thermo"time" switch I assume that it also has a time limit in the 2 second region.

Now that you have determined that you are getting current to the valve you need to determine if the valve is functioning. They sometimes get corroded and stuck.

You can do this a couple of ways. One is to remove the hose that goes from the valve to the stacks and put the end in a jar to see if it outputs gas when you crank the motor. Another way is to just feed current to the valve with the motor off and you'll here the electromagnetic valve click. This can easilt be done with a jumper cable from one of the hot terminals on the rear fuse block.

One thing I might add. I know you determined that the hot wire to the cold start valve is functioning but you also need to make sure that the filter assembly is grounded. So it's a good idea when you use your test lamp that you connect the ground side of the lamp to the filter assembly.

When I troubleshot my cold start system my problem was twofold. 1. No ground and 2. Corroded stuck valve.

Peterfrans · 01-18-2005, 02:53 AM

I hooked up a permanent test light for the cold start on my dash. On cold days it goes for a second or two for the first start. If it dies and I restart immediately, the time it works is less, which is fine, as it realy pumps a lot of fuel into the stacks.

LeeH · 01-18-2005, 05:18 AM

Sounds like the electronics end of my system is working about the same. Now to figure out if it's actually pumping gas.

Peterfrans · 01-18-2005, 05:49 AM

Thats easy to determine. Pull off the fuel hose from the solenoid and replace with a piece of hose that ends in a can. Now you just have to apply 12v to the solenoid on top of the fuel filter (with ign. on).

Peterfrans · 01-18-2005, 06:18 AM

there is a coil in the thermo time switch which warms the switch (does this make sense?). Above a certain temp the switch opens and the circuit to the solenoid is broken. The temp of the switch is dependend on
- ambiant temp
- engine temp
- coil in the switch

After a few starting attempts the switch will be so warm that is does not close anymore, hence no extra fuel through the cold start injectors