Electric Choke Voltage

[OldsFan]

Hey all - On my 85, I just started having some trouble and I am pretty sure it is electrical. 

A couple days ago, I noticed it started to diesel (run-on) after shutting it down once in a while and the idle seemed high.  I took a quick look at the choke and it is not opening all the way anymore.  Also, it isn't coming off of fast idle.  Could the high idle RPM (1800) and rich mixture when warm be causing the dieseling?  They seem like they could be related... 

Anyhow, I figured the choke coil crapped out.  I pulled the power connector to the choke coil and I am only seeing 5 Volts (engine off, ignition in run position).  If I connect it to the choke coil and measure the voltage, it sees no voltage at all.

Is there any reason a Quadrajet choke coil would get only 5V?  What is the best way to troubleshoot it if it is supposed to be getting a full 12V when the ignition is on?

Any help / ideas appreciated.  Thanks!

[enaberif]

Dieseling has nothing to do with the choke but more that there is something within the engine usually deposits causing it to re-ignite and not be able to start.

5v means where the coil is getting its juice from isn't a proper 12v source.

[swilliams]

I have had some of the same problems. Check this out http://forum.73-87chevytrucks.com/smforum/index.php?topic=28784.0

[OldsFan]

Ok, that link to the post helped a lot.  Thanks! 

Just in case someone reads this later - the wiring diagram shows what is going on.  The oil pressure switch keeps the choke coil heater from getting power if the engine is not running.  Instead, the dash light for the choke is on and it grounds through the choke coil. Disconnecting it turns the dash light off.  Once the engine is started and the oil pressure switch sees pressure and closes, full voltage is sent to the choke coil heater and the dash light is switched off.

I am now reasonably sure that my choke coil heater had gone bad because swapping in a new one solved the problem right away.  Comparing the old choke coil and the new one were light night and day - the heats up and appears to work much better.

As far as the dieseling goes, it appears to be related because the two issues started at the same time.  I am going to test it out over the next few days and see how things shake out.

[timthescarrd]

If your choke was not fully opening, the engine would be running rich, which can cause some dieseling