[HO455]

The electric choke I installed some 25k miles ago started to not work correctly. At I first assumed (The A word is usually a bad idea in my world. ) that the bimetalic coil spring had changed its shape some and needed to be adjusted. After several adjustments didn't fix the problem I went looking for some information on the interweb but there was little information on troubleshooting the components and what I little found was confusing.

So I did what any gearhead would do. I took it apart. That didn't reveal any physical defects which led me to suspect it must be something electrical. My trusty multimeter revealed I had 12.8 volts at the power terminal while the tuck was running. The other terminal showed 8.2 volts which only told me the heat sensor didn't have an open circuit so as long as it was still operating within specifications it was good.

The little bit of information from the interweb said
"Testing the ohms on a choke conversion thermostat. Only necessary if you suspect a problem.
Note: hitting the choke in a table will jar the spring inside to the correct position. It will also reset the Ptc and spring. All the superchokes should be round 10 ohms or less. 7-11 ohms When ohms aren’t inside the specs something is wrong inside and a quick smack may fix it. Bad ohms = 100k ohms -100 ohms etc. Must be tested on the big terminal and the brass on the bottom of the choke." So I took that to mean the ohms for the bimetalic coil should be between 11 to 7 ohms. Checking the ohms across the terminals I had 7.4 ohms so that made sense.

Checking the ohms on the temperature sensor wasn't very conclusive. With one meter lead grounded to the intake manifold and the other on the wire I measured 34.5 ohms. Which once again only proved it didn't have a open circuit. The part of the paragraph above that said 100k-100 ohms is bad makes me think that an ohm reading below 100 ohms is acceptable but, that again is an assumption based on the less than concise wording of the troubleshooting paragraph. The sensor attaches to the block with one of the intake manifold bolts which also grounds the sensor electrically. So I loosened and the retightened the bolt to see if the ohms reading changed, but it remained at 34.5 ohms so I needed to look elsewhere for the problem.

During a careful inspection of the bimetalic coil I noticed the power connector terminal was slightly loose on the rivet. I tried to see if there was loss of continuity with the ohmmeter and found that while wiggling the terminal it didn't loose continuity it ohms did fluctuate. To tighten the rivet I clamped a punch vertical in a vice and while holding the coil unit's rivet head (Photo #1) on the punch I used a center punch on the other end of the rivet. (Photo #2) After a couple of taps with a hammer the rivet was tight enough to keep the terminal firmly in place.

After reinstalling the coil unit I did a short test and the choke now seemed to work properly and this morning it worked as expected for the commute in to work. Hopefully that is the cure.