This ‘How To’ is to show folks how to fix a an uncommon problem. To my knowledge only I have had this happen and maybe JoeIsuzu.
Problem: Your glow system will not glow a cold engine and you have exhausted most of the usual remedies covered on the forum. The nature of this fault will tend to be intermittent, depending on temperature and humidity.
Tests: The following two tests can be made on a cold engine (colder than 50 degrees C) to see if you have a sensor leakage problem that can be ‘fixed’ by the process in this 'How To'.
Test 1 - - Find the yellow wire that connects to the temperature sensor switch on the thermostat housing and pull the bullet connector apart. If your Glow System will now operate normally (as if it were a cold engine) you have a shorted or leaky temperature sensor switch.
Test 2 - - Use an ohmmeter to measure the resistance of the yellow sensor wire to ground. If the sensor is good it will measure a large value of resistance: ie, 50k or more. If the sensor measures less than 50k it is leaky or shorted. Resistance of less than 3k can be considered close to a short and will signal the glow controller that the engine is HOT (even though it is cold) and will disable the glow controller. If you have a shorted sensor you will need to replace it. If the resistance is between 50k and 3k it will still signal the glow controller that the engine is HOT and that no glowing should be done. This is the resistance (leakage) range that this 'fix' will immunize the glow controller against.
Remember that all the above resistance measurements apply to a COLD sensor. A HOT engine SHOULD cause the sensor switch to close (short) and disable the glow function. The sensor switch is designed to close at about 50 degrees C.
What can you do if the resistance is between 50k and 3k?
-- You can replace the sensor switch.
-- Or, you can try to clean the sensor switch with soap and water and dry off real good. The problem I found with the switch was due to conductive contamination. Don’t know what from. Cleaning helped a little.
-- Or, you can dig the epoxy potting out from the switch with a hot soldering iron, carefully. Then test it and if good repot it with new epoxy. This worked on one for me.
-- Or, you could use my Rev 2 modification to the Glow Controller card to immunize the glow circuit to leakage resistances down to about 3k.
The glow controller modification consists of changing the glow disable threshold. This will require that one resistor be changed and another resistor be added to the glow card. I am attaching a schematic of the modified circuit with the changed resistors marked in green. I am also ataching photos of the modified card so that you can find the parts to change.
If you have no experience in working on a circuit card maybe you can find someone to help you. The two resistors needed can be found in an electronics store. Maybe Radio Shack.
~~~~~DON'T DO ANY OF THIS IF YOU DON'T HAVE THE PROBLEM~~~
Schematic Diagram showing the changed parts in green:
- R213 used to be 2k. The 1k is added.
- R213 is changed from 2k to 18k. The R213 designation is hidden under the resistor.
- The 1k resistor is soldered between the two pads as shown.
If your card was working OK before you made these changes it should still be working OK. But if your card was not good then making these changes will not fix it. The changes will only immunize the card against a leaky temperature sensor.
If you are not having any trouble with your glow system I recommend that you not make these changes. While this is fairly easy to do for someone with circuit card experience, others may have trouble getting it done right.
Paul