I'm going to replace the wiring harness on my 81 K-Jet soon and am planning for the job. I'm hoping a new harness will help smooth out the idle, as well as just being a good thing to do since I can see the old harness is deteriorating. I recently had the manifold off and replaced the injector seals, temp gauge sender, the heater hoses, the breather box, and all the vacuum lines under there. I also relocated the flame trap and cleaned up everything including the throttle body. Now that I have a new/used harness from from Dave Barton, I'm going in there again.

I'm thinking it would make sense to replace the following parts:

1. The rear under-manifold sensor/switch. I think it's the thermo-time switch that controls the cold-start injector.

2. The front sensor that sits under the manifold below #1. I think it's the ECT sensor.

3. Is Bosch the best brand for the two sensor/switches? Best source?

Questions:

Any thoughts or advice?

Anything I'm forgetting? I don't want to have to go in there three times. I want to catch everything on the second shot at it.


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Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 130K

From left to right mine are TVS (thermal vacuum switch), temp gauge sensor, and thermo-time switch.

What does the thermal vacuum switch do? Someone told me before that the front one is a Engine Coolant Temperature Sensor. Are they the same thing? Mine's an 81 non-turbo if that makes a difference. How do I tell which one my car has in that forward position? I need an educatiion. Thanks.
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Thanks to everyone for the help, Doug C. 81 242 Brick Off Blocks, stock, M46; 86 240, 130K

Need an education? You and me both. Except it is getting kinda late in life for me.

Well, all those things you see sense coolant temperature, so I guess your question is what does the Volvo parts guy call it.

It blocks flow until the engine gets about 2/3 warmed up, then supplies vacuum to operate the EGR system. I have one of those hand vacuum pumps with a gauge that makes testing vacuum operated stuff pretty easy.

The green manual refers to it as a "thermostat" and "wax thermostat". The parts fiche calls it a "valve" 1269355-2 when used in a B21FT, and a "thermostat valve" 1219547-5 in a B21E, B23E, B27, etc. but I about went blind without finding the drawing for a plain old B21F. Sorry.

The parts ref says the thermo-time sensor is 1219731-5 and your gauge sender is 460191-0, but that is something Wahler makes and very inexpensive from the part outfits.

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Art Benstein near Baltimore