I have a 94 Silverado 6.5 TD and this is my first winter with it. So far I really like it EXCEPT it is impossible to start below 15 deg F. It will cough but never catch. I have tried the stock and a magnetic heater to no avail. I will ohm out the glow plugs today & replace whatever needs it. I can use some help though:

1) There is a sensor or switch mounted under the doghouse cover, on top of the the rh side about midway on the engine. It has an electrical plug on one side and two vacuum lines out the other. The vac lines snapped off. What is this critter? I have the Haynes manual & Alldata subscription and it doesn't show up on either.

2) Is the aforementioned switch related to the cold start problem?

3) I can see 2 of the glow plugs on the psgr side. The others are buried. How do you get to them?

That's it for now. I appreciate any help you can provide. It's below 10 today and the truck is outside, so I want to be efficient in diagnosing the trouble.

Stauby

I ohmed out the glow plugs on the right side and all 4 were btwn 1.1 to 1.3 ohms. I can't check the left side where the truck is now. According to my manual they're fine. I remember the PO saying he replaced them recently so I believe they do not contribute to the cold start problem.

I found that the factory block heater had a broken wire. This was replaced and is now plugged in and heating away merrily. I also have the magnetic heater on the oil pan.

The switch/sensor I described earlier is square, mounted on the right side rear top of the engine, and has orange and black vac hoses. The black goes under the turbo and the orange to the lower left front engine- the air pump?

I still can't find any reference to this switch, unless it's part of the EGR system.

Any ideas?

It's the barometer. Replace the rubber hose, pcm is looking for 20" vac on that sensor.

its the wastegate solenoid, it does need to be repaired, but it won't affect startability.

I guess I didn't read that close enough.
Try unplugging the cts when it's that cold.

She runs! I guess the magnetic block heater wasn't enough on it's own. I'll check on the wastegate replacement tomorrow. Thanks guys!

Stauby welcome to the site,
Go to the FAQs above read RPO codes and see what configuration truck you have and update your signature, will help us trtoubleshoot your ride in the future, unless you have a L56 "S" for 8th VIN number you should not have EGR, does indeed sound like a WG as TDG clued in on.

yeapper thats what it sounds like to me too once I figured out his right and left where different than my driver seat view right and left.
BTW Welcome