EGR valve control solenoid question

[JohnG]

Dumb question of the day...
Is the EGR valve control solenoid supposed to make a noise after I turn the truck off? It’s tough to describe but it’s a buzzing sound that lasts 1-2 seconds.

Getting code 31. Also looking for vacuum leaks.

‘86 STX with 2.9
Thanks all!

 

[RonD]

No, with key off the 12v is cut to all emissions solenoids, could be you are hearing vacuum leaking on solenoid to EGR valve side
Engine side has no vacuum after engine is off, although in 1986 engine side could be hooked to the vacuum reservoir so would have vacuum to leak out, actually air in, lol

 

[JohnG]

No, with key off the 12v is cut to all emissions solenoids, could be you are hearing vacuum leaking on solenoid to EGR valve side
Engine side has no vacuum after engine is off, although in 1986 engine side could be hooked to the vacuum reservoir so would have vacuum to leak out, actually air in, lol

Thanks Ron. I’ll keep looking.

 

[JohnG]

No, with key off the 12v is cut to all emissions solenoids, could be you are hearing vacuum leaking on solenoid to EGR valve side
Engine side has no vacuum after engine is off, although in 1986 engine side could be hooked to the vacuum reservoir so would have vacuum to leak out, actually air in, lol

Hey Ron, should an 86 have a vacuum reservoir? Mine doesn’t.

 

[RonD]

It does, might be a smaller one, on top of heater box in engine bay

Or looks like a coffee can painted black, like this: https://am-ebay-images-items.s3.amazonaws.com/item/AM-2425854478.jpg

Vacuum reservoir is need for the cab's air direction controls: defrost, panel and floor, "climate control"

If you look in engine bay passenger side next to Blower motor housing you should see a black hose coming out of firewall, might look like a wire but its a vacuum hose
Follow it, it will go to the vacuum reservoir

 

[franklin2]

On his the vacuum reservoir is made under the air filter box. Hard to know it's even there. I think his EGR lines are red, and they should go to this box under the air filter box. And like you said, when vacuum is relieved you are actually letting air in. So if you look at the EGR solenoid, there should be a round black cap on top. Pull this off and there will be a little foam filter that should be cleaned every couple of years. This is how the air enters the EGR system when the solenoid closes the EGR valve. This foam can get clogged and the EGR system will not operate correctly.

 

[JohnG]

An update about 31 code, hopefully will help others.

Found this link. A great resource to help diagnose my 31 code: http://www.tomco-inc.com/Tech_Tips/ttt34.pdf

While checking the egr valve it would not hold vacuum so I replaced it. Still had the 31 code and the truck still wasn’t fixed. Super hard to start... cranked for 3-4 seconds before it would start. Worried that I would get stranded after getting gas.

Checked the egr pressure sensor (dpfe) using info from the above link and found it was was bad. Replaced it and the truck starts instantly, on the first hit!