'91 GMC c1500 popping noise in dash

xll_BR3W_llx · May 12, 2015

Howdy y'all,

Brew here, I have a pretty unique problem with my truck. She runs like a champ and does what she supposed to. But I do have what I think is an electrical problem during startup and shut down.

During startup,

After turning her over an firing her up, the passenger side of the dash makes a popping noise for about 10-20 seconds (2 pops a second)

After Shut down,

The same thing happens, same popping noise for around the same amount of time

Now I am an electrician in the military, so I plan on troubleshooting this myself by shooting some wires after pulling some things off. I was hoping y'all have heard of this problem or experienced it yourself so I would have an advantage as to what I need to pay attention to after yanking her apart.

Soon I will attach a video of the truck startup and shut down after being driven a bit.

Any Ideas will help, she's my first truck. 260k miles strong. Last two known owners seemed very neglectful of this issue and the truck as a whole.

Thanks again y'all

BR3W

sputtle · May 16, 2015

Well that is definitely interesting. I'm running components through my head that are located on that side of the truck. There's some vacuum lines for climate control and some control modules. I believe the control modules are for hazard lights and blinkers, but this was true on an older blazer. Your truck could be different.

Sounds like your fairly certain this is an electrical issue, but I think you should still stick your head down there and watch the actuators. The A.C. evaporator is also over there and could be doing something funny. But you're able to hear it, not me and that's probably the best info for diagnosis.

xll_BR3W_llx · May 19, 2015

Well that is definitely interesting. I'm running components through my head that are located on that side of the truck. There's some vacuum lines for climate control and some control modules. I believe the control modules are for hazard lights and blinkers, but this was true on an older blazer. Your truck could be different.

Sounds like your fairly certain this is an electrical issue, but I think you should still stick your head down there and watch the actuators. The A.C. evaporator is also over there and could be doing something funny. But you're able to hear it, not me and that's probably the best info for diagnosis.

Yea I was starting to think it may be an actuator of some sort as well. I'm thinkin for the blower that works with the cabin heating. I have been so caught up with goin out shootin lately I haven't gotten around to checking it out.

I do appreciate your help though, I will put a video up of the sound so you can hear it like I do.

thanks again,

BREW

CrawlinMike · May 28, 2015

It's the actuator for the cabin air. Under the passenger floorboard , very common thing to go out. I just reached under and unplugged mine. Left it closed so my air just recirculates.

70GMCTRUCKS · May 29, 2015

yes blend/mode door actuator is bad

grampadirt · May 30, 2015

Mine sounded like this...

I unplugged it until I could find the time to replace it.

xll_BR3W_llx · June 12, 2015

Howdy there,

Sounds like yall are pretty set on what it is, I did take a video of the noise it is nearly exactly the same as ol' boy's video ^ only difference is its a lot slower and lasts about half a minute. I will check it out tomorrow morning and get back to this an tell yall how it went.

I'll thank yall again for the advice

Also I am thinkin bout buying a '73 gmc crew cab 4x4 lifted bout 6" with mud tires. If I remember right its a new motor with less than 40k miles. is there anything I should look for specifically on that model? or is that a pretty good gen gmc?

BREW