'97 Suburban Making a rapid thumping sound near front passengers feet

The sound is coming from below the dash. It begins when I turn the key on, and thumps for about 15 seconds and stops, and then does it again when I shut the key off -- again for about 15 seconds, and it stops. Any ideas about the cause and resolution? Thanks in advance!

Reply to
briany8s
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It's the recirc. door actuator. Or "mode" actuator, I think GM calls it. It's a rotary actuator and you'll have to replace it. The jackscrew device in the actuator is damaged. The actuator is commanded to run for 10 sec. to move the door whenever power is applied to the system. The other actuators have position feedback and don't have this time delay circuitry. They stop when they get to the commanded position. My '93 3/4 ton Chevy pickup does this exact same thing and I haven't replaced the actuator as it looks like quite a job on my vehicle. I would imagine it will be on your suburban also. If you can get a copy of the schematic, you'll see the time delay in there. The gimbal on the jackscrew is screwing itself off the ends of the threads of the jackscrew and since it's spring-loaded, it pops against the threads for the 10 seconds of the time delay. (Think of loosening a bolt with a socket wrench and feeling the screw ramping off the top of the threaded hole when you continue to turn it after it's all the way out of the threads.) Mine still works to control the door just fine, but I'm also getting tired of listening to it and will probably fix it soon. Hope this helps and let me know how you come out.

Garrett Fulton

Reply to
gfulton

Bad fuel pump or regulator causing line pressure to vary and the lines to thump till it settle down (fuel pump runs for a bit a key on and key off even when engine is not running.

Reply to
TheSnoMan

Fuel pump does not run after key-off. Fuel pump is the least likely issue

Reply to
Battleax

Reply to
Merlin

It does on my 89 burb and has since it was new for between 5 and 10 seconds.

Reply to
TheSnoMan

sounds like a vent door motor going bad. Turn the heat on full blast to the vents and once you get good heat shut the key down. Turn the key back on and see if the heat changes with the thumping sound.

Reply to
Steve W.

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