Possible vacuum leak?

Tiny
MERRIL
  • MEMBER
  • 1992 CHEVROLET VAN
  • 5.7L
  • V8
  • 2WD
  • AUTOMATIC
  • 90,000 MILES
Van is a G20. I have an issue where I struggle to accelerate past 65 mph while going uphill. I can shift it out of overdrive into drive and then I'm able to accelerate up the hill. I also had a weird moment driving where I went from 70 mph to stopped traffic and the van jerked a little when shifting down. I also have another issue that may be related, air only comes out of the defrost + bottom vents and not the dash. I suspect a vacuum leak although I have replaced the hoses and am not sure how to test that or what to look for at this point.
Friday, July 19th, 2024 AT 6:20 PM

5 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
To me it sounds like you have a clogged catalytic converter, to be sure here is a guide to help you confirm the issue:

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Check out the images (below). Please let us know what happens.
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Saturday, July 20th, 2024 AT 10:58 AM
Tiny
MERRIL
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  • 3 POSTS
I was told by an exhaust shop that my cat has beads inside of it and will rarely go bad. I don’t think it’s exhaust. My gas tank does start to vacuum, and I have a vented fuel cap, but I don’t know if that would be causing the issue.
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Sunday, July 21st, 2024 AT 8:52 AM
Tiny
KEN L
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Okay, this van should have an EVAP system which operates as a closed system. Since there is a vacuum present inside the fuel tank can you please remove and test (blow through) the EVAP vacuum control valve? Here is a diagram, check out the images (below). Let us know what you find.
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Sunday, July 21st, 2024 AT 12:55 PM
Tiny
MERRIL
  • MEMBER
  • 3 POSTS
Are you referring to the EGR valve on the chart? It is totally stuck in the engine. I pressed on it without taking it out and it held a vacuum on my finger.
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Monday, July 29th, 2024 AT 9:42 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 54,137 POSTS
Sorry, I thought it was the EVAP control solenoid. It looks like it is built into the charcoal canister so that could need replacement, I would remove the canister to see if has gas in it which would make it bad and need of replacements. Another cause could be a vacuum leak. I would use a smoke machine or check out this video to help:

https://youtu.be/VvcFGzAyaXE?si=brkwqJZ-o8ay3Xqn

Please go over this guide and get back to us.

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Monday, July 29th, 2024 AT 10:18 AM

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