Vacuum leak - NEED HELP
Vacuum leak - NEED HELP
Hi, new to trucks totally, this is my first, it is a 1998 Dodge Ram 1500 4x4 with the 5.9 auto. The seller said that the O2 sensor was bad (downstream) and thats why it runs so rough and stalls, but when driving it home i heard a loud hissing like its sucking in air somewhere. i got out of the truck with it running to try to find where it was coming from but can not for the life of me find it. Is there any common places i should check? any help is appreciated
Record Breaker
Joined: Aug 2011
Posts: 1,095
Likes: 1
From: Southern Massachusetts
A bad upstream (before the cat) o2 can cause an off air/fuel ratio and make the truck run rough. The downstream is just a reference for the PCM to measure cat efficiency.
A vacuum leak will occur at the intake side, either a missing or cracked hose or a lack of a gasket on the throttle body or air cleaner. There's 3 or 4 vacuum ports (depending on model years) and hoses on the intake. Follow the hoses and look for cracks or holes, pull them off if you have to (engine off). Make sure the hoses fit snug on the intake ports.
The other possibility is a missing air cleaner gasket. There should be a gasket between the air cleaner and the throttle body. Also make sure the 4 bolts on the throttle body are torqued down enough to seal the throttle body gasket.
A vacuum leak will occur at the intake side, either a missing or cracked hose or a lack of a gasket on the throttle body or air cleaner. There's 3 or 4 vacuum ports (depending on model years) and hoses on the intake. Follow the hoses and look for cracks or holes, pull them off if you have to (engine off). Make sure the hoses fit snug on the intake ports.
The other possibility is a missing air cleaner gasket. There should be a gasket between the air cleaner and the throttle body. Also make sure the 4 bolts on the throttle body are torqued down enough to seal the throttle body gasket.
Last edited by Matt Nickerson; Nov 14, 2013 at 05:16 PM.
A bad upstream (before the cat) o2 can cause an off air/fuel ratio and make the truck run rough. The downstream is just a reference for the PCM to measure cat efficiency.
A vacuum leak will occur at the intake side, either a missing or cracked hose or a lack of a gasket on the throttle body or air cleaner. There's 3 or 4 vacuum ports (depending on model years) and hoses on the intake. Follow the hoses and look for cracks or holes, pull them off if you have to (engine off). Make sure the hoses fit snug on the intake ports.
The other possibility is a missing air cleaner gasket. There should be a gasket between the air cleaner and the throttle body. Also make sure the 4 bolts on the throttle body are torqued down enough to seal the throttle body gasket.
A vacuum leak will occur at the intake side, either a missing or cracked hose or a lack of a gasket on the throttle body or air cleaner. There's 3 or 4 vacuum ports (depending on model years) and hoses on the intake. Follow the hoses and look for cracks or holes, pull them off if you have to (engine off). Make sure the hoses fit snug on the intake ports.
The other possibility is a missing air cleaner gasket. There should be a gasket between the air cleaner and the throttle body. Also make sure the 4 bolts on the throttle body are torqued down enough to seal the throttle body gasket.
when i had the code pulled they said it was the downstream o2 that was bad, that wont make it run like crap?
Record Breaker
Joined: Aug 2011
Posts: 1,095
Likes: 1
From: Southern Massachusetts
Nope, just cant pass emissions with that.
Hall Of Fame
Joined: Jul 2006
Posts: 12,204
Likes: 10
From: Gainesville, Ga.
the sucking sound might be the normal sucking sound operation of the idle control as it tries to keep the truck running.
you should focus on the problem of it running rough and stalling. be aware of the sucking sound and that it might/might not have a vac leak, but generally a vac leak will just let in more air and cause a high idle, rather than "rough and stalling".
is your check engine light on? if so start by trying to get to your local parts chain store and ask them to read the codes. they'll do it for free. don't automatically do what they say. just WRITE DOWN all the codes (not someone's interpretation) and post them here.
edit - this recent thread deals with upstream and downstream O2 codes and has been a nightmare for this member. there's good info here - and you should start by soaking your O2 sensor threads with PB blaster or other penetrating oil. especially up north in the rust, they can be a pain to get out.
https://dodgeforum.com/forum/2nd-gen...g-2-codes.html
you should focus on the problem of it running rough and stalling. be aware of the sucking sound and that it might/might not have a vac leak, but generally a vac leak will just let in more air and cause a high idle, rather than "rough and stalling".
is your check engine light on? if so start by trying to get to your local parts chain store and ask them to read the codes. they'll do it for free. don't automatically do what they say. just WRITE DOWN all the codes (not someone's interpretation) and post them here.
edit - this recent thread deals with upstream and downstream O2 codes and has been a nightmare for this member. there's good info here - and you should start by soaking your O2 sensor threads with PB blaster or other penetrating oil. especially up north in the rust, they can be a pain to get out.
https://dodgeforum.com/forum/2nd-gen...g-2-codes.html
Last edited by dhvaughan; Nov 15, 2013 at 09:20 AM.