vacuum gauge
Thread Starter
Junior Member
Joined: Feb 2013
Posts: 19
Likes: 0
From: Bakersfield, CA
vacuum gauge
hi all,
i have a 2000 f150 v8 4.6 and i am having some vacuum related problem (i think) and i was wondering if anybody could tell me what it means when a vacuum lines collapses when you start the engine and how do i hook up a vacuum gauge to the engine? thank you all so much i've learned alot
i have a 2000 f150 v8 4.6 and i am having some vacuum related problem (i think) and i was wondering if anybody could tell me what it means when a vacuum lines collapses when you start the engine and how do i hook up a vacuum gauge to the engine? thank you all so much i've learned alot
Ford Owner
Joined: Aug 2012
Posts: 1,073
Likes: 138
From: Wichita Kansas
I am not sure what they mean when they say a vacuum line collapses either but I think they mean it is as if you pinched the line so there was no vacuum generated at the apparatus the vacuum is operating (like your EGR valve or your heating/AC system, PCV valve).
That being said, you should be able to visually see a bad vacuum line that is perhaps collapsed, pinched, or just plain damaged or ripped open and leaking. Or maybe it just got disconnected from the apparatus it was attached to. Before you get into a vacuum test, fix any issues you find with a visual inspection.
You want to connect your vacuum gauge directly to the intake manifold. Your gauge should have some instructions on how to hook it up. You want to start with a warm engine. Also be careful because you will be doing the test with the engine running so watch for moving parts like the fan and belts.
With the engine running, you should show a reading of between 17 and 22 inches of vacuum. If the reading is below this and IT IS STEADY, it usually means you have a leak between the manifold and the cylinder heads (manifold gasket leak). Before I got into changing the manifold gasket, I would try to snug down the intake manifold bolts and see it it made a difference. Snug each one down starting in the middle, a little at at time so it torques down evenly and you don't break anything. Final torque should be 15 to 22 foot pounds. Note: your mechanic will most like not want to do this and he may be right when he tells you that you need to change the manifold gasket. I am a DIY guy so I will try things with a low chance of working in the hope of saving some time and money.
If your vacuum reading is below the 17 to 22 inches of vacuum and is ERATIC/FLUCTUATING, you have some type of problem like a bad valve, bad piston rings, blown head gasket, or misfire spark plugs. You can fix a misfire spark plug but the other items mean major repairs or, as a practical matter, you are ready for a new engine. I am of the opinion, although others will disagree, that trying to rebuild an engine on an older vehicle is either not cost effective if done by a mechanic or beyond the capabilities of most DIY folks like me. I think it would be more cost effective to either have a factory rebuilt engine installed or taking a chance on a salvage yard engine from a known vehicle (my choice).
That being said, you should be able to visually see a bad vacuum line that is perhaps collapsed, pinched, or just plain damaged or ripped open and leaking. Or maybe it just got disconnected from the apparatus it was attached to. Before you get into a vacuum test, fix any issues you find with a visual inspection.
You want to connect your vacuum gauge directly to the intake manifold. Your gauge should have some instructions on how to hook it up. You want to start with a warm engine. Also be careful because you will be doing the test with the engine running so watch for moving parts like the fan and belts.
With the engine running, you should show a reading of between 17 and 22 inches of vacuum. If the reading is below this and IT IS STEADY, it usually means you have a leak between the manifold and the cylinder heads (manifold gasket leak). Before I got into changing the manifold gasket, I would try to snug down the intake manifold bolts and see it it made a difference. Snug each one down starting in the middle, a little at at time so it torques down evenly and you don't break anything. Final torque should be 15 to 22 foot pounds. Note: your mechanic will most like not want to do this and he may be right when he tells you that you need to change the manifold gasket. I am a DIY guy so I will try things with a low chance of working in the hope of saving some time and money.
If your vacuum reading is below the 17 to 22 inches of vacuum and is ERATIC/FLUCTUATING, you have some type of problem like a bad valve, bad piston rings, blown head gasket, or misfire spark plugs. You can fix a misfire spark plug but the other items mean major repairs or, as a practical matter, you are ready for a new engine. I am of the opinion, although others will disagree, that trying to rebuild an engine on an older vehicle is either not cost effective if done by a mechanic or beyond the capabilities of most DIY folks like me. I think it would be more cost effective to either have a factory rebuilt engine installed or taking a chance on a salvage yard engine from a known vehicle (my choice).
Thread Starter
Junior Member
Joined: Feb 2013
Posts: 19
Likes: 0
From: Bakersfield, CA
thank you for the advice and the information. after closer visual inspection i have 3 bad vacuum lines including the pcv hose. i've decided to just replace all my vacuum lines. my uncle works at the stealership (his words) and hopefully i can pick up a decent priced set. thanx again