This is a summary someone did on the second chance garage site that had short videos of all 15 scenarios. Maybe someone doesn't have the correct software or adobe installed, I don't know.
If one can get the short videos let the others know how you did it. They were very good.
"This is your typical vacuum gauge.
As you can see, its a temporary installation, and used only when there is trouble.
However many manufactures now sell gauges you can put on your dash or A-pillar so you can read vacuum on the go!
Its VERY important that you hook up your gauge to a constant vacuum source, otherwise the readings you will get are useless.
Some people prefer to measure in other units. For simplicity's sake. We're going to stick with in/Hg.
Now you're probably asking at this point,
"How in the hell can it tell me somethings wrong with my engine? Its just gonna move when I open and close my throttle plate. How useful is that?"
Well you are right! Under normal operating parameters the throttle fluctuation will cause the gauge to fluctuate normally. However outside of normal operating parameters, you will notice a difference in the gauges reading, be it at idle, or under throttle.
Here are some typical scenarios, Better explained by Second Chance Garage. (Color Coded based on severity. Red being serious and green being not serious.)
Scenario 1:
Engine: Stock at Idle
Gauge display: 15-22 in/Hg HOLDING STEADY.
Means: The engine is operating normally. The compression is fine, and there are no vacuum leaks or ignition anomalies.
Scenario 2:
Engine: Stock WOT or Rapid acceleration and Decel
Gauge Display: Drop to 0 in/hg and slow rise. On Decel (while engine is revved up) Increase to 25-30 in/hg and return to normal
Means: The engine is operating normally. During WOT the intake momentarily equalizes pressure resulting in the vacuum drop. During Decel the vacuum will increase due to the difference of pressure from the throttle being closed.
Scenario 3:
Engine: High Performance Cammed engines at Idle
Gauge Display: ~15 in/Hg Typically. Needle will shake slightly.
Means: Engine is operating normally. The needle shake is from valve overlap. As a result the vacuum level varies slightly as the valves are open at the same time. They real lower than stock engines due to high durations, and their high lift.
Scenario 4:
Engine: Worn piston rings and/or diluted oil
Gauge Display: 15-17 in/Hg @ Idle | 0 in/Hg @ WOT | 20-23 in/Hg @ Decel from WOT
Means: The piston rings are leaking allowing gasses to escape and results in lower vacuum.
Scenario 5:
Engine: Sticking Valves
Gauge Display: Flicking needle. Drops of 2-3 in/Hg while idling.
Means: When the needle flicks, the faulty valve is being triggered.
Scenario 6:
Engine: Burned or Constantly Leaking Valves
Gauge Display: Evenly spaced Downward flicking from Idle vacuum. Usually 6-8 in/Hg
Means: You're valves are burned and/or are constantly leaking!
Scenario 7:
Engine: Poorly Seated Valves
Gauge Display: Regular downward movements of 2-4 in/Hg at idle (not really a "quick" needle movement)
Means: One (or more) of your Valves are poorly seated.
Scenario 8:
Engine: Worn Valve Guides
Gauge Display:Regular swing of 4-6 in/Hg @ idle.
Means: To check slowly increase engine speed. If the needle slowly becomes steady, then you are safe to assume your valve guides are worn.
Scenario 9:
Engine: Weak Valve Springs
Gauge Display: Violent flicking of 10-14 in/Hg under gradual throttle increase.
Means: If the reading at idle was relatively steady, this usually means you have Weak Springs.
Scenario 10:
Engine: Slight Intake Leak or Late Valve Timing
Gauge Display: Low steady reading @ ~10 in/Hg at Idle
Means: Test your intake with carb cleaner or starter fluid in hopes for the engine to smooth or RPMs to change. If not and your intake is sound, then You have a lot of work to do in order to properly correct the issue.
Scenario 11:
Engine: Retarded Ignition timing or Poorly Gapped plugs and/or Defective Breaker Points
Gauge Display: A steady but "mediocre" reading at ~15 in/Hg. at Idle
Means: You may need to adjust timing. If accompanied by a regular pulsation (not a flicker.) Then check your plug gapping and/or breaker points if so equipped.
Scenario 12:
Engine: MAJOR Intake Leak
Gauge Display:Low steady reading of 3-6 in/Hg at idle.
Means: You have a serious leak, inspect all gaskets. If nothing is found, trace your vacuum system looking for cracked, split, disconnected hoses and loose fittings.
Scenario 13:
Engine: Blown head gasket
Gauge Display:Starts at normal then drops regularly.
Means: Usually made obvious by smoking and other symptoms, this is typical of a blown head gasket.
Scenario 14:
Engine: Clogged Exhaust System
Gauge Display: On start and idle, normal vacuum reading. As engine speed increases, vacuum slowly decreases.
Means: Your exhaust is plugged somehow. Inspect it. It is not always the cat, but sometimes the muffler too.
Scenario 15:
Engine: Maladjusted Idle Mixture (Typically carburated engines)
Gauge Display: Slow movement from 13-17 in/Hg
Means: Maladjusted F/A Mixture. Once adjusted reading will return to normal.
Now this is just many common scenarios that can be typically decipered using the obligatory vacuum gauge.
If you wanna see pictures along with the descriptions, You can do so here [this link is where the error occurs].
Which is a very useful resource.
I hope this has cleared up many questions about Vacuum Gauges, and hopefully everyone will throw one in their tool box just in case!
Happy Tuning!
(if anything needs to be added or changed, please let me know.)
Information culminated from both existing knowledge and knowledge obtained from Secondchancegarage.com"
If one can get the short videos let the others know how you did it. They were very good.
"This is your typical vacuum gauge.
As you can see, its a temporary installation, and used only when there is trouble.
However many manufactures now sell gauges you can put on your dash or A-pillar so you can read vacuum on the go!
Its VERY important that you hook up your gauge to a constant vacuum source, otherwise the readings you will get are useless.
Most gauges read in "Inches of Mercury" or abbreviated "in/Hg" or simply in.Hg
Some people prefer to measure in other units. For simplicity's sake. We're going to stick with in/Hg.
Now you're probably asking at this point,
"How in the hell can it tell me somethings wrong with my engine? Its just gonna move when I open and close my throttle plate. How useful is that?"
Well you are right! Under normal operating parameters the throttle fluctuation will cause the gauge to fluctuate normally. However outside of normal operating parameters, you will notice a difference in the gauges reading, be it at idle, or under throttle.
Here are some typical scenarios, Better explained by Second Chance Garage. (Color Coded based on severity. Red being serious and green being not serious.)
Scenario 1:
Engine: Stock at Idle
Gauge display: 15-22 in/Hg HOLDING STEADY.
Means: The engine is operating normally. The compression is fine, and there are no vacuum leaks or ignition anomalies.
Scenario 2:
Engine: Stock WOT or Rapid acceleration and Decel
Gauge Display: Drop to 0 in/hg and slow rise. On Decel (while engine is revved up) Increase to 25-30 in/hg and return to normal
Means: The engine is operating normally. During WOT the intake momentarily equalizes pressure resulting in the vacuum drop. During Decel the vacuum will increase due to the difference of pressure from the throttle being closed.
Scenario 3:
Engine: High Performance Cammed engines at Idle
Gauge Display: ~15 in/Hg Typically. Needle will shake slightly.
Means: Engine is operating normally. The needle shake is from valve overlap. As a result the vacuum level varies slightly as the valves are open at the same time. They real lower than stock engines due to high durations, and their high lift.
Scenario 4:
Engine: Worn piston rings and/or diluted oil
Gauge Display: 15-17 in/Hg @ Idle | 0 in/Hg @ WOT | 20-23 in/Hg @ Decel from WOT
Means: The piston rings are leaking allowing gasses to escape and results in lower vacuum.
Scenario 5:
Engine: Sticking Valves
Gauge Display: Flicking needle. Drops of 2-3 in/Hg while idling.
Means: When the needle flicks, the faulty valve is being triggered.
Scenario 6:
Engine: Burned or Constantly Leaking Valves
Gauge Display: Evenly spaced Downward flicking from Idle vacuum. Usually 6-8 in/Hg
Means: You're valves are burned and/or are constantly leaking!
Scenario 7:
Engine: Poorly Seated Valves
Gauge Display: Regular downward movements of 2-4 in/Hg at idle (not really a "quick" needle movement)
Means: One (or more) of your Valves are poorly seated.
Scenario 8:
Engine: Worn Valve Guides
Gauge Display:Regular swing of 4-6 in/Hg @ idle.
Means: To check slowly increase engine speed. If the needle slowly becomes steady, then you are safe to assume your valve guides are worn.
Scenario 9:
Engine: Weak Valve Springs
Gauge Display: Violent flicking of 10-14 in/Hg under gradual throttle increase.
Means: If the reading at idle was relatively steady, this usually means you have Weak Springs.
Scenario 10:
Engine: Slight Intake Leak or Late Valve Timing
Gauge Display: Low steady reading @ ~10 in/Hg at Idle
Means: Test your intake with carb cleaner or starter fluid in hopes for the engine to smooth or RPMs to change. If not and your intake is sound, then You have a lot of work to do in order to properly correct the issue.
Scenario 11:
Engine: Retarded Ignition timing or Poorly Gapped plugs and/or Defective Breaker Points
Gauge Display: A steady but "mediocre" reading at ~15 in/Hg. at Idle
Means: You may need to adjust timing. If accompanied by a regular pulsation (not a flicker.) Then check your plug gapping and/or breaker points if so equipped.
Scenario 12:
Engine: MAJOR Intake Leak
Gauge Display:Low steady reading of 3-6 in/Hg at idle.
Means: You have a serious leak, inspect all gaskets. If nothing is found, trace your vacuum system looking for cracked, split, disconnected hoses and loose fittings.
Scenario 13:
Engine: Blown head gasket
Gauge Display:Starts at normal then drops regularly.
Means: Usually made obvious by smoking and other symptoms, this is typical of a blown head gasket.
Scenario 14:
Engine: Clogged Exhaust System
Gauge Display: On start and idle, normal vacuum reading. As engine speed increases, vacuum slowly decreases.
Means: Your exhaust is plugged somehow. Inspect it. It is not always the cat, but sometimes the muffler too.
Scenario 15:
Engine: Maladjusted Idle Mixture (Typically carburated engines)
Gauge Display: Slow movement from 13-17 in/Hg
Means: Maladjusted F/A Mixture. Once adjusted reading will return to normal.
Now this is just many common scenarios that can be typically decipered using the obligatory vacuum gauge.
If you wanna see pictures along with the descriptions, You can do so here [this link is where the error occurs].
Which is a very useful resource.
I hope this has cleared up many questions about Vacuum Gauges, and hopefully everyone will throw one in their tool box just in case!
Happy Tuning!
(if anything needs to be added or changed, please let me know.)
Information culminated from both existing knowledge and knowledge obtained from Secondchancegarage.com"
