MustangWorks.com : Ford Forums - View Single Post

WHITE_SVT_SNAKE · 10-23-2003, 12:34 PM

Yeah, a bad TPS is like a good case of the clap... You don't want one...

... As to your question about vacuum yes it can be tested and it doesn't cost much to do this... All u need is a Vacuum gauge... u can get them almost anywhere (car related)... Any car parts place should have them... The only thing you have to worry about and that is difficult about this is how do u interpret the results of the gauge... Some general info and instructions on how to do this are as follows:

A vacuum gauge provides valuable information about what is going on in the engine at a low cost. You can check for worn rings or cylinder walls, leaking head or intake manifold gaskets, incorrect Carburetor or TB adjustments, restricted exhaust, stuck or burned valves, weak valve springs, improper ignition or valve timing and ignition problems... among a few other things i may have forgotten...

Unfortunately vacuum gauge readings are easy to misinterpret, so they should be used in conjunction with other tests to confirm the diagnosis.

Both the absolute readings and the rate of needle movement are important for accurate interpretation. Most gauges measure vacuum in inches of mercury (in-Hg). The following references to vacuum assume the diagnosis is being performed at sea level. As elevation increases (or atmoshperic pressure decreases), the reading will decrease. For every 1,000 foot increase in elevation above approximately 2000 feet, the gauge readings will decrease about one inch of mercury.

Connect the vacuum gauge directly to intake manifold vacuum, not to ported (throttle body) vacuum. Be sure no hoses are left disconnected during the test or false readings will result.

Before you begin the test, allow the engine to warm up completely. Block the wheels and set the parking brake. With the transmission in park, start the engine and allow it to run at normal idle speed.

Read the vacuum gauge; an average, healthy engine should normally produce about 17 to 22 inches of vacuum with a fairly steady needle.

Here are a couple of gauge readings and what they indicate about the engines condition.

1. A low steady reading usually indicates a leaking gasket between the intake manifold and cylinder heads or throttle body, a leaky vacuum hose, late ignition timing or incorrect camshaft timing. Check ignition timing then eliminate other possiblities...

2. If the reading is three to eight inches below normal and it fluctuates at that low reading, suspect an intake manifold gasket leak at an intake port or a faulty fuel injector.

3. If the needle has regular drops of about two-to-four inches at a steady rate, the valves are probably leaking. Perform a compression test or leak-down test to confirm this.

4. An irregular drop or down-flick of the needle can be caused by a sticking valve or an ignition misfire. Perform a compression check or leak-down test and read the spark plugs.

5. A rapid vibration of about four in.-Hg vibration at idle combined with exhaust smoke indicates worn valve guides. Perform a leak-down test to confirm this. If the rapid vibration occurs with an increase in engine speed, check for a leaking intake manifold gasket or head gasket, weak valve springs, burned valves or ignition misfire.

6. A slight fluctuation, say one inch up and down, may mean ignition problems. check all the usual tune-up items and, if necessary, run the engine on an ignition analyzer.

7. if there is a large fluctuation, perform a compression or leak-down test to look for a weak or dead cylinder or a blown head gasket.

8. If the needle moves slowly through a wide range, check for a clogged pcv system, incorrect idle fuel mixture, carb/TB or intake manifold gasket leaks.

9. Check for a slow return after revving the engine by quickly snapping the trottle open until the engine reaches about 2,500 rpm and let it shut. Normally the reading should drop to near zero, rise above normal idle reading (about 5 in.-Hg over) and then return to the previouse idle reading. If the vacuum returns slowly and doesn't peak when the throttle is snapped shut, ,the rings may be worn. If there is a long delay, look for a restricted exhaust system (often the muffler or catalytic converter). An easy way to check this is to termporarily disconnect the exhaust ahead of the suspected part and redo the test.

that should about do it... I hope this answers your question... I got kinda technical sounding but its not to difficult... if you have any questions drop me a line here at the forums or @ svt_snake@hotmail.com

David

10-23-2003, 12:34 PM	#9
WHITE_SVT_SNAKE Registered Member Join Date: Aug 2003 Location: Dublin, GA Posts: 29	Yeah, a bad TPS is like a good case of the clap... You don't want one... ... As to your question about vacuum yes it can be tested and it doesn't cost much to do this... All u need is a Vacuum gauge... u can get them almost anywhere (car related)... Any car parts place should have them... The only thing you have to worry about and that is difficult about this is how do u interpret the results of the gauge... Some general info and instructions on how to do this are as follows: A vacuum gauge provides valuable information about what is going on in the engine at a low cost. You can check for worn rings or cylinder walls, leaking head or intake manifold gaskets, incorrect Carburetor or TB adjustments, restricted exhaust, stuck or burned valves, weak valve springs, improper ignition or valve timing and ignition problems... among a few other things i may have forgotten... Unfortunately vacuum gauge readings are easy to misinterpret, so they should be used in conjunction with other tests to confirm the diagnosis. Both the absolute readings and the rate of needle movement are important for accurate interpretation. Most gauges measure vacuum in inches of mercury (in-Hg). The following references to vacuum assume the diagnosis is being performed at sea level. As elevation increases (or atmoshperic pressure decreases), the reading will decrease. For every 1,000 foot increase in elevation above approximately 2000 feet, the gauge readings will decrease about one inch of mercury. Connect the vacuum gauge directly to intake manifold vacuum, not to ported (throttle body) vacuum. Be sure no hoses are left disconnected during the test or false readings will result. Before you begin the test, allow the engine to warm up completely. Block the wheels and set the parking brake. With the transmission in park, start the engine and allow it to run at normal idle speed. Read the vacuum gauge; an average, healthy engine should normally produce about 17 to 22 inches of vacuum with a fairly steady needle. Here are a couple of gauge readings and what they indicate about the engines condition. 1. A low steady reading usually indicates a leaking gasket between the intake manifold and cylinder heads or throttle body, a leaky vacuum hose, late ignition timing or incorrect camshaft timing. Check ignition timing then eliminate other possiblities... 2. If the reading is three to eight inches below normal and it fluctuates at that low reading, suspect an intake manifold gasket leak at an intake port or a faulty fuel injector. 3. If the needle has regular drops of about two-to-four inches at a steady rate, the valves are probably leaking. Perform a compression test or leak-down test to confirm this. 4. An irregular drop or down-flick of the needle can be caused by a sticking valve or an ignition misfire. Perform a compression check or leak-down test and read the spark plugs. 5. A rapid vibration of about four in.-Hg vibration at idle combined with exhaust smoke indicates worn valve guides. Perform a leak-down test to confirm this. If the rapid vibration occurs with an increase in engine speed, check for a leaking intake manifold gasket or head gasket, weak valve springs, burned valves or ignition misfire. 6. A slight fluctuation, say one inch up and down, may mean ignition problems. check all the usual tune-up items and, if necessary, run the engine on an ignition analyzer. 7. if there is a large fluctuation, perform a compression or leak-down test to look for a weak or dead cylinder or a blown head gasket. 8. If the needle moves slowly through a wide range, check for a clogged pcv system, incorrect idle fuel mixture, carb/TB or intake manifold gasket leaks. 9. Check for a slow return after revving the engine by quickly snapping the trottle open until the engine reaches about 2,500 rpm and let it shut. Normally the reading should drop to near zero, rise above normal idle reading (about 5 in.-Hg over) and then return to the previouse idle reading. If the vacuum returns slowly and doesn't peak when the throttle is snapped shut, ,the rings may be worn. If there is a long delay, look for a restricted exhaust system (often the muffler or catalytic converter). An easy way to check this is to termporarily disconnect the exhaust ahead of the suspected part and redo the test. that should about do it... I hope this answers your question... I got kinda technical sounding but its not to difficult... if you have any questions drop me a line here at the forums or @ svt_snake@hotmail.com David __________________ 1996 Mustang Cobra Ported Factory Heads, New Performance valvetrain , BBK 62MM TB, Sean Hyland Spec Stage One Cams, Dual Friction Centerforce Clutch, Steeda Tri-ax, Mac Cold Air, Saleen Wheels (18x9 & 18x10), Among other things... "I Like anything Fast Enough to Do Something Stupid In"