Vacuum gauge..

bobtodd · 08-16-2002, 10:56 AM

I bought a vacuum gauge today and am wondering what I need to do and what to look for to see if I have a vacuum leak. I am guessing i need to plug it into a vacuum line somewhere near the tree. Are there more than one place to plug it in to check it? What kind of numbers should I have? Any info. would be great. Thank you!

joe4speed · 08-16-2002, 11:23 AM

Plug it in at any vaccuum source, I'm not sure what your vac should be with your cam, but mines around 20 in at idle with stock cam and heads.

bobtodd · 08-16-2002, 12:49 PM

I hooked the vacuum guage up and I am getting a reading of 9"-10". The motor doesnt exactly run perfectly smooth. Its got a bigger cam in it. From what I've been seeing on older posts, this seems to be low readings at idle. I held the motor at 2,000 rpms and the needle stayed right at 17". I have 10.5:1 pistons with 66 289 hi po heads...I guess they have smaller chambers, so I do have higher compression than a stock car. I didnt do any of the motor...the guy I bought it from built everything.
It doesnt have the smog pump. I've followed all the vacuum lines to the best of my knowledge to look for leaks but havent found any. Is there any way using the guage that I could find where a leak could be coming from?

PKRWUD · 08-16-2002, 06:44 PM

As far as tests with a vacuum gauge, where do I begin...

The vacuum that is created in a normaly aspirated engine (one that is not blown or turboed) gives you a great tool for diagnosing engine problems. Just about any internal engine problem can be identified with a vacuum gauge !!! I'll teach you some of the basics:
1) A steady reading of between 17" and 22" is considered normal for a stock engine.
2) A low but steady reading between 10" and 15" would be caused by retarded ignition or valve timing, or low compression.
3) A very low reading between 4" and 9" means you have a vacuum leak.
4) If the needle fluctuates as you increase the engine speed, you have either an ignition miss, a blown head gasket, a leaking valve or a weak valve spring.
5) A gradual drop in reading at idle means you have excessive back pressure or partial blockage in the exhaust system.
6) An intermittent fluctuation at idle means you have either an ignition miss or a sticking valve.
7) A reading where the gauge needle drifts anywhere between 12" and 22" indicates that your idle mixture is unstable. This is more common on carbureted motors.
8) A high and steady reading indicates that the ignition timing is too far advanced.
9) If, when you quickly close the throttle after running at 2000 rpm for ten seconds or more, the gauge needle DOES NOT jump two or more inches above what it is at idle, your piston rings are shot.
10) If the reading at idle is lower than normal, but the gauge needle fluctuates three inches on both sides of normal, your valve guides are excessively worn.
These are but only a few of the things you can learn about the condition of your engine with a vacuum gauge. Keep in mind that a blower or a turbo will create a false reading because the boost they create offsets the vacuum reading.

lx5091 · 08-16-2002, 07:14 PM

Nice post PKRWUD

I just copied that for future reference...

bobtodd · 08-17-2002, 10:28 AM

I guess I'll get out there and run some tests today. So if I am getting 9"-10" do you think vacuum leak or retarded ignition or valve timing? How exactly do you get a retarded ignition or valve timing off? Once again PKRWUD and his vast amounts of knowledge to the rescue

I have noticed that when I rev the car and let off the gas that the RPM's kind of hang there and gradually drop. Any ideas on what could cause this? It's not like it's sticking. It started happening after my long ordeal with setting my TPS.
Thanks for the help!

PKRWUD · 08-17-2002, 11:01 AM

What's the lift/duration on your cam?

Are you using the original ECM?

What is your timing set at?

What does your TPS read at WOT?

Take care,
~Chris

bobtodd · 08-17-2002, 11:31 AM

The only info. I have on the cam is that it is a 588 Ultradyne cam. I've emailed the guy I bought the car from a few times about specs on it and he never mentions anything about it.
What exactly is the ECM?
My timing is set at 16* I have 92 octane with 104 octane boost.
My TPS is around 4.20-4.50 at WOT

Will changing my timing have an effect on vacuum?

PKRWUD · 08-17-2002, 11:52 AM

The ECM is the computer.

Advancing your timing will raise the vacuum, while retarding it will lower the vacuum.

Your vacuum is very low, especially considering your timing is at 16 degrees advanced. It could be because of your cam. Try unplugging a vacuum line at idle, creating a vacuum leak, and tell me if the idle goes up or down.

Take care,
~Chris

bobtodd · 08-17-2002, 12:12 PM

I am going to run out to my parents to test the vacuum and coil. I'll let you know what happens. Thanks for the help!

PKRWUD · 08-17-2002, 01:30 PM

Post your results when you get back.

Take care,
~Chris

PKRWUD · 08-17-2002, 01:35 PM

Nevermind, I just saw your other post.

Take care,
~Chris

bobtodd · 08-17-2002, 01:44 PM

I'm still at my parents house..
Vacuum reading is still showing around 9"...it will bounce from 8" to 10", but with the cam the motor runs lopey. It mainly stays right on 9"
The needle does not fluctuate as I increase engine speed.
After holding rpm's at 2,000 for ten seconds and letting off the needle DOES jump up 2"
When I give it gas the needle drops to 0 and then goes up.
Everything seems normal except for how low it is reading. Should I mess with the timing and see what I can get from that? Maybe I am setting my timing wrong?
I created a vacuum leak by pulling another hose from the tree and the motor idled up, but you could hardly even tell.
Any ideas? I have followed all the vacuum lines. One of the lines runs into the fenderwell on the drivers side...the S/C line. Not sure where that goes so I cant really check it. All my smog pump is removed and I have looked that over too, to see if anything is unplugged. I'll check some more. Let me know if you have any ideas. Thank you.

PKRWUD · 08-17-2002, 02:07 PM

No, I don't think you have a vacuum leak because if you did, the idle should have dropped when you created another one. Since the idle went up, it leads me to believe you have no vacuum leak. Could just be the cam, but that's quite a cam! I'd leave the timing alone too, since it works for you, and you're not pinging.

Take care,
~Chris

08-16-2002, 10:56 AM	#1
bobtodd Registered Member Join Date: Dec 1998 Location: WI, U.S Posts: 255	Vacuum gauge.. I bought a vacuum gauge today and am wondering what I need to do and what to look for to see if I have a vacuum leak. I am guessing i need to plug it into a vacuum line somewhere near the tree. Are there more than one place to plug it in to check it? What kind of numbers should I have? Any info. would be great. Thank you! __________________ 91 LX - 10.5:1 pistons, ported 289 heads, Ultradyne 588 cam, Cobra upper/lower, MSD, JBA long tube headers, Flowmaster, Richmond 4:10, roll cage, monster tach...FUN!! 95 SHO - K&N filter

08-16-2002, 11:23 AM	#2
joe4speed He said Member...heh, heh Join Date: Sep 1999 Location: Jupiter, Florida U.S.A. Posts: 3,718	Plug it in at any vaccuum source, I'm not sure what your vac should be with your cam, but mines around 20 in at idle with stock cam and heads. __________________ *Joe!* 1988 GT, 13.58@101mph Check out my listing! Click here! Or my website:www.joe4speed.com

08-16-2002, 12:49 PM	#3
bobtodd Registered Member Join Date: Dec 1998 Location: WI, U.S Posts: 255	I hooked the vacuum guage up and I am getting a reading of 9"-10". The motor doesnt exactly run perfectly smooth. Its got a bigger cam in it. From what I've been seeing on older posts, this seems to be low readings at idle. I held the motor at 2,000 rpms and the needle stayed right at 17". I have 10.5:1 pistons with 66 289 hi po heads...I guess they have smaller chambers, so I do have higher compression than a stock car. I didnt do any of the motor...the guy I bought it from built everything. It doesnt have the smog pump. I've followed all the vacuum lines to the best of my knowledge to look for leaks but havent found any. Is there any way using the guage that I could find where a leak could be coming from? __________________ 91 LX - 10.5:1 pistons, ported 289 heads, Ultradyne 588 cam, Cobra upper/lower, MSD, JBA long tube headers, Flowmaster, Richmond 4:10, roll cage, monster tach...FUN!! 95 SHO - K&N filter

08-16-2002, 06:44 PM	#4
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	As far as tests with a vacuum gauge, where do I begin... The vacuum that is created in a normaly aspirated engine (one that is not blown or turboed) gives you a great tool for diagnosing engine problems. Just about any internal engine problem can be identified with a vacuum gauge !!! I'll teach you some of the basics: 1) A steady reading of between 17" and 22" is considered normal for a stock engine. 2) A low but steady reading between 10" and 15" would be caused by retarded ignition or valve timing, or low compression. 3) A very low reading between 4" and 9" means you have a vacuum leak. 4) If the needle fluctuates as you increase the engine speed, you have either an ignition miss, a blown head gasket, a leaking valve or a weak valve spring. 5) A gradual drop in reading at idle means you have excessive back pressure or partial blockage in the exhaust system. 6) An intermittent fluctuation at idle means you have either an ignition miss or a sticking valve. 7) A reading where the gauge needle drifts anywhere between 12" and 22" indicates that your idle mixture is unstable. This is more common on carbureted motors. 8) A high and steady reading indicates that the ignition timing is too far advanced. 9) If, when you quickly close the throttle after running at 2000 rpm for ten seconds or more, the gauge needle DOES NOT jump two or more inches above what it is at idle, your piston rings are shot. 10) If the reading at idle is lower than normal, but the gauge needle fluctuates three inches on both sides of normal, your valve guides are excessively worn. These are but only a few of the things you can learn about the condition of your engine with a vacuum gauge. Keep in mind that a blower or a turbo will create a false reading because the boost they create offsets the vacuum reading. __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

08-16-2002, 07:14 PM	#5
lx5091 Registered Member Join Date: Nov 2001 Location: Fall River, MA Posts: 467	Nice post PKRWUD I just copied that for future reference... __________________ '02 Explorer XLT 4.0L --Nice Vehicle '97 Saturn SL1--Soon to be ditched for a Ford!

08-17-2002, 10:28 AM	#6
bobtodd Registered Member Join Date: Dec 1998 Location: WI, U.S Posts: 255	I guess I'll get out there and run some tests today. So if I am getting 9"-10" do you think vacuum leak or retarded ignition or valve timing? How exactly do you get a retarded ignition or valve timing off? Once again PKRWUD and his vast amounts of knowledge to the rescue I have noticed that when I rev the car and let off the gas that the RPM's kind of hang there and gradually drop. Any ideas on what could cause this? It's not like it's sticking. It started happening after my long ordeal with setting my TPS. Thanks for the help! __________________ 91 LX - 10.5:1 pistons, ported 289 heads, Ultradyne 588 cam, Cobra upper/lower, MSD, JBA long tube headers, Flowmaster, Richmond 4:10, roll cage, monster tach...FUN!! 95 SHO - K&N filter

08-17-2002, 11:01 AM	#7
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	What's the lift/duration on your cam? Are you using the original ECM? What is your timing set at? What does your TPS read at WOT? Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

08-17-2002, 11:31 AM	#8
bobtodd Registered Member Join Date: Dec 1998 Location: WI, U.S Posts: 255	The only info. I have on the cam is that it is a 588 Ultradyne cam. I've emailed the guy I bought the car from a few times about specs on it and he never mentions anything about it. What exactly is the ECM? My timing is set at 16* I have 92 octane with 104 octane boost. My TPS is around 4.20-4.50 at WOT Will changing my timing have an effect on vacuum? __________________ 91 LX - 10.5:1 pistons, ported 289 heads, Ultradyne 588 cam, Cobra upper/lower, MSD, JBA long tube headers, Flowmaster, Richmond 4:10, roll cage, monster tach...FUN!! 95 SHO - K&N filter

08-17-2002, 11:52 AM	#9
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	The ECM is the computer. Advancing your timing will raise the vacuum, while retarding it will lower the vacuum. Your vacuum is very low, especially considering your timing is at 16 degrees advanced. It could be because of your cam. Try unplugging a vacuum line at idle, creating a vacuum leak, and tell me if the idle goes up or down. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

08-17-2002, 12:12 PM	#10
bobtodd Registered Member Join Date: Dec 1998 Location: WI, U.S Posts: 255	I am going to run out to my parents to test the vacuum and coil. I'll let you know what happens. Thanks for the help! __________________ 91 LX - 10.5:1 pistons, ported 289 heads, Ultradyne 588 cam, Cobra upper/lower, MSD, JBA long tube headers, Flowmaster, Richmond 4:10, roll cage, monster tach...FUN!! 95 SHO - K&N filter

08-17-2002, 01:30 PM	#11
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Post your results when you get back. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

08-17-2002, 01:35 PM	#12
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	Nevermind, I just saw your other post. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

08-17-2002, 01:44 PM	#13
bobtodd Registered Member Join Date: Dec 1998 Location: WI, U.S Posts: 255	I'm still at my parents house.. Vacuum reading is still showing around 9"...it will bounce from 8" to 10", but with the cam the motor runs lopey. It mainly stays right on 9" The needle does not fluctuate as I increase engine speed. After holding rpm's at 2,000 for ten seconds and letting off the needle DOES jump up 2" When I give it gas the needle drops to 0 and then goes up. Everything seems normal except for how low it is reading. Should I mess with the timing and see what I can get from that? Maybe I am setting my timing wrong? I created a vacuum leak by pulling another hose from the tree and the motor idled up, but you could hardly even tell. Any ideas? I have followed all the vacuum lines. One of the lines runs into the fenderwell on the drivers side...the S/C line. Not sure where that goes so I cant really check it. All my smog pump is removed and I have looked that over too, to see if anything is unplugged. I'll check some more. Let me know if you have any ideas. Thank you. __________________ 91 LX - 10.5:1 pistons, ported 289 heads, Ultradyne 588 cam, Cobra upper/lower, MSD, JBA long tube headers, Flowmaster, Richmond 4:10, roll cage, monster tach...FUN!! 95 SHO - K&N filter

08-17-2002, 02:07 PM	#14
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	No, I don't think you have a vacuum leak because if you did, the idle should have dropped when you created another one. Since the idle went up, it leads me to believe you have no vacuum leak. Could just be the cam, but that's quite a cam! I'd leave the timing alone too, since it works for you, and you're not pinging. Take care, ~Chris __________________ Webmaster: Rice Haters Club Jim Porter Racing Peckerwoods Pit Stop Support Your Local RED & WHITE!

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