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best vacuum leak test

 
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Old 02-10-2019, 10:11 PM
Will Joyce
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Unhappy best vacuum leak test

ok its me again with the high idle issue -have replaced ECM, ICM, temp sensor ,IAC, MAP sensor & the other sensor that runs to the distributor ( cant think of what its called right now ).

Previous posts have said ck for vac leaks , but would a vac. leak cause it to idle sometimes at 2500 rpms & other times 1500 rpms .

I have sprayed starter fluid , carb cleaner etc. & got no differece in idle speed . Have I read right --where some of you use propane to test for leaks -- If so how is that done & isnt that quite dangerous .

What is the best ,foolproof way to test for leaks or what else can I try to get rid of this ridiculous idle nightmare
 
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Old 02-10-2019, 10:43 PM
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the purpose of spraying carb cleaner,etc is if there is a vac leak it will suck the vapors in and there should be a change in RPM. Propane (from a torch sized canister) is the same and not really any more dangerous than carb cleaner,etc. If there is no change in RPM from a vacuum leak then you should probably start TESTING the sensors,etc, not replacing them until you acertain they are bad, otherwise you are chunking money away needlessly.

Start by pulling the codes from the computer, both Key On Engine Off and Key on Engine On. it may give you a better idea where to start looking.

A Haynes manual would probably be handy also. It explains how to test the various components and gives trouble shooting help.
 
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Old 02-10-2019, 11:58 PM
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The best vacuum leak test is by having a smoke test done. Then you can actually see where the leak is by watching for the smoke to appear. If you are not having luck finding it through the basic at home methods, I would find a local independent shop that has the ability to do this and just pay to have that done. Besides leaking at the base of the intake it could also be leaking at the throttle body or IAC or any other port where a line connects.

I would get an Innova 3145 and read the codes. There could be something simple hidden there.

High idle could be IAC or TPS.

https://www.summitracing.com/parts/ino-3145?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-innova&gclid=EAIaIQobChMIzO6JgfOy4AIVB7nACh026Q0AE AQYAyABEgJIcvD_BwE
 
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Old 02-11-2019, 07:37 AM
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I'm a big propane user to find vacuum leaks, as I find it easier to pin point than liquid sprays.
 
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Old 02-11-2019, 09:00 AM
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Originally Posted by Odisvan View Post
I'm a big propane user to find vacuum leaks, as I find it easier to pin point than liquid sprays.
Same here....

As was mentioned, if youbdont have access to a smoke machine, a shop should be able to do It for you. Might be $75, but it may be the best $75 you have ever spent.
 
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Old 02-11-2019, 09:29 AM
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Originally Posted by TexasGuy001 View Post
The best vacuum leak test is by having a smoke test done. Then you can actually see where the leak is by watching for the smoke to appear. If you are not having luck finding it through the basic at home methods, I would find a local independent shop that has the ability to do this and just pay to have that done. Besides leaking at the base of the intake it could also be leaking at the throttle body or IAC or any other port where a line connects.

I would get an Innova 3145 and read the codes. There could be something simple hidden there.

High idle could be IAC or TPS.

https://www.summitracing.com/parts/i...yABEgJIcvD_BwE
Thanks for all the respomses, no. 1 I cannot pull codes from this 87 302 by using a obd1 tester or the jump wire method -- ?? Have replaced all sensors& the ecm other than the 02 but I dont think this would cause a high idle if bad ? So this is the reason Im looking for vac. leaks . I listed all I have replaced on my 1st post . Yes I have replaced the IAC& TPS --Almost has to be a vac. leak ,right ? OR ?
 
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Old 02-11-2019, 09:35 AM
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Ok, easiest step in diagnosing a vacuum leak....

Cap off all the vacuum lines EXCEPT the fuel pressure regulator, the MAP sensor, and the Brake Booster that are branched out from the "tree" fitting on the plenum. This will isolate everything vacuum controlled or thar needs vacuum.

The exception is that the vacuum lines running to the Brake Booster,the MAP sensor, and the fuel pressure regulator are working correctly. You could temporarily cap the Brake Booster if not driving but diagnosing.
 
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Old 02-11-2019, 09:52 AM
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Originally Posted by timbersteel View Post
Ok, easiest step in diagnosing a vacuum leak....

Cap off all the vacuum lines EXCEPT the fuel pressure regulator, the MAP sensor, and the Brake Booster that are branched out from the "tree" fitting on the plenum. This will isolate everything vacuum controlled or thar needs vacuum.

The exception is that the vacuum lines running to the Brake Booster,the MAP sensor, and the fuel pressure regulator are working correctly. You could temporarily cap the Brake Booster if not driving but diagnosing.
Ok Thanks --will give that a try
 
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Old 02-12-2019, 01:09 AM
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Was your new TPS clocked correctly when installing it? If this isn't done it won't idle right.

Why are you unable to read codes? Is the EEC test port not making connection to your reader?
 
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Old 02-12-2019, 07:26 PM
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Really dont know why I cant get codes but Ive tried different ways multiple times -Im probably not getting a good connection somewhere .

How in the world do you clock a TPS??--Answer is no I didnt .

Yes the message I get from the reader is - tester needs to be hooked up to get code ( or basically not getting a signal)
 
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Old 02-12-2019, 07:32 PM
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Originally Posted by TexasGuy001 View Post
Was your new TPS clocked correctly when installing it? If this isn't done it won't idle right.

Why are you unable to read codes? Is the EEC test port not making connection to your reader?
* The tester reads it is not getting a signal
* no I didnt clock the TPS ---hOW DO YOU DO THAT ??
 
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Old 02-12-2019, 11:07 PM
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unplug your IAC/Air bypass valve to see how much your Idle drops, post the RPM.

What tester are you using ?
 
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Old 02-12-2019, 11:17 PM
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Originally Posted by vjsimone View Post
unplug your IAC/Air bypass valve to see how much your Idle drops, post the RPM.

What tester are you using ?
Accutron I think --when I unplug the IAC idle really drops Sometimes from 2500 to 1000 - I have run it without the IAC plugged in & it runs fine - When I start it cold with the IAC UNPLUGGED ,IT WONT HARDLY IDLE ( flucuwates a lot)
 

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