Engine 89 GT - Is this what a vacuum leak sounds like?

CtotheJ

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Apr 22, 2019
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I just got my 89 GT started after sitting for over 6 years, but it's rough idling and will die if I don't give it a little gas every few seconds. I can hear a very audible whining sound followed by what sounds like suction about every 5 seconds. When I turn the car off, you can hear it very clearly after the engine has stopped.

Anybody have any ideas where I should start looking? I'm not sure which hoses are vacuum or not.

Listen:
 
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jrichker

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Finding vacuum leaks

Revised 6 May 2018 to add carbon canister plumbing as a common leak area.

There is no easy way to find vacuum leaks. It is a time consuming job that requires close inspection of each and every hose and connection.

Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much from engine to engine that it may be difficult to detect small leaks. The engine in my first Mustang pulled about 16.5" of vacuum at 650-725 RPM, which I consider rather low. It was a mass market remanufactured rebuild, so no telling what kind of camshaft it had. Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure comparison is a reading taken when your car was performing at its best through all the RPM ranges and what it is doing now. Use one of the spare ports on the vacuum tree that is mounted on the firewall near the windshield wiper motor.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will change speed. Avoid using flammable substitutes for the oil such as starting fluid, propane or throttle body cleaner. Fire is an excellent hair removal agent, and no eyebrows is not cool...

After you have done the simple visual checks and the check for vacuum leak on the underside of the intake manifold, consider doing a smoke test.
Some of the guys here have built smoke machines used to find automotive vacuum leaks. They seem to work quite well and are made mostly with parts you would have laying around in your garage. Check out smoke machine vacuum leak - YouTube and see if there is one that you could build.

The vacuum line plumbing is old and brittle on many of these cars, so replacing the lines with new hose is a good plan. The common 1/8” and ¼” vacuum hose works well and isn’t expensive.

The PCV grommet and the power brake booster check valve grommet are two places that often get overlooked when checking for vacuum leaks. The rubber grommets get hard and lose their ability to seal properly. The PVC grommet is difficult to see if it is correctly seated and fitting snugly.

The hoses and connections for the evaporative emissions (carbon canister and purge valve) are other common sources of vacuum leaks. The large vacuum outlets on the bottom side of the upper intake manifold are common hiding places for deteriorated vacuum lines and caps over unused vacuum ports.

Fuel injector O rings can get old and hard. When they do, they are prone to leaking once the engine warms up. This can be difficult to troubleshoot, since it is almost impossible to get to the injectors to squirt oil into the fuel injector mounting bosses. If the plastic caps on the fuel injectors (pintle caps) are missing, the O rings will slide off the injectors and fall into the intake manifold.

Fuel injector seal kits with 2 O rings and a pintle cap (Borg-Warner P/N 274081) are available at Pep Boys auto parts. Cost is about $3-$4 per kit. The following are listed at the Borg-Warner site ( http://www.borg-warner.com ) as being resellers of Borg-Warner parts:
http://www.partsplus.com/ or http://www.autovalue.com/ or http://www.pepboys.com/ or http://www.federatedautoparts.com/

Most of the links above have store locators for find a store in your area.

Use motor oil on the O rings when you re-assemble them & everything will slide into place. The gasoline will wash away any excess oil that gets in the wrong places and it will burn up in the combustion chamber. Heat the pintle caps in boiling water to soften them to make them easier to install.



Diagram courtesy of Tmoss & Stang&2birds
mustangFoxFordVacuumDiagram.jpg



Vacuum leak due to slipped lower intake manifold gasket...

Ask Nicoleb3x3 about the intake gasket that slipped out of place and caused idle and vacuum leak problems that could not be seen or found by external examination. I don't care what you spray with, you won't find the leak when it is sucking air from the lifter valley. It simply isn't possible to spray anything in there with the lower manifold bolted in place.





Determining if you have a leak due to a slipped intake gasket as shown above. This test is only good if you can get the engine to run somewhere in the 1000-1700 RPM range
If your valve cover oil filler & PVC systems are still in the original configuration, try this:
Cap or plug the hose from the intake manifold to the PVC valve with a bolt.
Cap or plug the PVC valve with a piece of hose with a plug or bolt in it.
At that point the only vent for the crankcase is the tube from the oil filler neck to the throttle body.

Disconnect the tube that runs from the oil filler neck to the throttle body. Make sure the oil filler cap is on securely. Start the engine and put your thumb over the end of the tube that comes from the oil filler cap. If you feel suction, there is a leak. Another thing to do is to extend the tubing from the filler neck so that there is enough to stick the end in a jar or cup filled with motor oil. If it sucks up the oil, you definitely have a leak at the underside of intake manifold.

This isn't necessarily the definitive test, but it is the best thing I could come up with on short notice. If there is a lot of blowby, this obviously won't be of much help.

See the picture below to see the breather tube where in connects to the throttle body. It is close to the TPS and runs over the top of the IAC.

The following are diagrams courtesy of Tmoss & Stang&2birds





Surging Idle Checklist
You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D

It's free, I don't get anything for the use of it except knowing I helped a fellow Mustang enthusiast with his car. At last check, it had more than 250,000 hits, which indicates it does help fix idle problems quickly and inexpensively.





See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring

Fuel, alternator, A/C and ignition wiring

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

Vacuum diagram 89-93 Mustangs

HVAC vacuum diagram

TFI module differences & pinout

Fuse box layout
 

CtotheJ

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Apr 22, 2019
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I finally picked up a vacuum gauge and it looks like I do have a leak somewhere. It sounds like it's coming from around the fuel pressure regulator.
I think I'm going to try the DIY smoke machine unless anyone has any better ideas.

 

CtotheJ

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Apr 22, 2019
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I made a smoke machine and I have a small leak at the EGR...looks like it's coming from inside the metal housing.

There was also a lot of smoke coming from the end of the rubber hose that just has a plastic cap on the end that sits behind the upper manifold. Not sure what that part is called or if it's supposed to do that. Can someone identify this please:
629837
629839
 

CtotheJ

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Apr 22, 2019
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That's the PCV (Positive Crankcase Ventilation) valve.
I've done a bit of reading, and from what I understand this may be working as intended.
Am I correct in thinking positive pressure in the vacuum lines would get blown out of that valve?
That's pretty much what the name suggests, I just don't fully understand how the vacuum is connected with everything else.
 

General karthief

wonder how much it would cost to ship you a pair
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Pull your upper intake off and you should see a rubber grommet in the back of the intake, under that grommet should be a mesh filter. Replace the mesh filter and grommet then stick that pcv back into the hole.
 
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DemonGT

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If the PCV isn't installed into the lower intake where it should be it's not removing the positive crank pressure as it should. Probably why you have that air hiss after shutting down the motor, your motor is building pressure with out some where for it to go.
 
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Mstng93SSP

You have a nice rear end there Dave.
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The PCV valve you are showing needs to be pushed into the"hole" in the back of the lower intake. There is a rubber grommet that it pushes into Push that valve into the grommet and then see how it runs.
 
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CtotheJ

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If the PCV isn't installed into the lower intake where it should be it's not removing the positive crank pressure as it should. Probably why you have that air hiss after shutting down the motor, your motor is building pressure with out some where for it to go.
You were correct! I guess I must have dislodged that hose when I was taking off the upper intake the first time. Once I put it back into it's hole there's no more rough idle or hissing. Purrs like an angry kitten again, thanks a ton!

Thanks to all who've taken time to help me out with this. You're all rock stars!
 

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