Beginner's guide to hunting down a vacuum leak 101....(bad idle)

[bimmerjeeper]

Lots of threads talk about finding vacuum leaks, but often provide little detail or photos.
Can we make a master checklist to help beginners find vacuum leaks?
In order of most common vacuum leak, ideally with a photo.

Also, if a new XJ owner just feels like replacing every vacuum hose in the whole engine, is there an easy way to identify/accomplish this? Kit? List of hoses?

Here is my initial attempt at a comprehensive list.
Can we put it in the right order?
I will add photos if people can guide me to where to look:

• 2 CCV valves/grommets on the valve cover?
• Large bellows tube going into the throttle body (crack or seated improperly)
• Throttle body gasket (where it bolts to the intake manifold),
• All the hoses that come off the intake. (?)
• Can we identify all vacuum lines here?
• Lower injector o-rings (at the manifold),
• Loose intake/exhaust manifold bolts? That rear manifold bolt has a habit of loosening.
• Intake and exhaust manifold gasket.
• Check valve at the brake booster. It is a 1 way valve. To test just remove and blow into it. Should only be able to blow through 1 way.

Misc notes:
* During the period when you hear the whistle... pull out the engine oil dipstick slightly... this will induce a (another) vacuum leak... if the whistle vanishes... you will know that it corresponds to intake manifold vacuum changes... and so increases the possibility that it is a vacuum leak.

Vacuum leak near throttle body?
http://www.jeepforum.com/forum/f11/89-xj-vacuum-leak-153902/#post1104353

 

[LYKOS]

Good list!!!

I use an old school vacuum leak detector.

Open hood
Start engine
Allow to warm to operating temp
turn on a small propane torch but do not light
systematically start running the torch over the vacuum hoses and around various parts of the engine
Whenever the propane is sucked into a vacuum leak the engine idle will increase
Note location, repair and continue

 

[bimmerjeeper]

Yes, but can we identify with photos every single vacuum line?

 

[kastein]

depends on the year of manufacture.

84-86: The Bad Old Days. Carbs, TBI, lightyears of vacuum lines. Might as well just highlight the entire engine compartment.
87-90: Less-Bad Old Days: TBI or MPFI depending on engine, only a few miles of vacuum lines. EGR equipped. Goofy multi-vacuum-line connectors to simplify assembly at the factory, each half of the vacuum line octopus is available at NAPA.
91-95: OBD-I. MAP remote mounted, all sorts of vacuum lines but not as bad. Vac disconnect vehicles up till 92 or so have vacuum lines going to the transfer case and the front axle housing.
96-97 OBD-II (I think it's 97 not sure.) MAP mounted right to the throttle body (eliminates a vacuum line), no leak detection pump AFAIK, some other simplifications of the CCV system.
98-01 OBD-II (not sure about starting year, I know my 98 has it.) Leak detection pump system added, which adds a few lines and a DTC or six that tell you there is a leak in the system somewhere.

I'm sure I am missing some change years in there and one or two are probably inaccurate.

 

[jodaddy]

bad or dirty iac

 

[Ecomike]

LOL, we have a new to us 84, and with a blind fold on you can reach anywhere under the hood and a grab a fist full of vacuum lines!!!!! Like a snake pit it is!!!!:laugh3:

depends on the year of manufacture.

84-86: The Bad Old Days. Carbs, TBI, lightyears of vacuum lines. Might as well just highlight the entire engine compartment.
87-90: Less-Bad Old Days: TBI or MPFI depending on engine, only a few miles of vacuum lines. EGR equipped. Goofy multi-vacuum-line connectors to simplify assembly at the factory, each half of the vacuum line octopus is available at NAPA.
91-95: OBD-I. MAP remote mounted, all sorts of vacuum lines but not as bad. Vac disconnect vehicles up till 92 or so have vacuum lines going to the transfer case and the front axle housing.
96-97 OBD-II (I think it's 97 not sure.) MAP mounted right to the throttle body (eliminates a vacuum line), no leak detection pump AFAIK, some other simplifications of the CCV system.
98-01 OBD-II (not sure about starting year, I know my 98 has it.) Leak detection pump system added, which adds a few lines and a DTC or six that tell you there is a leak in the system somewhere.

I'm sure I am missing some change years in there and one or two are probably inaccurate.

 

[bimmerjeeper]

kastien, on a 1998, you're saying you'll get a ODB2 code if there is a vacuum leak?

 

[kastein]

yes, it depends on how bad it is and if the ECU catches it, but you should get a code. It may be a 99 when they introduced it but I seem to recall seeing the leak detection pump on my 98, it is on the passenger back corner of the engine compartment right near the AC receiver/dryer and the shock tower and makes getting to the HVAC blower motor a real pain in the ass.

 

[bimmerjeeper]

This implies it's on 98 and 99. See title.
Deleted by Moderator

 

[Talyn]

[*]2 CCV valves/grommets on the valve cover?
[*]Large bellows tube going into the throttle body (crack or seated improperly)

These two won't actually cause a vacuum leak that you or the PCM would notice. It won't run any different. However they will let unfiltered air in.

* During the period when you hear the whistle... pull out the engine oil dipstick slightly... this will induce a (another) vacuum leak... if the whistle vanishes... you will know that it corresponds to intake manifold vacuum changes... and so increases the possibility that it is a vacuum leak.

On our setup it won't. The intake isn't actually pulling that much air out of the engine at one time as it is limited by the back valve cover breather. Not to mention the front breather is open to the filter area.

Allow to warm to operating temp
turn on a small propane torch but do not light

Keep in mind that sometimes vacuum leaks are only noticeable when the engine is cold, so warming it up may not help. You can also use some sprays to find a leak. WD40, seam foam, etc. Watch what you are spraying as the spray may damage plastic and paint. Also, water works at times. spray or pour water over the test subject and the idle should change as well you may hear a crackling noise from the leak.

yes, it depends on how bad it is and if the ECU catches it, but you should get a code.

It also depends where the leak is. The PCM won't catch the leak in the vacuum line to cruise, the brake booster or the valve cover. In my experience the leak detection pump and the evap purge solenoid actually cause more leaks than they detect.

 

[Ecomike]

Watch what you are spraying as the spray may damage plastic and paint. Also, water works at times. spray or pour water over the test subject and the idle should change as well you may hear a crackling noise from the leak.

I would be very careful with water, if I used it all. The TPS hates water, the electrical connectors too, and too much water on a hot E-manifold can cause cracks IMHO.

A stethoscope is a great way to isolate noise sources and leaks!!!

 

[Outlander560]

stethoscopes are a great way to find leaks.....the best way is with a smoke machine which i use for evap leaks commonly found problems are the lines by the purge and by the leak detection pump or the pump itself (mentioned by Talyn are very prone to problems) i know most people don't have their hands on a smoke machine so the next best thing would be to that would be the stethoscope idea or even propane starter fluid.

I know what has not been mentioned yet is a Vacuum Tester hook it up to the manifold and tell us the reading normal operating motor should be around 17-21 inHG and depending on what the guage is doing can tell me what is going on with the motor causing this bad idle issue

CCV valve will not cause the problem do to no supplied vacuum to them unlike the PCV which works with vacuum.

The IAC IIRC was mentioned as well carbon build up can cause higher idle or rougher idle as well I take mine off and clean it with brake clean and a rag. Throttle body butterfly inspection would also be recommended as well.

In cases such as this you can try to hunt it down with all of the previously recommended just be safe and be patient it will take time. I also understnad you have bad idle but is the idle high or low what are your RPM's at idle?

 

[Talyn]

I would be very careful with water, if I used it all. The TPS hates water, the electrical connectors too, and too much water on a hot E-manifold can cause cracks IMHO.

Why would you be checking the hot exhaust manifold for vacuum leaks? And its not like you are pouring it on.

 

[Talyn]

CCV valve will not cause the problem do to no supplied vacuum to them unlike the PCV which works with vacuum.

The CCV orifice at the rear can cause a vacuum leak, but it would be after the valve cover in the elbow or the line going to the manifold. Even if there was no grommet on the valve cover it wouldn't cause a leak.

 

[Ecomike]

Why would you be checking the hot exhaust manifold for vacuum leaks? And its not like you are pouring it on.

I was concerned about your general "Pouring water statement" being done on the intake, right next to the exhaust, and the TPS, especially with the OP in this thread, LOL.:laugh2:

spray or pour water over the test subject

 

[Ecomike]

The CCV orifice at the rear can cause a vacuum leak, but it would be after the valve cover in the elbow or the line going to the manifold. Even if there was no grommet on the valve cover it wouldn't cause a leak.

To clarify, both the front and rear of the valve cover are under partial vacuum, BUT, the front side is being sucked on through the air filter in front of the throttle body (inlet side of the TB), and if leaking would not constitute the after the throttle body kind of vacuum leak one needs to find!!! The small hose on the rear of the VC, is attached directly to intake manifold, and if it is drawing outside air directly and not all from the VC (engine block), it is then a small vacuum leak, and can cause a small change in idle speeds if the tube is not blocked with crude.

 

[Outlander560]

The CCV orifice at the rear can cause a vacuum leak, but it would be after the valve cover in the elbow or the line going to the manifold. Even if there was no grommet on the valve cover it wouldn't cause a leak.

you are right when i pictured it in my head i fillowed the vent line to the intake tube...not the rear going to the manifold which indeed can cause a vacuum leak...sorry about that

 

[Talyn]

I was concerned about your general "Pouring water statement" being done on the intake, right next to the exhaust, and the TPS, especially with the OP in this thread, LOL.:laugh2:

Yeah, perhaps I should have said sprinkle instead. Pour could be interpreted as opening up a garden hose on it.