I need to find a vacuum leak. Does anyone have what the title says?

 

What are the symptoms of the vacuum leak?


There's lots of sources of possible vacuum leaks, and lots of vacuum sources.


To post diagrams and/or photos of the vacuum circuits would be an undertaking not too many folks would want to undertake.


Vacuum source circuits originate at your intake manifold are:


EVAP circuit
HVAC/Cruise Control circuit
LDP circuit
Brake Booster circuit
CCV circuit


Mechanical vacuum leak sources are:


Intake manifold gasket
MAP Sensor to intake manifold rubber elbow
Fuel Injector o-rings


You can isolate vacuum leaks from the intake manifold to the various circuits by removing the rubber couplings from the intake manifold an capping off the nipple on the manifold. If the vacuum leak stops, you've found the vacuum circuit that's leaking. Now it's up to you to visually inspect all the tubing, hoses, and couplings in the circuit to locate the defective part.


Mechanical leaks can be isolated by squirting water or starting fluid around the suspect areas and listening for a change in engine RPM or noise reduction.


I've probably overlooked something but I think you get the idea.


Here's a pic of the intake manifold sources. It doesn't include the LDP source.

 

Look on your XJs firewall...

 

It is just a check engine light that says vacuum leak. I think it may also be causing a missfire of cyl 3 and 6 at higher rpm. I have brand new spark plugs gaped perfect. The missfire happened when the rpms where at like 4k. The engine light started flashing.



I knew I saw the diagram somewhere I wasnt sure where it was though. Thanks.

 

Are replacement rubber elbows available at the dealer? I found the closest size I could at Autozone. The OEM one was completely dry rotted.

 

A very good investment is a FSM from pacificcoastmanuals.com the sell one in PDF for $7.95 that can be printed in part or whole for your year only XJ.


Info there found nowhere else like in Hayes manuals it is a dealer FSM.