finding intake vac leak on a 1998 buick lesabre3.8

[Austin Hansen]

i beleive this would work on any 3.8 gm v6 or any v style engine in which the air under the manifold shares the air in the oil pan(sorry i just don’t know how to describe it) any way get an obd2 scanner and view short term fuel trim and pull out pcv valve and plug hole with rag ( plug any air lines that go to the air box or intake assembly that come from inside the engine block or you will get a false reading) now watch the st trim and spray carb spray in through the oil fill hole and see if the trim goes rich (or negative) if does you have an internal vacuum leak at the intake manifold if it doesn’t then your intake manifold gasket is fine. I do not know all the technical terms and i am sure there are many different options on different cars the basic jist of all this is that with all holes plugged off and the st trim goes rich from carb spray being sprayed into oil fill hole you have a vacuum leak inside your engine.

Topic

[Carlos]

Do you have any pictures or video on this test. Maybe cause a fake vac leak and see results. Or kill an injector and see what happens, when you add carburetor cleaner. Intake gasket leak, plug or not working injector, injector o ring seal leak, and a stuck open EGR valve will cause it to run lean. My question is, how would carburetor cleaner pinpoint the cause. I love to see the video one day. :silly:

[Austin Hansen]

as for a video i don’t but the customer is going to bring the car back when she has money and i can do a video demonstrating this technique. if it were a dead injector i would have a miss there wasn’t a misfire on the vehicle an injector o ring leak wasn’t present because i sprayed carb spray over all possible areas for leaks. as for an egr leak i saw no trouble codes for the egr system and the egr system is separate from the internals of the engine since it takes exhaust gases to the intake manifold not air from the oil pan or internals of the engine. if it was egr i wouldn’t have had the fuel trim go rich from carb cleaner in the oil hole. This test is to see if the intake manifold gasket is bad and leaking and sucking in air which causes a lean condition. i will video tape the test when the car comes back.

[Author]

Replies