Excessive air in Crankcase

ANGELIQUE MOXHAM

MEMBER
2005 FORD F-150
5.4L
V8
2WD
AUTOMATIC
240,000 MILES

Hello, my truck has a major vacuum leak in the crankcase. Loud and when I open my oil cap it has lots of pressure, the air whips out and shuts the truck off. Same thing happens with the oil dip stick, the truck shuts off. It has all of the sudden 30 sensors fail and got stuck in limp home mode. I have done a lot of work and got all 30 codes down to the same 2 since the beginning. Lean Bank 1 and 2 and have reset truck over and over and the vacuum leak still comes right back after a few minutes of idling, and I believe it goes back into limp home mode because it automatically starts running rough on its own. After I clear codes, it idles with a high idle on its own like I'm stepping on the gas but does run great no vacuum leak sound or anything then it drops down and starts running really bad again. Any help would be appreciated.

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

We need to start with two things. Checking for a vacuum leak and a compression test.

The only way you are going to get this much pressure in the crankcase is by blowby, so we need to start with a compression check.

https://www.2carpros.com/articles/how-to-test-engine-compression

Basically, when you have compression escaping into the crank case then you get the loud noise coming from the oil cap.

The next thing we need to do is check for an actual vacuum leak.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

You could have two issues, but we need to start with the compression test because if it is low then nothing else matters because we need to rebuild or replace the engine at that point.

Please run through this and let me know what you find.

Thanks