Jumper Hissing and Fuel Consumption

Sounds frustrating! I had a similar issue with my old Volvo V70 – turned out to be a split in the intake hose after the MAF sensor but before the throttle body. The hissing sound is a classic symptom of unmetered air getting sucked in. That extra air throws off the fuel mixture, hence the increased fuel consumption and the check engine light illuminating. Have you checked all the hoses thoroughly, especially the ones that connect to the turbocharger, if your Jumper has one? Sometimes the cracks are on the underside of the hose and really hard to spot without taking them off. Does the engine misfire at all?

Thanks for the insight! Yes, it feels like a slight engine misfire especially when idling and the hissing is noticeable. I didn't think about checking underneath the hoses – that's a good point. You mentioned the MAF sensor. Could a faulty MAF sensor cause similar symptoms, even without a visible leak in the intake system itself?

A faulty MAF could cause similar symptoms, but the hissing sound really points towards a physical leak. With the misfire occurring and the hissing present, I'm still leaning towards a split hose, especially since you've got higher fuel consumption. Honestly, at this point, I'd recommend taking it to a workshop. They can do a smoke test to pinpoint the exact location of the leak. It'll save you a lot of time and headache in the long run.

You were spot on! Took it to a local shop, and they did a smoke test. Turns out there was a small split on the intake hose, right underneath where I couldn't see it. They replaced the hose and it cost me 100€. The hissing is gone, the check engine light is off, and my fuel consumption is back to normal. Thanks for pointing me in the right direction!