Hyundai Repair: Gas smell inside cabine and low compression cylinder, air ventilation, drive belts

Question
Hi HT,
I got a used Santa Fe 2002 2WD 2.4l 4cylinder with a 121 k miles.  When I turn the the A/C or air ventilation (hot) there is a gas smell coming from the hood. I went to the dealer and the technicians said the problem is the exhaust manifold that is cracked, and will cost a little more than $300 to have it replaced.  In addition, I have made a compression test to the cylinders.  3 of them (1, 2 & 4) have values between 150 and 170 psi, but cylinder 3 has a 90 psi!!.
Do you think that the gas smell is due to the cracked exhaust manifold or the low compression on one cylinder, or both.
The dealer told me that the low compression is not a issue of big concern!!. I don't belive it.

Finally, there is a noise in the hood, so as a preventive maintenance the timing belt and other drive belts and tensioner were replaced.  However, the noise is still there, and there is a little bit of vibration at idle speed.


Thanks in advance.


Answer
I think missing 50% of your compression on a cylinder is a huge deal.  Although this engine normally creates significant vibration when idling, but low compression like this will make it worse.  In addition, the low compression may result in unburned fuel and the fuel odor you describe.

If your vehicle seems to be running properly, I'd recommend rechecking the compression to be sure you didn't get an erroneous reading on the first test.  Compression that low would normally cause a performance issue.

I won't be able to tell you what your engine noise might be without knowing what it sounds like and the circumstances under which it occurs.  Typically, the easiest way to narrow down an engine noise is to use a long screwdriver as a probe and put your ear on the end to listen to different items on the engine.