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What makes a sucking noise only under load (boost conditions?) that also causes high HC readings?
My 740T failed an IM240 emissions test (on the rollers) with a high HC reading. The original test result was 1.03 Gpm. The standard for the car is .80 Gpm. It passed well within standards on NOX and CO2.
I changed plugs, cap, rotor, air filter and oil and filter. When the car was retested it scored better on HC .86 Gpm, still too high. The NOX and CO2 reading also went down.
Next, I pulled off the air intake hoses from turbo to air cleaner to throttle body, cleaned them with degreaser and carb cleaner. I cleaned the throttle body, pulled off the air control valve and sprayed it with carb cleaner and wiped out what I could reach. I cleaned the little plastic t-connector from the small hose that comes from the turbo hose over the valve cover to the oil trap and the hose from that connector down to the oil trap. And then, as if that wasn't enough shootin' in the dark, I pulled off the O2 sensor and sort of accidently rubbed it with some sandpaper to get the guck off it. I also sprayed it with carb cleaner.
I noticed a sucking/whining noise on acceleration on my way to the test. It failed. I had managed to double my HC reading to 1.83. NOX and CO2 were also up but passing.
I changed the O2 sensor. I checked for vacuum leaks (propane waved around hoses, etc.) trying to find the whine and could find none. I can only hear the noise while accelerating under load, not at high revs while stationary or with the wheels turning free in the air (I jacked it up). The retest showed very little change in readings. HC 1.76 and NOX and CO2 were slightly decreased.
1st test HC 1.03
2nd test HC .86
3rd test HC 1.83
4th test HC 1.76
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