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Discussion Starter #1
Range Rover SC 2008

Error codes P0051 & P0031

I have these two codes and am stumped as to the underlying cause. I can hear a sucking sound and some times a whistling sound from the passenger front side of the engine near the PCV valve. If I remove the oil cap the engine exhibits symptoms of a mass air leak as well as the same if the PCV valve is removed. The hissing sound goes away when the PCV valve is removed from the engine and hose plugged. However the hissing sound is not coming form the PCV valve. There is an occasional knocking sound from the engine when and I have gotten a knock engine error a few times but it is intermittent.

I have already replaced the following:

All 4 o2 sensors
Fuel filter
Upper intake manifold gaskets
Supercharger intake gasket
Throttle body gasket
PCV valve
Cleaned MAP sensor
Cleaned MAF sensor
Tested continuity with volt meter for shorts in the wiring to the o2 sensors
I tried to smoke test (inconclusive) at home but did not find anything so I took it to a shop where they told me I needed to replace the intake manifold rings, which were probable causing the issue. I replaced them this weekend and still having the same problem.

I am lost on what to do next I am looking for a shop here in town to do another smoke test and see if there is a vacuum leak causing these problems after I replaced the gaskets.

Any ideas or thoughts as to the cause of the issues I am having or what to do and test next that has not already been checked, replaced, or tested?

Thanks for all the help in resolving this issue I am still having.
 

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It defenitly sounds like a leaking vacum line, seal or connection making the sucking sound. Hence when you introduce another source for the air to get in the sucking sound goes away since the air intake will take the easiest path. I don't think the occasional knocking sound is related. If you have a steathascope or chunk of garden hose you can try and pinpoint the source of the sucking sound.

keep in mind the sucking sound may not be the source of the problem but rather the easiest path for it to draw air in. Could be a plugged air filter or breather somewhere forcing the air to be drawn in from somewhere else.

Sorry I couldn't be more help.
 

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Discussion Starter #3
I will try the hose method you suggested and see if I can narrow down the location of the sound; that would better direct my efforts to a smaller location. And solve one leak at a time if there are more then one. I was assuming that the knocking intermittent sound could be coming form the lean condition (codes p0051 and P0031) causing it to run rough.
Hopefully I can find a mechanic shop, which will do a smoke test for leaks also.
 
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