Re: VW Golf TDI Boost pressure neg deviation 17964 Archived Message
Posted by Dave Hill on August 17, 2009, 10:23 pm, in reply to "Re: VW Golf TDI Boost pressure neg deviation 17964"
Hi Darren """but a secondary air pump is not a compressor.""" I am not sure how to respond to that (OK I do ) I am not sure that your definition of a compressor, agrees with mine. In fact I am not why this has entered into the conversation Surely an air pump that increases the flow & pressure of an available charge could be considered to be a "compressor" ??? I haven't measured the pressure that my effort will produce. But when the secondary air pump is powered directly (i.e. not through any resistor) it delivers considerable pressure. But still this doesn't replicate the the extremes of pressure that you will see on a road test. Another issue that is not often discussed when thinking about smoke testing is... A certain amount of flow is needed in a circuit in order to evaluate a leak. If you imagine connecting your smoke generator to a complex arrangement of hoses or pipework. If you have a perfectly sealed system to test, then your smoke will not penetrate much further than the entrance. Without a "circuit" for your smoke to travel through, you will struggle to spot any seepage. I suppose you could argue that a porous pipe or gasket would give you the flow needed to expose a leak, But going back to my earlier comment about a leak that is only exposed by extreme pressures, then my point is made. In a “real world” example.... I had a differential pressure sensor fault on a 307 HDI a while ago. I found a burned pressure hose that looked like it had been exposed to a flame. The neighbouring pipe was untouched though. It was only after I found a split further up the hose, that I realised that it was the “flow” through the hose that had allowed the hot gasses to permeate from the Diesel Particulate Filter. If there was no flow, then the hot gases would not have travelled past the steel pipework (designed to withstand the temperature) & reach the rubber hose. The same thought must be applied to smoke testing! HTH Dave
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