- Re: Citroen Saxo 1.4 multi point IAW IAP.81 T Reg Archived Message
Posted by john weddup
on October 7, 2008, 7:13 pm, in reply to "Re: Citroen Saxo 1.4 multi point IAW IAP.81 T Reg"
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Michael is absolutely correct. In the good old days before cats we used to use tuning machines. I had a couple of bosch units(like the big cryptons). They would do cylinder balance checks where they knocked out spark to each cylinder in turn. You could see a percentage of speed reduction for each cylinder there by judging its output. With a 4 gas analiser(rare then) you could do further checks. You could see what oxygen, co, and hydrocarbon balances were. A cylinder misfiring do to low compression or no spark produces little or no co this however can be distorted as if engine and cat are hot unburnt fuel can be burnt in cat creating some co..The oxygen however goes high. A failed cat will always result in a higher lambda reading as the oxygen normaly used in conversion within cat to turn co into co2 will not occur. However any exhaust leaks after cat will confuse issue and any before lambda but after engine will also. I see many mot failures for co but the lambda is ok due to a massive exhaust leak. Solve the emmission problem and then lambda is high. So many times I hear people confused into thinking lambda reading on mot is to do with lambda sensor. They may be related but only because they are monitoring the same things, the relation between oxygen and other gasses in exhaust system. I do feel as the modern diagnostics rely so heavily on code reading the old black art of multimeter, oscilloscope, vacuum gauge, gas analyser, compression tester, compression loss tester, and general knowledge born of many years experience fixing what others cannot. regards john |