October 2020

BY Frank Massey L ast month, I was debating the opportunities with non-intrusive diagnostic techniques, and more to the point the reliability of results. I think it is important to accept, as with all skill- based process, the accuracy and results depends very much on experience. A second opportunity presented itself for this topic in the form of an Audi RS3 with a very sick engine. I’m going to make my thoughts truly clear at this point; I see no point in applying a potentially complex series of tests where simplicity prevails. The Audi RS3 is a prime example of this, with a totally dead cylinder. We must however understand all techniques where cost, accessibility and risk factors demand an evidence-based decision. With that cleared up let us review and discuss the series of tests carried out. The owner was somewhat vague as to the history of the problem. He explained the problem had been present for some time and hoped he could drive through it. As this topic will later confirm he has driven right into it. Mechanical resistance Due to the severity of the misfire, a decision to conduct a relative compression test was sufficient to confirm a serious internal engine defect. David and I were curious to challenge other options to determine the full extent of failure without component removal. Attaching a current clamp around the ground lead, we were able to compare the mechanical resistance to battery current consumption, this can also be performed with voltage drop or both. The logic here is that all cylinders should balance. This test will not confirm valve timing errors or low compression across all cylinders! However, if you apply the x3.5 rule to the amp/hr battery rating, you should be able to predict the correct work rate and rotation speed, assuming of course you have confirmed correct battery application and health status. We have no current consumption from cylinder 1 possibilities, problems with valve operation or piston to bore seal. The next test was to attach the first look sensor to the dip stick tube (see Fig.1), with the obvious aim of predicting potential cost and action plan. So, it about as bad as it gets, the drop in current draw is synchronous with a rise in crankcase pressure rise. Oh dear. Annette did a cost exercise with a new engine replacement and turbo, inclusive of labour with no change from £40,000. Ultimate techniques For the purpose of comparing in cylinder compression using WPS and first look in the exhaust we now move on to the ultimate engine internal analysis techniques. My interest here was to compare actual in-cylinder events and exhaust exit pressures in real time to ascertain any delay and if cylinder overlay could be used to confirm which cylinder event was responsible for the result. I will re-state my opinion here, having spent the first 20 years of my career as a professional engine builder I do not care which cylinder is faulty or what the internal fault is! Why? If I’m going to rebuild the engine, then it’s all coming apart for examination. Professional pride and reputation is priceless, so unfortunately nobody wants to pay for it! Having fallen of my soap box, I do accept as diagnostic technicians we must provide the customer with a factual and accurate estimate with the quickest low-cost process. apart from the fact I find in cylinder and vibration analysis fascinating. Important variables Before discussing the complexity of Fig.2, there are some important variables that affect results, remembering that we are dealing with pressure differential or absolute values 20 AFTERMARKET OCTOBER 2020 TECHNICAL www.aftermarketonline.net EVEN MORE NON-INTRUSIVE DIAGNOSTIC TECHNIQUES! Frank Massey continues his look at the benefits of non-intrusive diagnostic techniques. Cue the Audi RS3