October 2020

OCTOBER 2020 AFTERMARKET 21 EYEBROW www.aftermarketonline.net acturing of 9 nsumption % o a new OE or compar 7 ener o 79 % es up t AL EGR Remanuf sion s o ed t co-friendly and less CO2 emis E – y unit. cop gy c va VES V US TH WI GREEN GO none ed in ou +44 (0) 121 725 0180 ther information please call us at or fur F ds Uniform high quality standar – ailability v cellent a Ex – o age second t erv Range and co – atgr Newest technologies inter – oduction r pr ock.co .els t www m otherwise none of this will make sense. Assuming a good in-cylinder seal, the slower the piston speed, the greater the pressure differential. For example, cranking compression is approximately three times greater than when running at idle. This is because of pumping losses with a closed throttle, the descending piston creates an expanding volume that has more time to draw in a fresh air charge, therefore higher compression. A weak cylinder will accelerate up the bore quicker due to a drop in resistance, lower compression, and accelerate down the bore as the pumping losses are reduced, lower drag. The first look sensor in the exhaust will record an increase in pressure drop with a weak cylinder due to the lower initial compression followed by the expansion in volume and corresponding increase in pressure differential when the exhaust valve opens. This causes the classic intake pulse at the tail pipe. With the scope, green channel, and overlay triggered from cylinder 1 PCM ignition pulse, you can clearly see an extremely poor compression, erratic pressure rises and poor tower symmetry. The exhaust cycle is erratic with poor definition when the inlet valve opens. The expansion and intake voids are poor, also confirming a faulty cylinder seal. The first look image, red channel, shows multiple increase in exhaust pressure voids which I find unhelpful. It does not in my opinion add any useful diagnostic value. I’m happy to accept any alternative opinion. Fig.1 Fig.2