After numerous calls with same issue over the years I FINALLY came across a loyal (new) customer who not only believed me, but patronized his source of free Tech advice. We sent him 8 fresh Bosch injectors and problem solved. Had the old ones tested and just as I have been saying al along, they were shot. Backflow rates were 2x stock on 5 of the 8 and 1.5x stock on the remaining 3. Problem was solved with fresh injectors.