MY HUSBAND AND I BOUGHT SEVERAL OF YOUR BOOKLETS. WE USED YOUR BOOKLET TITLED "Diesel Performance Tuning and Repair" RECENTLY TO TEST A 79 240D AND IT FAILED VIRTUALLY ALL OF YOUR TESTS LISTED UNDER "Quick Inspection Checklist." THANKS VERY MUCH YOU SAVED US LOTS OF MONEY BY HELPING US JUDGE THE WORTHINESS OF THIS POTENTIAL PURCHASE. ANYHOW, MY HUSBAND DID THE TEST WHERE YOU UNSCREW THE CAP ON THE VALVE COVER AND SEE IF IT DANCES AROUND, OR IF SMOKE BLOWS BY, ON OUR GAS CAR. I'M WONDERING IF IT'S A GOOD TEST FOR GAS CARS AS WELL AS DIESELS? THANKS, B