Thanks Peter, That helps to clean things up. The plugs are really fouling though, so is this the O2 reading lean from an air leak and they adding more fuel than it can ignite? Just want to make sure I understand this? Larry also recommended a wire and cap change due to the age and mileage. I'll pick up some brake cleaner and check the injector seals as you suggest too. I changed them all on the 911 as they were hard.
Thanks again. Ed 300E On 15/05/07, Peter Frederick <[EMAIL PROTECTED]> wrote:
30% may be correct for key on, engine off. The Benz duty cycle (actually precent of time at 12V as opposed to 0V) is "backwards" from US practice, so a 20% reading on a US car will give you an 80% reading on the Benz. Not really an issue for you, as the continious "hunting" from 37-60% at idle indicates the computer cannot control the mixture properly, most likely due to air leaks large enough to cause misfire at lean mixture (leaking injector and injector holder seals on some but not all cylinders, or worse leaks on some than others). Spray a quick burst of brake parts cleaner onto each injector in turn -- most likely you will find that the meter swings rich each time (towards 100%) and the idle smooths out and picks up temporarily. Naturally, this means injector seals and holder seals. The reading should stay steady for a couple minutes when first started (until the O2 sensor warms up), then start to move. It should never stay perfectly steady, it should move up and down a small amount (less than 5%) constantly. It will read high (abover 50%) until the engine warms up some -- make all adjustments with the engine at full operating temp. The hoses are molded, you must get them from Rusty or some other source. I'm guessing yours are rock hard, mine were. Check for leaks and fix them before doing anything else, but likely the idle mixture is off, causing the hunting -- too lean, you get misfire and the O2 sensor reads way over lean (too much O2 because some cylinders aren't igniting), so the fuel gets turned up, at which point the O2 goes way low (too rich now that all cylinders fire and burn up the oxygen), so it leans out, misfires, and repeats. The overlean mixture is likely vac leaks, of course. After you get all the leaks fixed and check to make sure the cap, rotor, and wires are in good shape, set the idle mix. The screw is in the base of the "tower" sticking up between the fuel distributor and the air flow meter horn, works the same as the Porsche. Adjust in small increments to get close to 50% duty cycle, waiting a minute or two for the O2 sensor to respond after each adjustment. Peter _______________________________________ http://www.okiebenz.com For new parts see official list sponsor: http://www.buymbparts.com/ For used parts email [EMAIL PROTECTED] To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
