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Old 06-15-2003, 07:16 PM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
The next step should be to identify your problem. If the idle is rough chances are that the power derived from each cylinder is different. This can happen for many reasons but the first step is identifying the problem cylinders.

Probably the safest way is to remove the air filter and crack the injector lines one at a time while the engine is running (use a rag to sop up the extra gas, there won't be a lot if done quickly). Naturally the cylinder dies when this happens and should cause a noticable shake. The more it shakes the better that cylinder WAS running. if you have a weak cyl it will make very little difference when the line is cracked (be sure to wiggle the line as sometimes the line sticks and the fuel stays inside even with the nut loose).

If you can ID a cylinder try swapping injectors, plugs, plug wires etc. to see if the miss moves. Also try pushing down on the airflap to give more fuel.

If there is a moment where the engine runs good as you press the airflap down then the problem is that the car won't run on some cylinders at the lambda mixture. Remember that lambda is as lean as it can run with power and the system makes the richest cylinder that lean. All leaner cylinders are running at less than lambda mixture. To put numbers on it; idle CO is about .3 - 1.0% CO. Placing ones finger on the flap can easily run the mixture to 2-4% CO. When doing this if a injection circuit (STARTING ay the fuel distributor - of course it could be the fuel distributor) has less fuel it may get above 1% with some up to 4%. The car will run great but not in closed loop.

In other words if you have cylinders that are lean in closed loop they will misfire as the richest cylinders are the ones being controlled. Try again, if the injectors are measured with a differential flow meter they have to be within 10% on flow. The problem I am discussing above would happen if flow was much different than 10%.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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