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Old 01-08-2001, 12:43 AM
Gary Gronewald
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I have an 87 300E that has developed an intermittent flat spot during acceleration. Most often this happens from when the engine is idling. ie from a stop. After a few seconds it will pickup and be normal. It is not completely consistent. It doesn't always do it. Occasionally, it will happen while trying to accelerate from higher speeds ie passing. Any ideas? One mercedes mechanic suspects the air flow valve.

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Old 01-08-2001, 08:10 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
There is an electrical component to acceleration enrichment. The airflow potentiometer registers actual position and the computer calculates change of position. If the change of position happens fast enough extra current is fed to the EHA.

I have seen many cars running with their OVP relay dead which also kills accel enrichment and its a very suttle effect. I would check into secondary ignition capability. The 300E has two highly possible problems; the ignition rotor and the coil. These difficiencies can easily be tested with an secondary ignition scope. I had one just last week. Car ran at idle with 15kv firing voltage, if I pulled a wire the spike would only do 19kv. A new coil gave 35kv. The problem on this car was much like yours with added cold start problems. Everytime the engines voltage needs exceeded 19kv it went flat. This was worse cold but occured as a hesitation to a full stall depending on how fast the load was added.

The problem with rotors can be similar with a burned trace that becomes conductive at higher voltages. Hard to tell on the 103 motor because of the position next to the fan. On other cars (after seeing a low output by pulling a plug wire)I will watch the scope and see if I can raise the voltage to acceptable limits by pulling the coil wire away from the cap while running***DO NOT DO THIS UNLESS USING PROPER TOOLS it'll get ya.

[Edited by stevebfl on 01-08-2001 at 08:14 AM]

Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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