inthemedia

Hello, I have a 1988 560SEL with 158,000 miles that is stalling after about a minute. Here is what happens: The car starts up fine, but then after about a minute, the economy gauge starts to creep into the red zone, the idle becomes progressively rough, and by the time the economy gauge is almost completely to the right, the engine finally dies, unless I keep pushing down on the gas pedal. If I take my foot off the gas, the car stalls out. If I restart the car, it starts up fine again but then exhibits the same symptoms. This problem is very consistent and always repeats the same pattern.

Here's what I have done thus far: Checked all vacuum connections and hoses for leaks – none found. I replaced the fuel pressure regulator and the Electro-hydraulic Actuator since it recently developed a leak. The EHA has an adjustment screw on the back. I have not touched it and installed it just as it was set at the factory. Would an improper adjustment cause these symptoms?

Now on to the fuel pumps. I hooked a voltmeter to the fuel pumps and observed that the voltage remained steady at 13.6 volts throughout the test so no problem with the power. I tested the fuel pressure according to the manual and got 86 PSI at the test port (lower chamber of the Fuel Distributor) and 90 PSI at the connection going to the cold start injector which is exactly what the manual states the pressures should be. These pressures remained consistent even as the car started to idle rough and eventually stall out. This eliminates the fuel pumps and fuel pump relay. After 30 minutes, the pressure was still holding around 68 PSI indicating the fuel Check Valve was good.

Voltage on Pin 5 of the X11 connector indicated 13.6v so the EZL and Ignition Coil are both getting power. Resistance across the Crankshaft Position Sensor was 870 ohms which is within spec. The OVP Relay tested good and was delivering full battery voltage on pin 87 so the CIS-E Control Unit and Idle Speed Control units were both receiving power.

Up to this point, everything appeared to be as it should. I then hooked up a voltmeter across the EHA valve and noticed that the voltage across it steadily decreased as the engine began to idle rough and finally die. I tried this test several more times and it was consistent, just like the problem. Turning again to the manual, it shows that the CIS-E module controls the voltage to the EHA valve. My thought is that one of the sensors going to the CIS-E module is malfunctioning and causing the problem. Has anyone ever seen a similar problem like this and what should I test next? Thank you, TC

m00nsh0t

have you tried connecting a vacuum gauge? What the econ gauge is doing makes me think you still have a vacuum leak somewhere, and a vacuum leak after the air flow meter would be consistent with your symptoms.