Mercedes 300E Flooding

My 89 300E keeps flooding out on me. With the OVP disconnected it will run in a leaner mode. I replaced the fuel pressure regulator, accumulator, plugs and the o2 sensor. Keep in mind that I did replace the OVP relay
last october due to someone cross connecting the jumper cables, as the light were left on overnight. The car runs for a few minutes perfectly then slowly cuts out and wont start for a few more minutes and repeat. - Charlie Grianger- MOnmouth County NJ
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So, how many plugs foul black?
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only 1 plug fouls up a dry black, not wet
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I'm not sure if we've been down this road before, but what happens if you disconnect the O2 sensor?
Josh
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The reason I asked is because if the fuel distributor is bad... it will foul one or two plugs. Aren't you the one who disconnected the exhaust to find that still made no difference?
Did you ever replace the fuel filter? Did you ever had the fuel injection tested as far as the operating pressure? I am suspecting that you got several problems making this repair difficult. One possibility is fuel pump... but don't go running out to buy one. I think I have a spare if you needs it.
I want you to check all the spark plug wires for resistance... they should all be below 1300 ohm.
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I take that back, the plugs are perfectly clean. I am also getting pretty good fuel economy. Could the OVP relay go bad so quick? or ppart of the relay go bad so quick? The wires are recent. The fuel filter was changed also.- CHuck
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What about your fuel pump relay? What is the date stamped on the side of it?
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I replaced that last june
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At this point, I would have the fuel pressure tested. I think your fuel pump is failing.
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You think the fuel pump(s) is failing even if the car runs fine at high speeds? I reconnected the OVP relay this morning and the car drove for 2 miles and then the check engine ligh appeared and it started to buck then quit in a parking lot. I DCd the OVP relay and it started up. Could sometihng liek the cold start valve be stuck on; spraying fuel into the system? I did replace that last october...All help is appreciated..-Chuck
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If cold start valve is stuck on... all your plugs would foul out. Disconnecting the cold start wires woudl disable that device.
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I believe you are on the wrong track.
The function of the OVP relay is to protect the electronic circuits of the injection and ABS computers from excess voltage by shunting the overvoltage by a zener diode, thereby blowing the fuse.
The injection system then goes into failsafe mode, which means it operates by mechanical means only without computer control.
When you pull out the OVP relay, you force it in failsafe mode, and apparently this works fine, which means that the mixture (which is adjusted by the screw inside the tube accessible from the top of the air filter... do not touch it !) is OK and that the injection system in general is OK.
In normal mode, the mixture is fine adjusted by the fuel pressure regulator, which is controlled by the injection computer according to feedback from the oxygen sensor and inputs from air mass and temperature sensors.
So, the problem is most likely within this loop.
You already replaced oxygen sensor and fuel pressure regulator, so the next major point to suspect could be the potentiometer in the air mass sensor.
You can measure the input to the computer by a multimeter. With igntion on but without the engine running, the voltage should vary continously from approx. 0,5V to 4,5V proportional to the position of the air mass sensor plate.
I had a similar problem with flooding (except I could not start at all), and in my case I replaced the fuel pressure regulator (EHA) and thereby ruled this out as the cause of the problem. After trying to find the problem for months, I decided to replace it again, and whoops it worked immediately. So don't rule out the items, you have already replaced.
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Ok..this makes some sense...Where exactly do I hold the + and - points from my multimeter? -Chuck
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