Mercedes 300E Flooding

Chuckyg

unread,

Apr 18, 2006, 9:18:18 PM4/18/06

to

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

Tiger

unread,

Apr 19, 2006, 12:26:28 AM4/19/06

to

So, how many plugs foul black?

Chuckyg

unread,

Apr 19, 2006, 7:36:47 AM4/19/06

to

only 1 plug fouls up a dry black, not wet

Josh

unread,

Apr 19, 2006, 9:17:09 AM4/19/06

to

I'm not sure if we've been down this road before, but what happens if you
disconnect the O2 sensor?

Josh

Tiger

unread,

Apr 19, 2006, 10:47:24 AM4/19/06

to

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.

Chuckyg

unread,

Apr 19, 2006, 5:01:46 PM4/19/06

to

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

Tiger

unread,

Apr 20, 2006, 12:59:45 AM4/20/06

to

What about your fuel pump relay? What is the date stamped on the side of it?

Chuckyg

unread,

Apr 20, 2006, 7:14:28 AM4/20/06

to

I replaced that last june

Tiger

unread,

Apr 20, 2006, 10:18:18 AM4/20/06

to

At this point, I would have the fuel pressure tested. I think your fuel pump
is failing.

Chuckyg

unread,

Apr 20, 2006, 1:02:47 PM4/20/06

to

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

Tiger

unread,

Apr 20, 2006, 3:56:39 PM4/20/06

to

If cold start valve is stuck on... all your plugs would foul out.
Disconnecting the cold start wires woudl disable that device.

Jens

unread,

Apr 21, 2006, 3:42:59 AM4/21/06

to

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.

Chuckyg

unread,

Apr 21, 2006, 2:17:09 PM4/21/06

to

Ok..this makes some sense...Where exactly do I hold the + and - points from
my multimeter? -Chuck