1989 300E Follow Up

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Chuckyg - 06 Apr 2006 22:57 GMT

Hello: I posted back some time about some problems about my 300E cutting
out. I replaced a whole bunch of parts and went to the mechanic who
discovered fuel odor in the crankcase. The 02 sensor, and the cat were
replaced, all the header gaskets are tight and sealed with the oxygen
getting in brofe the 02 sensor. The car runs for a while then cuts out.
When the OVP relay is dissconnected the car runs fine after being warmed
up, as it is running in a leaner mode. It is certain that the motor is
getting flooded after the initial warm up. But with the relay DCd, it
runs. I bought the 02 sensor to the mechanic and he tested it, stating it
was sound. WHat is making my motor flood out?- Charlie, Monmouth COunty NJ

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T.G. Lambach - 06 Apr 2006 23:08 GMT

Given your description one can only suspect the OVP relay - even though
it was replaced not too long ago.

If you do choose to replace this OVP relay be sure you buy the right one
for this car.

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T.G. Lambach - 07 Apr 2006 00:40 GMT

Hi,

In the course of my "travels" on Usenet a kind soul posted this
explanation of the OVP relay. I don't know enough about electronics to
opine on its truth but you may.

The OVP relay protects the sensitive electronic circuits, i.e. your ECU
from high voltages.

It basically consists of a fuse, followed by a relay energized by a
small circuit, which has a zener diode built-in. This relay feeds the
the SRS, ECU and ABS (any others?). If the voltage goes too high, the
zener conducts, and shunts the circuit to ground, cutting out the relay,
and if very high, blows the fuse.

These relays get tired, as basically, it has to activate continuously
when the engine is running. 10 years ± is about the lifetime.

When it cuts out, your engine reverts to "dumb" mode, and won't
compensate for temp, O2, timing, etc.

SRS, ECU and ABS, that's all. And depending on model and/or # of
systems that are protected, there are different versions of OVP relay,
between 5 - 9 pins, and 1 or 2 fuses.

A cross-cable during a jump start can easily kill this relay.

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Chuckyg - 07 Apr 2006 00:54 GMT

Tom: I know that parts can go bad..... I did repalce the OVP back in
October of 05....--c

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Josh - 07 Apr 2006 01:42 GMT

If it's not the OVP then maybe the air flow meter is bad (I can't recall if
it was mentioned in your original post way back when). Wasn't it T.G. who
was successful at cleaning his with some electronics parts cleaner and a
pipe cleaner a while back? I was not as fortunate and had to replace mine a
couple of weeks ago and these are quite pricey so I'm hesitant to throw
(expensive) parts at your problem, but it may be worth a couple of bucks to
try cleaning it (the risk is that if you break it you'll need to buy a new
one whether it was bad or not). BTW, one free thing to check is for
obstructions in the air intake ahead of the air filter. If the car has sat
for any length of time who knows what might have nested in there... ;>

Josh

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Chuckyg - 07 Apr 2006 02:25 GMT

good sugestion.....but i think the car keeps flood out, becuase if the OVP
is hooked up, the car will cut out after a few minutes and then if it sits
for about 5 - 10 minutes, it will start back up...and the plugs were
getting a little fouled up...

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Martin Joseph - 16 Apr 2006 18:02 GMT

> good sugestion.....but i think the car keeps flood out, becuase if the OVP
> is hooked up, the car will cut out after a few minutes and then if it sits
> for about 5 - 10 minutes, it will start back up...and the plugs were
> getting a little fouled up...

Make sure to change out your oil, as all that gas leaking down will ruin it!

Marty

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Haas - 10 Apr 2006 00:27 GMT

I had a similar problem with my 1985 380SE. It turned out to be the ignition
control unit (ICU). Depending on where you buy this and whether it is
rebuilt, it could cost $150 - $400.

> Hello: I posted back some time about some problems about my 300E cutting
> out. I replaced a whole bunch of parts and went to the mechanic who
[quoted text clipped - 7 lines]
> was sound. WHat is making my motor flood out?- Charlie, Monmouth COunty
> NJ

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