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Car Forum / Mercedes-Benz Cars / April 2006

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Weak Starting, Warm. W124 230E '92

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Marcelo Mansilla - 27 Mar 2006 19:20 GMT
Hi, I was wondering maybe someone here could help me. This car has a slight
hard starting specially when warm.

When starting cold in the mornings it starts at first try, but weak,
hesitates at first but very soon comes strong. Later, after two - three
hours beeing off, with engine T° around 60°C, it starts at second or third
try, hesitating. But on the other hand, when it has been off for a short
while, say 15 min, it starts at first try and strong.

The car has 90k miles on the clock, spark plugs, wires, cap and rotor were
replaced recently. The fuel filter has 6k miles. The fuel pump and fuel
accumulator have never been replaced. The cold start valve works fine, I
think, I removed it and squirts fuel when the engine is cold, although I
don´t know if it is the proper amount.

I did a search and found out that maybe the fuel accumulator cant keep
static fuel pressure for warm startings (vapor lock), but if this is the
case, I wonder why the symptom appear on mornings, engine stone cold, and
cold start valve squirting fuel.

Otherwise car running is almost perfect, the only other little problem is a
slight unstable idle when warming up.

I would appreciate any idea.

Thanks in adavance.

Marcelo Mansilla
T.G. Lambach - 27 Mar 2006 22:26 GMT
I experienced somewhat similar problems with an E320 (after only 18K
miles). Perfect cold starts but poor hot starts after an hour or more of
being shut down. There was also a stench of fuel in the exhaust.
Starting was much quicker if I stepped on the accelerator.

The cause was one leaking fuel injector which I found by removing the
spark plugs after the engine was cold. One was wet with fuel.

So the motor was over fueled or choked from this leaking fuel injector.

The injector was replaced and the motor runs perfectly.

Hope this helps you diagnose your car's problem.

P.S. Try some Techron or similar fuel injector cleaner if you suspect
anything with the fuel injectors.
ws - 28 Mar 2006 04:53 GMT
Hi Marcelo,

I have a '91 200E, the engines should be similar, and had almost the
same exact symptoms. The mechanics suspected the fuel accumulator or the
injectors too, but it turned out that it was the fuel pressure regulator
that was the problem.

Regards,
WS

> Hi, I was wondering maybe someone here could help me. This car has a slight
> hard starting specially when warm.
[quoted text clipped - 24 lines]
>
> Marcelo Mansilla
Marcelo Mansilla - 28 Mar 2006 19:02 GMT
Thank you for these ideas, I'll do my homework and let you know.

Right now I'm waiting for the engine to get cold, to remove the spark plugs
and see.

At the same time, if I could, would like to check the fuel pressure
regulator. Is there an easy way to check it?, does anyone know how to?

Thanks

Marcelo Mansilla
T.G. Lambach - 28 Mar 2006 21:55 GMT
The fuel pressure regulator is a small can connected to the end of the
fuel rail. There's a small vacuum hose connected to it, going to the
intake manifold. Pull off that vacuum line - if fuel dribbles out, the
regulator is the problem. That fuel is flooding the motor.
Otherwise, pull the spark plugs as part of your continuing investigation.
Marcelo Mansilla - 28 Mar 2006 23:11 GMT
Many thanks, that was what I needed.

Well, I find out the pressure regulator, disconnected the small hose and
wasn't leaking any fuel, but there was somewhat liquid carbon sediment along
the bottom of this hose. Maybe it's slowly leaking small fuel drops,
or maybe it is the natural condensation of this area of the engine, don't
know.

With respect to the spark plugs, they were all dry, so I guess that neither
a leaking injector nor the pressure regulator are "flooding" the engine.

Just in case, I sprayed air intake cleaner on all the injectors. Idle stays
smooth.

Tomorrow, I want to disconnect the rubber hose back on the fuel accumulator
to check it. On thursday I will carry out a fuel pressure test on a shop.

Hope to find out something defective. I'm getting out of ideas.

Best regards

Marcelo Mansilla

> The fuel pressure regulator is a small can connected to the end of the
> fuel rail. There's a small vacuum hose connected to it, going to the
> intake manifold. Pull off that vacuum line - if fuel dribbles out, the
> regulator is the problem. That fuel is flooding the motor.
> Otherwise, pull the spark plugs as part of your continuing investigation.
Marcelo Mansilla - 29 Mar 2006 16:44 GMT
Ok, Today, checking the Fuel Accumulator:

Started the engine, then off.  I dissconnected the rubber hose back in the
fuel accum. What a mess, I'm soaked right now writing this :).... But, as it
ought to be, gas was coming out from the end of the hose, there wasn't any
fuel coming out from the end of the Fuel Acc.... so this device is fine.

Well, manometer will say last word tomorrow, nevertheless something is
telling me that there will be nothing wrong with dynamic or static fuel
pressure... Is there anything else to look at? ....Please...

Regards

Marcelo Mansilla

> Hi, I was wondering maybe someone here could help me. This car has a slight
> hard starting specially when warm.
T.G. Lambach - 30 Mar 2006 20:41 GMT
The question that ought to be resolved is whether the warm motor is fuel
starved or over fueled. When that is known the suspects can be narrowed
to a few.

Complaint: Slight hard starting when engine is warm.

Are you stepping on the accelerator when this happens?

If not, does the engine start immediately if you do step on the
accelerator while cranking - even if only a small amount?

When opening the throttle causes an immediate hot start - no delay -
indicates an over fueled condition (flooding).

Then the task is to find why a small amount of fuel is slowly leaking
into the intake manifold.
Marcelo Mansilla - 04 Apr 2006 20:48 GMT
Last few days I was stepping on the pedal on startings. It doesn´t improve,
in fact it gets slightly worse.
Does this mean that it's a poor mixture problem?... If so, what else to look
at?

Many thanks

> The question that ought to be resolved is whether the warm motor is fuel
> starved or over fueled. When that is known the suspects can be narrowed
[quoted text clipped - 12 lines]
> Then the task is to find why a small amount of fuel is slowly leaking
> into the intake manifold.
 
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