Starting problem 89 300SE, symptoms, observations and advice please

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Rob. Smith Contact options for registered users 's Avatar posted on
November 8, 2006, 4:09 pm
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Ok

I have a starting problem, observed I must say (now I think about it)
when cold.
It doesn't like to start when its cold. Occaisionally it fires, but
generally its a lot of cranking before it splutters into life. Once it
is running, it runs perfectly. i.e no coughing or anything, even under
load, so I guess I'm discounting the ignition system in this, or fuel
delivery once running (read on). I note that I hear the fuel pump run
under the floor for about a second as I switch on the ignition. It
does this every time.

I have a number of points I would like to raise for opinion:-
a)
My cold start valve has failed, or my fuel pump relay is not
activating this. Which is most likely?.
b)
My fuel pump relay is not receiving the 'I'm cranking' terminal 50
signal to tell the fuel pump to cut in again (maybe see below), or
activate the cold start valve. Is there any history on this?.
c)
My tacho signal is not getting to the fuel pump relay to tell the pump
that the engine is turning over and should re-start the fuel pump?.
d)
Is the CIS-E unit temperature output not telling the fuel pump relay
to operate the cold start valve and what should this signal be anyway
(analogue voltage or a digital [on/off] signal).
e)
Is the CIS-E unit working at all?  I must say it seems to regulate its
idle speed OK. I know the CIS can work without it.
f)
Is my fuel pump OK. The car has done about 180k miles and I guess its
the original pump. How long do they last (but all is well once its
fired up)?
g)
As I said, the thing is perfect once running. I have replaced the fuel
pump filter (new) and the fuel pump relay with a good 2nd hand unit,
though this reluctance to start  is more exacerbated now the weather
has turned cooler here (and I hadn't used the car for a week) in
Blitey.

Any opinions on the above (Tom?).

I'm happy to start detecting, but I'd prefer to start with the
probables before the possibles. Its dark and getting cold and wet and
miserable out there on the drive to be tinkering whilst wifey reels
off all the other 'more important' jobs to be done about the place.

Cheers...   Rob.

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macdrone Contact options for registered users 's Avatar posted on
November 9, 2006, 4:10 am
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Re: Starting problem 89 300SE, symptoms, observations and advice please

Mercedes is supposed to retard the timing on shutdown to allow for easy
cold start.  What ever controls that or whatever does it isnt working
possibly.


Rob. Smith wrote:


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Tiger Contact options for registered users 's Avatar posted on
November 9, 2006, 12:51 pm
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Re: Starting problem 89 300SE, symptoms, observations and advice please

I would suspect the CIS-E temperature sensor is faulty. If it is not
registering proper temperature for the fuel injection system, then it
woudn't be able to determine precisely amount of fuel to start a cold
engine.

Do you have problem starting a warm engine?



 

T.G. Lambach Contact options for registered users 's Avatar posted on
November 9, 2006, 12:58 pm
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Re: Starting problem 89 300SE, symptoms, observations and advice please

Hi Rob,

I don't like to start when it's cold either!

Sounds like the cold start valve isn't doing what it should - 10 to 15
seconds of spraying fuel into the intake while the motor is being
cranked. I don't know if it stops when the motor fires or just stops
from being timed out.

The 280E version has (i) a thermostat ON below 20 C, OFF above, (ii) a
thermotime relay whose ON time depending on temperature (coldness) and
(iii) the cold start valve. Failure of one knocked the whole system off
line. Your newer, fancy car probably differs somewhat from the 280E
design. The 280E's thermotime relay was the usual culprit in cold start
failure.

Hope this helps you.

Tom

 

Rob. Smith Contact options for registered users 's Avatar posted on
November 12, 2006, 6:35 pm
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Re: Starting problem 89 300SE, symptoms, observations and advice please

Hi Tom

You are correct about the simple elegance of my old 280E with the cold
start cranking enrichment ans stat. This 300SE system is a whole lot
more complex. I will need to do a bit more fault finding around the
system. I guess its easy enough to measure the resistance of the valve
that adds the extra fuel.
A number of the tests require that the engine be cranked. I wonder If
I just disconnect the starter solenoid at the junction box, so that I
can pretend I'm cranking but not actually do it. In this way, I may be
able to hear the valve clicking in and out (or not), and maybe hear if
the fuel pump kicks in (tho this may only happen if it detects tacho
pulses from the CIS-E bit of the system).
Also, the electronic manual is a litle unclear (to a non Merc mechanic
I guess) about the coolant temperature sensor/sensors. It talks about
a sensor, but the schematics show a kind of double sensor, one part
feeds the CIS-E and the other goes to the ignition amp. I guess there
is another sensor still for the temp gauge on the dash. I guess I'll
have a play under the hood. Just need good enough weather and
sufficient permission from wifey. She's got me a list of jobs to do.

Updates when I have em.

Cheers...   Rob.




 

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