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Old 08-02-2004, 11:41 AM
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Join Date: Apr 1999
Posts: 2,633
Exclamation M104 cold-start problem back!


Cold-start problem is back.

What would be the next steps ?

I'm thinking check fuel-pressure at fuel-rail at start-up, and leak-down over 8-hours.

Check fuel-pressure regulator.

Anything else ?

:-( neil
1988 E36T AMG
1993 500E

NEV wrote:

> Update:
> Checked all the sensors and the vacuum lines: all passed within spec.
> I decided to check the fuel accummulator (adjacent to fuel filter on
> W124) by plugging the rubber fuel-house and disconnecting it from the
> accummulator and draining out all the existing gasoline from the
> accummulator.
> Then I started the car, and found the accummlator leaking (e.g., not
> holding pressure).
> Now I could do two things:
> 1) replace the accummulator ($70);
> 2) by-pass the accummulator (wagon specific pn# 124.470.48.64 $15), like later year cars (1993+) with HFM/LH (my 1988 W124 wagon has an HFM C36 M104 engine in it)
> Since the accummulator is only needed with the CIS injected cars, I
> decided to by-pass the accummulator by installing the bypass-pipe, new
> copper crush-washers, and plugging the rubber fuel-line. I also
> replaced the fuel-filter (use 002.477.4401 for tandem pumps; greater volume; and dampening effect) and the fuel-pump check-valves (pn#
> , $12/each)
> BTW: here's a tip diagnosing hard-starts on HFM and LH cars assuming
> fuel-pumps are working:
> 1) hard "cold" starts with long cranks: check accummulator;
> 2) hard "warm/hot" starts: pull vaccuum line from fuel-pressure regulator and "sniff"/check for gasoline
> note: you "sniff" by waving you hand over the "source" and waving the
> (Chemistry 101).
> neil
> 1988 E36T AMG
> 1993 500E
> Stu Ritter wrote:
>> That took a bit of research.
>> The cold start system in the HFM system is the same as the LH system and
>> the
>> reference manual is the W140 intro.
>> Cold start additional fuel is supplied only by the normal injectors
>> being held
>> open for a longer period.
>> The sensors for cold start include
>> The engine coolant temperature sensor
>> Camshaft rpm from the cam position sensor
>> intake manifold vacuum from the EZL/AKR ignition control unit
>> and, last but not least,
>> the length of time the engine has been turned off.
>> Basic fuel quantity is determined by the air mass sensor and the
>> engine rpm.
>> after start enrichment is controlled via
>> coolant temp while cranking and gear selector lever position
>> warm up enrichment is
>> coolant engine temp at start up
>> intake air temp
>> engine speed and load
>> idle and partial load conditions
>> that's it.
>> Stu
>>> I'm experiencing cold start problems (1995 C36 M104 HFM), that is, the
>>> car doesn't start at the first crank as it normally does after sitting
>>> for more than 4 + hours/overnight.
>>> The ambient temperature is about 85-F.
>>> At the second crank, the engine catches at a low and rough 500 RPM
>>> (normal is about 900 RPM).
>>> If I give it some gas, black smoke comes out of the exhaust, however,
>>> the idle smooths out and returns to the normal 900 RPM idle speed.
>>> This does not happen after a "hot" or "warm" start.
>>> Is there a "cold start" valve/injector on the M104 HFM engines ? Could
>>> a vaccuum or air leak do the same ?
>>> FWIW, it just happenned one day.
>>> Regadless, what's the proper diagnostic procedure ?
>>> Thanks in advance,
>>> neil

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