M104 cold-start problem back!
Ugh.
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# > 000.090.03.10 , $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 > smell to your nose, DO NOT PLACE YOUR NOSE AT THE SOURCE AND SNIFF > (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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