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#1
11-07-2004, 04:05 AM
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Fuel pressure measurement Help W124 260E 1988 M103
I have built myself a device to measure the high and low chamber pressures (see the picture).
Measurements at idle: Upper chamber 5.7 bars; Lower chamber 5 bars; difference 0.7bar. The books difference should be between 0.4b and 0.5 bar. Is 0.7 are too big? Moreover when my engine idles badly, the low pressure oscillates of +-0.2bars around 5bars. When engine is idling smoothly no oscillation. Anybody has any idea on what is wrong? Another question; is there any connections available to measure the pressure on the check valves on the pumps?
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Keep us posted especially if your problem is solved Present cars: My car: E-class 420CDI, 2008, W211, V8, 180 000km Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km Son's one: GLK class, 220CDI, 2009, W204 Sold: E-class 260E, 1988, W124, Wonderfull car sold after 489 000 kilometres of reliable services (engine M103, clutch, brake system and 5 speed manual gear box all original). Sold: E-class, 320CDI, W210, 2000, 225 000km Last edited by cc260E; 11-07-2004 at 04:11 AM. 
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#2
11-07-2004, 10:41 AM
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Yes, .7bar is too much.
This is a very sensitive value. With proper value at .4bar, the normal range of lambda correction between -12ma to +12ma of EHA current will case the differential pressure to range from .3bar to .5bar. I would pull the electrical connector off the EHA when you are getting those large idle swings in pressure. Either that or measure the current. If the pressure is changing with the EHA disconnected, the most likely problem is a restricted internal flow control oriface. This usually means a new fuel distributor.
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Steve Brotherton Continental Imports Gainesville FL Bosch Master, ASE Master, L1 33 years MB technician
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#3
11-07-2004, 11:07 AM
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Thanks stevefbl
for the quick reply. I will measure the pressure with EHA disconnected one of these days and will let you know (now I need the car). What about adjusting EHA, like it is said in the post "adjusting EHA is posisble"? Does this adjustment influence the pressure difference? The car runs great ( no over concumption, no lack of power, no cold nor warm start problem so far...) except that at some erratic times it happen to stall or hesitate). I have changed a lot of things (see other posts I placed). Do you think your suggestion can explain the erratic stalling or hesitations
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Keep us posted especially if your problem is solved Present cars: My car: E-class 420CDI, 2008, W211, V8, 180 000km Wife's one: C-class 220CDI Sport Coupé, Euro, 2002, W203. 345 000km Son's one: GLK class, 220CDI, 2009, W204 Sold: E-class 260E, 1988, W124, Wonderfull car sold after 489 000 kilometres of reliable services (engine M103, clutch, brake system and 5 speed manual gear box all original). Sold: E-class, 320CDI, W210, 2000, 225 000km
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