|02-25-2011, 10:55 AM||#1 (permalink)|
Symptoms 560SEL Fuel Pressure Regulator?
I'm just wondering, what might be some symptoms of a bad fuel pressure reg?
On this 560SEL it has trouble with power while below operating temp and if you stomp on the accelerator, the throttle takes a bit to respond to the demand. However if you accelerate slowly it will climb in rpm fine. Once at 80 and everything warmed up, its fine.
The vent line at the regulator is broken, the nipple is MIA, I can feel a woosh of air coming out the back of the regulator. This makes me think the diaphragm is broken and the unit is not maintaining the needed pressure of 6.5 Bar (I think thats the number)
I dont have any CIS gauges to put on the system so I can't be 100% sure of the pressure. It just seems to want to stall out occasionally. I think this is due to too much fuel, as I recall reading that the FPR is more of a dampener than a "regulator"..
Let me know what you gents think....
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1982 - 300SD 144,000
1982 - 300SD 270,000
1989 - 420SEL 210,900
1989 - 560SEL 115,500
1990 - 300SE 263,000
1990 - 560SEL 156,000
1993 - 190E 3.0 225,000
1993 - 300E 191,000
|02-25-2011, 04:45 PM||#3 (permalink)|
Date registered: Jun 2004
Vehicle: 1987 420SEL
The dampener (accumulator in MB speak) is part of the fuel pump/filter assembly. It cushions the pulsing from the pumps. It also quiets the pump(s) operation to some degree. The diaphragm in the accumulator can rupture. That could conceivably result in a decreased system pressure. That could also cause hard starting after the car sits for some period. It's installed inline between the fuel pump(s) and pressure regulator.
There's a temperature sensor for the CIS system. That functions to enrich the fuel mixture according to the engine temperature. Is the economy gauge indicating anything unusual?
|02-25-2011, 05:01 PM||#4 (permalink)|
The economy gauges goes to 50% sometimes when the engine is just started and not at OP temp, If you leave it idle, it'll walk down to 0 and stall out... once the engine is up at normal temp the gauge runs normal.
|02-25-2011, 06:27 PM||#5 (permalink)|
You can get some idea of what your fuel pressures are doing with the Duty Cycle reading at Idle and at 2500rpm.
Might as well replace that DPR and see how it goes.
Probably get one pretty cheap?
Tom Johnson, Phoenix, Az
1973 240Z (Track only)
1970 240Z (Shell)
2006 Frontier DD
|02-25-2011, 06:50 PM||#7 (permalink)|
TAke a picture of what is broken?
5-15% DC is a sure sign of a problem.
Question is where exactly.
My I wouldn't mess with adjustments until you nail the cause of 5-15%.
|02-25-2011, 07:48 PM||#8 (permalink)|
a picture of the broken piece of the fpr?
on the back of it that is supposed to be a vent tube that gets fed back into the valve cover..thats not the unit from the 560SEL, but it the same...
5-15% might be the result of some adjustments...I remember we adjusted lambda and when the mixture was near the 50s the idle was higher than we liked like 800rpm at idle..or something like that..it was few weeks ago I'm not remembering clearly
|02-25-2011, 09:21 PM||#9 (permalink)|
It is fixed at the MB value or else it is AFU (see threads for High-Idle).
DC needs to be 50% at idle. It is important to make sure you have your DVOM probes correct so that pushing down the airflow plate momentarily enriches mixture and the DC should go Down (Lower %). Right or wrong, that is how I interprete the manual. Its a way to determine we are all using the same reference.
If you show 5-15% (call it 10% Average) you are very rich and the system is doing 90% of its total capacity to keep over-rich mixture in Control (14.7 AFR). When you add throttle the airflow plate causes over-enrichment due to exceeding the control range. Might cause flubbing and hesitation.
If you have your DVOM Probes backwards and in fact you are Super lean and when you tip in throttle the car will fall flat on its face. Aint got no gas.
The CIS-E is a Lambda (14.7) governor and has a limited control range. When I say "Rich" or "lean" but you are still reading some percent DC between 10% and 90% you are still 14.7 AFR but the system is nearly maxed out and any addition increaese or decrease in fuel takes you out of the control range of 14.7 and you will see DC infinitely 0 or 1 out of the range.
I spent a year learning this system by hard knocks and have my hands comfortably around it now. I have 50% average at idle and 35% or so at 2500RPM. THis puts me a shade on the too rich side at Wide Open Throttle by reference to my WB/O2 sensor and dyno runs. Just where I want it.
Hope I can help and return the favor to those that helped me. Its a tricky little system.
|02-27-2011, 12:25 PM||#10 (permalink)|
I'll adjust the lambda so that its near 50% at idle. Any problems in idle, I can assume is being caused by something else?
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