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Car Forum / Mercedes-Benz Cars / December 2006fuel pressure
i tested the fuel pressure at the fuel regulator and can only get a reading of 30 to 32 lbs no matter where i turn the screw. i guess this means the regulator is bad? can low fuel pressure cause flooding? What year? 450sl skrev: > i tested the fuel pressure at the fuel regulator and can only get a reading > of 30 to 32 lbs no matter where i turn the screw. i guess this means the > regulator is bad? can low fuel pressure cause flooding? 1973. my book says the pressure should be at about 74-78lbs That is right. If your fuel distributor. is original, then you need to replace your fuel filter first. Then I would replace your fuel pressure regulator. I am not sure on yours... on my old 380SE I had a needle on back of my fuel distributor... that has a big nut... whole needle unit comes out and has washers... these washers dictate the pressure level... but if yours is original, don't change the amount of washers... clean them out and replace. It is possible you need to have the fuel distributor rebuilt. I didnt realize that electronic fuel injected had a fuel distributor. Where is it located? >I didnt realize that electronic fuel injected had a fuel distributor. Where >is it located? well, I'm guessing you're referring to the EHA (Electro Hydraulic Actuator) which is a little black box mounted onto and behind the intake. The EHA regulates fuel pressure and therefore amount cheers I believe the EHA didn't come until mid 80'ies (the "E" models), making the fuel injection "electronic". Before it was just "direct fuel injection" (in contrary to carburator). So, to 450sl: The fuel pressure regulator provides a constant pressure input to the fuel distributor. The fuel distributor then provides a pressure proportional to the air mass and distributes this pressure equally to all injectors. Apparently the primary pressure is too low in your case. The cause could be: - fuel filter clogging the fuel passage - the fuel pressure regulator regulating to a wrong pressure - the fuel pumps not being able to provide enough pressure Since the fuel pressure is only half of the required, It could very well be one of the fuel pumps defective. Guenter Scholz skrev: > >I didnt realize that electronic fuel injected had a fuel distributor. Where > >is it located? [quoted text clipped - 4 lines] > > cheers I tested the fuell pressure before the pressure regulator and it is 0 should there be any pressure from the fuel pump? Its about 32 after the regulator. All plugs are fouling with black, so its definately over fueling. That fuel pressure is too low... I'd suspect fuel distributor is bad and leaking internally. 450sl schrieb: > I tested the fuell pressure before the pressure regulator and it is 0 > should there be any pressure from the fuel pump? Its about 32 after the > regulator. All plugs are fouling with black, so its definately over > fueling. I think, you measured the back flood hose. The fuel pump makes a current in a closed loop through the regulator back into the tank. Check the pressure regulator unit. Perhaps the little o-gasket is squeezed. If so, replace the unit completely.  SignatureRoland Franzius Yes, the fuel pressuere works, so that it relieves the pressure, which exceeds the threshold of the regulator, into the fuel return line. In this way, the fuel pressure before the regulator is kept at the desired pressure. So, the pressure of 32 is meassured at the input of the regulator and 0 is at the output. The pressure is too low, and the reasons can be: - the fuel pressure regulator opens at a too low pressure - the fuel pump cannot deliver enough pressure - the fuel distributor can have an internal leak (as Tiger says) The fouling of the plugs could indicate an internal leak, but it would have to be rather heavy, if the pumps cannot keep up the pressure. And I believe you would see something more than just fouling of the plugs with the amount of fuel that would be leaking. Tiger, do you have any exerience with that? Roland Franzius skrev: > 450sl schrieb: > > I tested the fuell pressure before the pressure regulator and it is 0 [quoted text clipped - 7 lines] > Check the pressure regulator unit. Perhaps the little o-gasket is > squeezed. If so, replace the unit completely. Yeah... one of my fuel distributor develeped that problem... old age. On my car it did it on one cylinder before I swapped it out. It fouled the plug and engine ran rough. More testing is required before pinning it on the fuel distributor. However, Bosch repair center can test the fuel distributor to tell you if it is a problem. At this age of the vehicle, anything can happen. The fact that he said "all" of his plugs are fouled... I am just not sure... I think it is best to let an experienced MB technician do the diagnostic test before replacing any parts. One more thing guys. I checked the pressure between the fuel pump and filter it is at about 38lbs. What should it be? Im wondering if the check valve is bad? There is always alot of pressure in the tank? Do you think the pump is weak? Still cant get more than 40lbs after the pressure regulator. Does the regulator increase or lower the pressure? Thanks again Fuel prssure out of the pump should be much higher... the regulator simply regulate the pressure lower to desired level... the fuel distributor is also supposed to regulate the pressure into the distributor. Last I recall, it should be around like 75 PSI or something like that... Check manual for actual specification. Thanks again, I was hoping it wasnt the pump, but it sounds like thats the problem. The book says 78 to 83 psi. Or it could be the regulator. Try to block the line to the fuel filter and measure the output pressure of the fuel pumps, to see if they can build up enough pressure (they have an internal bypass valve to limit the maximum pressure, so no harm will result from this). If the pumps build up the pressure OK, I would then first of all suspect the regulator. 450sl skrev: > Thanks again, I was hoping it wasnt the pump, but it sounds like thats the > problem. The book says 78 to 83 psi. 450sl schrieb: > Thanks again, I was hoping it wasnt the pump, but it sounds like thats the > problem. The book says 78 to 83 psi. Thats correct. Measure pressure with blocked hose. This will give you the maximum pump pressure. Measure the pump voltage. Could be the fuel pump relay eating some Volts. In the Bosch mechanic jetronic the pressure is adjusted by the number of levelling discs that pre-span the spring in the regulator unit. Common problem is cutting the o-gasket of the regulator during mount. The fuel will bypass the pressure regulator. Buy a new reulator unit - its cheap - and you will understand the mechanism. It comes with a high number of polished leveling discs in different thickness. The regulator is behind the big single screw at the top side of the distributor. SignatureRoland Franzius i checked the pressure , pinch the hose, the pump build up pressure very quickly, so ill try replacing the pressure regulator, and hope thats it. Fuel distributor is located under the air filter housing. |
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