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1991 Mercedes 420 SEL
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6 Posts
Discussion Starter · #1 ·
Fuel pressure regulator question guys-- My 91 420 SEL is running like crap, been dumping time and money in it, no luck yet. It runs fine till it wasrms up, then I get no accellerator response. I've already done fuel pump, filter, FPR, ICV, plugs wires. I do smell gas in the engine and have traced it to the fuel pressure regulator. The rubber hose was dry rotted where it entered the regulator. I pulled it out of the regulator and cut off the dry rotted piece and tried to stuff it back in, but it will not stay in. Will this rubber hose go back in once i have pulled it out? I checked prices on the fuel pressure regulator and its way out of my price range, so I'd really like to repair what I have. My beautiful car has been sitting for 6 months, I want to drive it again :crybaby2:
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1989 560SEL, 1988 300SEL, 1979 Toyota Cressida MX32, 2006 F150 Lariat
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1,547 Posts
by pulling that rubber hose from the rear of the fuel pressure regulator, I do believe its now destroyed and will need to be replaced. you can find them on ebay all day long for around $30 to $60 bucks. my bet is going to be on the fuel distributor itself. atleast thats what the problem was with my 560SEL. by the way, what part of Tennessee are you in? I do have a spare fuel pressure regulator and fuel distributor as well. if you are close enough, I might be able to help you out on this.
 

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Premium Member
2012 CL550 4MATIC Coupe - RIP
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10,029 Posts
The line being missing shouldn't effect how the car runs. It's just a vent line. In a pinch you could glue the line onto it with silicone or something.
Incorrect. That line is a vacuum line that actuates the FPR.

I did a whole write up of it HERE.

You can get one off eBay or the JY, just make sure that the rubber hose is good.
 

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1991 Mercedes 420 SEL
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6 Posts
Discussion Starter · #5 ·
wow mclare, that was an excellent write up on how to change the fuel pressure regulator!
speaking from experience, would the fuel pressure regulator cause the car to be unresponsive on accelleration and stall only when it warms up. The unit is clearly damaged since I did pull the hose out of it, but could the problem be deeper than that...... distributor?
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w126
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1,535 Posts
The DPR regulates this pressure based on the engine load. There is a pressure feed on the back that goes into the PCV return hose. This is what regulates the diaphragm and hence the pressure to the FD. You can see the DPR #40 coming out of the 3 O'clock position and then the return line goes into #74 the Fuel Cooler and then to #75 the Fuel Tank! Yes boys and Girls, If MB didn't put in a cooler then hot fuel could go into the tank and explode it and you!
In the K/KE-Jetronic(continuous) system, which the 126 uses, the system fuel pressure is held constant by the pressure regulator. The L-Jetronic(intermittent) pressure regulator does work similar to what you theorized and adjusts fuel rail pressure according to manifold pressure.

The fuel cooler is for vapor locking.
 
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