fuel pressure regulators 1985 380SL - Mercedes-Benz Forum
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post #1 of 11 (permalink) Old 05-15-2019, 11:42 AM Thread Starter
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fuel pressure regulators 1985 380SL

I have been troubleshooting a rough idle and intermittent hesitation when accelerating cold and I discovered fuel leaking out of a fuel pressure regulator, which this car seems to have two of. I don't see anything about these when looking at the Bosch CIS K-jetronic with Lambda information and if i followed the fuel lines correctly it looks like they are both in line with the frequency valve. What is the purpose of these exactly? Obviously I need to replace this regulator that is leaking but I was wondering if someone point me in the direction to some info on this part of the system that would be great. Quite pricey these guys seem to be too. Thanks.
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post #2 of 11 (permalink) Old 05-15-2019, 03:08 PM
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Can you please post pictures of the components in question and where are they leaking? That's worth a thousand words.

If it's the components that I am thinking of near the fuel distributor, those are used to smooth out the pulses that occur in fuel delivery to protect the sensitive components like the WUR and frequency valve. I read that in the FSM somewhere.

In my adventures down memory lane, I don't recall a thread about them leaking ever so this might be a first!
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post #3 of 11 (permalink) Old 05-15-2019, 03:26 PM Thread Starter
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Sure can. The one with the arrow on the drivers side of the fuel distributor is leaking through what would be the vacuum attachment on a normal FPR. It seems on this system its not regulated by vacuum and it is just a vent. Both of the regulators seem to vent into the breather hose on the passenger's side. The second is behind the fuel distributor.

I'm curious what kind of effect this could have on the performance. I'm sure it is where my gas smell is coming from. I discovered raw fuel in the breather tube when I took my air filter off.
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post #4 of 11 (permalink) Old 05-15-2019, 04:42 PM
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I could be wrong but I don't believe either of the things you circled in your pictures are fuel pressure regulators. If I remember correctly the fuel pressure regulator lives inside the FD in the outbound leg of the fuels journey back to the tank.

Look for a large nut on the drivers side rear (closest to the firewall) back of the FD. That nut holds the spring and spacers used to adjust the fuel pressure. I'll try to modify one of your pictures and point to the nut I'm talking about.

OK... I modified one of your pictures. If I am remembering correctly, the red arrow is pointing to the nut that holds the fuel pressure regulator mechanism inside the Fuel Distributor.

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post #5 of 11 (permalink) Old 05-15-2019, 09:36 PM
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This may have to do with what year.

Early CIS had the nut in the back that you would change washers to adjust fuel pressure and Jyuma pointed out. Later for all 86+ M117's had the pressure regulator that looks like what is shown in the first or second picture. I don't know when the change occurred but as far as I know the 560SL only has one.
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post #6 of 11 (permalink) Old 05-16-2019, 01:25 AM
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Quote:
Originally Posted by roncallo View Post
This may have to do with what year.

Early CIS had the nut in the back that you would change washers to adjust fuel pressure and Jyuma pointed out. Later for all 86+ M117's had the pressure regulator that looks like what is shown in the first or second picture. I don't know when the change occurred but as far as I know the 560SL only has one.
The OP lists an '85 380 as one of his cars and he also mentioned the frequency valve in the description of his problem. Again, if my memory serves (the older I get the less reliable my memory becomes) the frequency valve was only used on the 380 in '83, '84' and '85. That's what made me guess it was an M116 engine with the fuel pressure regulator internal to the FD.

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post #7 of 11 (permalink) Old 05-16-2019, 06:34 AM
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The frequency valve is on 450SL and 380SL with O2 sensor. It is part of the lambda control. Those diaphragms are called pressure regulators in the EPC.
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post #8 of 11 (permalink) Old 05-16-2019, 11:58 AM
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Quote:
Originally Posted by benzrider85 View Post
Sure can. The one with the arrow on the drivers side of the fuel distributor is leaking through what would be the vacuum attachment on a normal FPR. It seems on this system its not regulated by vacuum and it is just a vent. Both of the regulators seem to vent into the breather hose on the passenger's side. The second is behind the fuel distributor.

I'm curious what kind of effect this could have on the performance. I'm sure it is where my gas smell is coming from. I discovered raw fuel in the breather tube when I took my air filter off.
Thanks for this picture.

Those were exactly what I was thinking about. They're called fuel pressure dampers and are used to smooth out the pulses in the fuel system when you change throttle position. Think water hammer or in this cause gas hammer. They're similar in function to the fuel accumulator "aka reservoir" under the rear of the car.

The vacuum hoses you see are used as a safety precaution for when they leak. Allowing the fuel to be safely sucked away into the intake system to be burned instead of destroying your car. On older KJet vehicles, that wasn't there and it was later added. I could have sworn I read this somewhere in the FSM, but I can't find it.

The function of these devices is explained on page 20:
https://www.startekinfo.com/StarTek/...8/07.3-001.pdf

The forum messed up my pictures. The bottom image is the pressure dampener that OP and myself have. The top picture is the updated "tecalan element" that deletes the regulator. No doubt, it just looks like a fat hose.

In this case, it seems there is an updated hose that deletes the pressure dampener which is what I would recommend you replace the leaking element with.

@rowdie , does the EPC show the updated part number for this? Should just be a really long hose that deletes it out.
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post #9 of 11 (permalink) Old 05-17-2019, 04:54 PM Thread Starter
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Quote:
Originally Posted by okyoureabeast View Post
Thanks for this picture.

Those were exactly what I was thinking about. They're called fuel pressure dampers and are used to smooth out the pulses in the fuel system when you change throttle position. Think water hammer or in this cause gas hammer. They're similar in function to the fuel accumulator "aka reservoir" under the rear of the car.

The vacuum hoses you see are used as a safety precaution for when they leak. Allowing the fuel to be safely sucked away into the intake system to be burned instead of destroying your car. On older KJet vehicles, that wasn't there and it was later added. I could have sworn I read this somewhere in the FSM, but I can't find it.

The function of these devices is explained on page 20:
https://www.startekinfo.com/StarTek/...8/07.3-001.pdf

The forum messed up my pictures. The bottom image is the pressure dampener that OP and myself have. The top picture is the updated "tecalan element" that deletes the regulator. No doubt, it just looks like a fat hose.

In this case, it seems there is an updated hose that deletes the pressure dampener which is what I would recommend you replace the leaking element with.

@rowdie , does the EPC show the updated part number for this? Should just be a really long hose that deletes it out.
Thanks for the help and input. This dampener is between the warm up regulator and the fuel distributor. It looks like I have the updated version here as I do not have a dampener here. I do, however have the two in line with the frequency valve. These are shown on page 8, number 7 I believe, but they don't really talk about them in this document I don't think.


Quote:
Originally Posted by rowdie View Post
The frequency valve is on 450SL and 380SL with O2 sensor. It is part of the lambda control. Those diaphragms are called pressure regulators in the EPC.
Thanks rowdie. Any chance you have a part number on these from the EPC? (I miss when the EPC was free...) Any idea where to source one? It looks like they might be hard to get. Pelicanparts says the MB part is unavailable.
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post #10 of 11 (permalink) Old 05-17-2019, 05:22 PM
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I gave up the paid subscription when they went to the new format which sucks. I use these two free sites now. https://nemigaparts.com/cat_spares/epc/mercedes/ which is like the new EPC format and https://mercedes.7zap.com/en/eu/fg/car/

I tried the DVD sets from EBay that are supposed to have the EPC old version that runs on a Virtual Machine. Could not get it to work on three different PCs.
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