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Did you also change the filter? It includes the regulator I believe on that setup.
It's very possible you have a weak check valve/regulator, and the new pump is strong enough to overcome it but not going to reach the right pressure. Does your pressure hold with the engine off?
Im fairly certain there is a regulator in the other side from the pump, i'd replace that unit as well if you are only seeing 35psi running at the rail. I don't have WIS access anymore to be of further help unfortunately.
Im fairly certain there is a regulator in the other side from the pump, i'd replace that unit as well if you are only seeing 35psi running at the rail. I don't have WIS access anymore to be of further help unfortunately.
Thanks I ordered both. I went with MB Brand parts instead of rockauto parts this time. Just waiting for them to show up.
I just took a reading from my '08 GL450 while it was running. I'm getting a consistent 57psi. (FWIW- my fuel pump was replaced at around 150k mi. Did not replace the other side filter/sender etc)
The 35psi sounds too low.
Last edited by justin3219; Jul 16, 2021 at 05:02 PM.
I replaced the pump. I am wondering if something is goofy with my gauge at this point. I was seeing 20psi with the tank on ground. I replaced the pump and it jumped to 45psi. I bought an ultrapower pump from rockauto and it looks like it was junk. I looked at it more closely and certainly is a difference between pumps and filter.
I replaced the pump. I am wondering if something is goofy with my gauge at this point. I was seeing 20psi with the tank on ground. I replaced the pump and it jumped to 45psi. I bought an ultrapower pump from rockauto and it looks like it was junk. I looked at it more closely and certainly is a difference between pumps and filter.
I'm sorry I don't understand the above post.
Are you saying that you now have 45psi on the fuel rail?
Also, yes there definitely IS a difference between the fuel pump which is on the passenger side under the 2nd row seats, and the filter/sender unit which is under the 2nd row seat on the driver side.
BTW-Not sure if this helps, but the pump that you see in the pic above providing 57psi was purchased on Amazon. It's not a Genuine Mercedes unit. I think it was the cheapest generic one I saw at the time. Cost roughly $65+S&H as I recall.
Last edited by justin3219; Jul 18, 2021 at 06:33 PM.
I am seeing 45 psi at the rail after putting in the pump. The sending unit certainly looks like it has a fuel pressure regulator in it.
The first one was an $82 one from Rockauto. I bought cheap fuel sender from Amazon for $55. I bought MB branded ones the first time, but didn't put in the fuel sender when I saw the pressure go up a ton with just putting in the pump. I hope I don't have to drop the tank again to put in the MB fuel sender.
45psi still sounds a bit low. Hows the car performing?
I'm sure you don't want to replace that filter/sender unit but it sounds like you might need to. FWIW-I accessed my Fuel Pump thru the interior. It was a PITA too. Not sure which would be worse, dropping the tank or going thru the top. Sorry!
I have not driven it yet. I have to put the exhaust back in. My 2012 doesn't have the access covers on the floor. Drop the exhaust and driveshaft to lower the tank.
Well, everything it back together and it is really great. I put about 100 miles on it yesterday. I have not checked the FP since I lifted the tank back into place.
It is not the most enjoyable job, but with a quick jack and a pair of 5-gallon buckets for holding things, it was not bad.
I believe the ones that don't have the bolt on plates, you can still cut the sealant and remove the plate and change them from the inside. The design is similar, just glued on with seam sealer rather than bolt in pieces.
I believe the ones that don't have the bolt on plates, you can still cut the sealant and remove the plate and change them from the inside. The design is similar, just glued on with seam sealer rather than bolt in pieces.
It didn't look that way to me looking at it from top and bottom.
This seems like a great situation to learn from on the models where the tank has to be dropped: Change BOTH at the same time. (While you’re there…)
Glad to hear it sounds like your problem is resolved!
Yes, change both. I would also say use parts from a trusted OEM company as if the one you put in is bad it will lead to a large amount of frustration.
To avoid that I would also recommend getting a fuel pressure reading before putting the exhaust/driveshaft back in. It sounds pretty mean without the exhaust
on it.
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