Hey guys I did all my coils and plugs due to a Coil 1 fault. Simultaneously had aP0087 – Fuel Rail/System Pressure Too Low
fault, this makes the car rough idle or stall.

so I suspect fuel filter but I guess it could be a multitude of items. I have done some research but it’s a little confusing, is there no fuel filter in the engine bay only one with the sending unit? That’s what FCP said. Also, if it’s by the tank/in the tank is there anything accessible from under the rear seat or do I have to drop the tank?

thanks in advance and any drawings, videos, etc gladly accepted.

 

According to the WIS instruction I found, the filter is in the tank. Replacement requires draining and dropping the tank to get access to it.

 

Got it thanks. How do I get access to these WIS instructions? Is there a download link?

thanks@John Ha

 

Just in case you don't know, "WIS" is Workshop Information System and it nominally provides system information and maintenance/repair procedures for a lot of different Daimler vehicles, including the W166. It's normally included as a part of a Star system. Most anything you get will be bootleg unless you want to pay Mercedes for using it.

I bought mine on line in USB form long ago. I don't think the entity that I bought from (this was 5 or more years ago) is in the business any longer but there are other sources.

I'd check the Marketplace forum here first but there are other sources available outside of this community as well. You'll want to ask the seller whether your vehicle is covered in their software, since the older versions may not have the information applicable to your year and model. Also be sure that you get all the passwords for the different applications if you buy a used system, and that all the software works properly (allows printing, etc.)

There are versions on eBay that run using a virtual Windows application. My experience with those is that they are painfully slow and don't always work properly, so I'd tend to avoid those and try for something that will run as a standalone application on your Windows PC (which is what my USB-based product does after installing it)

Another alternative is to join BenzNinja. You'll have to buy the C4, laptop and the hard drive in addition to the membership, but if you want help with changing features or possibly troubleshooting an issue, it may be a good deal. The hard drive includes WIS, Xentry and a host of other useful software.

 

Just a thought from far left field - how old is the main battery (it's under the right front seat)? If it's the original it's probably a bit flakey. Flakey main batteries are known to cause all sorts of weird things. Might be worthwhile checking at least - it's a lot easier than dropping the fuel tank. :-)

Also, have you checked the fuel lines from the tank to the engine and on the engine? Maybe there's something visible that would be limiting the fuel flow - kinked line, ...

 

@John Ha Thanks for the info and suggestions.

updates: I got the reading from an advanced OBD reader, it had other underlying codes that pointed a potential bad MAP or Fuel pressure sensor. When I started investigating/confirming their location I swapped the MAP and because I had already replaced Intake Manifold gaskets I made sure the torque was set on the manifold bolts. Since then, I have not had any more issues. I still have a CE light despite removing the negative on the battery so I may need to clear CE with an OBD scanner.

I’m still not sure I actually fixed this, I have a HPFP and a Fuel Pressure Sensor available but I feel like the issue is on the low pressure side.

I’ll update as soon as I clear the CE light

 

To add to this, I had an issue on my flex fuel gle350 which was throwing misfire codes for cylinder 4 and 6 and low fuel pressure codes for that associated bank. My issue in the end was fixed with cylinder 4 and 6 injector replacement. In the beginning I was looking to blame the low pressure fuel pump and fuel filter in the tank as well but they are running fine.