I am trying to understand this fuel system on the SRT6 / AMG cars.

The fuel pressure regulator is integrated into the fuel filter. I understand that. I even understand the "returnless fuel rail" and that it reduces evaporative emissions by not returning heated fuel to the tank. I don't like it, but; ok.

I do not understand why the fuel filter/regulator has a hose going from what appears to be the regulator diaphragm to the charcoal canister. It is not a boost/vacuum referenced fuel pressure regulator, right? Does anyone have data logs of fuel pressure? Is it constant relative to atmospheric pressure? The fuel pressure seems to be constant, regardless of boost or vacuum in the intake manifold. So why the hose connection? Does the ECU selectively use vacuum/boost to adjust the fuel pressure for emissions?

 

The vent is to adjust the pressure to the atmospheric pressure. It should be about 60 psig. I used the VENT to feed in boost pressure to see if I could prevent high boost leaning. BOY DID THAT RICHEN THE FUEL CURVE> I now use that port with a regulator to add one psi boost to the fuel curve when my engine goes over 10 psig. at 15 psig boost my rail is now at 65 psi. This change prevented my leaning at high boost numbers, and Rob incorperated it into a kit for boost modulation of the rail pressure.

Single feed rail is fine with me as the pressure is more than equal front to back, only one injector is taking a few cc's of fuel per pulse at a time. Probably less than a cc typically, by a long shot.

Enjoy, Woody

I did have 80 psi at the rail at 20 psig boost for a test and was BELOW 9:1 air to fuel ratio - Woof

 

I think the reason is because the pressure is controlled by the spring rate, so the outer side of the diaphragm has to be at atmospheric pressure, any other pressure that side of the diaphragm would alter the fuel pressure relative to the atmospheric pressure. As there is fuel in the area the air, has to go through the filter, which is at atmospheric pressure, to lessen possible pollution by fuel fumes.
These fumes are sucked into the engine at times, how and when I do not know.

 

They are sucked into the supercharger snout via the purge valve. Located by the abs unit.

 

have you had a look at section 14 of the SRT6 manual?

 

from the internet - reportedly WIS SLK32....;>)

 

Billy, (or is it Bob?) I actually did look at section 14 of the manual. I almost forgot about it though. The line "degas to carbon canister" is the one I am talking about.

I am glad we all agree that the fuel pressure is atmosphere referenced only. That keeps it simple. The line to the charcoal canister seems unnecessary though. The regulator port could just be open to the atmosphere, but it's not, it connects to the charcoal canister. I removed and reinstalled this hose with the engine running and it did not affect fuel pressure at all. I also tried the same test when the engine was warmed up and the EVAP solenoid was pulsing pulling vapors from the charcoal canister, again, no affect.

I am thinking that maybe the connection on the charcoal canister is providing a port of atmospheric-pressure, filtered air for the regulator. To keep dirt from accumulating inside the regulator.

So the question is: if you are running an aftermarket fuel pressure regulator, what to do with the port on the charcoal canister? Plug it? Leave it open? Run a vacuum from it to the aftermarket FPR?

 

Plug it at the canister.

 

So looking back at your original post...
Some meanderings/observations/thoughts.....
Note - my fuel cap always seems to have a a slight positive pressure 0.5psi(?) when I go to fill up.
Anything over this and I guess the vent valve (76) opens to the canister - I'm presuming.

The canister would vent to atmosphere - eg: when you are stopped and filling your tank....about 1.5L/sec?
I'm not sure if AC (Activated carbon) extracts fuel - it must do...otherwise the vapours would be very strong - and dangerous.
Somehow this AC has to discard this buildup, I presume through fresh air into the AC when the engine is running and the -ve side of the manifold (pre SC) is open (purge control valve Y58/1).
The tank needs to suck air in also as you use fuel (max 0.05L/sec) or the tank cools down (possibly similar volume expansion/contraction rate of 0.05L/sec here). So the tank vent valve would have something like ....
+0.5psi = expell
-0.5psi = suck - it cant suck unless it is -ve (or it is pumped in - which it isnt).

The purge valve would have some sort of differential pressure setup...probably of a mechanical form - others may be able to add something here. eg: does it have wires attached?
when the manifold prs is -ve it opens and allows the canister to suck atmospheric*
when the manifold prs is 0 (stationary) the valve is closed and the canister would vent to atmosphere - eg: when filling the tank.
If its not an electrical setup - this would be the case all the time - if it has some sort of timer on it (electrical) then maybe it would other ECU ties.

I've been meaning to put some more thought into this, but have been a little busy with a home made OBDII logger setup I'm working on. So just some thoughts put out there for discussion.

* would this add to our "going lean" issues if we are pulling above stock cfms and our vacuum ex throttle is greater? - I dont think it would be a significant volume compared to 600cfm.

 

The purge valve (Y58/1) is a solenoid valve. When the engine is warmed up and the ECU feels like it, the purge valve pulses open and allows engine vacuum to draw fuel vapors into the intake from the charcoal canister. It is in the engine bay on the left-front shock tower (looking forward). You can feel it pulsing when it is operating. I think the majority of the air drawn in must be coming from the incoming air shown entering the charcoal canister on the drawing.

I think you are right about the vent valve (76) opening to allow fuel vapors to pass through and be trapped in the charcoal canister when refueling. It may be a one way valve because I believe the gas cap opens under slight vacuum and allows air to enter the tank as fuel is consumed.

 

I'm not sure on this - I thought it was a positive pressure??, but negative soundz safer - will check when next I'm in town.

b22b

 

The tank uses has a slightly lower pressure than the ambient pressure to keep all the vapors contained inside it and the charcoal canister There is one report here some years ago of something going wrong which caused such a low pressure in the gas tank that it was flattened by the atmospheric pressure. The person wondered why his gas tank took so little fuel.
Collapsed tank. (click)

 

Tunaglove wins all the bonus points.

I tried driving around with the charcoal canister line unplugged. I got a check engine light and a P0455 code: "EVAP system large leak".

Yes, I checked my gas cap, and it was on securely.

 

funny I always read it like..."fishy glove" or ...."tongue of love"....rather than "ton of glove".....
which is it buddy....
all of the above?...
;>)

 

Tuna Glove.
I'd post the lyrics but they would never fly here. LOl!

 

I understand this is an old thread, but the closest one to address my issue, and with the right guys it would seem. So before reading Tuna's advise "plug it at the canister", I had the vent tube connected to the vent port on my AEM FPR. The AEM diaphragm leaked and pumped fuel through this line because when I removed it, it sprayed pressurized fuel back out. Because of the diaphragm failure it leaked by full fuel pump pressure(E55 pump). My question is: Will the EVAP system eventually take care of all the fuel pumped into the canister, and is this an unsafe situation where I need to take the canister out and drain it?

 

Not knowing any better, and with the canister located that close to the exhaust pipe, along with not knowing what effect raw gasoline would have on the charcoal itself, I'd say replace the canister.
My 2 cents, for what it's worth.

 

I was afraid that was the response I would get, but thank you for your honest(and safe) response. Cost to replace the activated carbon canister could be rather high I would imagine. Anybody have any idea what the cost could be, let alone the actual availability of this canister? TIA

 

The canister normally traps fumes which are vented through the engine, if it is filled with liquid gasoline then I can imagine it taking forever to empty. I would replace it. There must be lots lying around in scrap yards.

 

Are you certain that the regulator is the source of the leak?