Repair-It

A combination of reading the forum (never read a forum without your tinfoil hat, every problem under the sun will be there and make you paranoid), and an occasionally unsmooth cold start idle and some also occasional hot idle in gear instability. Very slight instability really.

But evidently this damper is a wear item on these cars. So I bought one from FCP Euro so at least it has a lifetime warranty.

Being a returnless system with the regulator in the tank (no different than my STS), but being a much higher output engine than my STS, fuel rail pressure can vary with injector pulses. The job of the damper is to stabilize rail pressure so that injector pulses don't cause the pressure to fluctuate. Fuel pressure itself is a sensitive subject for these cars, with some extreme cases of fuel pressure issues (usually from failing pumps, a clogged in-tank filter or melted wires/relays/fuses), they can actually toast the #8 cylinder due to a lean condition. I don't want that and even though the damper can't really change average pressure, pressure instability doesn't seem like a good idea.

I've also seen people say these can cause fuel smell when the diaphragm fails but not always.

What I should do is throw my gauge on it and see if I can find any fluctuations under any conditions just for the record. I will probably replace anyway. Not too bad but have to pull the throttle body (which is in the rear). Supposed to be a pretty easy job and is definitely in the German car category of "why is this considered a maintenance item?" In any event, the damper, TB gasket and intake O-ring was only $78.70. That's pretty modest. So I will get to this at some point. Just want everything operating the way it is supposed to.

I went out late morning with the plan of washing the car. Then I was like....or I could install this fuel pressure damper. Might be more fun anyway.

Didn't take too long. Not sure it even took an hour.

First I wanted to check fuel pressure, just to see what the pressure was but more importantly if it was fluctuating which is what the damper is there to prevent.

77 psi. Man that is a lot of fuel pressure. For performance? This is a returnless system and I believe fuel pressure is constant so it has to counteract the intake manifold pressure under full boost. But rather than vacuum reference they just run this max pressure all the time, I guess. I don't even know how much boost this thing runs.
It was fluctuating a little but then as the idle dropped (cold start) it seemed to get worse. So I decided to go ahead with the job. I figured if it was super stable I'd save the part and check again after some miles. But the needle was bouncing around maybe +/- 5 psi at times (like quickly, at the rate of injector pulses) which doesn't seem normal.

First remove the air intake plumbing. One surprising thing is on this car you can remove the entire air intake from the snorkel that goes to the front all the way to the boot that goes onto the TB without a single tool. Yes, even at the TB there is no clamp. It just sort of slides on and has a bit of a clip.
Remove 4 T-30 bolts that secure the TB to the supercharger. The TB just comes off. Pull the blow off valve plumbing out of the bottom of the TB and then I just flopped it up out of the way. No need to unplug. You can't unplug at the TB; it's permanent. You'd have to unplug the other end.
Pull spring retainer that holds the damper. Takes a little fiddling. I ended up using some pliers. Then just twist and the damper comes out of the rail.
Installation is just....push it in and work it to get the O-ring to seat. The I used vice grips to slide the clip into place. This is the only thing holding the damper in and keeping fuel from gushing into the engine bay.
Clean off gasket surfaces on the TB and supercharger. I took my time and scraped and wiped and blew off with air. I also cleaned out the TB but I had previously done that when I installed my new intake air temp sensor so it didn't have much gunk in it.

I also primed the system to check for leaks since you can't see the damper with the TB installed. No leaks. Side note, when I initially hooked up the gauge, the rail pressure was zero. I feel like it is supposed to hold pressure but, meh. Probably due for some fuel pumps but not worrying about that now.

The rest of it is just the reverse of removal.

Tested pressure after. Still 77 psi (of course) and seemed pretty stable. Just a very small amount of needle wiggling. Not even 1 psi worth. Fixed!

I will monitor idle stability and other things but I did go on a short drive and everything seemed good.
After I first got the TB installed and torqued (10 Nm), I started it to make sure everything was good and it was.

2 weeks later, BAM: Herpes.

So I got my first check engine light. Very exciting. Only took 3.5 months.

I had a P0505 as the generic code and some indecipherable Mercedes code as the manufacturer-specific code (that showed up 3 times for some reason). Of course, the scan tool said I can reset and ignore (as the final option) so I just did that. I guess this means the idle was wrong basically and it seems like that would be most likely from a vacuum leak. Of course only 2 weeks ago I pulled my TB so maybe I screwed something up? Like I said I just reset it. Drove to work and home. No issues, no pending codes. In fact it idles between 2-3% throttle which according to a forum thread, is normal. So....fixed forever, and if it happens again, I'll pull the air intake and check out my work for any obvious issues (like hoses popped off).

https://forums.mbclub.co.uk/threads/55k ... iy.239905/

https://mbworld.org/forums/w211-amg/760 ... -data.html

Fixed!

after a a few shops and a professional smoke test there was a leak coming from the supercharger gasket (SC had to be fully removed)

throttle position at idle is over 2% and 3% in park now. No noise, drives great!

Mine is in the 2-3% range now so again...it's fine? Not sure why the code popped on. Not going to worry about it until it comes back.

Code came back. I reset it. It also appeared as a P20A2.
I guess I can check the hose described in the first two posts.
https://www.benzworld.org/threads/idle- ... e.2384817/

The hose in the third post is connected unlike that guy's.

I found the hose. Looks like an evap line. I say that because it runs to what looks like a purge solenoid and also the evap canister...

There was a zip tie where the hose meets the metal line so someone had been here before. But I was able to pull on it and move it on the line so it wasn't very tight. Probably installed in Georgia. It's cold here now. The end at the TB already had a hose clamp. The end near the elbow doesn't look like it needs to be clamped so I left it for now.

Cut off the ziptie and installed one of those premium fuel injection hose clamps.

Purge solenoid elbow.
Zip tie....I cut it off.
Hose clamp at the TB. Left it alone. It felt tight.
Pulled hose off. Looks fine?
I used the 12mm clamp (the 11-13).
From this kit (used on my STS trans cooler lines)
If I'm lucky this is all it was. Took 15 mins taking pictures. It seems to have caused this issue on other E55s. But honestly...that would have been an incredibly small vacuum leak. This is speed density. Leave it to the Germans to be like "zer iz unawzarized air into zee engine."

I probably can't call this fixed until another ~3 months pass so I'll revisit this thread.

Nope.

The freeze frame is odd. 450 rpm. That's not too high, that's too low....god the information on this stuff is so shitty and I have the FSM. Give me an old school GM flow chart and theory of operation, PLEASE.

I can't tell if this is a vacuum leak or if something else is up. Maybe....my TB is bad?? Who the hell knows what this is. I reset it again.

https://mbworld.org/forums/w211-amg/519 ... t-wtf.html

This time (after 2 other tries) I did this..
1) key off and un-plug TB connection
2) Turn key on and leave on for several minutes.
3) Turn key off,plug TB back in.
4) push pedal down once an the turn key on pos 2
5) with key on, push pedal down once and then wait 2 minutes for TPS to re-set .
6) turn key off and then start car and look at your 3.2% TPS in drive!

Some kind of TB reset procedure....

Also the conditions for malfunction seem to be when the engine is colder. There is definitely some rough idling when cold which I see as somewhat of a common issue. I guess something is leaking somewhere but the thing is this engine is speed density. It shouldn't act like it has a MAF and is getting unmetered air. But that's kind of how it acts.

Didn't this all start after I did the fuel rail damper, which required R&R of the throttle body?? Maybe I should just pull that back off, inspect and try another new gasket?? I was meticulous when I did it the first time though so it's frustrating. I could also smoke test it but I need to figure out the best place to stick the smoke.

The good news is I'll be driving this more regularly finally so I will get to observe operation and see just how often it throws a P0505. The forum also says the issue arises more under idle and return to idle conditions, like a stop and go slog. Maybe it's a TB issue? It's almost as if it cracks the TB more when cold and as it warms and whatever is leaking seals, the amount it needs to close is more than it should be so it throws the code, but that is a guess on my part. I'll work my way through it I think. There are definitely a few common vacuum leak areas on this engine and some leaks require removal of the supercharger.

I wonder if this was not caused by R&Ring the TB. Maybe by late Sept it had gotten cold enough for the intermittent vacuum leak to open up. That is interesting. I don't think the PO drove it much at all in colder weather either. And before him, it never saw cold weather. So this could be a very old problem. All I'm saying is maybe it has nothing to do with this repair.

So this does correlate.
A couple days prior to that post it hit a low of 44F and the next day the low was 45F. Before that it hadn't been cooler than low 50s. I mean it at least makes me feel better. Like I said I was meticulous about the TB thing. I could try smoke or like the carb spray method. Of course as it warms this may sort of hide again and will both make me not care and also make it hard to diagnose. Fixed until next fall?