bmoores

Took the car into the dealer this a.m. with a check engine light and they called saying that the codes were indicating a fluctuation between rich and lean fueling conditions. They've quoted $25XX to replace the fuel pumps. Anyone ever had this issue?

TIA.

Ben.

mellowyellow

What are the symptoms besides your CEL being lit? Problems starting? Inconsistent throttle?

Never heard of this being a known issue.

I am pretty sure the fuel pump is inside the tank, so it's probably a lot of labor cost. But $2500 sounds like a special dealer markup price for the Black Series.

I would invest in a ODBII code reader (since it sounds like you may not own one now), pull the codes yourself, and do some searching on mbworld for some common remedies.

jrcart

Fuel pump is $565, $2000 in labor sounds steep lol.

Get a second opinion, they are attempting a mass rape on you.

bmoores

Ironically, there are zero symptoms otherwise. No problems with start or throttle application. I did pull the codes and I don't have them in front of me. It was all fuel mix related. Intermittent rich/lean condition. No misfires. Definitely bizarre.

That was my feeling as well. The dealer is owned by a family friend so I've asked to go on a drive with the tech at lunch with a fuel pressure gauge on the car so we can see whether or not the pumps are really the issue. I've already been assured that if they replace the pumps and the problem isn't resolved it will be done at no cost. Apparently the tech is adamant that isn't the case ..... Will update this afternoon.

RBYCC

Unless there is something special about the BS fuel supply system, a pump doesn't intermittently affect AFR's...

If a fuel pump or fuel pressure regulator is not providing correct volume under pressure you'll notice a running problem and only at higher RPM it may lean due to inadequate supply...

I would guess that "intermittent rich/lean condition" would be more in the O2 sensor-ECU loop or a vacuum leak ?

I would think an old fashion volume and pressure test should be done to ascertain if the pump and or FPR is within spec....

Moedy

Some members with non bs clk's were quoted around the same price so it's not bs rape it's just stealer rape. They went out completely though

jrcart

Just a thought. These motors are known to be plauged by excessive oil blowby. Open up your airboxes and check to see if the filters are saturated in oil. If oil managed to get past the filters it has probably built up on your MAFs. It does not take much to hinder the reading of air flow through the MAF. If the MAF is reading improper airflow it will deliver the wrong amount of fuel and will result in a rich or lean A/F.

.....other than that I am at a loss, good luck.

primecut

Hi guys, sorry to bring a super old thread from the dead, but I got the P0191 code recently and brought it into the dealer. They are recommending to replace the fuel pump for around the same cost (At least price hasn't gone up since 2013 )

Anyway, my issue sounds the same as OP... no misfire, no hesitation, no limp mode... basically car drives perfect except for the light that comes on intermittently. It seems to me that it's a drastic fix since I don't get the sense the pump is failing at all...Any thoughts or insights would be appreciated.

I did a search on m156 p0191 and found a couple of threads where people replaced either the PCV Valve/Breather hose or purge valve. Not sure if I should push the dealer for additional diagnosis before we go down the fuel pump route.

qjumpr

Primecut,

I had that same code, car ran great though and the dealership I purchased it from had already replace the PCV set up and a bunch of other items before I took delivery.

After many hours of research I just decided to pull the fuel filter set up. It ended up being the pipe that ran from the fuel pumps to the filter, it looked like there was sludge on the inside of the pipe, possibly causing the fuel pressure code P0191.

I changed it out with a new fuel filter and never had the code come back. The fuel pressure at the rail was within range on normal driving, so it must have the most sensitive sensors.

The PCV should make a high pitched whine if its going bad.

primecut

Really appreciate the reply qjumpr! Just to clarify, when you said you pulled the fuel filter setup and it was the pipe, did you end up only cleaning the pipe and replacing the filter, but not the pump? Could I theoretically ask the dealer to pull the assembly without replacing the pump and diagnose the issue at the source? That does require me to trust their judgment though...

qjumpr

I replaced the fuel filter set up, but not the pump. The pump was fine, the filter part had the build up.

qjumpr

Here is the new filter set up with the clean white lines running to it and the old one with the orange build up. The new part cost me $449 from MB Parts Online, which is the part dept at MB Atlanta I think, so they are great to work with and its a MB tagged part.

Hope this helps.

Doctodd33

wonder if this is related to ethanol? Similar problems on boats with old fuel tanks and lines, but boats have an open fuel vent which attracts air and humidity. Only other similarity i can think of is that the gasoline in a boat isnt used as often as a BS unless it is a daily driver. Gas in a boat can sit for weeks/months if not used alot.

MOFLO

Speaking of ethanol and if there was an E85 tune for the BS, wonder if that would cause a premature failure of the filter or pump like above? Thoughts?

qjumpr

In my case the car had 62k miles at the time, so it was due for a change, but I was expecting to see the filter itself blocked, but the filter looked fine when I opened it up.

I do feel though that sometimes the quality of fuel really effects the performance in a M156 engine. Depending on other factors like age of car/miles etc.

Doctodd33

Ethanol eats plastic up more than gasoline. Those plastic fuel lines give me pause.

MOFLO

Appears the whole unit, filter and pump case, are plastic. If E85 is used, we would need a metal equivalent or something made from the proper plastic resin code (1-7). Wonder if the performance gains (higher octane) would make this worth pursuing or not....???

qjumpr

I think that the cost involved in changing parts to make it a E85 wouldn't be worth it. Better off spending the money on or towards other options.

Lets face it, if you are going E85 you are doing headers/exhaust/tune/etc etc anyway. How much added HP would E85 give you over a regular fuel tune once all those parts are installed.

Doctodd33

Avoid ethanol. Rec fuel.

MOFLO

Good points and I concur!

primecut

Thanks for all the info and input guys!

FYI - I was told by multiple people that MB updated the entire unit with a new version, probably in response to the failure rates. Any replacement will be with this new part. It's supposedly stronger and more reliable. So hopefully this is a good investment.

It does make me wonder if there was a recall for this at some point... if not then MB got away with this one.

andyy

Thank you for your helpful information!

I had on and off P0191 problem too, had absolutely no symptoms other than the annoying engine light on the dashboard. Had PCV and breath tube changed but didn't help, the problem was solved only after I changed a new fuel filter just as you did!

primecut

Just to update everyone, I got a 2nd opinion and ended up replacing the fuel pump altogether, and the problem has gone away. The car is running stronger than before so I wonder if the intermittent failure did have some effect (Or maybe it's all in my head). Anyway, problem solved!

Andyy - Glad to hear that you were able to just change the filter, I was told that some owners did the same and the light came back on, and ended up having to replace the pump at the end. Hopefully yours fare better! Good luck.

ml63amg_simon

Me too i have that problem with my ml63 AMG 2007

I have a ml63 AMG 2007
I have THE same problem 3699 p0191.

If i drive my car THE first 15 minuten i have full power , and than THE car goes slowly.
Parking THE car for 1 a 2 hours than i have 15 minutes full power.

I have replaced:
Fullpomp
Fullfilter
Fullmodule
Full sensor

No results..

Please help me

primecut

^ That sounds like a different issue than I had, even though your car is throwing the same code. I never experienced limp mode in my car. Did you do fuel pump replacement yourself? If not you should take it back to the mechanic as I assume they were the ones that suggested this as the fix...