Jaimemb

I recently change my HPFP to get rid of the limp mode on when one accelerate hard. About two days later i go to turn the car on in the morning and its ruins really rough almost like it wants to stall for about 45 seconds to a minute then levels itself out. Sometimes it'll make the CEL turn on other times not. When it does turn on it'll be the codes for cylinder misfires 1-4 and also random cylinder misfire. I read it could be the fuel injectors but not sure since it was fine before the pump change. thought it could be a vacuum leak but i haven't been able to find any. While driving if the revs are on about 2000 itll start to misfire a bit but wont run on the CEL. Any ideas as to what this might be would be greatly appreciated.

Jp Reyes

Did you ever get the issue fixed? Mine started doing this a few months ago.

chinatownabc

I have same issue as well any updates.

chabbs93

yeah me too lol anyone?

chinatownabc

same issue not solved I brought it back to the dealership and they said they csnt find thre issues causing it

CaliBenzDriver

What is causing rough cold start if the improper LEAN trim mixture forced to your engine by the ECU. What maintenance has been done so far vs. still missing ?

Any fault code current/stored?

How about these items:

• ignition plugs
• timing tensioner
• PCV Crankcase vent
• Oxygen/Lambda upstream sensor

It's easy and cheap to do yourself. After that, the engine will be smooth and strong like new.

chinatownabc

dealership said spark plugs they changed them no change, then they said the injectors are leaking. It's a bit weird because this only happened after the dealership changed the hpfp before that the car never had issues on start up. I do know they had to remove the intake manifold to do the hpfp I'm leaning towards a vacuum leak somewhere.




Message from service advisor indicating which codes were stored.

CaliBenzDriver

Great, I think you have all the clues necessary to rewind that problem back to the HPFP. This is what pressurizes the 3000PSI in the injector rail.

Everything is screaming: not enough gas!
All Cyl. misfire, O2 is extremely LEAN.

Leave the priceless injectors alone.... All cyl. are affected, not only one.

Take your car somewhere else than where this joke is played upon you. Let us know who these poker face jokers are. Now go to a local indy shop !✌️

God knows if the problem is not with the LPFP or filter starving the HPFP. Concentrate on getting a good fuel supply out of HPFP.

🤞

chinatownabc

The dealership i went to was Autobahn Motors in Belmont, they did say it could possible be the LPFP but its weird it would have all of a sudden fail when i brought the car in for the HPFP. This only occurs during cold start up or if you leave the car parked for about 8 hours or so. After the first cold start there is no additional misfire or hesitation during startup.

CaliBenzDriver

Great to hear all this... I went into the Belmont dealership when I was looking at ordering my car. I remember they had a beautiful V12 in the middle of the showroom with a pan full of engine oil under.

It sounds like your gas line is draining back empty into the tank. Once air gets in, it foams up with gas until its all gone.

The HPFP fittings need a perfect seal and have to be replaced each time they are disassembled. (Does your engine smell gas by any chance??)

The LPFP brings up gas volume go HPFP. Check the pressure sensor reads before/after cold starts...

Fuel delivery is where your problem is happening! You can ignore everything else.

chinatownabc

I will check again with the hood open i dont smell gas, i assume that it would be leaking gas constantly if the seal isnt perfect. In the E55 i was able to get fuel pressure in the fuel reading from the fuel rails idk where i can find it on the C250

CaliBenzDriver

use a scanner to read pressures... 21st century style

chinatownabc

When you mean gas line is draining back empty i assume your saying there must be a possible leak in the lines or seals causing air to mix with the gas.

I'll check with a local indy see if they can determine the fuel pressure through a scanner.

CaliBenzDriver

...perfect, this will be the end of your troubles 👍

Your modern direct injected car should get fixed in/out 1 shot instead of this ridiculous game of extortion by the factory trained experts.
They screw things up then never fix it ...

chinatownabc

Basically tell me about it i brought it back twice already and they kept telling me to throw parts at it basically. Telling me its the spark, the injectors, everything but the HPFP install because they say their tech is 100% on the install.

CaliBenzDriver

Yep, tell me about it
LPFP module can be a good trouble maker. Tell your indy to scrutinize it.

chinatownabc

so I was able to get a reading the the fuel pressure seems after shutting of the car the high fuel pressure drops and continues to drop . do you know where I can find high fuel pressure and low fuel pressure readings at idle? Or when the car is off?

CaliBenzDriver

The pressures are hosted in their respective controller :

• High pressure in ECU module
• Low pressure in LPFP module
  

chinatownabc

so I got the fuel pressure readings on the high and low,
high pressure: at idle around 1000psi at 3krpm it was around 1500psi

Low pressure is around 100psi

CaliBenzDriver

LPFP 100Psi: shows its able to supply plenty of volume to camshaft HPFP. No prob.


This points to high-pressure pump being unable to build up pressure. It should be in the ball park of 3000psi and you're only getting 1500 at most.

I am surprised the ECU is not poping a code for pressure low ! That's when you need Xentry tool to read exactly what's going on with the control valve.
You mentioned this part having being changed and that caused all this BS to start happening. Double check ie. re-do the teach-in pump adaptations.

Now you know where this problem is. No additional good parts got changed ✌️

chinatownabc

You still on here my guy?

CaliBenzDriver

The USS Midway now projecting peace

yes, on my way back from San Diego where we saw the Midway aircraft carrier

Have you made some progress ..?

chinatownabc

I had a indy take a look at it same they couldnt figure it out. I did do my sparks and valve covers. Did check that was no oil in the coils. I think ill redo the install of the HPFP. I was also thinking of getting a UV light fuel leak test kit to see if that might be a cause.

calitintz

If you figure out a solution please post.
my car has been at Mercedes for 7 weeks. Master tech and shop foreman has been on it. And they couldn’t figure it out, just got a call today for me to pick up my car, still cold start misfiring

chinatownabc

my car was there also for about 5 weks or so, did this also happen after the hpfp change? Is your car running lean as well?