144,000 Miles
Only engine code: P0300
Been in the freakin shop for 6 months guys

Work Performed by Mechanics
Initial Visit (Check Engine Light On, Cylinder Misfires Detected):
Performed an electronic diagnostic test and found fault codes for misfires in cylinders 2 and 3.
Conducted an engine compression test:
Found no loss of compression initially (compression was deemed good at this point).
Conducted an ignition test:
Found high resistance in the ignition coils for cylinders 2 and 3.
Replaced:
All spark plugs (due to wear).
Ignition coils for cylinders 2 and 3.
Cleared all fault codes.

The car ran perfectly for 5 days with no issues. I felt a slight shake day 3 but thought nothing of it as I figured I was just paranoid.

Second Visit (After Misfire Reoccurred with Blinking Check Engine Light):
Detected a strong gasoline smell and noted the misfire had worsened.
Replaced the fuel injector for cylinder 2, suspecting it was the cause of the misfire.
Re-tested cylinder compression:
Cylinder 2 compression remained within normal limits.
Checked ECU and wiring harness for oil and none was found.

This car has been looked at by two mechanics and I have spoken to a dozen other mechanics over the phone. Everyone has their 2 sense and I'm not sure what to do. Nobody can clearly tell me why it's misfiring rather just give hints at why it could be. I keep getting told they would have to tear my engine apart to figure the issue out. I keep asking the mechanics to double check the fuel system as when the car had a misfire the first time it did not smell like gas. The second time around IT REALLY SMELLED LIKE GAS!!! I mean the inside of the car reeks of gas every time I fire it up as well as the bottom middle of the car. I have mentioned this multiple time to the mechanics and they all just assume its deeper than that yet have not checked my fuel delivery system! The last thing is that the second mechanics said the first mechanic left a lot of loose parts by cylinder 3 which is by the firewall they claim. That's a red flag to me and they also said my air intake gaskets were destroyed! Oh, and the first mechanic said he did check fuel pressure for cylinder 2 and it was normal, yet the second mechanics said he was wrong and that the actual cylinder misfiring is cylinder 1! What the heck! Which one is it bc nobody seems to know.

Thoughts???
If you would like to put your 2 sense into this thread please do!! For reference I am not a mechanic and just a guy trying to get his beloved Mercedes running! Thank you!!!

 

Now now, just light up a smoke and ponder this one for a bit. Could be your High Pressure Fuel Pump and or corrosion in the lines from the tank. If I am not mistaken the filter is part of the pump assembly (and can be purchased in the second markets). Have y'all checked the fuel pumps and filters?

 

I, too, am leaning toward the fuel pump or fuel filter. They are located under the rear seat, so if there is a leak, you would smell it strongly in the "bottom middle of the car". I believe your car has a saddle tank that goes over the drive shaft. The pump is in one side and the filter is in the other side. If there is a leak in the fuel line (maybe due to corrosion) and air gets in, it will cause fueling problems. I recently watched a YouTube video where the fuel delivery was blocked by a clogged filter and caused all sorts of phantom issued. There are folks with an E-Class like yours that can probably offer more informed help.

 

Just not in the car!

 

@2012E can you provide your VIN or at least the full model designation? Should be something like 212.XXX.

 

Here are pictures to give you an idea.

 

 

I replaced both in-tank modules recently:

https://mbworld.org/forums/e-class-w...l-modules.html

I had a code for low pressure fuel system pressure implausible and one of the modules was leaking fuel. I would suspect that if you had a low pressure fuel line pressure problem, you would also have this code, but it's probably worth checking if one or both of these is leaking. I would replace them both at the same time if anything is off.

 

Random misfires, one injector, couple coils, plugs, no boots and 6 Mo in the shop for an increasing amount of new issues...

I don't see that getting better even knowing what may be wrong with it.
No1 issue is careless "parts-canon": change one part and screw up another. Paying to get things made worse.
You have the wrong shop involved here.

You mention that fuel used fine and now it's just a giant leak...

Your car needs maintenance parts before repairs. If not there you are with compounded issues and everything is out of control after repeated attempts.


Here is what should help :
-- everything that was tempered with need to be made right again then P0300 can be sorted out

-- check Hi/Lo sides fuel pressure
-- complete ignition part tune-up
-- scan whole chassis not just ECU
-- Read fuel trims

Don't replace any more good parts. Instead replace known bad maintenance parts, including tank filter and assiciated leaking O-Rings.

Everything must be working right else gremlins are self-feeding.

+++ How this got here... is help to climb out !!

1. Extra poor ignition
2. leaned out fuel map
3. forced misfires

> We recognize that scheme from ALT-LIN experiment: Same one!
Here we have the seasoned version of lag: "active CEL for random misfire faults"

 

Here is the VIN: WDDHF5KBXCA653579

 

@CaliBenzDriver
Thank you! I haven't spent more than $600 on parts as both shops put new parts in without charging me. All I have spent money on so far is Plugs, coils, and spark plugs granted the first shop refunded all the labor. I agree, wrong shops as they both chalk it up to mechanical without verifying.

 

@JettaRed thank you!!

 

@2012E any updates/progress?

 

So it is the Direct Injection engine with High Pressure fuel pump(s). My V8 has two of them, one for each bank. I don’t know if V6 has one or two of these pumps.

Check the cam shaft that runs the pump. You might have worn lobe on the shaft that does not give full stroke for the pump.

It could also be the pump lifter issue. It could wear between pump and the lifter not allowing full stroke for the pump but thus would cause issues for more than just one cylinder.

What tells about fuel pressure is that if the pressure is low the injector does not atomize the fuel correctly meaning all fuel may not burn, which also explains the misfire and fuel smell.

I would check the HP fuel pump and lifter next. Lifter and pump change is not that big of a job, at least not in my V8 it isn’t.

Also, if you can have fuel pressure measured after HP pump it might show the low pressure peak if that indeed is the issue.

 

@ChuangTzu Yes! I took it to a third shop and they are in the process of diagnosing it. They think it is related to the fuel pump like everyone there is saying and should get back to me in the next few days. I am hopeful because the first thing they did was tear my rear seat off.

I will keep everyone posted and appreciate the input tremendously!

 

Soooo the third mechanic thinks it's a valve timing issue. Any thoughts?

 

Don't ask us... ASK WHOM YOU'RE PAYING WHY is that else free if not repaired, right?

WHAT TROUBLESHOOTING STEP LEADS TO THIS DIAGNOSIS.

VVT gear is a usual repair for DIFFERENT ISSUES.