Todd Nielsen

Ok first off thanks for reading this. I’m trying to fix issue myself due to taking care of father who is terminally sick (no income).

Car has 80K on it, the other day I had a HUGE serge, not just a loss of acceleration but more like slamming on the brakes, then 1 sec later back to full power. Run the basic diagnostic check and get engine codes of P0304 & P0128.

Next day no codes, try driving again and I have heavy surging/stuttering above 2000 RPMs, notice engine light is back on, so pull codes again. Now I had 3 codes: 1/3 P0304, 2/3 P0128 and 3/3 P0304 P.

I swap plug with #2 and coil pack with #4, start car and no engine lights on again and start a drive around my house. The car feels better, it’s not surging as much, and it seems like the more I drive the better it is getting. After about 10 minutes the check engine light pops back on, start heading back to my house and a block from my house I have Heavy surging now at all RPMs. Pull the code and back down to one: P0304 P.

first what’s the different between p0304 & p0304p? And yes I’m sure of the code with a p attached.

due to swapping plug and coil with different cylinders and issue stays with #4 I’m eliminating plug/coil for now.

ive has suggests of MAP sensor, MAF sensor, speed sensor, vacuum leak, ground wire, etc.
Does anyone have a clue of what’s going on? And again no income so I’m limited, but been working on cars my whole life so I can fix it, just need help with locating the issue. Thanks in advance.

pmercury

iTrader: (2)

Faulty spark plug 4
Clogged or faulty fuel injector 4
Faulty ignition coil 4
Fuel injector 4 harness is open or shorted
Fuel injector 4 circuit poor electrical connection
Ignition coil 4 harness is open or shorted
Ignition coil 4 circuit poor electrical connection Insufficient
cylinder 4 compression Incorrect fuel pressure Intake air leak

Todd Nielsen

Not sure about plug or coil due to swapping to other cylinders and problem stayed on #4. Leaning towards clogged injector due to yesterday morning the car ran fine for 1hr, then started having acceleration issues again. Thinking about trying to get it into a shop to diagnose the problem, then fix it myself if possible and if not, who knows.

Rf12790

Any luck with this? I’m having a similar issue with my c250. The engine “stutters” when hard accelerating getting on a freeway or passing someone on the freeway.

Todd Nielsen

yea it was the high pressure fuel pump, it’s the secondary fuel pump on the back side of the motor. Parts cost about $700 from MB and a few hours to install.

Jms1

Hey Todd. How did you come to the high pressure pump?

Todd Nielsen

come to know it was the High Pressure Fuel Pump? I just did a lot of research. It’s easy to know when it’s going out, it literally stops the motor for a split second. When accelerating, well it’s not like you just back off the gas & the car coasts....... it’s more like your under full acceleration & your brakes lock up. It actually toss’ you out of your seat. Imagine you control the acceleration, and all the braking for your car is done by the passenger. Then while your accelerating your passenger stands on the brakes.

it seems like both Mercs & BMW’s suffer from this. They aren’t hard to swap out if you know how to work on cars.... just more annoying to remove everything else to get to it.