Hi,
I have a ML320 2000 with 165K miles. Code reader shows P0303, misfire in cylinder 3. After visiting a Mercedes Benz dealership, they told me I needed a new fuel pump, MAF, ignition coils and spark plugs with new wires! I declined the service because of the cost and the dealer's uncertainty that this would fix the problem.
I installed a new fuel pump (fuel lines were replaced @ 50K, spark plugs were replaced at 100K), all new spark plug wires, and 2 new plugs on cyl. 3 with a new ignition coil. It is still sputtering and eventually it chokes. I ordered an OEM MB MAF, coming in on Monday. If that doesn't solve the mystery, what is left to do?
Any advice will be considered and greatly appreciated.
Thanks in advance, John.

Possibly the injector is not working properly for that piston position? Otherwise, what you have replaced sounds very good basically and certainly won't hurt if you are keeping the car.

__________________
Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)

I suggest that you start with a basics..does that & all cylinders have correct compression.?

If so then swapping that coil & wires to a GOOD running cylinder would be a test of that part.

Even swapping spark plugs from that cylinder to another is a possibility..new parts can be defective.

Making sure that that cylinder doesn't have a vacuum leak..

Re-initialization of the crank sensor will rectify MANY running problems on the M112/113 engines on most 1998 & later cars.

A lean mixture can affect 1 cylinder ONLY if the that cylinder is already running lean or poorly..

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

My 98 ml320 got the same problems .
Code shows P0303, misfire in cylinder 3 also # 2 ,#1 .
Got all new spark plug and fuel pump but still run poor and Code shows up all 3 misfire (check engine light).

Please Help....

Thanks

I sure would like to read some success stories.

steve

__________________
Steve Danville
what i did myself.
CPS
rear shocks
MAS x 3.
SparkPlugs (twice)
Fuel pump & Filter
Window switch
replaced both failed horns with Honda horns.
Cleaned ERG Tube
Oil changes
Oil consumption Fix
Brake Pads
A/C Recharge
Anti-Freeze change X 2.
Front Shocks. Monroe. $90
Mercedes Warrenty Work:
Harmonic balancer,power steering clamp. Cat converters.Drive Shaft Bearing.s
Replaced Outer Lower Tie Rods and front lower ball joints at 156,000 miles

how is this done? thanks

Re-initialization of the crank sensor
Youre a Doctor- it would be nice to write that in laymens terms so poor red neck slobs like me understand it.

I replaced my crankshaft position sensor. Is that what re-initialzation is ?

steve

PS I am at the Mercedes Benz internet cafe---waiting for my new cats on my ML320. Hoping this will cure my poor idiling, missfireing, weak power at times and one stall. Yes I replaces my Mass air flow sensor last week. (and plugs after only 5,000 miles in a vein attempt to cure).

__________________
Steve Danville
what i did myself.
CPS
rear shocks
MAS x 3.
SparkPlugs (twice)
Fuel pump & Filter
Window switch
replaced both failed horns with Honda horns.
Cleaned ERG Tube
Oil changes
Oil consumption Fix
Brake Pads
A/C Recharge
Anti-Freeze change X 2.
Front Shocks. Monroe. $90
Mercedes Warrenty Work:
Harmonic balancer,power steering clamp. Cat converters.Drive Shaft Bearing.s
Replaced Outer Lower Tie Rods and front lower ball joints at 156,000 miles

did you get your ml working if so wot was the fault in the end thanks
i have the same problem

Hello. I have my engin light on and the code reads p303 misfire cylander 3. I replaced the coil and spark plugs and the the fuel injector, but, no luck.Any other advise?

Replacing the MAF cured my 2000 ML430 with similar symptoms.

Cheers,

Eddie

Yes, 99% of the time a "misfire" code means bad MAF sensor.

Think of it this way ... it misfired because it got a bad mixture, not necessarily because of poor spark.]

MAF sensors on these engines are notoriously unreliable and the ignition system isn't.

__________________
Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

I went through 3 MAF sensors before my problem was fixed. eBay parts didn't work on our '99 ML320.