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Discussion Starter · #1 ·
I have a strange problem which i hope someone may be able to shed some light on.
I have a 2001 320 manual gearbox, which when driving normally runs fine.
By normal I mean acceleration is gradual changing gears when revs not too high.
But if a put my right foot to the floor, when the rev's get to around 5 -6k the engine starts to misfire, the CEL comes on and the engine then runs lumpy.
The ODB11 tester I have reads P0300 multiple cylinder misfire on cylinders 6, 5, 4, 2.
I can reset and all is well until my right foot gets heavy again.
The plugs were changed in Aug 2013 prior to me buying the car, but the plugs are Bosch Super Plus FR8DPP33+, when I look on the bosch website and put my car details in the recommended plugs are either double platinum or iridium plugs.
Could the plugs be incorrect, and breaking down under load?
Because this only happens under high load I suspect it could be a nightmare to find the fault without spending a fortune.
Is it a common problem, I know it is when just driving, but mine is when im thrashing it.
Has anyone had the same problem and found the cure?
Thanks in advance.
 

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Other possibilities - Dirty Fuel filter. Weak fuel pump leading to low fuel pressure under high loads. Dirty injectors unable to deliver sufficient fuel under heavy loads. Wrong octane fuel.

If it was my car, I would run a bottle of Chevron Techron Clean-Up through the car and buy a tank of the best quality high octane gas I could find and see if anything changed.

Ed
 

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Don't rule out plug leads if they are still originals. Mine was a specific code to cylinder 3 which would sometimes cause the CEL light to come on when giving it some stick.
I would clear the code and everything was ok until the next time.
Traced it down to a plug lead on cylinder 3 so I replace both. It's been fine ever since.
 

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Discussion Starter · #7 ·
Thanks to all who have so far contributed, I know it could be one of several problems.
But if I start replacing plugs, leads / wires, coil packs, fuel filters, fuel pump, injectors, its going to cost me an arm and a leg. and even then it may not fix the problem.
I have now pulled all the info from the ODB2 but unsure what it all means.....see below.was hoping a few tech guys my be able to enlighten me a bit more ON THE READOUT.
DTC FRZF = P0300
FUEL SYS 1 = OL DRIVE
FUEL SYS 2 = OL DRIVE
LOAD PCT % = 71.8
ETC (F) =176
SHRT FT 1 (%) = 0.0
LONG FT 1 (%) = 1.6
SHRT FT 2 (%) = 0.0
LONG FT 2 (%) = -5.5
MAP (INHG) = 27.5
RPM (/MIN) = 4875
VSS (MPH) = 86
 

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Can't help with the above but there are things you could do to reduce the unknowns, swap coil pack 2 with 1 and see if the misfire moves, if it does chances are it's the coil pack, if it remains on 2 then possibly plugs or injectors, swap the plugs from one you know is firing OK and try again see if the misfire moves if the misfire stays then it's a fuel or timing problem. If you are having a lot of misfires and unburnt fuel going to the exhaust the CEL light would come on due to the increased hydrocarbons, if there is no CEL then the misfire could be due to lack of fuel IE injectors blocked or partially blocked.

I put some Bosch plugs in my wife's Ford Fiesta and they started to misfire within a month replaced them with NGKs and have had no further problems.

I also had a misfire on my 320 after I had booted it to pass a tractor on a windy country road, put a bottle of Techron in and had no further problems.
I would try the elimination process first and identify what is working and not before buying everything.

Regards Stuart.
 

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Discussion Starter · #9 ·
Hi Stuart and thanks
Sounds like a plan, CEL is coming on, so I now have a starting point.
I am away for a week from the 5th, but will keep a record of what i do, and the results if any as I go along.
 

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Discussion Starter · #13 ·
Back from a week in the sun so I have had a bit of time to do a few checks.
One thing I must mention plugs are bosch fitted August 2015 I have removed and inspected all 12 and they are a nice chocolate colour so no fouling and not running rich or weak, so for now im thinking these will be ok.
I bought a new coil pack and after a quick blast and engine light on, so out with the code reader, still multiple cyl misfires including the new one.
I have tested all of the plugs and leads for spak at tickover and all is good.
Just cleaned the MAF, I read on the forum that someone cleaned the the MAF but it made no difference so he disconected the battery for half hour and the car then ran perfect so thats where we are now, I will take it out as soon as rush hour traffic is over, and report back.
 

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2005 SLK55 AMG /2005 SLK350
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It's darned hard to find this kind of issue without a lot of practical experience with your engine, which I don't have.

How up-to-date is your car on its maintenance? Are you the meticulous proactive type, or the "let it go until it definitely needs it" type? If the latter, this might be a good opportunity to get caught up. Especially on the fuel and air filters.

The fact it's misfiring on all cylinders suggests a problem with fuel/air charge, not with spark.

It's noteworthy that one bank has such different LT fuel trim from the other. That suggests an issue with intake air leaking on one side. I would start by carefully listening to your running engine with a hose to my ear - concentrate around your intake manifold and listening for differences left vs. right side. Anything that sounds like hissing is suspect.

It could be so many other things though...
 

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Discussion Starter · #16 ·
Hi Efair
I only bought the car last September and its not my everyday vehicle so not been used very much over winter.
Yes I am up on maintenance, I’m an engineer by trade and up to 2 years ago work with spanners. Im now office based but still work on my Lambretta, vespa, VW transporter & now the SLK.
For me the SLK is still a learning process, and I work on preventative maintenance at all times.
You mention the LT fuel trim….where do I find what the codes mean and what they should be.
For instance what is Fuel sys 1 = OL drive????
DTC FRZF = P0300
FUEL SYS 1 = OL DRIVE
FUEL SYS 2 = OL DRIVE
LOAD PCT % = 71.8
ETC ( =176
SHRT FT 1 (%) = 0.0
LONG FT 1 (%) = 1.6
SHRT FT 2 (%) = 0.0
LONG FT 2 (%) = -5.5
MAP (INHG) = 27.5
RPM (/MIN) = 4875
VSS (MPH) = 86

This is the kind of info I cannot seem to find.
Could you point me in the right direction please.
 
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