P300 Multiple Cylinder Misfire 99 E300 - PeachParts Mercedes-Benz Forum

husk · #1 02-10-2008, 09:30 PM

I have been getting an occasional P300 code on my 1999 E300. I clear the code and it does not come back for months at a time. It happens occasionally. Any idea what this could be? Clogged Injectors? Any help would be appreciated. Also if I rev to about 1000 rpm I hear a noise like marbles rolling around, but this noise dissapears when the car has been warmed up. I am not sure if these two problems are related.

Parrot of Doom · #2 02-11-2008, 07:05 AM

I would get the cam chain and tensioner looked at with a noise like that.

wjjeng · #3 02-11-2008, 12:08 PM

fuel filters cured all of my recent ailments including strange noises - may want to consider

_________________
1995 E300 249,000

TMAllison · #4 02-11-2008, 12:37 PM

Wondering if an intermittent CPS losing its reference point while operating would cause the ECU to believe there was a misfire?

husk · #5 02-11-2008, 01:29 PM

When the P0300 code comes on, there is no change in the behavior of the car, no loss of power etc. This one has me baffled, I would take it to the dealer, but I am sure they would rip apart the whole engine and start throwing parts at it. Right now the car does not use any oil, runs strong, etc. The P0300 light really doesnt effect anything but it is kind of concerning to see it light up. You think it could be the CPS?

TMAllison · #6 02-11-2008, 01:46 PM

CPS is a very common fault on gassers; not so on ours. I assume they must also go out on diesels as it is the identical part but have no expirience with the symptoms.

Was just thinking that if the sensor lost its ref the ecu might "think" there was a misfire....I guess in that event the CPS and/or the K40 relay could be at fault.

DieselAddict · #7 02-11-2008, 04:14 PM

Quote:

Originally Posted by husk

I have been getting an occasional P300 code on my 1999 E300. I clear the code and it does not come back for months at a time. It happens occasionally. Any idea what this could be? Clogged Injectors? Any help would be appreciated. Also if I rev to about 1000 rpm I hear a noise like marbles rolling around, but this noise dissapears when the car has been warmed up. I am not sure if these two problems are related.

I don't know about the code, but that marble rolling noise around 1000 RPM is most likely combustion knock and not related to the timing chain. I get it too, especially with a cold engine. It's worse at higher altitude and lower temperatures. The fuel is simply not igniting as soon as it should. These cars really benefit from high-cetane fuel and they were probably designed for it. Try some cetane booster additive or biodiesel.

nhdoc · #8 02-11-2008, 04:28 PM

Knowing what I know about diesels and gassers I wonder what function the CPS does on our car other than supply an RPM signal to the tach and computer. The car really can't detect a misfire like it can on a gasser which has coils. I don't think it has a way to regulate the IP timing.

I'm not even sure if the P0300 code means the same thing on the diesel engine as it does on the gas version since so much of how the engine works is different. I think if it was my car and it didn't have any other symptoms but did this every couple of months I'd just reset it and forget it.

As for your other noise, I can say that my car also makes a bit of a pre-ignition pinging (actually more like a ticking) occaisionally. It is never very loud and only comes under light loading at 1-2K RPM. If I press harder on the pedal it seems to go away or at least get less noticeable. It doesn't do it all the time so again, I have learned to live with it and if and when it gets worse I will have to explore what's causing it.

DieselAddict · #9 02-11-2008, 07:33 PM

There's no such thing as pre-ignition in a diesel engine. In a gas engine that would be fuel igniting before the spark plug fires. The pinging that we're talking about is more of a post-ignition where the fuel ignites too late, resulting in a bigger explosion. I feel these indirect injection engines are really sensitive to fuel quality. I know on B20 my MB runs ultra-smooth, but on unadditized Safeway diesel it runs like crap. The Jetta with its direct injection seems less sensitive to cetane and fuel quality in general, but it still runs noticeably quieter and with less smoke on B20 than regular D2. When using D2 I always add some cetane booster because it helps a lot with combustion noise.

husk · #10 02-11-2008, 08:54 PM

the marbles rolling around noise is more noticeable if I rev up to 1500 rpm and let the throttle go, when the rpm's move down to idle, it starts to make the marble noise at around 1000 rpm. I remember on ebay 2 or 3 years back there was an E300 that had the P0300 Cylinder Misfire problem, and the head was off. I believe the owner was selling it as is back then. I hope I don't suffer the same fate

I will try to run some purge through the injectors, or perhaps change the injectors. Now that I think about it this P0300 engine code started when I ran B99 for a month.

mbdoc · #11 02-12-2008, 08:38 AM

The IFI computer constantly monitors the speed of the flywheel.
If there is any deviation of that speed then the computer will record a misfire.

After 2 consecutive "trips" with that problem the computer will record a misfire code P0 300.

Things that can cause misfires; compression, injector spray, & heat.

If a glow plug isn't warming a cylinder properly then that can cause that code.

If a valve sticks then you get that code.

If any injector doesn't deliver a correct spray pattern you will get that code.

The monitoring time is when the engine is above 20C, engine speed below 1400 RPM, & injection quantity is less than 30mg a stroke.

nhdoc · #12 02-12-2008, 09:40 AM

Quote:

Originally Posted by M.B.DOC

The IFI computer constantly monitors the speed of the flywheel.
If there is any deviation of that speed then the computer will record a misfire.

After 2 consecutive "trips" with that problem the computer will record a misfire code P0 300.

Things that can cause misfires; compression, injector spray, & heat.

If a glow plug isn't warming a cylinder properly then that can cause that code.

If a valve sticks then you get that code.

If any injector doesn't deliver a correct spray pattern you will get that code.

The monitoring time is when the engine is above 20C, engine speed below 1400 RPM, & injection quantity is less than 30mg a stroke.

Thanks for that great information!

hobbitss · #13 05-01-2008, 05:56 PM

Quote:

Originally Posted by M.B.DOC

The IFI computer constantly monitors the speed of the flywheel.
If there is any deviation of that speed then the computer will record a misfire.

After 2 consecutive "trips" with that problem the computer will record a misfire code P0 300.

Things that can cause misfires; compression, injector spray, & heat.

If a glow plug isn't warming a cylinder properly then that can cause that code.

If a valve sticks then you get that code.

If any injector doesn't deliver a correct spray pattern you will get that code.

The monitoring time is when the engine is above 20C, engine speed below 1400 RPM, & injection quantity is less than 30mg a stroke.

Many things to worry about....

Part way to work this afternoon my 98 E300D started to idle roughly at a light... Once on the highway I noticed a lack of power and a slight wiff of diesel, fuel economy reading on my ScanguageII was terrible... Boost and temp were ok but RPMs seemed a little high under load... WOT to get moving in highway traffic created a light smoke and more of the wiff of diesel...
I stopped before getting to work and let her sit for about 15 minutes... When I came back to the car I could smell diesel when I normally can not... She started quickly but still seemed to be missing (rough idle) and a couple of minutes in city traffic produced a P0300 Engine electronics code...
What is the next step?? Traffic is light when I head home but should I get it towed home instead just to be safe??
And is there anything I can check on before turning it over to a Dealer??

TMAllison · #14 05-01-2008, 06:14 PM

If you are smelliing fuel you ought to look for a leak.

Frothy fuel delivered to the inj(s) can cause loss of power, especially under load.

hobbitss · #15 05-01-2008, 07:31 PM

Quote:

Originally Posted by TMAllison

If you are smelliing fuel you ought to look for a leak.

Frothy fuel delivered to the inj(s) can cause loss of power, especially under load.

Funny you should mention that... I had to move the car so I popped the hood and was looking around before it got dark and I saw a leak on the second to last fuel line from the back on the IP... So I grab some metric wrenches to see if I can snug it up, couldn't seem to reach it with the wrench so I stick my hand in and the line pops off of the top... Looks like it had broken clean off...