Slight Miss on W202 (2000) C240

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Pendragon

Active Member
Joined
Apr 6, 2012
Messages
258
Location
Cardiff
Car
2000 Mercedes C240 Elegance (W202) with Multipoint Romano LPG Injection System
First of all let me say Hello from cold Cardiff and thanks for having me and apologies if this has been brought up before somewhere else on the forum.

Back in January I bought my Mercedes Elegance C240 (W202) on a "W" Reg (2000). I then had a Romano multi-injection LPG system put on it. Ran fine for a few weeks and then on idle I started to get a vibration/missing and a lag when pulling off and driving away although if I hit the throttle it will fly. It has 139k on the clock and has full Mercedes service history bang up to date. I have also given it a service for peace of mind including a good engine flush. Engine is silent.

Anyway, it was very noticeable. Sometimes I could turn the engine off and restart it and she would be fine for a short while but then it would start again.So I changed the leads, plugs, coil packs and Mass Airflow Meter but still it persisted.

Now I have diagnostic equipment but none of it will read this model so I took it to another diagnostics garage that had a Launch X431 and it came back with the following codes:
P0300b....Misfire Damages TWC
P0306b....."".....Cylinder 6
P0150 93/3.....02 sensor left
P0130 ............02 sensor Right
P0205 ..Injector Valve Cylinder 5
P0204 ..Injector Valve Cylinder 4
P0305b..Misfire Damages TWC
P0304b..Misfire Damages TWC

I then replaced both 02 sensors with new ones from Euro Parts in Cardiff and it seemed to run better although the problem still evidend....just not as much.

Took it to the Autogas fitters who adjusted the LPG mix as they said it was running a little lean and it drove all day like a new car until the next morning. Not as bad now but still missing especially between 900 & 1000 revs.
Took it back for another diagnostic but for some reason their Launch would not connect with it again.

I have ordered a laptop with a Mercedes multiplexer so that I can do this myself and use on other pre 2001 C Class Mercedes.

Has anyone got any ideas on this? someone said that I need to clear the existing codes in the ECU as it will still assume there is a problem. Disconnected battery over night but still the same.

Sorry for the long winded post but better to tell everything at once than bit by bit.

Grateful for any help from those who know.

Keith
 
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A code P0305 may mean that one or more of the following has happened:

Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

The advice I looked up says to try and reset the code logged and then see if the fault arises again. Others would probably point you in a better and more accurate direction but it seems that the issue lies with fuelling based on your info about the LPG conversion.
 
Thanks for the reply. I can discount the plugs,coil packs, leads and the 02 sensors as I renewed the lot. So, can a previously stored code cause the problem and if codes are cleared then it should be alright....possibly?

Compression is good and I know the Cat is fine.

By the way it makes no difference whether its on petrol or LPG. We shut the LPG down totally on the computer but still had the problem.

My Mercedes diagnostics equipment will not be here until the end of next week so cannot clear codes until then.
Will disconnecting the battery over night do this? tried it on another car without any success but not sure if that applies to all cars?

Keith
 
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Cheers for that Graeme, No, I used Bosch plugs supplied by Euro Car Parts which they said were for my car.

Keith
 
Cheers for that Graeme, No, I used Bosch plugs supplied by Euro Car Parts which they said were for my car.

Keith

First thing I would try then is to reduce the gap a little on the standard plugs [ SEE THE LINK POSTED ] and see how you get on.
 
Will give that a shot on Sunday since I am away tomorrow shooting a wedding.

What about the point of clearing stored codes? do you have any knowledge about this ?

Appreciate the help...thanks

Keith
 
I will have the equipment to do it at the end of the week if they send it out n Tuesday as promised.

Keith
 
I have bought it as I do car diagnostics as a side line business but not at dealer level so this will be a asset as there are lots of C Class owners with the same 38 pin under the bonnet port and who cannot get a diagnosis without paying the a lot of money. I charge very little but I get a lot of trade to read and clear fault codes and turn off dash lights. Annoying really as I can connect to virtually any car except the C Class prior to 2001 lol
 
Not sure this is anything to do with what's happening or not but doesn't seem right to me.

Just checked the oil cap and it has a greyish/brown grunge on it. So checked the dip and wiped it on some kitchen roll and that looks brown and a little runny. Now I only did a complete service 6 weeks ago.

Help, input, advice !

See pix below.
 
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Took it on a run of around 10 miles this morning. It started fine without the vibration but when I got to a T junction and was waiting to pull out the vibration was back but still only slight. What I forgot to mention, which may be important is that where the digital trip is on the dash I have a oil can symbol coming up with a "Hi" sign that is flashing at me in place of the miles I am driving and periodically I get a beep. Now it may be that when I did the service too much oil was put in it as the reading is over the max level but cannot remember if it was like that after it was done.

Sorry for being a pain in the backside but this is not my "thing" at all :cool: so the advice so far from you all is very much appreciated and being acted upon.

Keith
 
Difficult to say at a distance and for most folks LPG " normal running characteristics" are a bit of a grey area. First thing is to check your oil level when cold with a dipstick. As usual my advice is to aim for a level halfway between min and max to allow for some expansion of the oil unless the car is routinely burning large quantities of oil. I don't like the colour of the oil but that may be due to the engine oil flush you used. Worst case scenario is a cylinder head gasket failure brought on by "hot running" due to the LPG conversion but let's not go there just yet! Have you any indication the cooling system is pressurising when hot? You could also try the coolant headspace "sniffer test" with an exhaust gas analyser to check for the presence of combustion gases in the coolant? Checking the plugs when you regap them may also give some clues - sadly 12 to check/regap but maybe start with the cylinders that showed up on your fault codes?
 
Tomorrow I will be replacing the injectors that are showing up on the diagnostics test.
Will also be doing another compression test tomorrow before I replace them. I was wondering if the oil colour was due to the engine flush I used so after the compression test I will drain the oil out and replace it.
Still not sure about the "Hi" sign coming up though.
Temp gauge runs consistently at 80 and not getting hot.
Do not have a sniffer so that will be the last thing for me to try if all else fails as it will mean a garage job.

Totally dismayed by it all at the moment lol


Keith
 
I would have said the same thing as grober with regards to the head gasket failure, but without further exact diagnosis (with an indicator you could use already mentioned) it'll be just another 'could be' problem.

Have you tried cleaning the throttle body or checking it to see if there is any gunk in there?
 
Throttle body looked clean but I will take it off tomorrow and giving it a good cleaning anyway just to make sure but surely if it was the head the temp gauge would not stay at normal ?
 
Throttle body looked clean but I will take it off tomorrow and giving it a good cleaning anyway just to make sure but surely if it was the head the temp gauge would not stay at normal ?

Only if you had a massive leak in the gasket, if its just a minor leak it could be ok. Without a proper look it's difficult to say for definite.
 

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