Mercedes ML320 running issue 0 I'm lost

[curlyearly]

Hi all,

Have a recurring problem on my ML320. Just turned 50K miles. Always serviced. 50/50 main dealer / local garage.

Symptoms...

At tick over there's a slight hesitation, a bit like a loose plug lead but more subtle. Its more noticeable in "D" at tick over than when I put it in "N".

Sometimes, say 1 in 20, when I pull off its like a plug/s is not firing. Certainly the car will struggle to pull away, round-a-bouts and pulling out of a junction are an issue. Then, after, 30 seconds is clears itself. I can then drive 2-300 hundred miles without a glitch. But. Pull over, leave for fifteen minutes and restart and the 30 second hesitation is back.

The car has been to three garages (my local garage who I have used for years, a MB specialist garage and MB them selves). Items changed, in some cases by all as they like to use their preferred brand lines are; plugs, plug leads, lambda sensor, crank sensor, air sensor. I've spent hundred of pounds without success.

OK. The hand held computer I have is a "Memoscan". The four recurring codes I have are...

PO135. Pd 02/04. Generic 02 sensor circuit malfunction (bank 1 sensor 1).
PO155. Pd 03/04. Generic 02 sensor heater circuit malfunction (bank 2 sensor 1)
PO131. PD 04/04. Generic 02 sensor circuit low volts (bank 1 sensor 1)
PO306. Pd 01/04. Generic cylinder 6 misfire detected.

I'm a bit lost to be honest. Three garages are lost too. The car can go for a couple of months running great (petrol or gas) then play up. Perhaps a clue, or red herring, it always seems more troublesome in damp weather?

I welcome your thoughts, advice and hopefully solution.

Cheers all.
Earl

[rossko]

Is there something that makes you think the problem is related to running LPG?

It does sound like an ignition issue on cyl 6. This'd be an engine with twinned coils and dual plugs per cyl?

I can't think of anything that would cause an O2 heater fault code except a problem in the sensor, wiring, connector or petrol ECU, and perhaps there's a relay involved here. Be sure that is a "real" code and not something due to other's investigations, i.e. that it does recur after you clear it.

The other codes may be fallout from the above two issues.

[Tubbs]

If you restart during the rough bit does it struggle to start ? Only reason I ask is I had a pretty similar problem. Not lpg related at all. It was a cam sensor. But I'm struggling to understand the lambda faults if that was the case. The crank sensor also acts as an accelerometer. If the spark pulse is late it logs it as a fault on number 6.

[andy evans autogas]

what LPG system is fitted to it and when???. . is the problem happening just on gas or on petrol as well??. . give us a few more clues .....

[curlyearly]

The LPG system is BRC Genius Max. The fault happens more frequently on gas than on petrol. If run solely on petrol its hardly noticeable but if run on gas sometimes pulling (99.9% when restarting on a warm engine) can be so bad the car struggles to move. Give it ten seconds then all OK. Hope this helps.

[1975bay]

Cam poisoning sensor

[Tubbs]

That's 2 wild guesses for cam sensor !

[andy evans autogas]

possible regulator fault leaking gas into vacuum pipe and overfueling on initial start up. try pulling vac pipe of regulator as you switch of engine and check for gas leaking out (have car on gas first)