misfire cylinder 1 fault

[peterg1]

I will try to be succinct with this so here goes:-

Car - 2009 A 180, petrol with BRC lpg conversion (inc valve lube kit) 80,000 miles pretty well trouble free until a couple of thousand miles ago.

Fault - ocassional misfire on starting from cold which also closes down cylinder 1 making it undriveable on some occasions, ie very obvoius rough running and struggles to pull away. However on stopping after only half a mile then restarting it runs fine, despite this it is still usable as my daily car.

Action so far - i have my own code reader so i know it is allways cylinder 1 misfire when reading the code fault. The amber EML comes on almost every time I start whether it misfires or not, so it is a consistant/persistant fault.

First stop my regular MB specialist, they diagnosed unburnt fuel as the (probable) cause, changed spark plugs, fault still there, changed coil pack fault still there, they advised having the lpg system checked out. Note: Obviously this is a pure running on petrol fault as, a) it starts up on petrol, and b) I did try running the gas out and using exclusively petrol for a time but no change. Their theory was that it could possibly be taking air in somewhere.

Checked out by my regular auto gas specialist, run through all the pressure tests, everything fine, and their diagnosis was valve recession probably exhaust valve cylinder 1.

Having researched this it does seem plausible but at a repair bill well into four figures I'd just like to make sure I've covered all the options and possibilities?

So folks any other ideas? Such as could it be an engine managment fault, as it appears the fuel in is okay, the electrics (plug and coil) are okay, so by process of elimination what's left? Would a MB main dealer have any better diagnostic equipment?

I have tried to explain it the best I can but I am not in the motor/engineering background so please take that into consideration when reading this, (or replying). Basically a middle aged discerning motorist who went from an lpg Corsa to the A Class, to get quality with economy! Thanks Peter

 

[BlackC55]

I'm pretty sure that there is a document on the injectors failing causing a miss on number one. Email me your chassis number and I will check for you.

 

[BlackC55]

There is a document on this. (thanks for the email)

It could be an injector fault. It is documented on TIPS (your independent should have access to this) The remedy is a new injector or set of. A test on a Star is what is needed.

If the garage thinks its a valve issue did they do a compression check?

 

[peterg1]

Thanks for that, I suspect what is happening when garages run the diagnostic checks becuse the car is warmed up it shows the previous fault, misfire/unburnt fuel cylinder 1, so they are sort of working on a process of elimination, the independant MB replaced the common electrical components, then suggested get the lpg system checked, the autogas/BCR dealer checked the gas system found that okay and perhaps based on anecdotal evidence of newer lpg conversions concluded that it must be valve recession!
In fact if you look on the autogas UK site (think that was where I saw it), there are a lot of post 2006 cars which they recommend not converting without upgrading the valves as well.

Anyway armed with your info I will go back to the MB indie, as changing an injector is gonna be a lot cheaper than a head rebuild. I'll let you know how I get on.

 

[peterg1]

Okay...update after 2 days in biggest Mb indie in area:
Possible injector fault, switched number 1 & 4 injectors - fault still there!
Misfire cylinder 1 on starting from cold, and frequently switching it down but runs fine when restarted from warm mile or so later.
So really now having eliminated all the basics, ie spark plugs, coil and injector their next suggestion is to have the ECU, sent off for testing, repairing or just remapping to see if that is breaking down when cold, strange as you'd expect problems to occur when it heated up?
Does that sound plausible?
Incedentally they haven't given me a bill yet as this was based on a free diagnosis to then cost what the repair/fix would be. Plus they were quoting a 10 day turn around which seems a bit lengthy when comparing some of the internet sites.
Grateful for any advice on what to do next?
In that as appreciative as I am to the garage I could just pay them something for their labour and post off the ECU myself to a recommended establishment. It is just a 'plug and play', remove and replace item is it not?
Thanks Peter.

 

[BlackC55]

Have they done a compression test?

Have they checked the fuel pressure?

 

[gazz]

A cylinder leak down test on the cold engine would be useful too, to pinpoint if valve sealing is the problem.

 

[peterg1]

Okay, the next saga on 'misfire cylinder 1' - still deciding what to do?

Right the independent garage hajd the car for the best part of a month and sent the ECU to 2 different test places, apparently the first couldn't replicate the ignition circuits?

So the second one, (I have the computer print out but couldn't work out how to scan it on to here) has basically diagnosed that it is an irapairable fault, (by him at least) so will need a new/replacement unit.
I will try and explain the printout:-
Second page box titled;
Intermitent - fault detected more than once, not present (Mode 7)
ECU Fault code Description
E8 P0606 Processor control module (this is asterisked by the guy is the faulty circuit/module)

The garage was helpful said as the car was still a usable everyday car, balanced against the £1100 for a new ECU, plus then the reprogramming of it, and the uncertainty that the LPG conversion could possibly be implicated in its malfunction anyway they just charged me the test fee plus minimal labour costs and said basically go away and think about it?

Obviously the fault is still there, more annoying than incapacitating the car, but I'd still like to get it fixed, but is getting a whole new ECU the only option? That sounds I bit last resort to me. Are these things that iraparable or would a second hand one be too much of a gamble?

So any ideas much appreciated.

 

[BlackC55]

Have they done a compression test? Have they checked the fuel pressure?

Have you done this? ^^

 

[ChrisA]

P0606 Mercedes-Benz Description
The Engine Control Module (ECM) continuously monitors its internal memory status, internal circuits, and output signals to the throttle actuator. This self−check insures that the ECM is functioning properly. If any malfunction is detected, the ECM will set the code and illuminate the engine light.

Possible causes
- Engine Control Module (ECM) Harness power supply circuit is open or shorted
- Engine Control Module (ECM) Programming
- Faulty Engine Control Module (ECM)

Tech notes
Check the ECM fuse, if fuse is OK try erasing the code first and if the code comes back you may have to reprogram or replace the ECM/PCM.

When is the code detected?
Indicates the ECM has experienced an internal memory fault.

Possible symptoms
- Engine Light ON
- Engine may not start