Misfires and fluctuating advance timing on idle

[DavidS]

Sharing this in the hope someone has seen similar. I re-mapped my 200 with Celtic, and had timing and misfire problems with latching error codes. That got me into a long process and analysing with an OBD monitor. (Autel AL519). I finally decided to revert the mapping back to factory default.

Since reverting the map, I still get occasional misfires shown on the Autel, but they have not generated a latched error code. They are listed under On-board Mon Test; Mis-fire Cyl 1-4 Data; Misfire counts Last. I will get a few registered on any drive, but no particular cylinder is worse than another. e.g. short drive of 3 or 4 miles = 1 or 2 misfires shown for each cylinder. I think these are real, as I occasionally feel the car stutter on pick-up. These errors never latch and are reset when stopping the engine. On a long drive - 90+ mins - I might get 5 misfires per cylinder. (BTW - there are historical latched misfire values shown under EWMA Misfire Count (1 or 2) and these don't get reset on switching off the engine. I wonder if there is an easy way to reset those values?)

The other thing that I've noticed is the advance timing fluctuates a lot on idle. Under: Live Data; SparkADV degrees, on idle (e.g. 800rpm, no throttle) I will see fluctuating values from 9 to 21 degrees. If I apply a small amount of throttle to hold the revs at 1200 for example, I will get a constant 27 degree reading, so it seems the variability is all at idle.
Am I worrying about nothing? Any advice gratefully received.

 

[Pedro]

Misfires should never ever be ignored especially in direct injection engines & if the Knock sensor as I might suspect maybe triggered you have detonation issues & as has been said previously remaps are fine but may come back to haunt you & adding power to any car will mean a a lot more wear on the coil packs plugs etc as an afterthought from working on many cars not just my own the software can become corrupted & can ever corrupt itself if all the wrong parameters are being installed or interfered with which means the ECU & BSI or both may need to be sent off for reprogramming if the problems persist

 

[DavidS]

Thanks for the input Pedro. A little more background. I have always suspected the power wasn't great, but as this is the only 200 I've ever driven I can't be sure. I didn't test for misfires before I had it re-mapped. Celtic stored the original software from my car and reloaded that same version again when the re-map was reverted. So the car "feels" like it did when I originally bought it second-hand. The plugs and coil packs have all been changed, and I try to run on 99 Octane (I think it is marginally better). I suspect the variation I'm seeing in the advance timing on idle is wrong, but have never seen it on a normal 200. I found the Autel allows me to graph the data for certain live parameters, and I'm attaching screenshots of my engine on idle (the data isn't all from the same instant). Do you think the knock sensor could be faulty?

 

[lfe]

I think the cylinder head had to be removed, probably the detonation caused damage, also on the piston head.

If roughness has been created, hot spots are created that cause more detonation.

An endoscopic camera could also be inserted first.

 

[DavidS]

Wouldn't that sort of damage indicate one particular piston/cylinder? It could be general damage of course (which sounds very expensive). I'm wondering if anyone has tried looking at the state of their engine in idle mode? Are these kinds of variations normal? (I'm thinking that noone would actually go looking unless they felt they might have a problem?

 

[lfe]

I don't know if these advance variations are normal or not, if the car has a stable idle I don't think it will be a problem.

If there is detonation damage it will probably be in all cylinders.

 

[DavidS]

Thanks. I'd really like to see how a "normal" engine behaves on idle before I think about taking the head off. Whether these graphs mean anything is actually wrong. I could go to a main dealer to see if they have an opinion, but that could get costly. I may just be chasing ghosts at the moment. I feel like I need to know what the baseline behaviour should be.

 

[Pedro]

From your graph I'm ruling out the knock sensor as your engines not pinging possibilities it could be cam/crank sensors pointing to timing being retarded?
Checking the fuel trims (important) to rule out timing issues from the chain /tensioner set up
Check the upstream/downstream Lambda sensor functions as it can detect fuel air ratio issues & perhaps clean the Maff sensor & maybe replace PCV valve in the rocker cover as the seals fail over time I have changed the one on my 200 & its not a major job to replace
Overall I would be eyeing the crankshaft sensor as a start ?

 

[DavidS]

From your graph I'm ruling out the knock sensor as your engines not pinging possibilities it could be cam/crank sensors pointing to timing being retarded?
Checking the fuel trims (important) to rule out timing issues from the chain /tensioner set up
Check the upstream/downstream Lambda sensor functions as it can detect fuel air ratio issues & perhaps clean the Maff sensor & maybe replace PCV valve in the rocker cover as the seals fail over time I have changed the one on my 200 & its not a major job to replace
Overall I would be eyeing the crankshaft sensor as a start ?

Thanks Pedro it gives me a direction to go in. What do you mean about checking the fuel trims? How do I go about that?

 

[Pedro]

Just plug the scanner in & search menu for high & Low fuel trims & check whilst the engine is running it will hopefully show you the graph measured readings when I did mine it was when the car was under load & at idle this told me my pump was knackered as the fuel pressure was dropping like a brick on acceleration but stabilising on idle I must mention its handy to have someone reading the screen as your driving the car if possible as one of my lads did makes life easy

 

[Pedro]

Thanks Pedro it gives me a direction to go in. What do you mean about checking the fuel trims? How do I go about that?

Sorry I should have mentioned the Exhaust Camshaft sensor first as this is a red flag on these engine's

 

[DavidS]

Thanks Pedro! I'll get back when I've investigated further.

 

[Pedro]

Found this in my documents file very strange one this not all that dissimilar to your issue ?

 

[DavidS]

Found this in my documents file very strange one this not all that dissimilar to your issue ?

Hi Pedro, I guess this chap was having actual fault codes show up, I just have the odd misfire(s) shown for the last run - no codes ever latch as DTC errors. Again, I may just be chasing ghosts?

Regarding the fuel trims, I guess the high and low fuel trims are labelled as SHRTFT1 and LONGFT1? Here are a couple of graphs showing the fluctuations on idle, and then when revving. I don't know how these compare to the errors you saw on your car?

 

[Pedro]

Mine were mostly peaks & troughs I'm assuming the first long term trim fuel graph was at idle & the second under load ?
The 1st long term looks way off range & the second appears erratic unless its the scanner ?
When mine were measured the Idle were uniform but acceleration dipped under load revealing a serious drop in fuel rail pressure I went for the pump because of the loss of power in a very short space of engine speed loss but other things to consider could be fuel rail pressure & sensor ?
Also its not unknown for injector issues to cause this problem something to consider when trying to pin down this fault related to timing/fuel-air ratios including MAFF performance & sparking-detonation with erratic irregular idling included

 

[DavidS]

The Long fuel trim idle image is just showing a variation from -3.1 to -2.3 ( a change of 0.8) The long fuel trim revving is me blipping the throttle showing all the spikes (which cover the range of 11.7), before I hold the revs around 2500 which shows a plateau at the end around a value of 8.6.

Would injector issues tend to show a particular cylinder failing?

Is there a diagnostic for measuring the fuel rail pressure? As you say, if this is low then supply to each injector could be highly variable.
I tend not to suspect this, as if I kick the throttle it will really respond on the road and it doesn't hold back.

I expect what I'm seeing has a common cause affecting all cylinders rather than related to just one.
I keep coming back to the odd idle behaviour and whether that is to be expected. I wonder if a 20 degree swing in spark advance on idle makes any sense at all? It implies to me that the ECU is trying to rapidly vary the timing to deal with some odd inputs. Or could timing chain/tensioner wear affect idle performance but be negligible at higher revs? My engine has done 81,000 on the original chain.
Too many unknown parameters and my grasp is not clear enough to guess.

 

[Pedro]

Some try to fix this issue by swapping injectors over as long as they are working ok we did it with my sons BMW tourer cleaned them up stuck a dose of REDX in it & it went like a dream
Regarding the timing its possible as the Chain & tensioner wear can contribute to lumpy idle & hesitation on acceleration & the 200 also has the VVT system so never rule out a issue with cam timing with but you had this car remapped so is it a software corruption that is causing the problem ?