250 Missfire count rising on throttle lift off + high knock counts?

For the last years I've been hunting for a intermittent fault where my engine cuts out aggressiveley (possibly boost cut or some torque limiter). More info on that is in this post: https://rsmegane.com/threads/intermittent-power-loss-engine-cut-missfire.14706/

Now I've upgraded the Torque app abit and found some irregularities, missfire count goes up into the hundreds after a 30 minute drive. However, it only counts the misfire on throttle lifts into engine braking or shifting - and especially at low rpms. No missfires felt/heard or any seeming loss of power.

Knock counts are also high (attatched screenpic show historic values) and there is one cylinder that is significantly lower than the other ones. Cylinder four is significantly higher. Accounting for mileage of the car I get approximatley one knock every 20km or so, and the numbers seem to be rising at that rate.

My question is: shouldn't off throttle misfires be impossible? Are missfires counted using the TDC/crank sensor - and if so, could it be faulty? Could it be that the car drops a bit of fuel to make the pops and bangs that throws it off? (on standard map).. Or could there be a problem with crank case ventilation which affects crank speed on throttle lift?

Other known variables:
1. Front o2 sensor heat shielding has dried up and perished, didn't think it would affect much but I did get some wierd readings last night. Will keep monitoring.
2. Coolant temp sits comfortably between 80-84 degrees Celsius. Which seemed low but from what I've read the thermostat should open at 83-84 degrees?
3. Throttle opening on cold start idle is 17%, and on warm idle slightly below 14%
4. Running an ecu test i get a "fail" on "catalyst monitor bank 1" (secondary o2 sensor?) but I'm unsure what the Count represents. (see second screenshot)

No other known issues, gas mileage very acceptable for my driving style.

 

*Correction* obviously cylinder 1 was the one with the higher knock count..

 

I have not, is it something that can be tested by the dealers or is it simply a replacement item? and do i need to have a look at fuelpump and fuelfilter in that case?

 

Thank you for your guidence! Will run some tests tomorrow. Did get some wierd O2 readings at warm idle today again. Moved the sensor wire by hand and the swings made more sense but I don't know if moving the wire was the reason. Last screenshot is after I moved wire.

Simultaniously I think i heard a scraping or something noise on belt side of engine. Made video but cellphone is dead so will try to get it up tomorrow aswell. Cylinder 1 misfired on idle (misfire count on cell, noticed nothing).

Thank you again

 

Thanks for the tips Arch. There is a decent mapper however I'm not sure they've worked on meganes before? Maybe that isn't so important for theese purposes. Closest RS specialist is in another country.

 

First off, thank you everyone for your insights! Been going at it alone, just feels good to have some new paths to pursue

Haven't been able to tinker with it today as i'm dealing with some issues with the ticker simultaniously. All day at the hospital..

Did however call my service guy at renault and asked him if he saw something in the software when i had it in for cambelt service.

He said it did show that the software was not standard so I'm guessing it's tuned.

Had a reciept in the car from tuner but figured it had been returned to standard since max boost was 1150mbar which i believe is standard max for a 250?

Anyway, have some parts to swap but, next on order is possibly o2 sensor and hopefully a return to stock software if the ecu isn't locked. (Tuner went out of buisness so in that case i'm screwed)

If that doesn't work I'll have a look at the fueling bits.

Thanks again!

 

If it is a poor tune the irony in that I've wanted an rstuning map for years, but put it of because i didn't want to tune a poorly running car is going to stay with me a while btw..

 

I Think i could use the vehichle diagnostic function at the end of a journey to view a summary of all missfires with Torque PRO. To get the individual cylinders i had to download an addon called "Advanced EX for RENAULT", it has some extra PIDs you can install. Choose the Laguna III 2.0 (M4R) Engine, which isn't exactly the same but i guess it's the closest.

 

Wow, thanks guys!

Feel a little bit better knowing I'm not alone then

Haven't had much chance to fiddle with the car theese few weeks, but i did gap the plugs down to 0.6mm, no change in missfires but the car did feel slightly better at the top revs, max boost did increase to 1200mbar too. not sure what to make of that really, was hot as balls though so might be why.

Car going into storage for wintertime now so won't have time to map it or swap that o2 sensor. But i will dig up this thread and update on any success or failures next season.

Thanks again for the support guys

 

Yes! It would seem there was a few things. The knock counts where reduced to half by changing from 5w-30 oil (poured in there by dealer) to 5w-40. Even the knock count i had though was not enough to warrant any concern i was told. Guessing some of it could have been phantom knocks by noisy valves? Maybe.

The harsh engine cut was a bad map by a swedish tuner, got a new one from henk and it hasnt happened since. He had also seen the fault code before (DTC 061A). Also gained about 40nm and 25 hp which was welcomed!

Stuttering on cold idle and missfires on throttle lift of i am suspecting is just a caracteristic of this engine? Anyways. Car runs absolutley fantastic at this point so not too worried about it.

Will update my other thread once i'm 100% the cut out failure has been all sorted.

 

Exactly. Honestly i dont think there is any need to worry unless you get several knocks in a quick succession. They are essentially just responding to a frequency so anything that gets to them at that frequency will register.