Misfires, power loss, coil pack was changed recently but problem came back

[shiyan]

My car has been misfiring a lot lately, sometimes it gets so bad that there's loss of power as well.
When there is loss of power the engine sounds slightly different and fuel use goes up a lot. It's not really possible to accelerate much when it happens, not even when I shift down a gear.
A restart of the engine seems to cure it.
Some perhaps relevant info:
- I've perhaps foolishly removed the glass wool under the bonnet at the end of last winter. I can get warm air but it takes a few minutes. Engine temperature has always been steady at just under half.
- Had almost the same problem on track about 2 months ago, was then diagnosed as a worn out coilpack, coilpack was replaced and the problem dissapeared. Was slightly different that time because before the coilpack was replaced the engine didn't rev quite right even after a restart.
- Engine seems to have a reprogrammed ECU, rev limit seems to be 7800, during the coil pack repair the Renault specialist couldn't read the fault codes at first attempt, was able to read it once I told him the ECU might not be original.
- Timing belt was changed 2 weeks ago at a Renault specialist near Nurburgring, I was not there the whole time so I can not verify whether all the right locking tools were used, I definitely remember seeing the one on the side of the engine head on the gearbox/battery side, not sure if I saw the one on the belt side.
- Oil was also changed by same specialist, I'm not certain if it was the right grade of oil.
- Engine was fine afterwards on track, but I nearly ran out of fuel on track and experienced some fuel starvation.
- Experienced power loss on the way back home after that Nurburgring trip.

 

[JackJack]

- I've perhaps foolishly removed the glass wool under the bonnet at the end of last winter. I can get warm air but it takes a few minutes. Engine temperature has always been steady at just under half.

if you mean the black sound deadening then that wont cause the problems you've got loads of people rip it off

 

[shiyan]

if you mean the black sound deadening then that wont cause the problems you've got loads of people rip it off

yeah that's what I mean

 

[JackJack]

yep that won't cause any problems.

sounds obvious but have you checked the plugs?

 

[shiyan]

yep that won't cause any problems.

sounds obvious but have you checked the plugs?

How do I check the plugs, do you mean buy a new set and change them?

 

[franx]

i'd be changing the upstream lambda by now.. expensive at 60+ pounds but sounds like could be it

 

[shiyan]

i'd be changing the upstream lambda by now.. expensive at 60+ pounds but sounds like could be it

Ah thanks, any particular reason you suspect it's the lambda sensor? Thanks so much.

Is that 60+ pounds just for the sensor or is that labour included?

 

[franx]

"When there is loss of power the engine sounds slightly different and fuel use goes up a lot. It's not really possible to accelerate much when it happens, not even when I shift down a gear."

this and the restart solving it temporarily, sounds like it. Just the sensor over here in Holland is 90euros,
it's doable to take on yourself. First one on the exhaust closest to engine.

 

[Silent_Scone]

failing coilpack will be more noticeable under load, does it still misfire when stationary? I would check plugs before you do anything else

 

[MicKPM]

Deffo check the plug especially to see if the plug wells are swimming in water... leaking washer jets do occur and without the sound deadening material it will find its way in to these bores. Misfiring when up to temp plus the car noticeably using more fuel can also be attributed to a faulty CTS also. Its okay blaming an Ho2 sensor based on previous experiences but its my experience that knowing is better than guessing!

A simple test, though not 100% conclusive, would be to simply unplug the CTS (Note, the cooling fan will kick in when you unplug this so mind your fingers) and then the Upstream/Downstream Ho2's in turn to see if the problem disappears.

I say its not a conclusive test because without the sensor(s) the standard ECM will resort to a predetermined known "Safe" set of lookup tables and run the car without taking the post-cat fuel readings in to account. Again, this isn't a fool proof method as it could also be a CTS related issue and with the car in a safe mode it will also disregard these sensor readings to (and run in an over-fuel condition to protect in cold environments). Ideally, another diagnostic session paying close attention to the live data screens will say for sure if its Ho2 or CTS and a failing/failed sensor *should* be obvious to whoever is behind the screen but this might not be the cheapest route for you as I know only too well how bad the motorists in the Netherlands are treated as my best friend lives in Den-Haag and I regularly have emails from him asking for help (Shame it usually means a visit )... the mind boggles as to why he insists on owning a car tbh when its far pricier than the UK and the public transport system is so good.

Mick

 

[shiyan]

"When there is loss of power the engine sounds slightly different and fuel use goes up a lot. It's not really possible to accelerate much when it happens, not even when I shift down a gear."

this and the restart solving it temporarily, sounds like it. Just the sensor over here in Holland is 90euros,
it's doable to take on yourself. First one on the exhaust closest to engine.

Thanks

Guess it's the Bosch item?

failing coilpack will be more noticeable under load, does it still misfire when stationary? I would check plugs before you do anything else

When I had the problem it was the same at idle, very slow to rev and no power

Deffo check the plug especially to see if the plug wells are swimming in water... leaking washer jets do occur and without the sound deadening material it will find its way in to these bores. Misfiring when up to temp plus the car noticeably using more fuel can also be attributed to a faulty CTS also. Its okay blaming an Ho2 sensor based on previous experiences but its my experience that knowing is better than guessing!

A simple test, though not 100% conclusive, would be to simply unplug the CTS (Note, the cooling fan will kick in when you unplug this so mind your fingers) and then the Upstream/Downstream Ho2's in turn to see if the problem disappears.

I say its not a conclusive test because without the sensor(s) the standard ECM will resort to a predetermined known "Safe" set of lookup tables and run the car without taking the post-cat fuel readings in to account. Again, this isn't a fool proof method as it could also be a CTS related issue and with the car in a safe mode it will also disregard these sensor readings to (and run in an over-fuel condition to protect in cold environments). Ideally, another diagnostic session paying close attention to the live data screens will say for sure if its Ho2 or CTS and a failing/failed sensor *should* be obvious to whoever is behind the screen but this might not be the cheapest route for you as I know only too well how bad the motorists in the Netherlands are treated as my best friend lives in Den-Haag and I regularly have emails from him asking for help (Shame it usually means a visit )... the mind boggles as to why he insists on owning a car tbh when its far pricier than the UK and the public transport system is so good.

Mick

Thanks! I'll see if I can find the 3 sensors. I assume the 2 lambda sensors are near the cat but not sure where the coolant temp sensor is, will search.

 

[JackJack]

one lambda is before the cat (upstream) the other after (downstream)
coolant temp is on the cylinder head iirc

 

[shiyan]

one lambda is before the cat (upstream) the other after (downstream)
coolant temp is on the cylinder head iirc

Thanks.

The problem dissapeared over the last few days but was there again this morning. I'm just wondering whether if the coolant temperature sensor can be broken if the dashboard temperature meter seems to be indicating ok?

 

[shiyan]

My ECU has been changed or remapped so it's not OBD compliant any more. Unfortunately i could not read any fault codes, but with my OBD reader I could still keep an eye on things such as fuel system status, coolant temperature, O2 sensors 1 and 2.

Coolant temperature seemed pretty steady at around 82 degrees C. O2 sensor 2 (downstream) was pretty steady around 0.37~0.38V.

When I had the misfire, O2 sensor 1 (upstream) was showing 0V instead of fluctuating up and down, and the fuel system status was showing "open loop" instead of "closed loop".

I guess that means the culprit is the upstream O2 sensor.