Mazda 6 2.5 - runs terribly when hot
Discussion
2010 Mazda 6 2.5 petrol NA on 112k. Totally standard.
When cold it runs nicely, everything is smooth and the idle is spot on.
If I drive and get on the motorway/dual carriageway very soon into the journey it will sit at 65mph on cruise no issues for a while.
If I drive around town however using the revs and gears more often, once the engine is up to temperature it develops an issue which is most obviously on very partial throttle such as driving at 30mph in 4th. It's as if the throttle is being applied and removed very quickly. When I then come to a stop the revs will keep dropping to the point the engine will nearly stall.
There is a direct correlation between how hard the car has been driven and how bad the jerking and idle gets. If I rev it out in 2nd and 3rd, the jerking will become really bad immediately. If I then turn the car off, the next time I come to restart it, say next day, it may take 3+ seconds of cranking to start but will then run perfectly until it is warm and the issues start again.
When it is jerking it doesn't feel like it's one cylinder causing an issue, it seems like a more overarching issue.
There are two O2 sensors, one is a traditional O2 sensor and the other is a wide band sensor.
I have already:
1) cleaned the MAF
2) checked the throttle body which looked clean as a whistle
3) checked the spark plugs which are all iridium in good condition with no obvious fouling
4) air filter is nearly new
5) I have disconnected the battery and then followed the recalibration process for the TPS and throttle body.
There is no EML
Anyone have any ideas of what is causing the issue?
When cold it runs nicely, everything is smooth and the idle is spot on.
If I drive and get on the motorway/dual carriageway very soon into the journey it will sit at 65mph on cruise no issues for a while.
If I drive around town however using the revs and gears more often, once the engine is up to temperature it develops an issue which is most obviously on very partial throttle such as driving at 30mph in 4th. It's as if the throttle is being applied and removed very quickly. When I then come to a stop the revs will keep dropping to the point the engine will nearly stall.
There is a direct correlation between how hard the car has been driven and how bad the jerking and idle gets. If I rev it out in 2nd and 3rd, the jerking will become really bad immediately. If I then turn the car off, the next time I come to restart it, say next day, it may take 3+ seconds of cranking to start but will then run perfectly until it is warm and the issues start again.
When it is jerking it doesn't feel like it's one cylinder causing an issue, it seems like a more overarching issue.
There are two O2 sensors, one is a traditional O2 sensor and the other is a wide band sensor.
I have already:
1) cleaned the MAF
2) checked the throttle body which looked clean as a whistle
3) checked the spark plugs which are all iridium in good condition with no obvious fouling
4) air filter is nearly new
5) I have disconnected the battery and then followed the recalibration process for the TPS and throttle body.
There is no EML
Anyone have any ideas of what is causing the issue?
Is the car running at normal temperature? I've seen examples of cars with a faulty thermostat and/or ECU temperature sensor. This can allow the engine to run fine in cold start/warm up but then continues running a richer fuel mix when not required which can cause it to run rough.
Also things like coil packs can develop hairline cracks which are opened up more when the pack is hot and then shrink back when the engine cools.
Also things like coil packs can develop hairline cracks which are opened up more when the pack is hot and then shrink back when the engine cools.
LordLoveLength said:
Clean the egr valve - make sure it’s not gummed up and sticking.
I think this might be the winner. I tried unplugging the egr and driving the car and when cold it had the exact same driving characteristics as it does when it's hot. I'll take it off and inspect it tomorrow. How hot is it running?
My 2008 2.5 Mazda 6 had an odd fault where it would run fine until a little over normal temp.
After coming off the motorway and pulling away from a stop, the throttle would sometimes not respond.
I think it is a self protection and cuts the throttle during overheat. Start/stop driving was very bad.
Overheating got worse.
New thermostat sorted the overheating and throttle problems
Replaced the long life FL22 coolant at the same time. 6 litres needed annoyingly.
https://www.mx5parts.co.uk/coolant-premixed-fl22-l...
My 2008 2.5 Mazda 6 had an odd fault where it would run fine until a little over normal temp.
After coming off the motorway and pulling away from a stop, the throttle would sometimes not respond.
I think it is a self protection and cuts the throttle during overheat. Start/stop driving was very bad.
Overheating got worse.
New thermostat sorted the overheating and throttle problems
Replaced the long life FL22 coolant at the same time. 6 litres needed annoyingly.
https://www.mx5parts.co.uk/coolant-premixed-fl22-l...
Thanks all for the suggestions. Checked/cleaned everything suggested.
I got the ODBII reader and Torque app running earlier to check the temp, which remained constantly between 88-91 degrees Celsius.
I added in all of the other displays to see if there was anything abnormal, and noticed when the car was running badly that that the pre-cat o2 sensor was reading between 0.1 and -0.1 which from research is way out and would suggest the sensor is FUBAR. Quite how that isn't triggering an EML I don't know but does appear to be the issue. I'll get one ordered and fit it and report back.
I got the ODBII reader and Torque app running earlier to check the temp, which remained constantly between 88-91 degrees Celsius.
I added in all of the other displays to see if there was anything abnormal, and noticed when the car was running badly that that the pre-cat o2 sensor was reading between 0.1 and -0.1 which from research is way out and would suggest the sensor is FUBAR. Quite how that isn't triggering an EML I don't know but does appear to be the issue. I'll get one ordered and fit it and report back.
I spoke too soon about the O2 sensor. The car has two sensors, an AFR sensor just after the manifold and an O2 sensor after the cat. The AFR measures in mA and the readings seem to be okay. I monitored the AFR (commanded) and AFR (measured) whilst the car was misbehaving. The commanded measurement stays at around 14.60:1 and the measured was always around that figure, moving from about 14.2-15 sometimes but generally very close to 14.60.
When I then parked up I opened the bonnet whilst the car was idling badly and the engine could be seen to rock ever so slightly as the revs dropped and bounced back. I unplugged the MAF again and the car really struggled to run. I then plugged it back in and the engine idled perfectly within 5 seconds and the engine was perfectly smooth and looked like it would have passed the 50p test 🤨
I'll check the TPS sensor readings again when I drive the car tomorrow. I seem to recall it read around 12% when off throttle and then rose proportionatey the more I pressed the pedal.
When I then parked up I opened the bonnet whilst the car was idling badly and the engine could be seen to rock ever so slightly as the revs dropped and bounced back. I unplugged the MAF again and the car really struggled to run. I then plugged it back in and the engine idled perfectly within 5 seconds and the engine was perfectly smooth and looked like it would have passed the 50p test 🤨
I'll check the TPS sensor readings again when I drive the car tomorrow. I seem to recall it read around 12% when off throttle and then rose proportionatey the more I pressed the pedal.
SystemOfAFrown said:
Surging at idle is commonly caused by vacuum leaks, e.g. a split or rotted vacuum hose. A sticking idle control valve is also a possibility, but vacuum leaks are more common IME.
I've checked the vacuum and it seems to be very low. I've made a video of the Torque readings whilst it was idling badly.[youtube]https://youtube.com/shorts/-5PfimNImlk?feature=share[/youtube]
- edit* YouTube doesn't seem to work but here are the figures from the screenshot
Edited by deadmau5 on Wednesday 3rd May 19:05
Don't know if any use but I captured some data from my 2008 2.5 Mazda 6 when it was playing up.
Either Torque or Forscan while driving and some idling following driving.
https://1drv.ms/x/s!AtCz6AtB1md4gY8YP9nzJXdfl3BFoA...
I think the yellow marked area on sheet 2 was where the throttle stopped responding.
As I said earlier, I think mine was cutting fuel or throttle when overheat detected.
Drove and idled fine other than that.
Was in 2018 and no problems since
Either Torque or Forscan while driving and some idling following driving.
https://1drv.ms/x/s!AtCz6AtB1md4gY8YP9nzJXdfl3BFoA...
I think the yellow marked area on sheet 2 was where the throttle stopped responding.
As I said earlier, I think mine was cutting fuel or throttle when overheat detected.
Drove and idled fine other than that.
Was in 2018 and no problems since
imck said:
Don't know if any use but I captured some data from my 2008 2.5 Mazda 6 when it was playing up.
Either Torque or Forscan while driving and some idling following driving.
https://1drv.ms/x/s!AtCz6AtB1md4gY8YP9nzJXdfl3BFoA...
I think the yellow marked area on sheet 2 was where the throttle stopped responding.
As I said earlier, I think mine was cutting fuel or throttle when overheat detected.
Drove and idled fine other than that.
Was in 2018 and no problems since
It's a shame that you didn't have the coolant temp logged as well. Can you remember what the coolant temp reading was? Either Torque or Forscan while driving and some idling following driving.
https://1drv.ms/x/s!AtCz6AtB1md4gY8YP9nzJXdfl3BFoA...
I think the yellow marked area on sheet 2 was where the throttle stopped responding.
As I said earlier, I think mine was cutting fuel or throttle when overheat detected.
Drove and idled fine other than that.
Was in 2018 and no problems since
I did some more sensor reading yesterday. I drove 18 miles, almost all dual carriageway, at about 60mph on cruise. At the end of the journey the car was still driving nicely and the idle was spot on. The only two things different were the vacuum and fuel flow. I'm now pretty certain I have an intermittent vacuum leak, as when the vaccum is lower than about 20in/Hg at idle the car runs like s
t. The car seems to be compensating with higher fuel flow to keep the AFR in range. I'll try and get everything inspected today.
Screenshot after this journey:
I then completed the same journey in reverse except this time when I got home the car was running badly again. Screenshot at this point:
t. The car seems to be compensating with higher fuel flow to keep the AFR in range. I'll try and get everything inspected today.Screenshot after this journey:
I then completed the same journey in reverse except this time when I got home the car was running badly again. Screenshot at this point:
Edited by deadmau5 on Sunday 7th May 10:05
deadmau5 said:
It's a shame that you didn't have the coolant temp logged as well. Can you remember what the coolant temp reading was?
3 topics from when I had the problems.There is some reference to temps in the serpentine topic
https://www.pistonheads.com/gassing/topic.asp?h=0&...
https://www.pistonheads.com/gassing/topic.asp?h=0&...
https://www.pistonheads.com/gassing/topic.asp?h=0&...
deadmau5 said:
I did some more sensor reading yesterday. I drove 18 miles, almost all dual carriageway, at about 60mph on cruise. At the end of the journey the car was still driving nicely and the idle was spot on. The only two things different were the vacuum and fuel flow. I'm now pretty certain I have an intermittent vacuum leak, as when the vaccum is lower than about 20in/Hg at idle the car runs like st. The car seems to be compensating with higher fuel flow to keep the AFR in range. I'll try and get everything inspected today.
Screenshot after this journey:
I then completed the same journey in reverse except this time when I got home the car was running badly again. Screenshot at this point:
You reversed down a dual carriageway on cruise! t. The car seems to be compensating with higher fuel flow to keep the AFR in range. I'll try and get everything inspected today.Screenshot after this journey:
I then completed the same journey in reverse except this time when I got home the car was running badly again. Screenshot at this point:
Finally had a chance to look at it again today. I did the 'dollar bill test' where you hold a piece of paper over the exhaust whilst it's running. If it continually blows the paper it's good, but unfortunately for me every few seconds the paper was getting sucked up against the pipe showing there is a compression issue, likely from an exhaust valve. This would corroborate the lack of vacuum at the same time.
I'll get the compression tester on it soon and identify which cylinder and then take it from there. I imagine it's going to need the offending valve(s) removing and cleaning though. Ballache!
I'll get the compression tester on it soon and identify which cylinder and then take it from there. I imagine it's going to need the offending valve(s) removing and cleaning though. Ballache!
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