Misfire on overrun

[ozvtr]

Did blocking off the hose from the purge valve to the inlet manifold eliminate the symptoms? Or just make it a bit better?
If it didn't eliminate it then your problem is probably some where else.
Have you checked the security of the inlet manifold (for leaks) and the vacuum line to the brake booster?
Any other symptoms that you haven't mentioned?

[NickCUK]

There is probably a procedure for calibration of the motorised throttle using a diagnostic tool. It would be worth trying that before making modifications to the system.

Yes there are two procedures regarding the throttle body and pedal, have tried both of them.

[NickCUK]

Did blocking off the hose from the purge valve to the inlet manifold eliminate the symptoms? Or just make it a bit better?
If it didn't eliminate it then your problem is probably some where else.
Have you checked the security of the inlet manifold (for leaks) and the vacuum line to the brake booster?
Any other symptoms that you haven't mentioned?

Blocking off hose seems to have improved matters but maybe not completely cured.

Tried it with the EVAP disconnected and blanked-off on the stretch of road on which the problem is usually very noticable: very little hesitation, in fact what there was could have been me imagining it. Unfortunately not conclusive though as it was ten degrees colder and damp, need to wait for the next extremely hot day to be certain.

[NickCUK]

Just a thought, and this is a real long-shot but could the Lambda sensor be made to an incorrect calibration?

Changed that six months ago with one from Euro Car Parts, not sure I ever noticed the overrun misfore anytime before that. Could it be reading higher that it should causing the ECU to aim for a weak mixture.

[PaulC5]

Copy parts are not always as good as ones from a dealer so the only way to see if it is the one from ECP is to pay the higher price at a dealer. Do not even bother trying to find another cheap one since it could be more wasted money.

[ozvtr]

I haven't had much problem with "Chinese knock off parts". I've replaced O2 sensors, petrol fuel injectors and solenoid valves. Having said that, I'm prepared to take full responsibility for any failures!!
It would be stupid of me to recommend the Chinese stuff over the OEM. But think about this; where are most of the OEM parts made these days??

I don't think it would be the O2 sensor. The engine might run richer or leaner but I cant see how it would cause misfires only under particular circumstances. I would lean more toward a spark problem. Having said that, as I said, I'm suffering a similar problem with my engine but I cant work that one out. So you could take my advice with a grain of salt!

[NickCUK]

I haven't had much problem with "Chinese knock off parts". I've replaced O2 sensors, petrol fuel injectors and solenoid valves. Having said that, I'm prepared to take full responsibility for any failures!!
It would be stupid of me to recommend the Chinese stuff over the OEM. But think about this; where are most of the OEM parts made these days??

I don't think it would be the O2 sensor. The engine might run richer or leaner but I cant see how it would cause misfires only under particular circumstances. I would lean more toward a spark problem. Having said that, as I said, I'm suffering a similar problem with my engine but I cant work that one out. So you could take my advice with a grain of salt!

Well I have now had an experiment using an old (intermittantly faulty) oxygen sensor, got to drive for about twenty minutes before the emissions control failure error came on.

Interesting thing was this had much the same but far worse misfire on overrun which certainly suggests it is caused by the ECU. Maybe designed this way and can't be changed.

[ozvtr]

got to drive for about twenty minutes before the emissions control failure error came on.

This comes from the downstream sensor and probably indicates a rich mixture that the catalytic converter cant handle. This only indicates that the upstream (old faulty) sensor is old and faulty...LOL!

Interesting thing was this had much the same but far worse misfire on overrun which certainly suggests it is caused by the ECU. Maybe designed this way and can't be changed.

I'm not sure that this proves anything. Only that a faulty O2 sensor exacerbates the problem. It appears to show that there is not enough spark to ignite the air/fuel mixture. So there is either too much fuel or not enough spark?!

[NickCUK]

Is it possible this could be caused by spark plugs of too hot a rating?

Just been reviewing the history and am reminded that I had NGK Iridium ILFR6B plugs in for six months but eventually concluded that these were causing
a slight misfie at low throttle openings under load. Then changing to slightly hotter rated Denso KH16TT plugs which solved that particular problem. However could these new set of {hotter} plugs be causing the overrun misfire as not sure I ever noticed it previously.

[ozvtr]

I would have assumed that the engine ECU would cut the fuel on deceleration.
The old carburetored engines would back fire on deceleration if you had a lean mixture. In later cars with carburetors, there would be devices to keep the throttle open (very slightly) on deceleration.
Could you have a leaky injector? Whats the fuel economy like? Are the spark plugs black?

[NickCUK]

I would have assumed that the engine ECU would cut the fuel on deceleration.
The old carburetored engines would back fire on deceleration if you had a lean mixture. In later cars with carburetors, there would be devices to keep the throttle open (very slightly) on deceleration.
Could you have a leaky injector? Whats the fuel economy like? Are the spark plugs black?

Spark plugs colour ok. Fuel economy 40mpg according to dashboard, 37mpg according to my manual petrol log.

[NickCUK]

Is there any chance that it is because the Denso KH16TT plugs are Nickel, has anyone else had misfire issues caused by using Nickel plugs?