- Joined
- Aug 31, 2013
- Messages
- 144
- Points
- 45
Hi all,
Sorry for yet another misfire thread. I have been reading around old threads and webpages for help and now I'm looking for advice specific to my problem.
The symptoms: misfire felt at seemingly random intervals when accelerating in higher gears. To set the scene, I pull away in 1st without any misfire, but if I only take it up to a crawling speed and slip into 3rd and put high demand on the throttle the odd misfire can be felt. The same happens at a slightly higher starting speed and going into 4th.
I found this to be the best way to reproduce the problem but I is also noticeable during 'normal' driving.
My plan of action (taken from a webpage):
• Ignition System
– Fouled/worn spark plugs
– Shorts, leaks or open *circuits in secondary ignition wiring/components => No signs of damage, no sparking at night and no unusual resistance readings using a DMM
– Defective ignition coil(s) (COP or DIS) => tested using DMM and is within spec
– Intermittent ignition *module/coil driver
– Low system voltage => Battery and alternator working as expected
• Mechanical => Head gasket recently replaced (problem present before replacement) and head refurbished
– Carbon deposits
– Worn valve train/burnt valves
– Loose timing belt or chain/valve timing
– Head gasket failure
– Worn rings, piston mechanical damage
• Air/Fuel System
– Low fuel level/poor fuel quality
– Throttle position sensor
– False air/vacuum leaks
– Clogged fuel filter
– Low fuel pressure/volume
– Open or shorted injector coil
– Damaged injector driver
– Injector ground/power supply *circuit problems
– Clogged injectors
– Stuck (open) EGR valve => Punto's don't have an EGR
– Low system voltage => Battery and alternator working as expected
• False Misfires
– Rough road
– Heavy acceleration when cold
– Loose motor or transmission mounts
– Transmission/torque converter *mechanical faults
There are no fault codes logged.
The engine is idling well and removing a HT lead or injector gives noticeable change in the quality of tickover.
This is certainly happening in closed-loop mode but I need to do some more testing to see if it also happens in closed loop mode - results to follow.
I have a full set of OBD tools and a registered version of MES so I can graph a load of sensors. I have had a couple of looks at revs (crank sensor) which seems to be fine which is also backed up because the engine is easy to start.
I will do a compression test soon to double check the mechanical side of things - results soon.
My next port of call is graphing the lambda sensor but I don't feel I can interpret the results as I'm not very hot at this. I'm keen to avoid being a parts changer and actually diagnose what is wrong here. What would you do next?
Sorry for yet another misfire thread. I have been reading around old threads and webpages for help and now I'm looking for advice specific to my problem.
The symptoms: misfire felt at seemingly random intervals when accelerating in higher gears. To set the scene, I pull away in 1st without any misfire, but if I only take it up to a crawling speed and slip into 3rd and put high demand on the throttle the odd misfire can be felt. The same happens at a slightly higher starting speed and going into 4th.
I found this to be the best way to reproduce the problem but I is also noticeable during 'normal' driving.
My plan of action (taken from a webpage):
• Ignition System
– Fouled/worn spark plugs
– Shorts, leaks or open *circuits in secondary ignition wiring/components => No signs of damage, no sparking at night and no unusual resistance readings using a DMM
– Defective ignition coil(s) (COP or DIS) => tested using DMM and is within spec
– Intermittent ignition *module/coil driver
– Low system voltage => Battery and alternator working as expected
• Mechanical => Head gasket recently replaced (problem present before replacement) and head refurbished
– Carbon deposits
– Worn valve train/burnt valves
– Loose timing belt or chain/valve timing
– Head gasket failure
– Worn rings, piston mechanical damage
• Air/Fuel System
– Low fuel level/poor fuel quality
– Throttle position sensor
– False air/vacuum leaks
– Clogged fuel filter
– Low fuel pressure/volume
– Open or shorted injector coil
– Damaged injector driver
– Injector ground/power supply *circuit problems
– Clogged injectors
– Stuck (open) EGR valve => Punto's don't have an EGR
– Low system voltage => Battery and alternator working as expected
• False Misfires
– Rough road
– Heavy acceleration when cold
– Loose motor or transmission mounts
– Transmission/torque converter *mechanical faults
There are no fault codes logged.
The engine is idling well and removing a HT lead or injector gives noticeable change in the quality of tickover.
This is certainly happening in closed-loop mode but I need to do some more testing to see if it also happens in closed loop mode - results to follow.
I have a full set of OBD tools and a registered version of MES so I can graph a load of sensors. I have had a couple of looks at revs (crank sensor) which seems to be fine which is also backed up because the engine is easy to start.
I will do a compression test soon to double check the mechanical side of things - results soon.
My next port of call is graphing the lambda sensor but I don't feel I can interpret the results as I'm not very hot at this. I'm keen to avoid being a parts changer and actually diagnose what is wrong here. What would you do next?
Last edited:
