Discussion
Hi all! My 280i developed a mysterious misfire. It ran perfectly up until this point. The car seems to start fine and run fine cold. As the temperature rises it begins to misfire. Tried to isolate the problematic cylinder by removing cap wires one at at a time. The culprit was not obvious. I had previously installed new plugs, wires, cap, rotor and fuel filter. I do have a very leaky exhaust system. Could the Oxygen sensor be confused?
Any advice is appreciated. Thanks!
Any advice is appreciated. Thanks!
Welcome to the fold, great to hear from Wedge owners around the world!
I don't think UK cars had oxygen sensors (no catalysts required) so I suspect folks in the UK/Europe won't be able to help if that's the problem. I'd have thought that a leaky exhaust would affect low engine speeds but not high ones; does the misfire clear at high engine speed?
I don't think UK cars had oxygen sensors (no catalysts required) so I suspect folks in the UK/Europe won't be able to help if that's the problem. I'd have thought that a leaky exhaust would affect low engine speeds but not high ones; does the misfire clear at high engine speed?
Suggestions -
1) Is misfire throughout rev range, or is it worse at idle or low throttle ? In which case it could be an injector.
On the 'K', the worst case for an injector is when working at low fuel amounts.
They can partly fail, but start working when fuel flow goes up.
Also may explain why it's OK when cold ?
[ Revving without load on car won't necessarily load injectors a lot - need to drive it]
2) I have once had a spark plug which failed only at certain times, truly weird. Only confirmed it by changing it.
If not just one cylinder, then check
3) coil and ignition amp (fails when warm) or even the resistance wire (unlikely, but possible). Check connections etc. etc.
4) dizzy cap and rotor arm would normally be on the list, but you got new ones....... but it's not entirely unknown for a brand new lead to be faulty.... just be suspicious !
1) Is misfire throughout rev range, or is it worse at idle or low throttle ? In which case it could be an injector.
On the 'K', the worst case for an injector is when working at low fuel amounts.
They can partly fail, but start working when fuel flow goes up.
Also may explain why it's OK when cold ?
[ Revving without load on car won't necessarily load injectors a lot - need to drive it]
2) I have once had a spark plug which failed only at certain times, truly weird. Only confirmed it by changing it.
If not just one cylinder, then check
3) coil and ignition amp (fails when warm) or even the resistance wire (unlikely, but possible). Check connections etc. etc.
4) dizzy cap and rotor arm would normally be on the list, but you got new ones....... but it's not entirely unknown for a brand new lead to be faulty.... just be suspicious !
Edited by RCK974X on Thursday 20th August 21:35
mrzigazaga said:
Hi...I don't ever remember having a mis-fire on my UK 280i in the 3 years of ownership...I had numerous hot start issues or running on 5 cylinders or not starting at all..Mine was a SOB for ages but no mis-fires...Could be something to do with a sensor??....
Hot starts on the 2.8 was always bit dodgy, even on Ford originals - they modified the setup on later models ...RCK974X said:
Suggestions -
1) Is misfire throughout rev range, or is it worse at idle or low throttle ? In which case it could be an injector.
On the 'K', the worst case for an injector is when working at low fuel amounts.
They can partly fail, but start working when fuel flow goes up.
Also may explain why it's OK when cold ?
[ Revving without load on car won't necessarily load injectors a lot - need to drive it]
2) I have once had a spark plug which failed only at certain times, truly weird. Only confirmed it by changing it.
If not just one cylinder, then check
3) coil and ignition amp (fails when warm) or even the resistance wire (unlikely, but possible). Check connections etc. etc.
4) dizzy cap and rotor arm would normally be on the list, but you got new ones....... but it's not entirely unknown for a brand new lead to be faulty.... just be suspicious !
Number 3 would be my first choice, check coil to see if it is super hot.1) Is misfire throughout rev range, or is it worse at idle or low throttle ? In which case it could be an injector.
On the 'K', the worst case for an injector is when working at low fuel amounts.
They can partly fail, but start working when fuel flow goes up.
Also may explain why it's OK when cold ?
[ Revving without load on car won't necessarily load injectors a lot - need to drive it]
2) I have once had a spark plug which failed only at certain times, truly weird. Only confirmed it by changing it.
If not just one cylinder, then check
3) coil and ignition amp (fails when warm) or even the resistance wire (unlikely, but possible). Check connections etc. etc.
4) dizzy cap and rotor arm would normally be on the list, but you got new ones....... but it's not entirely unknown for a brand new lead to be faulty.... just be suspicious !
Edited by RCK974X on Thursday 20th August 21:35
Is the wiring original???, the coil is expecting a reduced voltage after the key is returned to "run" after starting.
If the coil is receiving continuous 12v it will eventually fail.
Thank you all for your helpful suggestions! The postmortem seems to suggest that the problem was the coil. I installed one (not a correct one) and things dramatically improved. It took a while to clear the fouled plugs but it ran good. After a couple days of running I do still get some hesitation but nowhere near what it was. Thanks again for the help!
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