x300 misfire
 

Hi all I have a misfire while car is idling and when i pull away. it dissappears at around 1500 RPM .whilst idling with the headlamps on they pulse visibly in syncro with the misfire .I occasionally experience negative charge on voltmeter in cab along with what sounds like belt slip squeel although the belt is new and correctly tensioned.The misfire is less pronounced when the engine is properly warmed up .There are no fault codes logged.Has anybody any ideas pleaseTrust everyone is well
Regards Alec

Could possibly be low output from your alternator. That would be the first place I'd check since it seems to be making a noise. Could mean the bearings are on their way out.

Hi Alec,

Repetitive misfires will typically trigger at least one diagnostic trouble code such as P0300, often accompanied by a cylinder-specific code in the P0301-p0306 range.

Are the misfires random, or regular and evenly spaced?

Are you certain that you are hearing/sensing misfires, or could it be something like an interruption in fuel supply/pressure, a malfunction in the idle air control, etc.?

Cheers,

Don

Hi Don definately a rythmic misfire which only occurs at idle and up to 1500 rpm.This makes me wonder if 95 leaper is on the right track as I have alternator issues as well.
I have a good used unit which I will swap out and see if it makes a difference
Alec

Hi Alec,

I can't think of how a failing alternator could cause rhythmic misfiring unless one coil is more susceptible to low voltage than the others. If your problem goes away when you swap in the other alternator we'll all cheer along with you, but if not, you might search this forum for all the many odd issues that have been solved by replacing a coil that was failing but not triggering a P0300 code. If I recall correctly, SNG Barratt still has some Made in Japan coils that are supposed to be the equivalent of the original Diamond units. You would only need one to swap in for each coil to see if the problem goes away.

Cheers,

Don