mis-fires how to tell

[Seight-v8]

How can i tell if my engine is mis-firing......can it be done by watching the knock sensor readings on the vems gauge???.

or is there a better way......

My engine seams lumpy on idle at about 1000rpm, but dont know how much of this is down to my piper 285 cam, just want to make sure is not mis-firing.

cheers

scott

[dnb]

The Piper 285 is a fairly mild cam, so it shouldn't be all that lumpy.  What plugs are you using?  I have recently switched from the B7ECS to another resistive type with longer electrode(will find a box and let you know) and this has improved the idle a bit, plus cleaned up the noise I was seeing on the ECU and made the LCD work properly.

As for finding the misfire, I have always looked at the tooth timings for the trigger wheel.  I think they are the "individual cylinder power" measurements in Vemstune, but I am not too sure since I usually look at the raw data.

[Seight-v8]

Yes i've looked at the "individual cylinder power" and i have some really big differences like -312us......these seam to match up with the knock readings i worked out for a mis-fire.

Strange just looking at a previous log its cylinder 4 & 7 and these share a coil pack, so maybe a fault with a coil, might try swapping it around with another one and trying again.

Currently i am running NGK BPR6ES plugs.

cheers

scott

[dnb]

I'm using BPR7ES plugs, so looks like we've had the same idea.  TVR originally suggested B7ECS which is a bit silly for electronic ignition...

The individual power measurements seem to relate to ignition channel rather than cylinder number.  This isn't immediately obvious from the documentation.  (I believe the knock is the same, so at least its consistent)  I usually get confused at this point and have to double check, but usually it works to indicate misfires.  It's quite noisy at idle and low RPM, so there can be false alarms and general causes of worry.  I generally see 2 slow cylinders at idle with this method, but it all goes right at light load and above.