Looking for guidance on this... My 86 328 developed an apparent ignition mis fire on the way home from Tutto Italiano on the 4th. It feels like ignition related but time has not permitted much diagnosis as I have a business to run also. My question is: Would removing the plug wires from the spark plugs individually to isolate the cylinder in question harm the ecu ? Other than a few seconds of unburned fuel in the cylinder are there any other potential issues ? Thanks, Steve
Most likely culprits are either a burned through extender or a bad ignition lead. The extenders are easy to check - just pull the leads off the plugs & have a good look at them. To check the ignition leads properly you really need to pull the distributor caps & check end to end continuity. With the spiral wound leads they can break in the middle but still work for a while because the spark jumps the gap inside the lead - but it gets worse over time till it stops working. You should be able to check the extenders in 15 minutes, the leads would take you an hour or two by the time you remove everything & put them back.
Thankyou ! I will look into your suggestion tomorrow. We service corvettes at my shop and the ignition systems on the C1 - C3 vettes are prehistoric and simple to diagnose... We don't want to loose an ecu if that's possible. Vintage vettes with oem transistor ignition systems will destroy a module if plug wires are removed while the engine is running unless its been upgraded to a solid state unit. That's why the hesitation.
I'm not sure what the Ferrari will do if you pull a plug wire while its running - but replacing the ignition unit would be very expensive so I'd err on the side of caution. Checking the extenders is done without the engine running.
If your extenders are black (rather than red), it can be tricky to see if there's anything wrong. In which case, check resistance with any multimeter. Adds 10 seconds to the job.
Plug extenders are red and I hope to get to it later today. Any ideas on possible ecu damage if the plug wires are removed individually when the engine is running ?
I thought you would be more likely to damage the coils than ECU. There's no direct connection between the ECU and leads. Whilst your checking the leads also check inside the coils where the leads to the distributors fit. If a lead hasn't been secured into the coil correctly it will eventually burn the coil terminal. This happened to mine after the lead had been loosened during a service by someone inadvertently dislodging it. Result - occasional misfire especially at low RPM.
I just went through this with my 83 QV, 8 new extenders & the problem is fixed. Now it runs better than it ever has.
