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I’ve been having this really annoying misfire on my 2008 base vette and it’s at 120k miles so I’ve just been going down the parts list I’ve doneSpark plugs
Spark plug wires
Coil packs
Clean throttle body
MAF sensor
Check for vacuum leaks
Upstream O2 sensors
Exhaust manifold gaskets
Cleaned grounds
Checked fuel pressure when misfire wasn’t noticeable was 55psi at idle but I don’t know what it is when misfiring because I’m usually driving. Sometimes turning off and on the car fixes misfire. Sometimes misfire appears after driving a while sometimes few seconds after start up. When misfiring fuel system is on open loop fault.Maybe cam position sensor? When misfire is very noticeable service traction control system warning comes up as well. Any help would be much appreciated.
Have you checked for trouble codes that could lead to a particular cylinder? If the misfire is random, have you looked at live scanner data for MAF, MAP, Fuel Trims, etc.?
I recommend as a DIY’er anything beyond plugs and wires you will have great difficulty diagnosing a misfire without the advanced equipment needed…you already fired the parts canon without much success…T/C light will always illuminate when you have a misfire.
I took it to two mechanics one said maybe fuel pump going the other said clogged injectors not atomizing properly. Parts cannon gives me something to work on at least 😅
Your MAP reading of 38kPa at idle seems about right. Does it hold steady at that value or does it fluctuate? A fluctuating MAP value would indicate a vacuum leak.
Unfortunately you really can’t diagnose a misfire with live data…unless a shop uses a labscope they will only be guessing…I use a labscope to diagnose misfires so I don’t guess…below are some waveforms I use to see where the misfire is…fuel, spark, compression…if you show these waveforms to a repair shop or even a dealership and they don’t know what these are find another shop !!..as far as your EQ or Lamda you are a little on the rich side…did those 2 idiot mechanics do a fuel injector balance test to see if your injectors are clogged or check the fuel pump under load ??..it is cheaper spending an hour for diagnostic time than changing more unneeded parts…and BTW it’s not a cam sensor.
Relative compression test…in picture no compression #8 cylinder. Secondary Ignition Coil pack current on left and fuel injector current on right. Fuel injector voltage
Took it to dealership just for diag today I guess we’ll see what the culprit is soon hopefully. I’ll call and ask about the labscope. When misfire is not too noticeable computer shows 0 misfires at or above 2k rmp. When it is misfiring bad feels like the car is running on 4 cylinders and is gonna shake itself apart at any rpm.
Took it to dealership just for diag today I guess we’ll see what the culprit is soon hopefully. I’ll call and ask about the labscope. When misfire is not too noticeable computer shows 0 misfires at or above 2k rmp. When it is misfiring bad feels like the car is running on 4 cylinders and is gonna shake itself apart at any rpm.
A dealership will only replace parts and they probably don’t use a labscope but you can ask.
Multiple/Random Misfire
