I have a 1992 3000gtsl. It was misfiring and running rich so I changed the spark plugs. But its still misfiring. How do I diagnose what it could be?
Bad fuel, worn spark plugs (which you replaced), bad coils/wires/PTU, engine harness issues, clogged injectors, clogged fuel filter, timing, vacuum leak, bad O2 sensor, worn piston rings, gummed up valves, sensor issues, etc.
The list is kind of all over the place but you’ll likely want to do some basic checks (compression test, leak down test, verify timing, etc.) before throwing parts at it. Some things (like fuel filter and plugs/wires) are maintenance items and you can do those to just eliminate potential causes. However, before doing anything too invasive, I’d recommend some additional testing/diagnosis before going that far.
Is the problem on idle or just at certain rpm?
I cant really hear it at idle but if i hold it at really low rpm you can hear it clearly
You can start with the easy stuff. Increase idle until misfire starts. Then unplug 1 HT lead at a time. If you get a lead that makes no difference when you unplug it, it would suggest a faulty lead or coil.