This one came in today with a check engine light on and a complaint of running rough and won't accelerate past 30MPH.
Checked the codes.
Some misfire freeze frame.
Reset and went for a test drive.
Codes P0300, P0302 and P0303 come back right away. scan data shows a constant misfire on cylinders 2 & 3. Engine doesn't actually run rough I think the customer confused the limp mode rev limiter with rough running.
Looking at Stuff
Coil #2 primary side.
Coil #3 shows the same.
Spark? looks good enough to me. Jumps a 30kV gap looks blue enough to rule out a secondary issue.
The car has around a 100k on it so maybe a valve is sticking?
MAP sensor voltage looks OK < .90v with the engine hot @ idle. Pretty much rules out a sticking valve or the valves being out of adjustment.
Fuel trims look OK live readings weren't far off from the freeze frame. No vacuum leaks, all hoses secure and accounted for.
How about engine compression? > 150psi on each cylinder
Plugs? Not exactly new but looked OK. Some minor oil varnish around the ceramic.
How about bad injectors? To be honest I didn't even bother checking. Injectors on these motors rarely fail.
Fuel pressure? Around 50psi, good enough for me.
So how about that Crank Position Sensor code?
Looks OK to me. No drop outs. Signal looks clean. Connector is secure.
What about water intrusion? Seems to be the most likely. And it did snow a few days back.
Unfortunately by the time the car came in the connector was dry. Pins looked pretty clean hit it with some dielectric grease and plugged it back in.
What's the deal?
Before anyone says check the injectors, it's not the injectors.
I thought this would be a good problem for someone to think on.
Instead of just posting the solution I'll give someone else a chance to respond and be a hero.