Hi everybody, new to the site and let me get to my problem...
Ok, check engine light came on and so did VSC light, I feel lost of power, hesitation from the engine. 1st. scan code. P0304 - misfire cylinder #4, inspect spark plugs - looks ok I replace it 10k ago. Ohm test spark plug wires - there is continuity. Ohm test Coil pack and all thee of them gave the same reading so I'm guessing they are still good, just be on the safe side I swap the coil pack from #1 to #4. Install everything back together, clear code and fire it up and let it run for a while. Check engine came back on with the same code p0304. Ok, now I test for power to the fuel injector. There is pulse (flashing) from the injector harness connectors with noid light kit, I can hear injector pulses with a stethoscope. Just to make sure that injector #4 is not clog I swap #1 injector to #4 injector....Install everything back together again and clear code and fire it up and let it run a while again. And the P0304 and VSC light up again!! Now, this is where I am stuck...did I miss anything??
I have fuel, spark....the only thing I have not done is compression test but I don't think it is likely to be the problem. Let me know if you have any idea, I have been playing with this car for 2 days and running out of ideas. Thank you for reading.

 

Could also be any of these:


Open or short in engine wire

Connector connection

Vacuum hose connection

Ignition system

Fuel pressure

Mass air flow meter

Engine coolant temp. sensor

Compression pressure

Valve clearance

Valve timing

ECM

 

You are just pulling codes - how about you do something along the lines of watching the misfire count. Most good scantools should be able to do live data, and graph the output for misfires... Just because you have a code that is specific to that cylinder doesn't necessarily mean its not affecting the other cylinders as well, just maybe misfire count isn't high enough to set the code for them.

Watch misfires for all cylinders as well obviously and if there are zero in all other cylinders, then you most likely have a wiring issue, or a burned valve / low compression in that cylinder.

While watching the misfire count, it wouldn't be a bad idea to go on a test drive and see when it does it. Does it misfire at idle, under constant speed cruising, or acceleration, or all of the above? Does it misfire on rough roads more than smooth roads?

Without seeing the car myself, it's hard to come up with other possibilities, as you have been pretty thorough in your diagnosis. I would honestly look to a compression test first, and then check wiring (watch the misfire counter as you shake wires to the coil packs, the injectors, etc)

Ooh, one last thing I just though of - you tested spark plug wires for continuity, but that doesn't mean anything... They could be arcing through the wire, or right past the plug through the air gap in the boot. This wouldn't necessarily be easily detectable, especially if happening down inside the spark plug hole. You might try swapping a spark plug wire as well, or just substituting one for testing.

 

Thanks for the input, for some reason toyota and lexus doesn't let you see misfire count on the scanner. There was one thing that I forgot to swap was the spark plugs, and yes it turn out to the a bad spark plug, when I look very closely I can see a small small tiny hair line crack on the spark plug. I figure if I replace it less than 15,000 miles it should be still good. Right??
In three days trying to find the problem was pretty fun, what a challenge!
Now it's time for an Oil change!!

 

what scantool were you using?

IIRC, I've watched all kinds of live data on the lexus'....

anyways, too bad you didn't replace the plugs... typically if you are going to pull one, might as well replace it, even if just testing... just makes a lot of sense...