Car is throwing P0300 and P0304 codes, Auto with 44k miles


Background;
Topped the oil off this morning was 1/2 a quart low (have notched the dip stick).
Put 10 miles on the car this morning to work.
This afternoon drove out to company building from the base to get a part. Left to go back to the base, I was entering the roadway and needed to cross over three lanes so I got on it pretty good. Noticed a lot of black smoke coming out of the exhaust.


Car seemed to run ok back to work on base (4 miles).


When I left work to go home the car started to run rough and was bucking, yellow engine light (CEL?) was blinking on and off.


Scan gauge II showed a P0304 (#4 cyl misfire).
revved the engine multiple times hoping something would clear, nope. car almost wanted to stall, would smooth out somewhat with more throttle.
By the time I got home (6 miles) the CEL light was solid and I also had added a P0300 code (may have happened after revving the engine).


I cleaned out the BSH can again (did it 2 weeks ago) did have some oil/water mix in it 1.5-2 oz.


Swapped coil 3 & 4
pulled plug 4 and cleaned it.


No difference, still runs rough and codes set again after clearing.


Removed the battery for 30 minutes, no difference.


Scan Gauge shows around 700 FPR at idle, goes up with throttle increase.


Walnut shelled the intake valves and replaced plugs about 2k miles ago, that's when I added the BSH can.


Have been looking at different posts with these codes, HPFP?


Black smoke a coincidence?


Got 5 gallons of gas yesterday (shell 93 octane), was at 2 red carrots.


Any thoughts?


Now I have to take the Honda minivan to GA tomorrow!!!


Thanks, Glenn

 

Consistently in Cyl number 4?
If the coil swap did not change the misfire, and since its not a p0354 (or some other circuit code for a specific coil) I would try pulling out the plug on number 4, and checking for wetness, or unburnt fuel....The black smoke tells me its running rich, and that's unburnt fuel.

If you pull the plug, pull that plug, and one other and compare. Take a picture and post of the plugs also if you have time.

Good luck!