Could the Cat's be bad and no DTC?

[Tacticalsaint]

I'm still fighting a losing battle it seems. The only DTC I get is P0300 and its killing me. I've done a complete tune up even new fuel injectors, and distributor, fuel filter, plugs, wires ect.... So I'm running out of options and money. Would any of you know if Cat's be bad and no DTC? I would assume not but stranger things have happened. Please help I miss driving it. It still is a beauty in the driveway lol. Thanks guys!

[Towncivilian]

Have you checked for air intake leaks? Ensure the air filter is sealing properly, too. A compression test may be in order as well. Clean EGR valve & hoses.

What spark plugs, wires, distributor did you use?

[Tacticalsaint]

I have taken the entire air assembly out cleaned and check and reinstalled also cleaned the MAF with proper cleaner. I use NGK all the way. The distributor I got from Buy auto parts.com It was their house brand with 1yr warranty. The EGR, I have not cleaned, how would I do that? it appears to function properly. I did let it run for bout 15 20min the other day and noticed it seems to misfire in a cycle about every 20-30 sec and lasts about 10-15 sec.(the misfiring event) By Standing at the tail pipe and lessening. When I clear the code it still misfires but DTC will not trip unless at or about 2000rpm 1725rpm the last time I induced it. I've also replaced the ECM. I've also checked the ground wires cleaned and such. VAC lines I've checked and some I replaced.

[Towncivilian]

I'm afraid I'm not sure on the exact procedure on EGR cleaning since my Pathfinder doesn't have an EGR system. I'd imagine you could take the valve off and spray it with brake cleaner and ensure the hoses aren't restricted either, maybe blow some compressed air through it - but since you've checked them all I doubt they would be restricted.

I suggested EGR because page EC-267 of the factory service manual suggested it, among other things. It may be worth trying to follow the diagnosis procedure that begins on EC-268 as best as you can, as well.

Did you ensure the gap on the spark plugs was correct before installing? They should be within spec from the factory and the NGK plugs I used I didn't check and my Pathfinder has no problems, but it would not have hurt to double check.