Hi. I'm trying to track down the source of a random missfire code p0300. Am now looking into fuel system.does anyone know if the fuel pumps grow week over time or is it a, work or not working type of part,nothing in between. Thanks for any input.

 

What engine are you working on?

Any other codes ??

Yes fuel pump can get old and tired !!

Cheap after market ones can fail in a few hours

I think your looking in the wrong direction easy to check the fuel pressure

How do the plugs look ??

When did you last change the wires ??

 

Thanks for the reply ..
It's the 3.4 5vz-fe engine. I put new plugs and leads on it 2 months ago. The code I'm getting is p0300 random misfire,no others.
The plugs all look pretty good ,a tiny bit of black moistness on 2-3 of them I'm asuming due to missfire.I've resistance tested the coil packs ,they are within specs. Today I'm going to put the old spark plug leads back on just to be sure the new ones don't have a problem.
A month ago I was hearing a vacuum leak,found it to be an injector with bad o ring seals. Replaced the o rings on it and all the other injectors too.
While I had them all out I bench tested them all and forced carb cleaner through them while tapping power lead to 12v battery;When I was done they were all spraying really well. Reinstalled the injectors ,new intake manifold gaskets and it was running better than it ever has.
The intake gaskets were not toyota brand,I've picked up a stethascope to have a better listen around the new gasket area today.
I pinched the return fuel line trying to increase pressure with no change to rough running . Next step with fuel is to rent a fuel pressure tool.
you're thoughts?