I recently bought a 2003 mazda b3000 with the 3.0l. it didn't idle very well and couldn't pull itself down the road. it chugged and had a dead miss. I got the valve cover off the exhaust side to find a broken valve spring. I got it changed and the motor sounded worse. We figured out pretty quickly the cat was plugged solid as mouse nest fuzz and junk came out of the tail pipe and no smoke. like zero smoke. we cut the pipe off behind the cat and cleaned it out. the problem was still there. sometimes the code would be a p0303 for the cylinder three misfire and other times it would show a 301 302 and 303. along with a simple engine misfire. we did plugs wires coil pack. we kept trying it and for two days it started to run better, the backfire had almost went away and it was gaining power back. however today it started failing again. it will cut in and out. one minute it runs like it should and the next it cant even pull itself onto the hoist. I have a few ideas as to what I should do next but I would appreciate anyone who can offer some ideas as well. when it pops it almost sounds like the pop is coming back into the intake side. plz help

 

Do u have a vacuum gauge? I’d suggest putting one on at idle, just to make sure there isn’t valve issues... I seem to remember 3.0 having soft valve seats for a couple yrs.😉

 

Welcome to the forum

Yes, with misfires spark plugs are the first to check or change, but THEN if little to no improvement, you really need to do a compression test

All spark plugs removed FIRST
Then do the test one cylinder at a time and WRITE DOWN the results

3.0l Vulcan engine should be about 155psi with good battery for cranking

Reason to do compression test next is because its really a waste of time and MONEY to buy other "maybe this will help" parts, if its IS a compression issue

 

Compression and spark. I forgot to mention of course I have done a compression test as well as there is spark at every cylinder. The problem is intermittent. Thanks for the quick replies so far!

 

How old is the fuel ?

 

What were your compression test results? Did you do both dry and wet tests?