Got an 04 Blazer 4.3L, had a catalytic converter replaced, the guy who replaced it said looking at the discoloration of the catalytic, he said unburnt fuel is coming down the exhaust and igniting in the catalytic. I started by checking the spider injector and fuel pressure regulator, the gauge goes to 60 psi when started, you turn the engine off within a minute it's down to 15 psi, I'm thinking a slow leak. Anyone seen this or had this issue?

 

Seen a fuel pressure regulator do this and also a fuel pump .

 

I think this scenario is doubtful if the SES light is not coming on from either a misfire or inability to control fuel mix properly. Not to say that fuel pressure should leak down to 15 psi in a minute. Just doubt that fuel pressure leaking down as you say is the cause of your converter going bad. But I have been wrong before.

 

If the pressure was a constant 60psi while idling, wouldn't that put more suspicion on the regulator and spider? I mean to get inside the exhaust you pretty much have to go combustion chamber and out the exhaust valve. Would a weak spark plug or plug wire be a culprit?
I was planning on pulling off the intake, reconnecting just the fuel line and have someone turn the key to accessory and watch the regulator and spider injectors to visually verify any leaks, I will check the plenum floor for any signs of washing too. I just wanted to know if anyone had any other ideas before I dive in. The cat died of old age being it's an 04 model.

 

no SES light. Also had an O2 sensor, downstream I think.

 

O2 sensor replaced, damn I can't think straight today, too much coffee or not enough lol.

 

Wouldn't too much fuel to the point where unburnt fuel passes through the cylinder (to the converter) cause a misfire and result in a SES light for a misfire? That's my point.

p.s. Have you seen the sticky at the top of the 2nd gen forum on fuel pressure testing?

 

ok I did check the thread regarding fuel pump testing and can do that without cracking open the plenum

 

FYI a lot of the upgraded MPFI spiders regulate fuel pressure to 58psi instead of 60+ requirement as described in the sticky. Other than that, IMHO the sticky is golden!!

 

Is it worth the cost to covert to a multi port spider?