i have the L35 (w-vin) 4.3 vortec with cmfi. when i take off it bogs and sputters like its missing. also it smells like its burning rich and will blow thick black sutt out of the tail pipe. i thought the catalytic convertor was stopped up so i removed it, i put new plugs, plug wires,fuel filter and ive run some injector cleaner in it but i cant seem to fix the problem. dont think its the tranny or the head gasket. any ideas,please give me your insights, im just an old school shade tree Ga boy and these computers and sensors give me fits. sorry for rambling,please help if you can
thanks,David

 

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You most likely have a bad FPR (fuel pressure regulator). To narrow it down, you could remove the upper plenum and pressurize the fuel system, inspecting for leaks.

 

i had the exact same problem. Everyone told me it was the fuel pressure regulator. So i spent the 50 bucks and put it in. when we went to check for leaks had a 5 foot stream of gas fly out of the two feed lines that come in from the side of the intake manifold and go to the spider. Make sure you get the gasket and check that. That i am very sure is your problem. You will know right away when you remove the plenum cause the driver side will be pressure washed and the passenger side will be all carbon. The part is 100 bucks or so at dealer, not many parts places have them. don't even have a name that i know of just spider feed lines.

 

These lines are the "nut-kit" as they are commonly referred to as. They rarely fail if they have not been moved since new. Most often, they fail after the spider has been removed and reinstalled without replacing the lines. Always replace the nut-kit when servicing the CPI spider.

Lindertech.com has some good prices on these parts!

 

ya ur problem 99% lies within the plenum. its either 3 things. the FPR, nut-kit, (like mentioned) or the entire spider assemble needs to be replaced. i've had 2 of those 3 go bad and had similar symptoms as u.

to check for leaks in the plenum, take the upper plenum off (about 10 bolts and a few other lines and such to disconnect) and turn the key to the on position. this will send fuel to the injector and u will be able to see any visible leaks. this is a great test to see if the plastic fuel lines leak. also check for clean and dirty areas in the plenum. a clean 'golden' type of area means there has been fuel there and it has burned off. sometimes u will even find fuel puddled up inside of the lower plenum.