Agent_Orange

So the 99 5.7 had the CEL on. run the scanner and pops... you guessed it P0300. further diagnosis shows a couple O2 sensors and misfires on 3,5, & 7. start with the normal stuff. cap rotor wires plugs.... nothing same CEL. Also did I mention it the exhaust smells super rich. well it does. so then I pull the intake and it's caked with soot n grime. couple hours cleaning it up pulling the poppets and external cleaning the injectors and replaced the fuel pressure regulator while I was in there. put it all back together (Looks intimidating at first for the newbies to a wrench, but just remember where you unplugged all the harnesses and which bolts go where. I'd never worked on anything newer than a 83 so 99 technology blew me away!) I digress. P0300 GONE!!! P0303 in it's place and now it has a rough idle. Thoughts what I did wrong if anything?


Man, I miss my 83 K5...

Agent_Orange

The more I research (this site and others are awesome!) and always looking for the most inexpensive fix I found it may be carbon build up on #3 valves. SeaFoam here I come! hope it's not a cracked head on the left bank. these 5.7's are so super sensitive to even the slightest abnormality that might effect optimum efficiency.

Agent_Orange

SeaFoam 1/3 gas, 1/3 oil, 1/3 through the brake booster into the intake. lots of impressive white smoke, some small thudding back fire and low n behold......






Still a miss fire on #3. also when I put it in drive she stumbles n stalls. Any other avenues I should pursue. I'm running out of shade tree mechanic ideas and don't have the equipment/tools/knowledge to get to far into the motor.

in2pro

Have you checked for any vacuum leaks?

Agent_Orange

all the obvious lines are connected but as far as the intake seal and spider control seal I believe I reinstalled them properly. how would I test one of those mating surfaces seals?

Agent_Orange

Ran it down the road today. stumbling, no power CEL flashing. limped it home and coded P0300 is back. this truck sucks!!

in2pro

How does the distributor look? a random misfire could be a worn distributor shaft and or gear.... pull your distributor and compare it to a new or re-manufactured one at the auto parts store...

Agent_Orange

it's not the random P0300. after new cap rotor plugs wires and a fuel pressure regulator plus a thorough cleaning of the intake it's just a misfire on #3 P0303. and I can't find any obvious vacuum leaks (i.e. all lines are connected to where they should be and no breaks in the lines.)

in2pro

With the engine running a can of starter or choke cleaner fluid sprayed around the intake should reveal any leaks with a change in engine response to the fluid getting sucked into the combustion process.
If you are only getting one single mis-fire then I would think its back to plug/wire or distributor cap...
You could also perform a compression check to see if all cylinders are within spec of each other...

Agent_Orange

so lets get down right systematic... Suck Squeeze Bang Blow


Suck...the intake is sealed tightly. no change in RPM when starter spray was applied around the intake. the Throttle Body and intake were cleaned spotless when I put in the new fuel pressure regulator.


Squeeze... I still have to do a compression test.


Bang... the particular cylinder in question has "good" spark. a nice deep blue and all plugs are gapped accordingly. I might re pull the intake and check that particular poppet injector to ensure it's not clogged. but I have run just about every kind of snake oil I can find to clean the injectors seafoam, marvels, stp injector cleaner (but if it's flat out plugged no cleaner in the world will help)


Blow... exhaust smells like fuel.




so assuming the comp test is in 10% of all other cylinders I can only imagine it to be a mechanical malfunction i.e. bent rod, cracked head by #3, blown gasket (but coolant/oil is clean and showing no signs of oil or coolant loss)


I'll keep you posted what I find on the comp test boys.


Thanks