scooter00754

[]Ok here gose i just got a chevy van vortec 305 or 5.0 and it runs rough and drinks the gas missis all the time i also smell gas so it seems very rich to me i have put in a new cam sensor checked fule pres. plugs wires cap rotor( ac delco) fule filter and the air filter are all new and i get the p0300 now im looking into this as close as i can and i have found that with the pcv removed from the port on the valve cover that i have some vacuum at the port in the valve cover why is this intake or vavles i have vacuum at the pcv valve and every were it should be but why dose it suck through the valve cover any help would be great thanks Roland[:'(]

John86

wat is sucking thru the valve cover?? how many miles r on ur van. wat yr is it?

scooter00754

year is 1999 has 193 mi. seems to have vacuum at the pcv port in the valve cover will run and drive but runs very rough

John86

well it's supposed to have vaccum at the pcv port it gets it from the intake. do u have a way to see if it's missing all all cylinders or more a specific cylinder? u could have bad fuel, restricted exhaust system, bad ignition coil or connections. could even be mechancial failure. how long has it been doin this?

golfer

Just a brief background :

PCV = positive crankcase ventilation system prevents crankcase vapors being discharged into the atmosphere. It's vitally important that crankcase fumes be drawn off by the PCV system , if it's working poorly or not at all this will allow a rapid buildup of sludge , water , acids , etc. that will shorten the life of the engine.

Basically there is fresh air introduced into the motor from one side and gets circulated through and the mixed fumes leave through the other side. Whenthe fumesleave the engine they go to the intake manifold where they are drawn into the cylinders and burned. To prevent upsetting the air/fuel ratio in the intake manifold the PCV metering valve is placed in the linebetween the crankcase and the intake manifold. The PCV valve basically has a valve and a spring.

At idling speedthere isless blow-by generated and engine carburation is less capable of handling a large volume of crankcase air. So at idle there is a strong vacuum that pulls the PCV valve plunger forward toward the spring pressure , this forces the air to flow through a small metering hole which restricts the amount of air to the manifold.

As engine speed increase the blow-by increases and carburation system can absorb more crankcase air. The vacuum drops low enough to allow the spring to move the plunger midway allowing the air to pass through the metering hole as well as around the plunger.

During periods of high speed or heavy acceleration engine vacuum drops and blow-by increases. This will cause a reverse flow and engine fumes will flow through the connecting hose from rocker cover to the air intake filter where they will be drawn into the throttle body air horn along with the regular air charge.

When the engine is stopped there is no vacuum and the spring closes the valve . This prevents fumes from percolating into the intake manifold which would cause hard starting.

A slow , rolling , rough idle , with back flow could indicate the valve is tightly plugged or in the closed (engine stopped ) position.

If the valve is stuck in the normal operating position ( fully open ) , frequent stalling and fast , rough idling may be present.

The PCV valve is one of ... if not the ... most overlooked maintenance items. Especially curious why especially when it only costs a few bucks.

scooter00754

thanks i have never noticed the reversing of vacuum at the pcv the draw is slight but it is there hmm ,wierd any way im not sure how long its been doing this i just got it the truck seem to lack power,gets like 8or9 mpgs at best,and i smell gas alomst all the time ,has code p0300,missis badly i have driver it about 600 miles since i changed the oil and it is still clean so it had to have some kind of mantince i get a soild vacuum of 18 gose right to 0 if i hit the gas and to 24 or 5 when i let off fule is 57 when ideling and gose to 60+ when i give it gas and drops to about 40 when i let off and gose right back to 57 at idel i have cleaned the egr,new cam sen.new acdelco cap plugs rotor wires fule and air filter it starts greatbut runs badly i have also noticd that my ses light will not come on i have tried every thing i get codes but no light im going to check the bulb if i can get to it im at a loss with what to try next and i also check the spark at the end of every wire and seem to get a constistant orange spark through a spark checker thanks Roland

John86

r ur plugs wires wired properly? have u checked the timing?

scooter00754

yes the wires were installed corectly but i will tripple check tomorrow along with the timing im just about to drop it off as nutthing seems to help

golfer

You mentioned it smells rich with fuel while misfires may do that things like engine temp. sensor, intake air temp sensor , vacuum leak and of course the ever so famous intake manifold gasket leak could be contributing to your problem.

scooter00754

i have good solid vacuum,would my needle hold stedy with a bad vacuum leak ? running and at 180' or so it also pops from exaust my next task is a wet/dry compression test but man is a pain in a van i may just lomg block it or switch it out with a good 5.7 but dam the cost of it all it is a work van so it dont have to be perfect but the gas milage is killing me i will let you know what i find with the compression test