Truck Trouble?PCV Valve?Running rough....

[LandfillLumber]

Hello, well my old tired truck is acting up again it just started running really rough like it was running on 7 cylinders or it is running out of gas.It ran fina all day then I went to drive a mile down the road and it did it right from the start of the engine.I thought it was a little cold at first but that was not the issue.I noticed I had a couple spark plug wires laying on the engine that had melted so i replaced them and it did nothing for the rough idling.I also noticed a PCV valve missing on the passengers side of the engine that appears to feed into the air cleaner??This is my biggest question is would the PCV valve missing cause this and does it go into the air cleaner( I can't see any other place it would go).Thanks for the help in advance,Victor

[sbishop]

I would say you have a vacuum leak...if your pvc valve is missing you gotta have a vacuum leak.

I can't remember how i tested for a vacuum leak...but i think i recall spraying carburator cleaner around the engine...if the rpm's go down...you have a vacuum leak....spray it around the vacuum hoses...carb if you have one!

mine is an 84 ford f-150 4x4 300ci!

[DanG]

The PCV valve will only cause that problem if it is plugged up.  If it is missing, that obviously ain't it.  Your troubles could be caused by any number of things; bad spark plug or plug wire, cracked distributor cap, worn rotor, trash in carb, or as sbishop said, a vacuum leak.  Maybe it is just time to do a general tune-up. ;)

[jamesamd]

I would say you have a vacuum leak...if your pvc valve is missing you gotta have a vacuum leak.

I can't remember how i tested for a vacuum leak...but i think i recall spraying carburator cleaner around the engine...if the rpm's go down...you have a vacuum leak....spray it around the vacuum hoses...carb if you have one!

mine is an 84 ford f-150 4x4 300ci!

The RPM will go up,if the cleaner is petrolem based ;D

[pappy19]

Could be fuel filter or bad plugs/wires too.

Pap

[sawguy21]

The Ranger was doing that. The EGR valve was sticking open due to old age, it was badly corroded. It is under a plate on the intake manifold, try giving the cover a rap with the handle end of a screw driver. If that makes a difference you found a problem. What DanG said, sounds like the old girl is due for some TLC.

[Don_Papenburg]

Start pulling and replacing plug wires while the engine is running .  If it smoothes out with one wire off  you got serious problems .  The old 292 on my dads old 4400 combine was running rough ,pulled wires till we got to 5 and the thing smoothed out ran like new , put it back and it ran rough again .  In his case it was a head gasket

[SPIKER]

could be many things as above, use a heat gun to check for cold exhaust manifold temps @ exhaust ports all fo them should be +/- 25degrees for good runing eng.   cold means no spark or hot means running lean not enough fuel or stuck open plugged injector and or dripping injector depending on the temps.

engine runs cold when too much fuel or  no fuel so additional troubleshooting needs done for each case.HF has 25 buck laser guided heat guns that are plenty accurate for this type of testing...

might also help to know year & truck brand & engine brand as there are quirks for each one which someone may already know..

Mark

[low_48]

I've had EGR troubles with my old Astro van, but it mainly acted up while accelerating. Idle wasn't good, but not really bad. Have you checked the plugs? Might have to do a compression check.