My truck has been running with a half full fuel filter since I bought it. Running great I might add. Yesterday I drove it and it was running rough and when I would give it gas it would spit and cough unless I eased into it real slow. I checked and the fuel filter was almost dry and there was only a trickle of gas coming in. I parked it in the drive way let it idle for a while. It would idle fine, run smooth but could not get a full stream of fuel. Put it in the garaage last night, went out this morning and the filter is full of fuel. Never seen it totally full. Does this sound like a fuel pump issue or possible restriction somewhere and it worked its way loose? JW
You can check your fuel pressure with a vacuum /pressure gauge. Just disconnect the fuel line and connect the pressure end to the gauge and start the engine up. The gauge should read 3-4 pounds. Then you can do a volume test by letting the fuel run in to a coffee can while the engine runs at an idle. It probably wouldn't hurt to change the fuel filter either. If the fuel line is restricted you can take off your gas cap then blow a little air through the fuel line to see if it is clear. Also check your cap and make sure it is vented properly, cause if it's not venting it will create a vacuum and your engine will starve for fuel. One last thing, in one of the previous posts on this site there was a Carb. not sure what kind , that had a internal filter right where the fuel line connected to the Carb and was causing problems. I hope this is enough Info. to help you solve your problem.....Big Tim
Fuel Flow Also ; Disconnect the fuel line where it connects into the fuel pump , have a BIG pan underneath the truck asnd observe the fuel as it gushes out in a stream as big around as the inside diameter of the pipe ~ it *must* make a curved stream . if it dribbles out or makes a 90° bend down , there's a restriction in the primary fuel feed and it'll only get worse as the pump sucks on it ~ 99 % of the time , it's in the valve on the bottom of the fuel tank so drain the tank before remove this valve , you'll be amazed at how much crud is in it . Once you have 100 % primary fuel flow , you can move on to other things , a new pump will not overcome poor siphon .
Nate, my truck does'nt have a valve on the bottom of the tank. The fuel comes out the top of the tank via the sending unit assembly,the tube then goes down the side of the tank and through the floor. I replaced the sending unit assembly a while ago because my fuel gauge did'n't work.( It does now.) This unit has a fine mesh screen over the end of the tube. In the next couple of days I will replace the fuel filter with the Wix one you recomended, make sure the fuel lines are not plugged, replace the gas cap and refuel. Hopefully this will solve my problem. JW
Yabbutt ; You still need to check the siphon before doing anything else . or , you can do it the hard way , I'm too lazy .
Update Ok. I changed the fuel filter and checked the gas line from Carb to tank. No restriction, good fuel flow. Idles smooth and revs smooth when sitting on the driveway, but when I drive it, it still coughs and chokes after shifting and accelerating. Any ideas what my next move should be? JW
How hot was it the day you were out driving it? Read up on vapor lock and heat saturation problems besides the dirty gas line/tank that Nate is talking about.
Flat Spots There's a few things but first , disconnect the fuel line at the carby and slip a bit of paper between the ignition points (prevents sparks) and crank the starter ~ how much fuel gushes out and how far is the stream ? once again , it must GUSH out in a healthy , solid stream as big around as the inner diamter of the pipe ~ a goodly 4" ~ 5" before turning downwards . if it does this , your pump etc. is fine . if not , go back and find the problem , you're still suffering fuel starvation . Next : engine off , remove the air cleaner and peer down the carby , operate the throttle by hand , once ~ it is imperative that the first time you open the throttle ,you clearly see a stream of fuel squirting out ~ if not , the accellerator pump circuit is bad and must needs be corrected before anything else , these old tech long intake manifold engines suffered off idle flat spots from new and GM constantly made tiny changes to the carbys trying to fix it . All is well ? (no fair thinking it's O.K. , you've gotta take the time to check every item even if you did so before) , next thing is to let it idle and spray starting fluid (note : NOT carby/brake cleaner , WD40 etc.) all around the base of the carby and then each intake to head joint , there's three and you'll need to spray up from underneath too (prolly burning your hand in the process) as some leak only from below . Once in a while the bakelite insulator between the carby and the intake manifold will crack and drive you crazyas it always seems to crack on the inside where you cannot see it but air is easily sucked in under load they're cheap so unless it's *perfect* , replace it , no gasket goes between it and the intake manifold and only a super thin gasket should be used between the carby and insulator . Also , once in a while the two big flat headed screws holding the cast iron base to the pot metal carby bowl will loosen up and cause this sort of thing . I'm assuming you've checked the spark and it's blue or white and the timing is dead nuts and doesn't jump around and you didn't recently replace the condensor as they occasionally are bad right out of the box , usually failing as the engine warms up .
Vapor Lock Charles, it was in the upper 90's that day. Vapor lock was something I also thought about. After it clears are there other problems that develop? Would this screw up the timing? I have not checked that yet. I made sure all the screws and bolts are tight on the carb to make sure there is no air leaks. The truck runs fine when sitting still, I can rev it up and still good but when I drive it thats when it spits and sputters when I shift and try to accelerate. JW
Wires Crossed? Could this be the problem? These wires Don't appear to be in the correct order. Could someone confirm this. Possibly send me a picture of the correct order? I had a guy do a compression check & it appears as though he put the wires back on wrong. Thanks, JW
Crossed Wires My #3 and #4 spark plug wires were reversed. Switched them, test drove, now runs smooth as butter. Don't know why this would affect the fuel system but runs great now. Maybe two different problems. Thanks for everyones help. This is a great forum for advice. JW
Plug Wires & Firing Order This is an easy one to remember , think about Women : 15 is TOO YOUNG 36 is TOO OLD 24 is JUST RIGHT BTW : you neglected to say " immediately after I fiddled with the ignition system it began to choke and sputter " , that's why no one figured it out ~ you left out important information .
