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Why is my truck doing this

S

Sparky

1/2 ton status
Joined
Aug 20, 2000
Posts
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Location
San Antonio(summer) Texas A and M (school year)
The other day I am driving down the street and all of a sudden my truck starts drving all kinds of screwed up. Didnt happen gradualy just all of a sudden. It hardly ran above 2000 rpm and idles like crap. I nurse it home, and drive it the next morning and its fine again, but only to screw up and do the same thing later. (Only seemed to happen when my girl friend was with me. I think she bad mouthed my truck one too many times or something. hahaha)

So I start checking the obvious stuff. First i looked for vacum leaks and didnt find any. Next, I pulled the cap off the distributor and checked to make sure the mechanical advance wasnt screwed up or anything funny like that. Found that some stuff was worn out under the cap so I replaced the cap and roter, and while I had it apart I tested the coil and the ignition module and both checked out. (the capaciter is new so I dont think thats a problem) Put it all back together and the same problem persisted so I replaced all the spark plugs. I have headers so I figured they might have gotten hot one to many times or just decided to stop working right once they got hot. At the same time I took the carb apart to make sure there wasnt anything obviously wrong, and it all looked good. I had rebuilt it less than a year ago so I didnt acid bath it or anything this time. Put the thing back together with new gaskets and a new fuel filter and now it has new problems.

Now, it starts up and idles fine, but will hardly drive untill it warms up. Once it warms up it runs pretty decent except above half throttle. As in, as soon as i open the secondaries up it falls on its arse or back fires a bit. I replaced the accelerator pump and it works fine when i watch it squirt fuel every where when the truck is off so that shouldnt be a problem. I have adjusted the spring for the secondary air flap valve/metering rods in just about every place possible, and it has the same problem. Additionaly, now it seems to be going through fuel like crazy. Smells really rich, not when it idles, but as soon as I start driving it while its still cold or as soon as I open the secondaries.

So anyone have any idea what the problem is. Obviously, it sounds like i screwed some thing up in the carb, but can anyone tell what I did from these symptoms. I have rebuilt mine, and taken it apart a couple of times as well as some friends carbs and never had any problems before. Does it sound like I bent a metering rod putting it back together? Didnt tighten the seats down enough or the needle fell off the float?

I appreciate any help anyone can give me. I have to drive it home about 150 miles from school in a few days, and I need to get it fixed as soon as possible.

PS The carb is a quadrajet, and the distributor is an HEI. I did not check the timeing because I dont have a timeing liight at school /forums/images/icons/frown.gif

Ryan
 
are ya sure yer gettin enough fuel? maybe the fuel pump is bad. thats all i would be able to think of. or ya can check for crimps in the fuel line. that happened to me. it was a real bad crimp. hope this helps. later.

jacob
 
I would check the choke setting, sounds to me like it the choke may be staying on after the motor warms up, also look on the side of the carb and make sure nothing is keeping the choke from going off. You might also want to check your air cleaner and filter. Or you may have gotten some bad gas, did you just put some gas in your truck when the problem started ?
 
Have you changed the HEI module?

It sounds llike this MIGHT be getting hot and failing...
Does it fail like this when it is warmed up or all the time?

Good luck.
 
I feel like the problem lies in the carb. Specifically in the choke. If it's running rich, obviously you are getting enough fuel. Check the plugwires while you are under the hood. Make sure the butterflys are opening properly, otherwise you wouldn't get enough air for the amount of fuel.
 
exact same problem. it was the fuel pump. If you're runnin the q-jet, buy a new fuel pump, put a big in line filter on it, and get rid of the filter inside the carb. That made a huge difference for me.
 
Checked all that stuff, and its all good. No crimps in the fuel line. The choke works just fine. In fact, its already 90 degrees here so it pretty much barely comes on anyways. The more I think about it the more I think its timeing related. When its cold, it hardly runs (i'm guessing) because the fuel is still cool coming into the combution chamber so its not igniteing untill right around top dead center, and then when it warms up the fuel ignites slightly before TDC making it run a little better, but still dosent have have enough advance making it slugish. Then when I get on it and the fuel really starts coming in it dosent have enough ignition advance to keep up at all.

I finaly found a friend here at school that has a timeing gun with him so we are going to go check it later. I will update after that.

Ryan
 
Mine did the exact same thing. It was the fuel pump. That's not something you can check externally either. You can pull the fuel line off the carb and have a buddy turn it over (undo the coil wire on the HEI first to make sure it won't fire up) and see how much comes out. It should gush like a fire hose. If it's not working right, you get all kinds of problems that make you think it's the carb or timing. Mine was real gradual too, so it took me awhile to figure it out. I could be wrong, but it sure sounds like what I went through.
 
i had a camaro that did this once, it happened right after i changed to holly carb with a torker series manifold. me and
three gearheads couldnt figure out why it work like magic for two days, then all of a sudden it started messing up like
you said, we even went back to the stock stuff and it still did '
it. it was the coil all along.
 
Well, I got a timeing gun and my problems are now all solved. Some how the timeing jumped to like 2 degrees after top dead center. I dont know how becasue the distributor did not move. I guess the timeing chain stretched or something. Maybe it skipped a tooth. Last time i had the timeing cover off it was starting to look a little stretched, but it wasnt that bad. Anyone see any reason the timeing could have jumped that much all of a sudden? I dont think it is possible the distributor moved becasue the bolt holding it in place was plenty tight.

Ryan
 
Grim,

Actually, a stuck advance was about the first thing I checked when i pulled the whole thing apart. I guess I should check it again since the timeing got thrown that far off. I wouldnt want the advance to become unstuck and throw me up to like 20 or 30 degrees of advance at idle. /forums/images/icons/wink.gif
Thanks

Ryan
 
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