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OK, I got an interesting one here

cybrfire

cybrfire

1 ton status
GMOTM Winner
Joined
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Location
Iowa
First a little history on the truck.

My shop truck is a '79 3/4 ton full time Chevy. It sat for 5 years rusting away when I bought it for $150 bucks.

Fixed some minor issues with things here and there. Did some brake work and ended up replacing the heads. Major cracks in the old ones. Had to grab a fuel tank out of another truck to put in this one.

Here's the deal, driving around in town is no problem. My shop is 15 miles on the dot from my driveway. When I leave in the morning almost like clock work 7 miles later the thing will start to chug. I mean CHUG! enough to were you can hear the slack in the u joints.:D

Seems fuel related but not really sure. Switched out filters and swapped out fuel pumps. Checked lines for pinching and so on but nothing there. Pulled the carb apart and cleaned it up.

Any suggestions? Similar experiences. Biggest part of the problem is it doesn't do it in town so nothing to check when I get to the shop.
 
Oh, another thing is when it chugs on the highway, if you pull over and leave it running and just sit there for a few minutes its good to go again.
 
Ok... here's a strange idea for a strange problem. When you swapped out the gas tank.... hmmm... is the tank still vented properly? Try driving it to the shop with the gas cap loose/off.

Otherwise. I would look for a heat related issue. Possibly electrical. Might have an ignition coil on the ragged edge of failure. Gets too hot and starts going whacko. Stopped on side of the road, idling, the engine fan would cool things down a bit, especially in Iowa in the winter.
 
couldnt be losing compression on the highway could it? if the heads were cracked i would guess that there is a pretty good chance the block is cracked too? checked the compression on it?

what about the ignition system? my daily driver used to run great, except when you let it warm up in the mornings...found out the rotor button was gone. only the spring making contact with the rotor.

but it seems that you are focused on the fuel system. put at pressure gauge on it?

just some thoughts.



ryan
 
Jagmeister said:
Ok... here's a strange idea for a strange problem. When you swapped out the gas tank.... hmmm... is the tank still vented properly? Try driving it to the shop with the gas cap loose/off.
Click to expand...

good idea
 
I had something sorta kinda like this happen to me once before, but mine wasn't as consistent as it sound like yours is. Mine truck would run a few miles, start running like crap, and then die. You could wait a few min. then it would restart and run a few more miles and repeat. The problem ended up being water in the fuel. I dumped in a bunch of heat and it got happy again, and so did I :D. Dunno may be worth a try if you can't find anything else.
 
reminds me of my buddy's old caprice - the sock on the end of the pickup was either clogged or collapsed and it acted like that.
 
I doubt its your issue, but my friend had a weird problem that came and went,

turned out to be the 12 volt to the cap, it was loose and was moving around enough to cause issues,
 
a similar case...

I had a friend with a 62 Valliant slant six with the same dilema as yours..we replaced just about everything trying to get it not to stall after you drove 10-15 miles..ran perfect until you got that far,then it would bog out and stall like it ran out of gas or spark..

We put on a new cap,rotor,gas filter,coil,ballast resistor,junkyard distributor,new points and condenser,rebuilt the carb,and put an electric fuel pump in it too--added "dry gas" by the gallon,carb cleaner--..it ran exactly the same,like it was haunted or something..we wanted to push the POS off a cliff after a month of money wasted and time dicking with it!...:mad:

My friend got disgusted with it,and traded it for a ratty 72 Chevelle (the Valliant was in MINT condition,it was his aunts car originally..but it was a dorky looking 4 door ,so off it went!...)..he was very happy to be rid of it,and the Chevelle ran decent,had a 327 4 spd,but was all dents and rusty..

About a week later,the Valliant pulls in his yard,with the new owner at the wheel..he said he found the problem..he pulled out the gas tank,and said about a dozen ping pong balls came out of it when he flushed it out,:eek1: --he thought it might have had water or dirt in the tank,or maybe the "sock" was clogged like "Hack" suggested..but when he saw those ping pong balls,he knew he found the problem..

I guess the car had to run 10-15 minutes to suck them down against the "sock" in the gas tank,and stall it out--then a few minutes later they would float back up,and it started right up again..car ran great for 2 years after that...:doah: ..too bad we never pulled the tank out!..his aunt wasn't happy he traded the car at all..:crazy:

So it COULD be something in the gas tank--or the vent and gas cap as suggested already..lets us know what you find!!
 
I had a 77 Mercury that did the same thing. I found my distributor shaft was broke when the motor was warmed up good it would spatter and chug. Changed distributor and had no more problems.
 
All good suggestions. I've been thinking about the tank as well. Scrapped out a few vehicles in the past six months and the tanks are always the first thing to come off. Have about 5 of them sitting outside the shop waiting to be crushed before taking them to the scrap yard. Not sure which vehicle this tank even came off of. I'm gona pull the cap off today before I head out and see if that makes a difference. I'll keep ya'll updated.

It's a cheap old truck so I have a hard time throwin cash at the problem especially when I dont' know which way to throw it. I'd rather it happened all the time so a person would have a chance to diagnose something.
 
I had that exact same issue w/ my '74. It turned out to be a worn fuel pump. It would run like a champ at idle and just cruising around (for the first few miles). Then it would do the exact same thing. I put on a new fuel pump and problem was solved. Basically, the fuel pump was just weak enough that it couldn't keep up with the engine, but fast enough that it wouldn't show itself easily. Talk about a week long headeache till I figured that one out!:doah:
 
2High4U said:
how in the hell did they get in there!?
Click to expand...
Old drag racers would put them in an opponents car. It wiould run fine for about half track, then it was done. That car does not have the reducer in the fill neck for unleaded fuel. The balls will drop right in.
Probably put in by some local punks.
 
I had that happening to my truck when I bought it. Took me 4 days to get it the 40 miles to home. Changed the fuel pump....twice. Replaced some cracked lines that I suspected were sucking air, it eventually just went away.
 
Well, fuel tank venting has been eliminated. On to the next suspect. Might just as well do a tune up. Coil and all its due anyway.
 
cybrfire said:
First a little history on the truck.

My shop truck is a '79 3/4 ton full time Chevy. It sat for 5 years rusting away when I bought it for $150 bucks.

Fixed some minor issues with things here and there. Did some brake work and ended up replacing the heads. Major cracks in the old ones. Had to grab a fuel tank out of another truck to put in this one.

Here's the deal, driving around in town is no problem. My shop is 15 miles on the dot from my driveway. When I leave in the morning almost like clock work 7 miles later the thing will start to chug. I mean CHUG! enough to were you can hear the slack in the u joints.:D

Seems fuel related but not really sure. Switched out filters and swapped out fuel pumps. Checked lines for pinching and so on but nothing there. Pulled the carb apart and cleaned it up.

Any suggestions? Similar experiences. Biggest part of the problem is it doesn't do it in town so nothing to check when I get to the shop.
Click to expand...
Unhook the feed line to the fuel pump and give it a few shots of air. The pickup sock may be clogged with varnish/crap. If it is, the shot of air will probably blow it right off, along with the sock.:D
 
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