Engine troubles??

[BIGTEN]

Truck was running fine couple weeks ago and all of a sudden it barely stays running, I have to keep my foot on the pedal to keep it goin and when you let off it shakes and sputters and is extremely quiet. I changed all the vacuum lines to the carb but still the same, did the starting fluid trick to see if it got sucked into anything but nothing. This is extremely baffling?? I took it out the other day to see if I had fixed anything and went down the street it wont go past 35 and the auto trans stays in gear for about a minute and then shifts over. I can have the pedal to the floor and its like it doesn't want to move, but it does if that makes any sense. Its a 350 sb all stock with all the smog setup with a q-jet 350 trans if that helps. Also when you move the gas pedal in the right spot just a touch the carb sounds like a sucking vacuum dont know if this is normal or its just the engine getting its air?

[Corts60]

I can't remember, do 350 trans have a vacuum modulator? When you describe the trans holding 1st gear for a long time that sounds exactly like the modulator is not getting vacuum. And that would also mean you have a vacuum leak down there if the line is ruptured.

[86c20]

what year is your truck? my 86 did the same thing come to find out it has a computer controleed dizy i swaped it out and no more problem

[bk2life]

possible accelarator pump dead. and with the cold weather its having a hard time tryin to run.

not going over 35mph would make sense of not shifting to well either.

alot of suckin vacuum noise, that one has me puzzled. vacuum line popped off maybe?

post more info

[motornut]

yup I'd check the intake vac line to mod valve
mine was acting up all of a sudden,the hose bit came off

[mrolds88]

Is it making a whistling sound all the time? Is it idling fast? Those two would indicate a vacuum leak. I would double check the timing. Since a LOT of squarebodies used that plastic and aluminum cam gear from the factory, it almost sounds like the timing chain jumped to me. Easiest way to check it is to turn the engine over until the tming mark lines up on the timing cover and pull the distributor cap. If it doesn't line up, that would be the first suspect. Also while you have the cap off, you can check just how sloppy the timing chain is. All you have to do is rotate the crank backwards until the distributor moves. Shouldn't have more than about 5 degrees.

[BIGTEN]

Its a 79 square, I changed the vac mod not too long ago so probably not that. I'll check under there for ruptured lines and such.

[bilfman]

Brake booster vac leak?

[Zebb]

Float stuck maybe or some crud got sucked into the carb?

[motornut]

a thought
when i did mine carb lines i had a air leak
I had to tap the tube back into the carb housing
meaning the small tube sticking out the side of the carb,pulled out when pulling off the old tubes
looked ok,but had to tap them in

[ZMAR]

My 84 does the exact same thing. I.e. sounds like it has a HUGE cam, won't idle, and won't go over 30. I have to hold the throttle halfway down to even start it. The only difference is it is overheating. I have no idea wth is going on!
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[BIGTEN]

Ok this morning changed the booster check valve, grommet and line put a quart of oil cus it was low. It acts like its normal starts up fine idles a little fast but something is still wrong. At this point I have no clue?

[BIGTEN]

Finally figured it out, had some vacuum hoses flip flopped to a thermal check valve for emission control!! Now she runs better than ever.

[Corts60]

Well done!