Truck runs very very rough

[alwaysbroken]

hey yall so I’ve got this 77 k10 it’s my first truck it’s a 350 with a sm465 she’s been running very rough as of like a week ago I can’t find any vacuum leaks or anything. I just replaced the fuel pump about 300 miles ago and she starts up every time no problem but she can’t idle and is even more sluggish and stalls… I’ve been scouring the forums and got some ideas but better to hear from other people as well

Here’s a video
https://share.icloud.com/photos/0f44mBJn4PVGGFdmo8lx4ChfA

 

[Sad Sack]

Sounds awful.
Heads up - You're going to be asked for a lot of info.
First thing I'd do is if all the important items responsible for air-fuel-spark have been checked as satisfactory, would be to do a compression test, let the guys here know the outcome of that.

 

[fast 99]

If a vacuum gauge is available steady or not? What is the vacuum reading? Will eliminate or confirm numerous problems with that diagnostic information.

 

[Chevy 88]

I cant download a random video for security reasons, but I assume its running bad.

Spark plug wire fall off?
Fouled spark plugs?
Bad fuel quality?

 

[texdave]

I cant download a random video for security reasons, but I assume its running bad.

Spark plug wire fall off?
Fouled spark plugs?
Bad fuel quality?

I thought you had to download the video too, but you can actually just click on the vertical rectangle video screenshot at the bottom to play the video in the browser.

@alwaysbroken Besides replacing the fuel pump, anything else that you changed, adjusted, or otherwise touched? Any maintenance done since you had the truck? Initial reaction for me is a fuel issue and/or a heavy miss but more info and checks will be needed to isolate the issue.

 

[xm20k]

Fuel filters clean?
Q jet has a small cartridge style filter in the inlet at the carburetor.
Before you bought it did it sit for a while? Mabey sucked up a bunch of junk from tank and the filters and /or carb is plugged up.

 

[75gmck25]

General rough running is often due to one or more spark plugs misfiring, or there is a vacuum leak. For example, I once had a backfire pop the PCV valve up out of the grommet and the resulting vacuum leak caused a really rough idle.

Look at articles on how to do a cylinder balance test by pulling one spark plug wire at a time and seeing the effect on idle. The basic idea is that if each plug is contributing equally, then as you pull each one (and leave the others in place) it should drop the idle about the same amount. The process does work, but it’s never fun to try pulling spark plug boots off on a hot engine.
One weak cylinder could be a bad plug or wire, pushrod off the rocker, low compression, etc.

You can test for vacuum leaks by spraying a fluid around carburetor gaskets and joints, intake manifold, and near any vacuum fittings to see if the idle gets richer and smoother. Most folks use carburetor cleaner and the small plastic tube that comes with the can, since it temporarily plugs the leak and does not hurt the carburetor. You can even carefully spray plain water in small amounts, since it will temporarily plug air going into the leak. An unlit propane torch also works, but I think it takes more finesse to turn it on and off and modulate flow while working on a running engine.

 

[alwaysbroken]

Sounds awful.
Heads up - You're going to be asked for a lot of info.
First thing I'd do is if all the important items responsible for air-fuel-spark have been checked as satisfactory, would be to do a compression test, let the guys here know the outcome of that.

Yes every every plug is getting spark and it’s getting fuel. air is maybe a different answer I havent found any vacuum leaks but that doesn’t mean there present

Sounds awful.
Heads up - You're going to be asked for a lot of info.
First thing I'd do is if all the important items responsible for air-fuel-spark have been checked as satisfactory, would be to do a compression test, let the guys here know the outcome of that.

fuel is present,spark is there, air might be a different answer I haven’t found any vacuum leaks but that doesn’t mean there not there the only other thing I did was disconnect my smog pump and put a delete pulley but I just got rid of the t off going into the egr with a solid line

 

[fast 99]

One side of the idle circuit restricted? remove both mix screws, squirt a little carb cleaner in each side then follow with compressed air if available, re-install screws.

Reach under the egr valve and try to pull the diaphragm up with finger tip or alternate use a vacuum pump. If no change, likely held open with a piece of carbon.

New fuel pump quality is very poor, has the pressure and volume been checked?

 

[alwaysbroken]

General rough running is often due to one or more spark plugs misfiring, or there is a vacuum leak. For example, I once had a backfire pop the PCV valve up out of the grommet and the resulting vacuum leak caused a really rough idle.

Look at articles on how to do a cylinder balance test by pulling one spark plug wire at a time and seeing the effect on idle. The basic idea is that if each plug is contributing equally, then as you pull each one (and leave the others in place) it should drop the idle about the same amount. The process does work, but it’s never fun to try pulling spark plug boots off on a hot engine.
One weak cylinder could be a bad plug or wire, pushrod off the rocker, low compression, etc.

You can test for vacuum leaks by spraying a fluid around carburetor gaskets and joints, intake manifold, and near any vacuum fittings to see if the idle gets richer and smoother. Most folks use carburetor cleaner and the small plastic tube that comes with the can, since it temporarily plugs the leak and does not hurt the carburetor. You can even carefully spray plain water in small amounts, since it will temporarily plug air going into the leak. An unlit propane torch also works, but I think it takes more finesse to turn it on and off and modulate flow while working on a running engine.

Yeah I’ve dealt with the pcv valve flying off from backfire and it did run rough for a day after I figured that one out but it kinda happened out of nowhere I was driving fine stopped at the gas station since ole truck was about to run on E and has ran god awful ever since…drained the tank and put 5 gallons of Sunoco 94 to see if that helped at all and nada

 

[alwaysbroken]

One side of the idle circuit restricted? remove both mix screws, squirt a little carb cleaner in each side then follow with compressed air if available, re-install screws.

Reach under the egr valve and try to pull the diaphragm up with finger tip or alternate use a vacuum pump. If no change, likely held open with a piece of carbon.

New fuel pump quality is very poor, has the pressure and volume been checked?

I was unaware the q-jets had actual idle screws I think it could possibly be nasty fuel that clogged it since she was running a little low on fuel about a quarter tank when I stopped at the gas station put some fuel in her and she’s been running like ass ever since

 

[Ricko1966]

99 cent tune up. Take off the air cleaner,rev the engine up and down with the throttle lever on the side of the carb. Now while you have the revs high put a wadded up towel over the carb intake,work your throttle lever up and down like full throttle to idle and back. The high vacuum and no available air will sometimes suck debris out of carb passages. It will be hard to restart it will be flooded so pedal to the floor cranking to restart. The fact you were low on fuel and that brought on the problem is why I'm suggesting this also check the carbureator inlet fuel filter.

 

[fast 99]

can try dribbling fuel or spray carb cleaner in each front venturi when running. If one side is restricted engine will smooth out. Of course be careful. Always have a fire extinguisher near when messing with fuel.

 

[75gmck25]

The other time I had a really rough running truck was when I was replacing a thermostat and the carburetor accidentally sucked in a piece of RTV I had scraped off the thermostat housing.
I found it when someone suggested I use a mirror held at an angle to look down the carb when it was running. One side of the primary looked normal, but the other side was dribbling in raw fuel because the small piece of RTV was blocking the air through the Venturi.

 

[Broken85]

Get it to like 1500 RPMs and spray carb and choke cleaner in it until it almost stalls out. Do it like a dozen times. We have to do this once in a while because all the trucks are running on the same 85-86 octane fuel the tractors get. Should get a nice idle after that.