Engine Chugging and Vibrations

[Big Orange 78]

78 Chevy K20 w/454 and edelbrock 650 cfm carb w/ th350 tranny. Chuggs when i press on the accelerator around the 25 mph - 45 mph range. Especially noticable when going up hill or when the engine is under a heavy load. Rebuilt the carb and changed the fuel filter to get rid of a flooding problem, however chugging still remains. Still does it and it is more noticable now then before. I am thinking it is a ignition issue. Also I get a vibration when i step on the gas from it seems the front of the truck. Vibration goes away at higher speeds i.e. 65 or higher. But it returns when it get back down around 40-55 mph.I am thinking it is a tire or maybe my drive shaft. does it in 2nd gear as well. Any help is much appreciated!

[Chris Guthro]

Shot in the dark but what kind of shape are your plugs in? and maybe the vibration could be a wheel bearing? does it make a howling/whistling noise?

[Big Orange 78]

just replaced all the bearings and races front and back, and u-joints as well. haven't checked the plugs yet.

[85sierraclassic]

the chugging and what not sounds like plugs could have alot to do with it, since you had flooding issues and havent replaced them since that was taking care of. might even have to do a little with the vibration mine was using oil and fowling plugs really bad and then they would do it. the truck would pick up a pretty bad vibration when it was under load and would cut out but would some what go away if you were running down the road at a higher rpm.

[notyo_cheez]

Fuel pump.

[Big Orange 78]

fuel pump does look pretty old and beaten up. Do you think i am losing pressure at the pump and that is the cause of the intermitten loss of power?

[cr34t3d_by_d4rkd3n]

idk if a 78 has a highway spark controll but if it did thatd be an obious sign of ignition.... pull the plugs, let is know the color and condition, but tho knows, where r u feeling the" chugging" floor boards? wheel? pedal?..

[Big Orange 78]

chugging and loss of power is definately engine, its just dieing off and losing power, stuttering and then its fine for a few minutes until i press on the gas again.

[notyo_cheez]

Originally Posted by Big Orange 78

fuel pump does look pretty old and beaten up. Do you think i am losing pressure at the pump and that is the cause of the intermitten loss of power?

Good possibility. I learned in troubleshooting engine problems is look at simple and cheap first.

If cap, rotor, wires and plugs are all fine next step is fuel, by substituting a clean fuel filter for a suspect and the problem persists check the pump. If the fuel pump has a leak in the diaphragm you can still start it but you'll get that chug under load, happened to me once with a '76 Monte Carlo. It behaved just as you described, new fuel pump fixed it especially when it died on me completely and left me stranded.

[notyo_cheez]

While you have the fuel pump off drop your tank and pull your sending unit. Check the sock for contamination, blow out the lines, etc. so you can rule out any delivery issues.

[BlackTopMotors]

I agree with starting with the basic items first...think big tune up.

Sometimes its as simple as a dirty or too small of and air cleaner/the carb is starving at higher rpms. Bad set of wires, plugs...

Move through each item systematically.

Best to you! Hope you get it resolved soon!
.
.
.

[Big Orange 78]

here are some photos of the plugs. all the threads seem to have a light coat of il around them. some of them smell like gas. they all appear to look the same they have grayish deposits on one side, and a little scorching on the other.

[Big Orange 78]

I was reading somewhere that edelbrock carburetors like about 4.5-6psi. if i need to replace the fuel pump, will i need to get a regulator as well?

[Big Orange 78]

took it for a drive and the surging and the chugging seems to have gone away. but the vibration remains. all my weights are still on rims, everything has fluid in it... i.e. trans, diffs, transfer case. drive shaft still has the weight on it. its really bad at 50 mph and especially noticable when i let off the gas. when i let completely off the gas it goes away. but it is seems to be a pulsing vibration from the front end right side. thats just what i can feel while driving it.

[cr34t3d_by_d4rkd3n]

Originally Posted by Big Orange 78

took it for a drive and the surging and the chugging seems to have gone away. but the vibration remains. all my weights are still on rims, everything has fluid in it... i.e. trans, diffs, transfer case. drive shaft still has the weight on it. its really bad at 50 mph and especially noticable when i let off the gas. when i let completely off the gas it goes away. but it is seems to be a pulsing vibration from the front end right side. thats just what i can feel while driving it.

when my truck did that,(vibration) i dropped a drivers side upper ball joint, put the tire thru the fender. Come to find out every joint is toast, my camber, toe is way off due to steering and ball joint slop, she pushes like a duck down the road.

[cr34t3d_by_d4rkd3n]

Originally Posted by Big Orange 78

took it for a drive and the surging and the chugging seems to have gone away. but the vibration remains. all my weights are still on rims, everything has fluid in it... i.e. trans, diffs, transfer case. drive shaft still has the weight on it. its really bad at 50 mph and especially noticable when i let off the gas. when i let completely off the gas it goes away. but it is seems to be a pulsing vibration from the front end right side. thats just what i can feel while driving it.

okay imma say it..... U Joints!?

[Big Orange 78]

as i was driving this mourning and i was turning into the parking lot i could hear a loud clunk as i turned my wheels to the right. further investigation.... my right side ball joints are crap... not one... but both. so that pretty much sums up the vibration problem. thanks for everybodys help. gonna replace my ball joints this weekend hopefully it will fix the problem.

Thanks for all the advice and help!!

[notyo_cheez]

Originally Posted by Big Orange 78

as i was driving this mourning and i was turning into the parking lot i could hear a loud clunk as i turned my wheels to the right. further investigation.... my right side ball joints are crap... not one... but both. so that pretty much sums up the vibration problem. thanks for everybodys help. gonna replace my ball joints this weekend hopefully it will fix the problem.

Thanks for all the advice and help!!

Suggestion: depending on the age of the other steering/suspension pieces do uppers and lowers on both sides, and while you're at it replace upper and lower control arm bushings as well. Spend a little bit more on the poly bushings and you'll only have to do it once. You'll need a spring compressor and a pickle fork, some WD40, an entire afternoon and a LOT of patience. Find an auto parts house or machine shop that has a hydraulic press and do the bushings and lower ball joints for you while you wait, and save yourself a ton of grief.