Dilemma - 1979 Chevy K20 4x4 SOS

[t-bear95]

I recently purchased a 1979 Chevy K20 Bonanza 4X4 for $2500.  Soon after purchasing it i was going highway speeds for about 30 miles and then the problems started.  It runs and drives but stalls in the city and really starts to stutter at highway speeds.  I was able to keep up 75mph for those first 30 miles but it all of a sudden stated to sputter and backfire and just generally seem to want to die.  I got it home after a tow and replaced the battery, spark plugs, air filter, as well as replaced the oil filter and changed the oil and replenished transmission fluid.  It still continues to lurch back and forth after a few miles at freeway speeds.  I have no idea what the problem is but i need it fixed, ASAP!

The reason being I am moving back to Florida after a shorter than expected stint in Utah.  Now my question is what can I do and will it make it?  I have researched trucks in Florida and the prices are much higher than the $2500 i paid.  I would really like to keep so any input at all would be greatly appreciated!  Help Please!!!!  Thank you!

[bd]

Check and replace the fuel filter.  When you get the old filter off check it for sediment and rust particles.  Rust will be an indication of water in the fuel tank for an extended period, which may require further assessment.

[Irish_Alley]

[t-bear95]

I can see the fuel filter through the glass and there doesnt seem to be any debris. Is there just the one between the fuel pump and the carburetor or is there another one?

[bd]

You can't rely just on visual inspection to determine if a filter is restricted.  Take it off of the vehicle, drain the fuel out of it, then blow through it in the same direction that fuel flows through it - just avoid swallowing any fuel.  There should be very little to no resistance if the filter is okay.  Visual inspection is to determine if there is a large quantity of debris trapped in the filter, and what that debris might be.

If you are running a Rochester Quadrajet carburetor (the original factory type for V8 engines), there may be a pleated paper filter inside the carburetor under the fuel inlet nut (image, below).  You will need to remove the steel fuel line from the carburetor using a 5/8" line wrench and then remove the steel inlet nut using a 1" open-end wrench.  Be sure to use a flare nut wrench on the fuel fitting to avoid crushing the fitting.  If the original style fuel filter is still in place, it will be directly behind the 1" nut along with a spring that presses the filter into the nut.  When reassembling the nut and fuel line, wrap the line fitting with two complete revolutions of Teflon tape and be careful to avoid crossthreading either of the fittings.  Carefully check for fuel leaks afterward.

In addition to the above, you should verify fuel pressure and transfer using a proper gauge.

[t-bear95]

I got lost there. It has a 750cfm edelbrock carb. if i posted pics would that help?

[bd]

The Edelbrock uses an external fuel filter, so pay attention to the first and last paragraphs, above.  In addition to what I posted earlier, there's a nylon fabric sock on the fuel pickup in the fuel tank, which serves as a pre-filter/water separator.  Occasionally, they will restrict when there's severe sedimentation in the tank.  If your in-line filter is relatively clean, the fuel tank sock isn't likely an issue. 

You should also check your fuel tank(s) for proper venting.  If air can't enter the tank(s) as fuel is used, eventually the fuel pump won't be able to overcome the vacuum created in the tanks and fuel delivery to the carburetor will cease.

While you're working on the fuel system, check your fuel pump draw, pressure and delivery, as well.  Make sure the fuel system functions as it should.

[t-bear95]

how would i check for all those things? and where could i buy a new fuel filter?

[Irish_Alley]

fuel filters are at the parts store i run one of the glass filters, you can by replacement filters for them also

[t-bear95]

checked fuel filter and air passes through with no problems. How could ireach the filter in the carb itself?

[Irish_Alley]

edelbrock doesnt have a internal filter. the only thing left is the sock. but if you where to start it up now would you have a problem with it? does it only do it when hot? does it do it at a certain rpm?

[Irish_Alley]

do you have a miss? how does it run at idle what about if you where to rev the engine in neutral how does it act? also pull the vacuum line off the egr and plug it see how it runs then

[Lt.Del]

ok, you've checked the electrical aspects....how about the gas?  Fuel filter new?  No kinks in fuel line?  How old is the gas pump?  Have any issues going up hill under heavy load?
another possibility is the catalytic converter (if you have one) being clogged w/ carbon or rust.  Or, a common exhaust obstruction on these things is if you have stock exhaust right side manifold....the valve is stuck closed that allow heat to go thru intake when engine is cold, then supposed to open up allowing exhaust thru the pipe. Possible vacuum leaks as well.

[t-bear95]

fuel pump is brand new, one of the first things i changed. i did check for kinks, found none. It mainly sputters and lurches when going up or down hill actually. It has pure straight pipes all the way back so that may be different from factory exhaust. How could i check for a vacuum leak?

[t-bear95]

Starting it up is a whole other problem. there doesnt seem to be a pull of fuel to the crab so sometimes i have to take off the air filter and pour some gas in that way. Could that be a vacuum leak and is loss of power a symptom of a vacuum leakage?