73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: t-bear95 on July 31, 2013, 05:19:51 pm
-
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!
-
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.
-
(http://www.naioa.com/v2/modules/Forums/images/smiles/iamwithstupid.gif)
-
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?
-
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.
-
I got lost there. It has a 750cfm edelbrock carb. if i posted pics would that help?
-
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.
-
how would i check for all those things? and where could i buy a new fuel filter?
-
fuel filters are at the parts store i run one of the glass filters, you can by replacement filters for them also
-
checked fuel filter and air passes through with no problems. How could ireach the filter in the carb itself?
-
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?
-
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
-
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.
-
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?
-
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?
-
I am wondering if your pick up coil is starting to go. Those wires get brittle and just before they break sometimes they will have a drive-ability issue as you are describing. When the vacuum advance kicks in to compensate as in going up hills the advance plate moves?? Just giving you another thing to check. You may try unplugging the vacuum advance and plugging it and take it for a drive...
-
So on level ground it runs fine ? Does it still run fine at any speed while on level ground ?
-
how would i check for all those things?
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?
Begin by physically inspecting all of your rubber fuel lines between the tank(s) and carburetor for cracks and/or loose connections. Make sure clamps are installed and snug where hoses slip onto metal fittings.
Procure the proper gauge (http://www.summitracing.com/parts/anm-cp7802) (pictured below) and measure fuel pump pressure (5 - 7 PSI), fuel pump vacuum/suction (>20" Hg), and fuel pump delivery/flow (>1 qt in 30 seconds of cranking).
Be very careful when working with the fuel system, especially when checking fuel pump delivery. Avoid all sparks or flames. Insist on help from a level-headed assistant; don't work alone. Have a fire extinguisher handy and make sure both you and your assistant know how to use it! Have rags available to immediately wipe up any fuel that spills or leaks. Enriched fuels are very flammable and can cause severe chemical burns, so BE CAREFUL!
To check fuel pump pressure:
Connect the fuel pressure gauge according to the instructions supplied with the gauge, directly to the fuel line leading to the carburetor. Have an assistant crank the engine for ~7 seconds while you watch the gauge and record the reading. If pressure was below 5 PSI, replace the pump.
To check fuel pump suction:
Remove and plug the 3/8" fuel supply hose that comes from the fuel tank from where it attaches to the fuel pump. Be careful of fuel that may siphon from the tank or drain from the pump. Connect the vacuum gauge directly to the 3/8" fuel pump nipple. Have your assistant crank the engine for several seconds while you watch the gauge and record the reading. Reconnect the tank supply line to the fuel pump. If suction was less than 18" Hg, replace the pump.
To check fuel pump delivery:
Verify that the fuel line coming from the tank has been properly reconnected to the 3/8" nipple on the fuel pump. Verify there is adequate fuel in the tank. Remove the fuel line from the carburetor and direct it into an "empty" one-gallon container, such as a gasoline can or an old antifreeze bottle, etc. You may need to extend the fuel line with a rubber hose to reach the container safely; be mindful of any fuel that may or could potentially leak or spray, to minimize the risk of fire and injury. Have your assistant crank the engine for 30 seconds while you carefully direct the flow of fuel into the container. Reconnect the fuel line to the carburetor, wipe up any spilled fuel, then measure the amount of fuel pumped into the container. If fuel delivery was less than 1 quart in 30 seconds of cranking, replace the fuel pump.
-
t-bear95:
You had two separate threads running on this same topic. They have just been merged!
-
sounds like your float level need reset, but i'm no carb guru so take with a grain of salt.