My name is Scotty I have an 82 pickup 4x4 that is missing under load and hesitating. I have pretty much tried everything i can think of from carb rebuild, vacuum lines, fuel pump, fuel filter, spark plugs nothing has fixed it.

here is what is happening, it seems to be happening more when the engine gets warm. while driving under load truck misses and feels like it doesnt get gas for a second any help would be greatly appreciated


thanks
scotty

 

Have you checked for a vacuum leak at the base of the carb where it meets the manifold and where the manifold meets the head?

 

Have you modded the engine recently? What's your ignition timing?

Look down the carb venturi's, do you see a squirt of raw fuel when you begin to apply throttle? You should. Let us know if you don't find vacuum leaks.

 

It seems likely that it is a fuel delivery issue - especially if you can verify that there are no vacuum leaks. Here's what I would do:

1. Check your timing first. Get it up to temperature and verify that it is running at 5* BTDC at 950 RPM max with the vacuum advance pinched off. The FSM says 5*, but I found that my truck likes something around 8*.
2. Check your fuel filter(s) again. Some trucks have two (one on the frame rail beneath the filler neck and another on the passenger side fender wall). If you can't see inside of them, I would cut them open to see what kind of debris you may have in there. I run see-through fuel filters that have changeable elements so I can see exactly if and/or what is clogging the lines. Filters can clog up quickly if you have the problem in step 5 like I had.
3. Check your fuel lines - if they look cracked and deteriorated from the outside then they are probably just as bad on the inside. You can get a dozen feet of fuel hose from your local auto parts store for $10-20.
4. Check your fuel pickup tube/sock. The whole assemble unbolts from the top of the tank (mark your fuel lines as you take them off) and it is possible to get it out without dropping the tank. Sometimes the fuel sock gets clogged. The part number is 77023-12050 and is available at the dealership for something like $20. Here's a picture of it:
   
5. Check your fuel tank for debris. Take of the tank skid plate and you'll find a drain plug. Drain the fuel out into a bucket and look for rust scale and other debris. If you have debris coming out of your tank then you'll want to drop the tank and get it cleaned out. You can drop a handful of screws in the tank and vigorously shake it until you can't lift your arms to knock off any rust scale. Usually, this is good enough, but there are gas tank sealers out there that you can use although I've always been weary of them. If you have old fuel in the tank, you'll definitely want to drain it and toss it. As the ethanol in modern fuel breaks down, it attracts water and creates large particulates that gum up engines and fuel delivery systems. Rinse the tank thoroughly WITH GAS. Just grab a gas can with a couple gallons of fresh fuel in it and run it through the tank until no more debris comes out. When I cleaned my tank, I used a coffee filter in a strainer to strain the fuel as it came out of the tank so that I could run it back through again if I didn't get all the debris out.

I had a similar problem like you before I started rebuilding my truck. I could drive for about 15 minutes with no problem and then all of the sudden my truck would start stalling and bucking. I could stop and come to an idle and it would run fine until I got going again. I could even let it sit for about a hour and it would run fine again for about 15 minutes before acting up. The problem was that I had so much debris in my tank that it was clogging my fuel filters just enough that it would starve the engine of fuel at higher RPMs. I would do a roadside swap of fuel filter elements and it would be good for another 15-20 minutes until more debris piled up in the fuel filter again.

 

A fuel delivery problem certainly could be to blame. I also had an 84 2WD with intermittent poor running issues which came down to a plugged fuel filter.

Lots of things can cause this kind of behavior, including ignition problems and carb tuning.

 

thank you for the response i have been busy at work and was not able to work on my truck at all i have the next few days off and will try cleaning out the gas tank. I am not 100% sure it is not vacuum but i have looked several times and have not found a leak and i replaced any vacuum lines that looked bad. i also do not know if there are two fuel filters i have only been able to find one.

 

I'm not sure where you live, but if you don't have emissions regulations in your state, I would highly recommend desmogging your engine. It is quite possibly one of the best things you can do under the hood of your truck - improves fuel efficiency, eliminates 90% of potential vacuum leaks, cleans up the engine bay and pisses off environmentalists! The cost isn't too bad - you can get all the block off plates that you need from LCE for around $130 and an extra $260 if you decide to go with a Weber carb. It is extremely easy to do and I created a desmog tutorial thread to guide people through the steps - the link is in my signature below.

But bottom line is, try to eliminate all variables to figure out your issue - obviously the debris in the fuel is a likely culprit, but you never know until you go through all the steps. Just keep eliminating variables and you'll find your problem. Just start with the easy, low/no cost ones first.

 

kawazx636 i live in california smog is pretty strict here but thank you for the suggestion!

 

I had an issue like that but it only happened very rarely, and only at highway speeds.

Not sure what solved it...but I have the feeling it was replacing all the rubber fuel line. Like kawazx636 mentioned, pretty cheap, mostly easy to get at.

When it starts deteriorating it can actually flex or bulge under load when hot.

 

Any updates?

Also, if you do de-smog, you can get the plates from LCE as suggested, or if you don't care about looks you may use pipe-threaded plugs to fill in the holes. They work just as well, they just don't look shiny but are much, much less expensive.

They'll thread right into aluminum (EGR port on pass side rear head) and you can tap the exhaust manifold and thread them in with some kind of sealer, as well as using the stock air injection center-mount bolt as a plug with sealer for the center hole.

The crossover at the rear of the head may be left alone.