Backfiring and skipping

When was the last time it received new spark plugs, plug wires, a distributor cap, and rotor? Because it sounds like it is time for a tune up. Let us know.

I changed the plugs, cap, and rotor last week only thing that has not been changed are the wires.

Bad wires can cause the car to run badly. They could be cross firing, where the spark jumps from one wire to another because the insulation is old and weak. It could also be that you switched wires by mistake. Attached is the firing order for your engine. Please double check that you have the wire correctly connected. If that is not the problem, then I would suggest changing the wires, as they likely need to be done.

That is the order they are in. I will try changing them and see how that goes.

Also what plugs did you use? The wrong plugs can can cause the car to run like crap.

i Changed the wires today and just got new spark plugs last week,i have regular AcDelco spark plugs,non platinum

Is it possible that the distributor got turned a little bit when you were working on it? An adjustable distributor, like the one in your car, could easily cause the poor running that you're describing.

i had it adjusted and everything sounds fine at idle speed but when i give it some gas it starts to skip and pop.

It might be too advanced. Turn it back just a hair and tighten it down. See how it does. If it's not in the ignition system, then the next thing I'd think about would be the catalytic converter. The simplest way to check it is to take the upstream O2 sensors out and run the car to see how it does. It'll be loud as heck, but if it feels much better, it's because there's no back pressure restricting the flow of exhaust through the cat.

i dont have any cats on it, its straight piped

Ah well it's not that then. Next thing I can think to check would be the fuel filter and pump. If you haven't replaced the filter in a while, go ahead and do it. As far as checking the pump, we have a how-to guide for that. https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

You can borrow a fuel pressure tester from AutoZone for free (just pay a deposit, it gets refunded when you return it). I'm also attaching ALLData's guide on checking fuel pressure. If you decide to go with the pressure tester method, you should get 5.5 to 6.5 PSI.

i changed the fuel pump and its still popping and misfiring at about 3000rpm

This is a different expert. The first thing I would do is a complete compression test.If you find any weak cylinders, do a leak down test.

This engine is pretty famous for wearing off cam lobes. A broken valve spring will give you those symptoms also. They have also been known to pull out the rocker hold down stud.

May be a weak valve spring, ok when idleing but at higher speeds not strong enough to keep the valve closed when other cyclinders are on compression stroke. using a test light short out each wire at the spark plug while it is reved u a bit. Shorting out the plug, you will hear a difference on a good cylinder and there will be no change on a bad one. We used to do that years ago and I learned it from my father.

You can also do something called a running compression test, when you remove the shraeder valve from the tester and run the engine. That will show up things like that.

if one my valves springs is broken or worn would i have to rebuild the heads or just replace the spring?

You can change a valve spring without removing the head using compressed air.

and if my cam is flat or worn id have to change that,correct?

is there anyway to find out if my cam is worn without removing it from the motor?

Yes, you would have to replace it. You can usually see something like that by watching the rockers but if necessary you can measure the lift of the cam lobe. You would also have a loose rocker clacking if nobody cranked it down.

I would also suggest to look at the manifold vacuum. If it fluctuates then you have a burnt valve. So a running compression test would be a good idea to identify the bad cylinder.

Does this have a 4bbl carburetor or is this that tuned port injection (TPI)?

it has an edelbrock 500 cfm carb on it

Are the back barrels opening?
Actually the popping out the tailpipe indicates a too rich fuel mixture, so the back barrels would have to be either opening too soon or dumping too much fuel when they do open.
I am not that familiar with the workings of an edelbrock carb to which if they have separate jets fro the front or rear but I was just asking about the fuel system cause it seems to me as though that is where the problem lies simply because of the fact that the problem isn't there at idle or just off idle but rather when at high rpm.
Anyhow on the exhaust valve not seating, I learned a trick years ago to test for an exhaust valve not seating, but I think it can only be done at idle cause it involves stretching a crisp new dollar bill across the tailpipe like you were taping someones mouth shut and hold it tight, and if an exhaust valve is not seating fully every once in awhile the dollar bill would try to suck in.
Another thing on checking for a misfire is to use a temperature gun on each exhaust manifold runner to see which is cooler than the others.

yes

yea ive tried the dollar bill trick and no suction, and it idles fine maybe a slight pop or mis but it seems fine at idle but when i drive it accelerates good until about 3000rpm and it starts to run rough and if i accelerate harder it spits through the carb,backfires and skips bad.

try resetting the computer, there may be a chance it is picking up the wrong signal from the engine. you can have it done at most auto stores and up until 1985, if I remember you can do it yourself. Disconnect the positive side of the battery, take the wire and ground it to the body or a good ground. Let it sit for a minute. Then reconnect it to the battery. grounding it out will clear any codes. Notice you will have to drive it about 50 miles before the computer completly resets its self. The 305 5.0 has a computer number 16060631, that is for the carburated engine

from what i was told there isnt a computer on it, the only thing electrical on it is the ignition system;distributor,altenator,and battery. no ecm

Spits back through the carb is exactly the opposite of back firing out the exhaust pipe.
Backfiring out the carb is usually due to too lean of a fuel mixture, or crossed ignition spark plug wires, a blown head gasket, timing chain that jumped, intake valve not seating.
If there is any fireballs coming out the carb air horn when snapping the throttle open and I suggest you remove the air cleaner, then either crossed spark plug wires, an intake valve not seating fully or a blown head gasket. If like a white mist backfiring then timing chain jump. If just popping back out the carb without any mist or fire, then a too lean fuel mixture.

Understood,it does both mostly out the tailpipe though. But under a heavier acceleration it spits

Stand back there by the tailpipe and smell. Does the exhaust burn your eyes? If so the engine is running too lean. Let the exhaust from the tailpipe blow onto your hand, then smell your hand, does it smell like gas/ If so, you are running too rich. If this has 2 tailpipes and a true duel exhaust , meaning no y pipe feel is both exhaust gases are hot, if one is much cooler than the other that is the engine bank with the problem.
Also at idle listen if there is any popping or spitting any fluid out either tailpipe.
Perform a cylinder balance test to find out at least which cylinder or cylinders are misfiring. Then remove the spark plug and smell if the brand new spark plugs already smell like gas meaning it's running too rich or if they are already covered in motor oil meaning you either have a problem with rings or leaking valve seals. To do a cylinder balance test wear some thick gloves and use insulated pliers and remove each spark plug wire one at a time at the distributor cap and put it back on and listen for the engine to misfire, stumble and rpm drop slightly, meaning that cylinder is working.

The ECM is under the dash on the passengers side. there are two screws that hold it up in place.

Does this even have a feedback carb on it?
have you tried unhooking the ignition timing wire yet, to knock the ecm out of the equation, so the ecm will not be adjusting the timing? If not, try that.
Unless this has just a drop-in hei with no ecm even hooked up to it.
Also, if this intake manifold has an egr on it , make sure the egr isn't leaking or sticking open, at idle reach under the egr and press the pintle open, the engine should stumble or die, if not then the egr is leaking or stuck open.

it has a drop in hei distro, and im not sure if it has and egr valve on it, i dont think it does.

Then I don't see how the ecm would be affecting it, even if it does have one hooked up.

And yet another possibility is that I am almost sure this originally had an egr but with that edelbrock on there and the fact that you said you didn't think or know that it had an egr might mean that it don't. An egr actually helps cool the combustion chamber cause the exhaust gas is a lot cooler than the combustion chamber and engines that are designed to have them usually run hotter combustion temperatures if the egr's are removed. With that you get the pinging and knocking associated with the excess temperature so people usually set back or retard the ignition timing in order to get rid of the pinging and knocking but then with that done the idle is too low, so they crank up on the bae idle. Now what happens is the carb throttle actually uncovers the main metering section of the carb and the carb begins to drip raw gasoline down the throttle bores and you will get that spitting and sputtering, gas fouled spark plugs, misfiring and popping out the tailpipe. As easy way to tell if the carb is dripping like that is to look down the carb air horn once the engine is warm, choke open and idling and look, with a mirror and flashlight, so it don't backfire right in your face and see if gas is dripping on the throttle plates. If so and if you don't want to purchase an intake manifold with the egr hole, then you could install a curve kit in the distributor, changing the springs and weights and also try to setup the timing just at idle, by either switching the vacuum hose to the distributor from vacuum that isn't present at idle to vacuum that is and probably right from either the intake manifold or I believe on the edelbrock there are your choice of ported and non-ported vacuum fittings right there on the front. Or an adjustable vacuum advance kit. You may have actually more than just 1 problem with this engine so better check out all the possibilities.

Engine performance issues are another symptom of a possible problem with the ECM. If the ECM has any issues, it may throw off the timing and fuel settings of the engine, which can negatively affect performance. A faulty ECM may cause the vehicle to experience a reduction in fuel efficiency, power, acceleration. back firing through the carburator or exhaust. There is a spark problem, backfiring through the carb, usually mean a bad valve weak intake valve spring, or crossed spark plug wire. backfiring through the exhaust can mean the same thing except that a exhaust valve may be bad. Take a compression check. Don't rely on doing it once but a couple of times. If there is a 20 pound difference in any one you might have found the problem, but I still think it is a timing issue. There is one subject we had not discussed, check all the vacuum lines. Sometimes they look good but underneath there may be a small crack. rubber hoses rot over time so check them out.

so i took it to a mechanic today and he said it could be the magnetic pickup coil in my distributor, and i also did some research on what the symptoms would be for a bad pickup coil and the truck is having the same symptoms.

I'll interject something stupid!

Check Mr. Distributor's mechanical advance weights, maybe the spring that draws them back in broke. Maybe they are stuck?

The Medic

I changed the distributor and it runs like a champ. I really appreciate all of the advice. Only problem now is a little bit of white smoke emitting From the exhaust. Very faint though any suggestions on what I could do to stop that?