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Old 11-05-2012, 05:04 PM
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Truck bogs when accelerating

Ok I've got a '84 C-10 with a carbureted stock 305 with a set of headers on it and just today it started to bog down something fierce. I drove it probably 8 miles to a friends place and it drove there completely fine. But after talking to them and I went to leave *time frame of 15 minutes* and I got on the road and started to accelerate and it didn't want to go above 35 mph. Like it sounded like it had bad spark plugs which I later checked and they were fine. But then it slowly accelerated up to speed limit where after cruising at a constant speed it would pop every 5 seconds *oh yea it has open headers that's how I heard the exhaust pop* the popping sound I heard only happens when I'm driving at high speeds and then let off the gas blah blah blah no back pressure happens all the time. But not when I'm driving at a constant speed. Also when I'm driving at 60 mph and I punch the gas it bogs down kind of and then SLOWLY accelerates. Sounds like it's bouncing off a rev limiter, which it doesn't have. But I am stumped. Cause the carburetor was rebuild last year, the plug wires are fine and the spark plugs aren't fowled up.

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Old 11-05-2012, 05:31 PM
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How is your advance curve set, what carb, are the vacuum pods hooked up, secondary pod, the accelerator linkage adjusted? You mentioned just enough to tell people nothing.
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Old 11-05-2012, 05:49 PM
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Quote:
Originally Posted by BraveLil305 View Post
Ok I've got a '84 C-10 with a carbureted stock 305 with a set of headers on it and just today it started to bog down something fierce. I drove it probably 8 miles to a friends place and it drove there completely fine. But after talking to them and I went to leave *time frame of 15 minutes* and I got on the road and started to accelerate and it didn't want to go above 35 mph. Like it sounded like it had bad spark plugs which I later checked and they were fine. But then it slowly accelerated up to speed limit where after cruising at a constant speed it would pop every 5 seconds *oh yea it has open headers that's how I heard the exhaust pop* the popping sound I heard only happens when I'm driving at high speeds and then let off the gas blah blah blah no back pressure happens all the time. But not when I'm driving at a constant speed. Also when I'm driving at 60 mph and I punch the gas it bogs down kind of and then SLOWLY accelerates. Sounds like it's bouncing off a rev limiter, which it doesn't have. But I am stumped. Cause the carburetor was rebuild last year, the plug wires are fine and the spark plugs aren't fowled up.
Sound's like the fuel supply isn't keeping up to demand. Could be the pump is crapping out or a filter is plugging up.

Bogie
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Old 11-05-2012, 06:13 PM
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The timing isn't the problem. When I say STOCK 305 most people would know that it would have a quadrajet on it. I checked the filter and it was fine. I've had a fuel pump go out before. It is not the fuel pump.
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Old 11-05-2012, 06:21 PM
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What have you checked, if it is not timing or fuel pressure. From your post there is only enough information to guess. You do want help correct.

Put an exhaust system on it.

It started today, what did you change.

disable the accelerator pump, see if you can recreate the problem.
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Old 11-05-2012, 06:29 PM
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I came here because I was hoping someone would know what's wrong with it. If I knew what the problem was I'd fix it, not come here. What did I change that made it run like that? Nothing. Put exhaust on it? I've never had a problem the last year and a half without any. It's not timing, fuel pressure, spark plugs, plug wires and the carburetor doesn't need rebuilt. I'm stumped.
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Old 11-05-2012, 06:35 PM
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sounds like youre stumped.

Start by verifing the timing curve. Look at your vacuum connections. Make sure the choke and accel pump is functioning properly. The egr stuff sounds like it has been removed. Never had plugs make a sound when they go bad? That year 305 may have the tdc indicator at 12' oclock, you took that into consideration.

Popping at speed could be fuel puddling. Did you get cranking compression or a clt those are indicator for a internal problem.
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Old 11-05-2012, 06:39 PM
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Why on earth would I remove my egr stuff? Popping at speed isn't fueling it's called no back pressure. Based on what you just mentioned I know none of that is the problem.
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Old 11-05-2012, 06:44 PM
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Originally Posted by BraveLil305 View Post
Why on earth would I remove my egr stuff? Popping at speed isn't fueling it's called no back pressure. Based on what you just mentioned I know none of that is the problem.
Wth, you are aware of the egr door in the exhaust manifold. You said you put headers on. They could be headers with egr system, but you never mentioned that.

It is up to you to do the required diagnostics.

Its not based on what i mentioned.
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Old 11-05-2012, 06:49 PM
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There is an egr tube on the headers. Why would I check compression. I said it's bogging not throwing a rod or dropping rings. Can I get an opinion from somebody other than you?
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Old 11-05-2012, 08:49 PM
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There is an egr tube on the headers. Why would I check compression. I said it's bogging not throwing a rod or dropping rings. Can I get an opinion from somebody other than you?
Sure, I'll throw my hat in the ring.

1.) Cool the attitude. Nobody gets paid here.

2.) DO some diagnostics. Just because the fuel pump didn't crap out in exactly the same way it did last time doesn't mean that it's not on its way out.

Do at least a haffarsed test of the fuel delivery system. Disconnect the fuel line where it connects to the carb and put a length of clear hose on it, along with a clear glass or plastic bottle to collect the fuel in.

Use 2 wenches, preferably a flare-nut wrench on the tube nut, and the other to support the carb fuel filter fitting.

Disconnect the coil wire so the engine can't start. Make sure that you are in position to observe the fuel flowing into the glass jar. Have a buddy crank the engine for you. What you should see is a strong steady surge of fuel with each stroke of the pump arm. It should pump enough to fill a pop bottle in 3 strokes. The fuel should NOT have a bunch of foamy type bubbles in it.

Replace that cartridge fuel filter while you have the fuel line off. The filter is really cheap, and it should have a black rubber check-valve inside the inlet. Do not remove it. It's there to stop the fuel from siphoning out of the float bowl.

OK, so if your fuel delivery and filters are good, it's time to check your spark.

That truck will have HEI on it, and it should throw a very strong blue spark. If you have a spare plug, ground it to the engine block use it on each plug wire, and check each one.

Have a good look at the cap and rotor, especially the rotor. As I said, those HEI systems throw a very strong spark. If your plugs are fouled, or wires or bad, you will have a lot of resistance. I've seen them get to the point where the spark will take the path of least resistance ... burning a hole right through the center of the rotor (under the spring) to the distributor shaft. When that begins to occur, it will misfire real bad.

Checking the mechanical aspect (compression test, visual inspection of valve train components, etc) was a great suggestion as well ... one that you immediately dismissed with your vast years of experience.

Basically, an internal combustion engine needs 3 basic components to run.
Compression
Fuel
Spark

Good Luck.
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Old 11-05-2012, 10:24 PM
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Fuel and Compression were never concerns of mine. We narrowed it down to ignition. More specifically the distributor. Which we're getting tomorrow.
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Old 11-06-2012, 09:16 AM
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Originally Posted by BraveLil305 View Post
The timing isn't the problem. When I say STOCK 305 most people would know that it would have a quadrajet on it. I checked the filter and it was fine. I've had a fuel pump go out before. It is not the fuel pump.
Popping back is indicative of a lean mixture or late timing.

Removing the EGR leans the mixture

Adding headers leans the mixture

Running open exhaust leans the mixture

Plugging fuel filters leans the mixture there's one in the tank

Vapor lock will make the engine behave like this

Water in the fuel will make the engine behave like this

Failing fuel pump leans the mixture

Collapsing fuel lines lean the mixture

The Q-jet has many failure modes which will lean the mixture metering rods stuck in the down position for example, dirt caught in jets or passages, sometimes Q-jets sometimes just die and you can't identify where or why.

When the engine gets old the cam timing gears and chain wear the cam falls out of time with the crank. Distributor position timing in relation to the crank has nothing to do with this because you can adjust the distributor to the crank independent of the cam's coordination with the crank. As the cam falls out of time the engine will increasingly show a hesitation with back fire, this will get worse over time with a general loss of power, finally it will quit, if you’re lucky the valves and pistons won't collide but more often than not they do with expensive result.

But you replaced a fuel pump once which makes you a mechanical genius so not a lot I can add from here.

Bogie
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Old 11-06-2012, 10:04 AM
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Originally Posted by oldbogie View Post
Popping back is indicative of a lean mixture or late timing.

Removing the EGR leans the mixture

Adding headers leans the mixture

Running open exhaust leans the mixture

Plugging fuel filters leans the mixture there's one in the tank

Vapor lock will make the engine behave like this

Water in the fuel will make the engine behave like this

Failing fuel pump leans the mixture

Collapsing fuel lines lean the mixture

The Q-jet has many failure modes which will lean the mixture metering rods stuck in the down position for example, dirt caught in jets or passages, sometimes Q-jets sometimes just die and you can't identify where or why.

When the engine gets old the cam timing gears and chain wear the cam falls out of time with the crank. Distributor position timing in relation to the crank has nothing to do with this because you can adjust the distributor to the crank independent of the cam's coordination with the crank. As the cam falls out of time the engine will increasingly show a hesitation with back fire, this will get worse over time with a general loss of power, finally it will quit, if you’re lucky the valves and pistons won't collide but more often than not they do with expensive result.

But you replaced a fuel pump once which makes you a mechanical genius so not a lot I can add from here.

Bogie
Popping back is caused by the no back pressure.

EGR wasn't removed.

I said the fuel filter is clean and I just replaced the sending units in both tanks two weeks ago so the suck up screens aren't clogged and I know it.

This truck has never had vapor lock before and it's not gonna unless it's 120 degrees out.

I don't think the fuel pump would be failing if it starts on the first time every time and runs perfectly fine at idle.

The engine only has around 120,000 on it.

I never said anything about the engine dying. It just runs bad above 35 mph.

But then again I don't know anything about being a mechanic since my dads been one for 35 years. Not like I've never replaced an engine by myself before.
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Old 11-06-2012, 10:33 AM
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If you know why it is popping you shouldnt have asked. You should have strarted out with question on how to tune a car to cruise with open headers. That said , you can run open headers and not pop. Open headers is not the cause. My 85 c10 can drive around just fine with the exhaust unhooked. Im just not a dumb *** .

have you checked the est for proper operation, you have already altered the egr system with aftermarket headers, look there too.

If you dad is the shizzee, why is it not ship shape. You probably disrespecting and he doesnt want to help you. So now youre here. Suck it kid.
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