Hi All,

I swapped out my 1982 300 six with a new 300 six long block last October. I can't remember if I had an ignition miss before that or not. I have had a sporadic one since then, about 25 pops per minute.

The truck got a new cap, rotor, plugs and wires. The timing is dead on. I reused the original distributor. The truck has the DSII ignition module (also reused).

A friend suggested that the distributor is wearing out. Does anyone have an opinion to confirm this idea? If so, what should I replace it with. My concerns are longevity, fuel mileage and performance, in that order.

Secondly I have an small exhaust leak out of the manifold (riser heat tube plugged up by PO and rusted solid). I would like to put on a new header but again I'm seeking advice with the same criterea as above.

Thanks in advance for your ideas!!!7

 

Tough one to diagnose over the Internet. Sometimes new parts can be bad out of the box. It sounds like it might be a sparkplug or plug wire. If you have the old wires, substitute one at a time and see if the miss goes away.

Did you check the gaps of the sparkplugs?

Check all vacuum hoses for leaks.

Regarding the distributor... take off the cap and rotor and then see if you can wiggle the shaft?

 

Thanks for the ideas, sorry I hadn't gotton back to respond, I'm working a lot of overtime now.

I'll look at all the ideas mid-week.

Thanks.

 

Also check that the carb is still firmly bolted on as they have a tendency to shake loose.

 

Thanks for the advice!!! Finally had a chance to check out all the suggestions, here's the results:

The plugs were gapped perfect, .042 if I remember correctly, slight amount of whiteness to them, I run lean.

The cap had a tiny bit of white corrosion, I sanded it off.
The rotor was also cleaned up, it looked real good though.
The wires were all good, firmly seated, newly replaced.
No vacum leaks.
I took off the air cleaner and made sure the carb was firmly mounted, it is.

When I took off the rotor I gently grabbed the distributor spindle (name?) where it sets, I was able to turn this by hand back and forth about 5 minutes each way (if it was a clock).

After all of the above the misfire is still present, albeit reduced by about 25%.

What do you all think?

 

Looks like you have most things covered. But, although you made sure the carb is tight you really don't know that you don't have a leak - either at the carb base or intake manifold-to-head gasket. One trick is to spray carb or brake cleaner at the gaskets, or use a propane torch without the flame - just the propane coming out slowly. If you find a leak the engine will speed up as it will pull the cleaner or propane in through the leak and burn it.

As for the distributor shaft, if you grabbed the top where the rotor goes on it should rotate one way due to the springs in the mechanical/centrifugal advance. But I wouldn't have thought it would turn both ways.

 

Thanks Gary,

I took your advice and used carb cleaner and sprayed it around the gasket where the carb mounts to the intake manifold. No change in engine idle speed.

I ordered a new reman distributor (single line vacum advance, just like the original), installed it yesterday, adjusted the timing, still have a miss. The truck seems to have a bit more power but still misses.

Is it possible that my fuel mixture is causing this? If so I'm still glad the distributor is changed. It had 190,000 miles on it most likely.

Thanks in advance for your input!!

Ralph

 

Ralph - It is very possible that the mix is causing a miss. A lean mix will do that. So open up the screw 1/8 or 1/4 turn and see if it helps.

 

Gary,

I looked in the stikies to find a Carter 1 bbl carb diagram and couldnt find one. I dont want to screw up the adjustment. Do you or anyone know where I can find the diagram?

 

My Carter YFA will give a lean pop in the exhaust if the fuel mixture is set too lean as well. My jets are really one size too small. It needs a size or two bigger jet as the mixture screw seems like it's turned out decently far.

Grab a vacuum gauge, hook it to manifold vacuum, and adjust it for the highest vacuum reading you can obtain. Once you've got the highest vacuum reading, adjust it a little back and forth no more than 1/2 turn to see if you can get it to smooth out any more. Mine runs good about 1/4-1/2 turn lean from full vacuum and no popping in the exhaust.

 

I can't get a hold of a vacum gauge today. I did find the mixing screw, opened it up 1/4, then 1/2 turn, no difference. I then went drastic, opened it up so much that I started smoking out the exhaust. Very rich, still popping.

I then took it so lean it idled rough, backed it off 1/2 turn from there and it seems like where it was before I opened the hood. Not sure what else to do. My plugs have about 10000 miles on them since the engine swap. Even though I checked them all out I might just replace them.

The carb is a reman, bought about a year ago right after I put in two new gas tanks.

 

If it still misses after all that then it could be one of a bunch of things, like a vacuum leak on a hose that goes into the intake close to one or two cylinders. Or a bad plug wire, although I should give problems under load rather than at idle.

 

I put the new plugs in, gapped to .044, no change.

 

Try pulling one plug wire at a time while the truck is running. When you pull the wire it should start running rougher. If you pull a wire and it doesn't change then thats your bad hole.

 

If you don't have a vacuum gauge to set your fuel mixture, try this:

Crank the motor and run it up to operating temperature and fully warm. The best way is to take it for a short drive, maybe a mile or two and come back.

Take your mixture screw, and start slowly screwing it in to where the motor starts to run funny/shake more than normal. Now, slowly turn the screw out and enrich the mixture while keeping track of how many turns you enrich the mixture. When it starts to stumble again, stop. Take that number, divide it in half, and turn the screw in lean that many turns.

So let's say I've got my motor running. I lean it out until it starts to stumble, this is my starting point. I turn it out 4 whole turns before the motor is too rich and starts to stumble again. This means I need to turn it IN 2 more turns so that it's right in the middle of too lean and too rich.

This gets you really close to where it should ideally be.

It could be possible that he has an exhaust valve on one cylinder that isn't sealing completely. Before going that route, it's best to eliminate all of the other possible problems.

Is all of the emissions equipment on the truck still present, or has any of it been removed?

If it's not a lean backfire, then it has to be something else. You can use a multimeter and check resistance in ohms on all of your plug wires. Any wires that aren't on par resistance wise with the others would be ones that need to be replaced. Are all of your plug wires tight as well? Are any of them touching? Is your firing order right?

The firing order is 153624, and the distributor rotates clockwise. This motor is incredibly tolerant with how it's treated, and many people sometimes mix up the firing order and they'll run it on 5 cylinders.

If this doesn't fix it, then you need to look at having your ignition module, your coil, and your distributor all tested. If any of them test out bad, I'd change them out.

Next, is the miss intermittent or is it rhythmic and constant? If it is intermittent, then we might not be looking at ignition problems, but problems elsewhere like bad emissions components.

EDIT:

It could even be something as simple as a leaking $2 PCV valve.