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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

300-6 Idle miss

 
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Old 01-23-2019, 06:45 PM
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300-6 Idle miss

I have a miss at idle on my '84 F150, 300-6. Compression is very good, has new plugs, wires. Runs smooth and strong down the road, just has a miss at idle. Vacuum lines are all good. I did observe, the green wire with yellow stripe going to the coil connector had bare wire showing where it came out of the plug.Could that be the issue? What else should I check?? It did have some stale gas in it, maybe 3 or 4 gallons I finished filling it up with fresh gas
 
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Old 01-23-2019, 07:54 PM
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Adjust the idle mixture screw and see if that helps it.
 
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Old 01-23-2019, 07:58 PM
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Make sure your intake is tight. '80s motors and '84s in particular like to loosen up the intake.
 
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Old 01-23-2019, 08:21 PM
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Thanks I'll try both of those. Like I said, while driving it runs smoothly, is just at idle when it has the miss
 
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Old 01-23-2019, 11:01 PM
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Check your cap and rotor. My truck misfired a lot at idle and shook the truck a tiny bit each time. I thought it was normal for carb motors till I popped the distributor open and found the contacts totally worn down!
 
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Old 01-24-2019, 06:44 AM
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Originally Posted by can0fspam View Post
Check your cap and rotor. My truck misfired a lot at idle and shook the truck a tiny bit each time. I thought it was normal for carb motors till I popped the distributor open and found the contacts totally worn down!
Thanks, I'll check it too
 
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Old 01-24-2019, 10:15 AM
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Grab the air cleaner and rock from side to side. If there is movement, check the 1/2" nuts which secure the carburetor. Not too tight, though. If they are tight, check the carburetor. Sometimes the two halves loosen. To tighten, the carburetor must be removed and turned upside down to access the screws.

With the engine idling [be very careful], grab the wire loom [harness] and shake it. If the engine stumbles, most likely there is a short.

There is a vacuum tree on the intake manifold located under the carburetor. It is difficult to see with all the vacuum lines [especially for 1984 - 1986 models] and there are about 6 ports, some unused. The unused ones should have a rubber cap, which over time can crack and create a vacuum leak. I have found that the port which is on the cab side and nearest the engine is often cracked or missing, due to being near the hot exhaust manifold and being out of sight.
 
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Old 01-24-2019, 03:50 PM
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In looking at the wires going into the dist cap, I think a couple (or more) may be crossed.
 
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Old 01-25-2019, 05:17 PM
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Here are a couple shots of the wiring at the distributor. terminals inside the dist cap had some rust colored oxidation on them. Going to have module tested to see if it might be bad
 
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Old 01-25-2019, 08:29 PM
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uugh, another computer controlled six.
 
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Old 01-25-2019, 08:35 PM
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Originally Posted by Franklin2 View Post
uugh, another computer controlled six.
It didn't have a feedback carb on it, was wired like this when I got it.No catalytic convertor.Also, Looks like the SPOUT connector plug is gone, not sure if that would cause any problem
 
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Old 01-25-2019, 09:19 PM
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If you have stuff missing, it's probably not running right. No computer controlled carb means no throttle position sensor. The computer controls the timing, there are no advance weights inside your distributor, and no vacuum advance either. If a bunch of junk is missing, you should probably convert it over like everyone else does.
 
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Old 01-25-2019, 09:34 PM
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Originally Posted by Franklin2 View Post
If you have stuff missing, it's probably not running right. No computer controlled carb means no throttle position sensor. The computer controls the timing, there are no advance weights inside your distributor, and no vacuum advance either. If a bunch of junk is missing, you should probably convert it over like everyone else does.
I do have a Duraspark module, besides the distributor what else will I need to convert it? Any certain years I need to look for?
 
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Old 01-25-2019, 10:14 PM
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You need a short harness between the dist and the box. If you look hard enough, there may be some plugs under the hood already for the box's other connections. The distributor needs to be a six cylinder, the harness can come from any duraspark equipped car or truck, any engine, so long as the wires will reach.
 
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Old 01-26-2019, 03:04 PM
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Went to a nearby salvage yard this morning, and scored a Duraspark distributor and the complete harness out of an '83 300 for $50, what I grabbed is in the first photo. Second photo shows the 2 plugs on the fender of my '84, are these what I will use? Anything else I need to buy?

 

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